Title:
Portable volume cycle respirator
United States Patent 3910270
Abstract:
A portable respirator, of the volume cycle type, is powered by and supplied with compressed medicinal gas, requiring no electric power. The respirator is capable of operating in an automatic mode in which a fixed volume of gas is supplied to the patient for a first selected period of time, exhalation is prevented for a subsequent second period of time, and then the patient is allowed to exhale for a subsequent third selected period of time. The respirator can also operate in a demand mode, in which each cycle is triggered by the attempt of the patient to inhale. The respirator shifts automatically from demand mode to automatic mode cycling and triggers an alarm in the event that the patient becomes too feeble to attempt to inhale. The respirator may also be used as an anesthesia ventilator during surgery.
US Patent References:
Respirator
Bird - June 1965 - 3191596
Respiration apparatus
Beasley - December 1965 - 3221734
Respiration apparatus
Gage - August 1966 - 3265061
Monitoring system for respiratory devices
Winchel - May 1967 - 3316902
Respiratory augmentor with electronic monitor and control
Carlson - December 1967 - 3357428
Respirator
Bird - June 1965 - 3191596
Respiration apparatus
Beasley - December 1965 - 3221734
Respiration apparatus
Gage - August 1966 - 3265061
Monitoring system for respiratory devices
Winchel - May 1967 - 3316902
Respiratory augmentor with electronic monitor and control
Carlson - December 1967 - 3357428
Application Number:
05/445758
Publication Date:
10/07/1975
Filing Date:
02/25/1974
View Patent Images:
Export Citation:
Assignee:
Bio-Med Devices, Inc. (Stamford, CT)
Primary Class:
Other Classes:
128/202.220
International Classes:
A61M16/00; A61M16/00
Field of Search:
128/145.8,145.6,145.5,146.4,146.5,142.2,142.3,142.4,188,191,197,202,203,2.08 73/401 137/624.14 235/21ME
US Patent References:
Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Recla, Henry J.
Attorney, Agent or Firm:
Blum, Moscovitz, Friedman & Kaplan
Parent Case Data:
This is a continuation, of application Ser. No. 287,936, filed Sept. 11, 1972, now abandoned.
Claims:
What is claimed is
1. A portable volume cycle respirator powered by gas pressure alone, comprising means for supplying medical gas to a patient for inspiration during a first period of time, pneumatic logic means for preventing, for a preselected second period of time exhalation of gas by said patient subsequent to said first period, valve means for permitting exhalation of gas by said patient during a third period of time subsequent to said second period of time.
2. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes a pneumatic oscillator circuit comprising first and second sources of pressurized gas; first normally-closed fluidic gate means having an output port, a dump port, an input port connected to said first source of pressurized gas, adjustable first flow restrictor means connected between said first source of pressurized gas and said input port, and a control port, said first gate means output port being normally connected to said dump port for flow of gas internally from said output port to said dump port, and being connected internally to said input port to receive pressurized gas therefrom when pressurized gas is applied to said control port; second flow restrictor means connected to said first gate means dump port to control the rate of flow of gas therethrough; second fluidic gate means having first and second control ports, a dump port, an input port connected to said second source of pressurized gas, an output port connected to said first control port to apply pressurized gas thereto, and valve means responsive to gas pressure applied to said first and second control ports and said input port, said second gate means output port being connected internally to the associated input port when the sum of the pressures at said input port and said first control port exceeds the pressure at said second gate port by a predetermined amount and being connected to the associated dump port when the pressure at said second control port exceeds the sum of the pressures at said first control port and said input port by a predetermined amount; fluidic output circuit means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output circuit means and said first gate means control port; fluidic circuit means connecting said first gate means output port and said second gate means second control port and including first reservoir means for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second gate means second control port.
3. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby periodically increasing the duration of the pulse put out by said oscillator circuit.
4. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit said fluidic output circuit means includes first time delay means for shaping said oscillatory output signal.
5. A portable volume cycle respirator powered by gas pressure alone, as defined in claim 4, wherein the pneumatic logid means includes a pneumatic circuit said first time delay means includes third fluidic gate means having a control port, an input port and a dump port, said third fluidic gate means input port being internally connected to the associated dump port when pressurized gas is not applied to the associated control port; second reservoir means having an input and an output; third flow restrictor means connected to said second reservoir means input; and fluidic circuit means connecting the series connection of said second flow restrictor means and said second reservoir means between said third gate means control port and input port.
6. A portable volume cycle respirator powered by gas pressure alone as defined in claim 5, wherein the pneumatic logic means includes a pneumatic circuit said output circuit means further comprises a fourth fluidic gate means having a control port, an input port, an output port and a dump port; a third source of pressurized gas connected to said input port, fluidic circuit means connecting said input port of said fourth fluidic gate means with said output port of said second fluidic gate means and said output port of said fourth fluidic gate means with said input port of said third gate means, said fourth gate means output port being alternately connected internally to one of said associated input and dump ports in response to the presence or absence of pressurized gas at the associated control port; fifth gate means having valve means, biasing means acting in said valve means, first and second control ports, an input port, an output port and a dump port; fourth and fifth sources of pressurized gas connected respectively to said first control port and said input port of said fifth gate means; and fluidic circuit means connecting the input port of said third gate means with said second control port of said fifth gate means, said input and said output ports of said fifth gate means being internally connected by said valve means when the pressure at said second control port of said fifth gate means plus the force exerted by said biasing means exceeds the pressure of said fourth source of pressurized gas by a predetermined amount, and said output port and said dump port of said fifth fluidic gate means being internally connected when the pressure of said fourth source of pressurized gas exceeds the sum of the forces of pressurized gas at said associated second control port and said biasing means.
7. A portable volume cycle respirator powered by gas pressure alone as defined in claim 6, wherein the pneumatic logic means includes a pneumatic circuit comprising fluidic circuit means connecting said output port of said fifth gate to said control port of said first gate.
8. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes pneumatic oscillator circuit comprising a first fluidic gate means having a control port, a supply port, a dump port and an output port, a first pressurized gas supply connected to said input port, an adjustable first flow restrictor in said connection between said first source of pressurized gas and said supply port, a second flow restrictor connected to said dump port and a reservoir connected to said output port, said output port being normally connected internally to said dump port, a second fluidic gate means having a control port, a supply port, an output port, and a dump port, a second pressurized gas supply connected to said input port, first reservoir means in said line connecting said first gate output port with said second gate control port, fluidic output means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output means connecting said output circuit means and said first gate means control port; said first reservoir means serving for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second means second neutral port.
9. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a third fluidic gate means having a control port, an input port and a dump port, said control port being connected to the output port of said second fluidic gate means, a third flow restrictor and a second reservoir connected in series in that order between said control and input ports of said third gate means, said third gate means with said third flow restrictor and said second reservoir constituting a delay means.
10. A portable volume cycle respirator powered by gas pressure alone as defined in claim 9, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fourth pneumatic gate means having a first control port, an input port, a dump port and an output port, a third pressurized gas supply means connected to said input port, a third reservoir connected to said output port means and a fourth flow restrictor connected to said dump means, said control port of said fourth fluidic gate means being connected to said output port of said second fluidic gate means.
11. A portable volume cycle respirator powered by gas pressure alone as defined in claim 10, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fifth pneumatic gate means having a control port, an input port, an output port, and a dump port, said control port being connected to said control port of said first fluidic gate means, said third reservoir having an output line connected to said input port of said fifth gate.
12. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby increasing the duration of one of the signals put out by said oscillator circuit.
13. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1, including means for indicating pressure failure within said respirator and indicating termination of breathing by a user, said means including an audible oscillator circuit and an audible signal actuator, said audible oscillator circuit comprising a pneumatic gate having a control port, first, second and third output port, a gate diaphragm biased to hold said first output port closed, a first orifice connected to said first output port, a tank and a second orifice connected in sequence between said conrol port and said second output port, said third output port being automatically connectable to a source of non-pulsating pressurized gas in case of an emergency when it is desirable to sound an alarm, said gate diaphragm closing said third output port when said input port is pressurized, said audible signal actuator comprising a diaphragm valve having an input port connected to said second output port of said gate, said valve diaphragm being biased toward said input port, a rod so connected at one end thereof to said valve diaphram as to move to and fro in an axial direction in consonance with movement of said valve diaphragm, and a bell the other end of said rod protruding outward from said diaphragm and being positioned to strike said bell when moved by said valve diaphragm.
1. A portable volume cycle respirator powered by gas pressure alone, comprising means for supplying medical gas to a patient for inspiration during a first period of time, pneumatic logic means for preventing, for a preselected second period of time exhalation of gas by said patient subsequent to said first period, valve means for permitting exhalation of gas by said patient during a third period of time subsequent to said second period of time.
2. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes a pneumatic oscillator circuit comprising first and second sources of pressurized gas; first normally-closed fluidic gate means having an output port, a dump port, an input port connected to said first source of pressurized gas, adjustable first flow restrictor means connected between said first source of pressurized gas and said input port, and a control port, said first gate means output port being normally connected to said dump port for flow of gas internally from said output port to said dump port, and being connected internally to said input port to receive pressurized gas therefrom when pressurized gas is applied to said control port; second flow restrictor means connected to said first gate means dump port to control the rate of flow of gas therethrough; second fluidic gate means having first and second control ports, a dump port, an input port connected to said second source of pressurized gas, an output port connected to said first control port to apply pressurized gas thereto, and valve means responsive to gas pressure applied to said first and second control ports and said input port, said second gate means output port being connected internally to the associated input port when the sum of the pressures at said input port and said first control port exceeds the pressure at said second gate port by a predetermined amount and being connected to the associated dump port when the pressure at said second control port exceeds the sum of the pressures at said first control port and said input port by a predetermined amount; fluidic output circuit means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output circuit means and said first gate means control port; fluidic circuit means connecting said first gate means output port and said second gate means second control port and including first reservoir means for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second gate means second control port.
3. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby periodically increasing the duration of the pulse put out by said oscillator circuit.
4. A portable volume cycle respirator powered by gas pressure alone as defined in claim 2, wherein the pneumatic logic means includes a pneumatic circuit said fluidic output circuit means includes first time delay means for shaping said oscillatory output signal.
5. A portable volume cycle respirator powered by gas pressure alone, as defined in claim 4, wherein the pneumatic logid means includes a pneumatic circuit said first time delay means includes third fluidic gate means having a control port, an input port and a dump port, said third fluidic gate means input port being internally connected to the associated dump port when pressurized gas is not applied to the associated control port; second reservoir means having an input and an output; third flow restrictor means connected to said second reservoir means input; and fluidic circuit means connecting the series connection of said second flow restrictor means and said second reservoir means between said third gate means control port and input port.
6. A portable volume cycle respirator powered by gas pressure alone as defined in claim 5, wherein the pneumatic logic means includes a pneumatic circuit said output circuit means further comprises a fourth fluidic gate means having a control port, an input port, an output port and a dump port; a third source of pressurized gas connected to said input port, fluidic circuit means connecting said input port of said fourth fluidic gate means with said output port of said second fluidic gate means and said output port of said fourth fluidic gate means with said input port of said third gate means, said fourth gate means output port being alternately connected internally to one of said associated input and dump ports in response to the presence or absence of pressurized gas at the associated control port; fifth gate means having valve means, biasing means acting in said valve means, first and second control ports, an input port, an output port and a dump port; fourth and fifth sources of pressurized gas connected respectively to said first control port and said input port of said fifth gate means; and fluidic circuit means connecting the input port of said third gate means with said second control port of said fifth gate means, said input and said output ports of said fifth gate means being internally connected by said valve means when the pressure at said second control port of said fifth gate means plus the force exerted by said biasing means exceeds the pressure of said fourth source of pressurized gas by a predetermined amount, and said output port and said dump port of said fifth fluidic gate means being internally connected when the pressure of said fourth source of pressurized gas exceeds the sum of the forces of pressurized gas at said associated second control port and said biasing means.
7. A portable volume cycle respirator powered by gas pressure alone as defined in claim 6, wherein the pneumatic logic means includes a pneumatic circuit comprising fluidic circuit means connecting said output port of said fifth gate to said control port of said first gate.
8. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1 wherein the pneumatic logic means includes pneumatic oscillator circuit comprising a first fluidic gate means having a control port, a supply port, a dump port and an output port, a first pressurized gas supply connected to said input port, an adjustable first flow restrictor in said connection between said first source of pressurized gas and said supply port, a second flow restrictor connected to said dump port and a reservoir connected to said output port, said output port being normally connected internally to said dump port, a second fluidic gate means having a control port, a supply port, an output port, and a dump port, a second pressurized gas supply connected to said input port, first reservoir means in said line connecting said first gate output port with said second gate control port, fluidic output means connected to said second gate means output port for transmitting the oscillatory output signal produced at said second gate means output port; feedback means connecting said output means connecting said output circuit means and said first gate means control port; said first reservoir means serving for controlled filling and emptying in response to the state of said first gate means to apply pressurized gas to said second means second neutral port.
9. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a third fluidic gate means having a control port, an input port and a dump port, said control port being connected to the output port of said second fluidic gate means, a third flow restrictor and a second reservoir connected in series in that order between said control and input ports of said third gate means, said third gate means with said third flow restrictor and said second reservoir constituting a delay means.
10. A portable volume cycle respirator powered by gas pressure alone as defined in claim 9, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fourth pneumatic gate means having a first control port, an input port, a dump port and an output port, a third pressurized gas supply means connected to said input port, a third reservoir connected to said output port means and a fourth flow restrictor connected to said dump means, said control port of said fourth fluidic gate means being connected to said output port of said second fluidic gate means.
11. A portable volume cycle respirator powered by gas pressure alone as defined in claim 10, wherein the pneumatic logic means includes a pneumatic circuit further comprising a fifth pneumatic gate means having a control port, an input port, an output port, and a dump port, said control port being connected to said control port of said first fluidic gate means, said third reservoir having an output line connected to said input port of said fifth gate.
12. A portable volume cycle respirator powered by gas pressure alone as defined in claim 8, wherein the pneumatic logic means includes a pneumatic circuit further comprising a sigh circuit which at predetermined periods places a fourth flow restrictor in series with said second flow restrictor, thereby increasing the duration of one of the signals put out by said oscillator circuit.
13. A portable volume cycle respirator powered by gas pressure alone as defined in claim 1, including means for indicating pressure failure within said respirator and indicating termination of breathing by a user, said means including an audible oscillator circuit and an audible signal actuator, said audible oscillator circuit comprising a pneumatic gate having a control port, first, second and third output port, a gate diaphragm biased to hold said first output port closed, a first orifice connected to said first output port, a tank and a second orifice connected in sequence between said conrol port and said second output port, said third output port being automatically connectable to a source of non-pulsating pressurized gas in case of an emergency when it is desirable to sound an alarm, said gate diaphragm closing said third output port when said input port is pressurized, said audible signal actuator comprising a diaphragm valve having an input port connected to said second output port of said gate, said valve diaphragm being biased toward said input port, a rod so connected at one end thereof to said valve diaphram as to move to and fro in an axial direction in consonance with movement of said valve diaphragm, and a bell the other end of said rod protruding outward from said diaphragm and being positioned to strike said bell when moved by said valve diaphragm.
Description:
BACKGROUND OF THE INVENTION
The use of a respirator is indicated in a wide variety of medical conditions such as chronic pulmonary emphysema, chronic bronchitis, pulmonary edema, dyspnea, pneumoconiosis, pulmonary arteriosclerosis, bronchial asthma, among others. It is also applicable for use during surgery as an anesthesia ventilator, for postoperative support, in treatment of a patient who is comatose or in shock, and, in short, in support of any patient unable to maintain normal autonomous respiration.
In the design of a respirator, it must be taken into account that the respirator may be used in a hospital or in surroundings where no electrical power is available, and, moreover, the respirator must be suitable for use with patients of any age from infancy through adulthood to geriatric.
Respirators fall into two categories, either (1) pressure cycled or (2) volume cycled. In the first category, medicinal gas, which includes filtered air, oxygen and mixtures containing oxygen is supplied to the patient until a fixed pressure is reached. In the second type, medicinal gas is supplied to the patient until a fixed volume has been transferred. Pressure cycled respirators, up to now, have been more popular because of the fact that the mechanism involved is relatively simple and the cost, consequently, is relatively low. The principle control device in such a respirator is some type of pressure-actuated valve having various combinations of diaphragms, springs, magnets, etc. which switch from supply to exhaust when a pre-set pressure is reached. They have the additional advantages of being small, light-weight and consequently easily portable. In general, they have means for allowing triggering of the supply of gas by means of an attempt by the patient to inhale. The principle disadvantage of this type of respirator is that it cannot maintain delivery of a pre-set volume of gas to the patient if resistance to gas flow develops either in the air-way to the patient or in the patient himself.
The volume-cycled respirator has the important advantage of being able to deliver a constant tidal volume independent of a change in the patient's compliance and resistance developing in the air-way. Moreover, it is possible to include accessory features with a volume cycled respirator. Such features are periodic maximal inflation (sigh), effective humidification of the medical gas, multiple alarm systems informing the operator of various types of difficulties which may occur and simple adjustment of the quantity of medical gas to be supplied to the patient.
Volume-cycled respirators of the prior art have been high in cost, and of large size and weight, as the result of which they have not been truly portable. Moreover, they have involved a large number of components and moving parts, resulting in the need for frequent maintenance and presenting problems of reliability. Also, in common with pressure cycled respirators it has not been possible to vary the amount of gas delivered over a sufficiently wide range so that a single unit could be used in the treatment of both pediatric and adult patients. Finally, no unit is available which can be powered by pressurized gas alone.
SUMMARY OF THE INVENTION
Pressurized medicinal gas is supplied at a constant flow rate to a rigid tank. An air supply tube runs from the rigid tank to a means for connecting the tube to a patient. The means may be a face mask, a nose mask or even a tube inserted into the trachea of the patient. Intermediate of the rigid tank and the patient are a normally closed valve, a fine filter and a humidifier.
A signal generator using pneumatic logic, powered either by the source of medicinal gas or by an auxiliary source of compressed air which need not be as pure as the medicinal gas, opens a normally closed valve in the main air-way to the patient for a fixed period. Close to the end of the main air-way connecting with the patient is a side tube at the end of which is a normally open valve. The normally open valve on the side tube is held in closed position by a signal from the signal generator when medicinal gas is being supplied to the patient. At the end of the fixed period which is adjustable, the valve and the main air-way are closed, and shortly thereafter the signal to the valve in the side tube is cut off. At this point the side-tube valve opens and the patient exhales through the side tube. It should be noted that the system is fail-safe in that disconnection of the signal generator from its source of pressurized gas allows the exhaust valve to open so that the patient can breath through the side tube.
As aforenoted, medicinal gas is supplied to the rigid tank at a fixed rate. During inhalation, the pressure in the rigid tank drops and during exhalation the pressure in the rigid tank rises to its original value. In the event that the compliance of the patient increases or resistance in the main air tube increases, the volume of air delivered to the patient will decrease on the first cycle after the resistance develops. As a consequence, the pressure in the rigid tank will not drop as far as it normally would during inspiration, and on the next expiration the pressure will rise to a value higher than normal. Since the rigid tank is being supplied with gas at a constant rate, the pressure in the tank will rise until the volume delivered to the patient on each cycle will equal the volume delivered to the tank during each cycle, thus restoring the conditions under which the patient is fed with the desired quantity of medicinal gas on each cycle.
In the event that the patient is too weak to make any attempt to inhale, the signal generator logic operating the medicinal gas supply under the conditions described is said to be operating in "automatic mode." However, it is possible to modify the logic so that each cycle of inspiration and exhalation is initiated or triggered by an attempt of the patient to inhale. Under such conditions, the respirator is said to be operating in the "demand mode." This method of operation is preferable when the patient is strong enough to attempt to breath. However, it carries with it the dangers that the patient may become enfeebled and too weak to attempt to inhale. The present invention includes a shift circuit which changes the mode of operation from demand to automatic in the event that the patient fails to attempt to inhale within a pre-set number of seconds subsequent to the end of exhalation.
The logic includes a maximal inflation circuit termed a "sigh" circuit which provides for a deeper inhalation after a preset number of inhalations of normal volume.
Where a respirator is being used in a region such as a hospital where a supply of compressed air is usually available, the compressed air, if properly filtered, can be used both for the main source of medicinal gas and as the power for the logic circuit. An automatic substitution circuit is provided in the present invention so that if the main supply of compressed air fails, connection is automatically made to an auxiliary tank which may contain either compressed air or medicinal gas. In this way, the patient is protected against failure of the main supply.
An object of the present invention is to provide an improved volume cycled respirator which is powered by pressurized gas alone and which is portable.
Another object of the present invention is to provide an improved volume cycled respirator utilizing a rigid tank instead of the usual bellows or bag.
A further object of the present invention is to provide an improved volume cycled respirator in which a rigid tank is supplied with a medical gas at a fixed controlled rate.
Still another object of the present invention to provide an improved volume cycled respirator including control by a signal generator consisting of fluidic logic elements and which may be powered either with medical gas or with clean compressed air.
Another object of the present invention is to provide an improved volume cycled respirator which is simple in construction, inexpensive, highly reliable, easy to operate and requiring virtually no maintenance.
Yet another object of the present invention is to provide an improved volume cycled respirator which is sufficiently portable and simple to operate so that it can be used while a patient is in transit in a vehicle such as an ambulance, a police car or a fire engine.
Yet a further object of the present invention is to provide an improved volume cycled respirator suitable for treatment of pediatric, adult and geriatric patients.
Still a further object of the present invention is to provide an improved volume cycled respirator which automatically switches over to an emergency source of medical gas in the event that the main power supply fails.
Yet a further object of the present invention is to provide an improved volume cycled respirator in which provision is made for connecting the patient directly to the ambient atmosphere in the event of complete system failure.
A particularly significant object of the present invention is to provide an improved volume cycled respirator having both visible and audible alarms to indicate any anticipated type of malfunction, including failure of a gas supply and loss by the patient of the ability to attempt to inhale.
A still further object of the present invention is to provide an improved volume cycled respirator which may be used as an anesthesia ventilator.
A further object of the present invention is to provide an improved volume cycled respirator with means for an automatically volume compensated periodic maximal inflation (sigh) wherein the periodic sigh does not change the average rate of supply of medical gas to the patient.
A still further object of the present invention is to provide an improved volume cycled respirator having a cycle in which is present a plateau period at the end of inspiration to allow equilibration of the various compartments of the patient's lungs and during which patient's alveolar pressure may be measured.
A further object of the present invention is to provide an improved volume cycled respirator having means for accurately mixing a plurality of gases to form a desired medical gas composition.
Yet a further object of the present invention is to provide an improved volume cycled respirator having means for controlling both the inspiratory time and the expiratory time.
Yet another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the expiratory resistance thus providing means for retarding the rate of expiratory flow.
Still another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the end expiratory pressure so that it is either above or below ambient pressure.
Another object of the present invention is to provide means for interconnecting fluidic logic elements without the use of tubing.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 is a block diagram showing the principle components of a volume cycled respirator in accordance with the present invention;
FIG. 2 is a block diagram of a volume cycled respirator in accordance with the present invention indicating how gases are mixed to form a suitable feed to a patient, and giving a diagrammatic key to components;
FIG. 3 contrasts essential components of the present invention with analogous components of the prior art;
FIG. 4 is a diagram of the signals emitted by a pneumatic logic system in accordance with the present invention where the respirator is to operate in automatic mode;
FIG. 5 is a schematic diagram of the basic oscillator circuit of the logic system for operating the respirator in automatic mode;
FIG. 6 is a diagram of the signals necessary for operating the respirator in demand mode;
FIG. 7 is a diagram of a signal generator system showing how a demand circuit is coupled with the basic oscillator circuit;
FIG. 8 is a shift circuit which renders the demand circuit inoperative in the event that the patient becomes too feeble to inhale;
FIG. 9 is a diaphragm-operated demand valve in section with a diagrammatic representation of a signal generator for supplying a triggering pulse;
FIG. 10 is a sigh circuit which can be connected to the basic oscillator circuit to cause a deeper inhalation than usual at controlled intervals;
FIG. 11 shows how failure of the system or enfeeblement of the patient causes alarms to sound and become visible;
FIG. 12 is a block diagram of the portion of the respirator adjacent to the patient using same;
FIG. 13 shows diagrammatically the valve through which exhalation normally takes place and a redundant valve for connection of the patient to the ambient air in case of total system failure;
FIG. 14 is a diagrammatic representation of a circuit which makes it possible to measure the alveolar pressure in the patient's lungs at the end of inhalation and alternatively to measure continuous system pressure.
FIG. 15 is a device for maintaining the pressure in the patient's lungs above atmospheric at the end of exhalation;
FIG. 16 is a device for lowering the pressure in the patient's lungs below atmospheric at the end of exhalation;
FIG. 17 shows schematically how interconnections may be made between fluidic circuit components by means of grooves molded or otherwise formed in flat plates; and
FIG. 18 is a schematic diagram of a simplified signal generator for operating the respirator in automatic mode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principle of operation of the present invention is exemplified in FIG. 1 where a medical gas supply 21 which may consist of relatively clean compressed air, or oxygen, or an anesthetic is connected to a patient through a quick disconnect 22, a check valve 23, a filter 24, where the filter is fine enough to remove relatively coarse particles and droplets of oil, a pressure regulator 27, an on-off valve 26, a flow meter 28, an adjustable flow control valve 29, a rigid tank 31 having pressure relief valves 32 and 33, a remote-operated normally-closed valve 34, a patient manifold 36 fitted with a fixed maximum pressure relief valve 37 and an adjustable pressure relief valve 38, an ultra-fine filter 39 for preventing infection of the patient, a humidifier 41 which may also be used for medication of the patient and a tube 42 leading to the patient and fitted with connecting means (not shown) which may consist of a face or a nose mask or a tube inserted into the trachea of the patient. Adjacent to the patient is a side tube 43 leading to a normally-open valve 44 through which the patient can exhale. The signals which open normally-closed valve 34 and close normally-open valve 44 are delivered by signal generator 46. Signal generator 46 consists entirely of fluidic-logic elements powered by pressurized gas supply 47. It is possible to use medical gas supply 21 for powering signal generator 46 but in general it is wasteful of relatively expensive medical gas. The signal from the signal generator which operates normally-closed valves is termed A for convenience and the signal which operates normally-open valve 44 is termed signal B for convenience.
Further detail, particularly with respect to the medical gas supply, is shown in FIG. 2, where, in the example shown, each source has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. The usual medical gas supply, is supplemented with an emergency supply, usually of oxygen. Emergency supply 48 has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. In the event of failure of the regular supply, the pressure in supply line 49 becomes inadequate to hold normally-open valve 51 in closed position whereupon valve 51 opens and the emergency supply 48 of oxygen becomes available to the system. Check valve 52 prevents backward flow of oxygen in the event of failure of the normal medical gas supply. It is convenient to use a single switch for 4 on-off valves 53 which are used in starting up and shutting down the system, three of these being in the medical gas supply lines and the fourth shutting off an audible alarm signal. Flow control valves 54 control the rate of flow of each of the components of the medical gas, the rate of flow being shown by flow meters 56. The medical gas components flowing through the flow control valves 54 are mixed in rigid tank 31 and then passed through the air-way as aforenoted. Line 60 connects the patient manifold to a snap sensor (FIG. 11) in the fluidic logic circuitry 46 the function of which will be detailed below. Valve 57 is normally open and is held closed whenever power is supplied to the signal generator 46. In the event of failure of power to the signal generator, valve 57 opens and furnishes an additional connection between the patient and the ambient atmosphere.
Three-way valve 58 connects pressure gauge 59 either to the patient directly through the main air-way so that continuous system pressure may be measured or to the air-way through signal sampling circuit so that the patient's alveolar pressure can be measured.
As aforenoted, the principal differences between the respirator of the present invention and those of the prior art lie in the fact that a rigid tank is used instead of the previous bellows or piston or bag and in the fact that the present system is operated completely by means of pressurized gas so that the assembly is much simpler than those of the prior art. The differences are indicated schematically in FIG. 3.
The wave shapes sent to normally-closed valve 34 and normally-open valve 44 by signal generator 46 are shown in FIG. 4 wherein zero on the ordinate axis indicates the absence of a signal and a one indicates the presence of a signal. The C-pulse is put out by the signal generator in addition to A- and B-pulses, the purpose of the C-pulse being to make it possible to measure alveolar pressure in the lungs of the patient at the end of inhalation. The alveolar pressure is measured in the interval between the end of inhalation which is indicated by time 1 on the abscissa of the diagram and the beginning of exhalation at time 2. The period of time between 1 and 2 is indicated by the letter d. An interval between the end of exhalation and the beginning of inhalation is also introduced between times 3 and 4 to allow sufficient time to elapse for exhaust valve 44 to close before inlet valve 34 opens. The time interval between numerals 3 and 4 is indicated by the Greek letter delta in FIG. 4. It should be noted that inhalation takes place on the output of the signal whereas exhalation takes place in the absence of a signal from the signal generator due to the fact that valve 34 is normally closed and valve 44 is normally open. The basic oscillator circuit in the signal generator is shown in FIG. 5. The circuit in this form, that is, without accessory circuits, operates in what is termed "automatic mode." In this mode, it is assumed that the patient is too feeble to attempt to breath by himself so that medical gas is supplied in selected volume and at a selected frequency to the patient and the elasticity of the patient's chest and thorax are relied upon for exhalation over a period which again is adjustable subject to the discretion of an attendant. The pneumatic circuit of FIG. 5 consists of 10 pneumatic gates numbered from 1 to 10 each having a control chamber with ports 1 and 2 therein and an output chamber with ports 3, 4 and 5 therein. Each control chamber is separated from the output chamber by a diaphragm as shown schematically, and each diaphragm with the exception of that in gate 4 is biased toward port 1 by a spring. Movement of the diaphragm toward port 1 closes port 4 and opens port 5; movement of the diaphragm toward port 2 opens port 4 and closes port 5. Port 3 is always open and is regarded as the output port. The triangles in the Figure indicate connections to what is in general a single source of pressurized gas. The circles labelled C 1 to C 3 are gas reservoirs and the facing arcs labelled R 1 through R 8 are orifices. The orifices with an arrow therethrough are adjustable. The combination of C 2 and R 5 acts as a delay line and the delay is indicated by the Greek letter delta. Similarly the combination of R 6 and C 3 acts as a delay line and the combination is labelled with d. The arrows labelled A through D at the right hand edge of the diagram indicate the destinations of the output signals of the basic oscillator circuit. The letter N indicates that the point designated is pressurized; the letter F indicates that the point is unpressurized. A=F indicates that a signal in the form of pressurized gas is being sent to the appropriate valve (34), and similarly for B, C and D.
As aforenoted, port 3 is generally but not necessarily the output port for transfer of pressure to another logic element. One of the other ports in the output chamber may be used to vent pressure and is termed a "dump port." Where the vented gas need not traverse a flow-rate-restricting orifice, the venting is termed "quick-dumping."
The operation of the oscillator circuit will be understood from Table 1 which shows the condition of the circuit at each stage and from the explanation which follows. In the table and in FIG. 4, t i is the period during which the patient inhales and t e is the period during which the patient exhales. The total period during which valve B (44) is closed is labelled t B .
The state of the Basic Oscillator Circuit operating in Automatic mode, i.e., without demand signal from the patient is shown in FIG. 5 for t=3. The state corresponds to the circled points in FIG. 4.
TABLE I ____________________________________________________________ ______________ AUTOMATIC MODE CYCLING TIME Control Input Output (FIG. 4) Gate No. Port/State Port/State State (Port 3) Notes ____________________________________________________________ ______________ 1. Initial 4 1 off 5 open ON 3 1 on 5 open OFF 10 1 off 5 open OPEN Quick dump 1 2 off 5 closed OFF (A) 2 1 on 4 open ON 7 2 off 5 closed OFF 8 1 off 5 open ON (B) 9 1 on 4 open ON (C) 5 1 off 5 open OFF Through Orifice 6 1 on 5 closed OPEN 2. d 7 2 on 5 open ON 8 1 on 5 closed OFF (B) 9 2 on 4 closed OFF (C) 5 1 on 4 open ON 3. t e 4 1 on 5 closed OFF 3 1 off 5 open ON 10 1 on 5 closed OPEN 1 2 off 5 closed OFF 2 1 off 4 closed OFF 6 1 off 5 open OPEN Quick Dump 7 2 off 5 closed OFF 3. t e 8 1 off 5 open ON (B) 9 2 off 4 closed OFF 5 1 off 4 closed To Through Atmosphere R 1 4. δ 1 2 on 5 open ON (A) 5. t i 4 1 off 5 open ON 3 1 on 5 closed OFF 10 1 off 5 open OPEN Quick Dump 1 2 off 5 closed OFF (A) 2 1 on 4 open ON 6 1 on 5 closed OPEN C 3 Filling 7 2 off 5 closed OFF 8 1 off 5 open ON (B) 9 1 on 4 open ON (C) ____________________________________________________________ ______________
At time 3 signal B should be on, signal A should be off and signal C should be off. Now, referring to Table 1, we see that on gate 4, port 1 is marked on indicating that there is pressure at this point. Consequently, port 5 is closed and port 3 is unpressurized or as is designated here, off. Gate 3, port 1 is off, supply port 5 is open, port 3 is on, and consequently, port 1 of gate 10 is also on. This closes gate 10, port 5 and reservoir C 2 starts filling through R 5 . Gate 1, port 2 is off so gate 5 is closed and there is no A signal, which is as it should be according to FIG. 4. At gate 2, port 1 is off, port 4 is closed and port 3 is off. Consequently, gate 6, port 5 is open so that reservoir C 3 is connected to the outside atmosphere through port 3 and must be empty. At gate 7 port 2 is off, so supply 5 port is closed and port 3 is off. Gate 8, port 1 is therefore off connecting the supply at port 5 to port 3 so signal B is on, which again corresponds to FIG. 4. It should be noted that gate 8 is an inverter, giving a signal at port 3 when port 1 is unpressurized and vice versa.
At gate 9 both ports 1 and ports 2 are unpressurized, so the biasing spring in the control compartment moves the diaphragm to close supply port 4 as the result of which there is no signal coming through port 3 and signal C is off, again corresponding to the diagram. The signal D is always on when the system is connected to a supply of pressurized gas. Failure of the gas supply, turns off signal D, opens valve 57 to connect the patient with the external air, and causes alarms to become audible and visible. Orifices R 7 and R 8 are introduced in order to lower the pressure of signal D.
As can be seen from FIG. 5, all of the gates with the exception of gate 4 have biasing springs in the control chamber. This spring is omitted in gate 4 in order that the supply pressure at gate 5 should be adequate to move the diaphragm in gate 4 when both ports 1 and 2 are unpressurized. The supply pressure at gate 4, port 5 is reduced by orifices R 3 and R 4 in order that pressurizing port 1 will move the diaphragm against the pressure coming from port 5 without the aid of the usual biasing spring. The principle of operation of the volume cycle respirator can now be presented in terms of automatic mode cycling. Medical gas flows at a constant rate into a rigid tank 31. The output from the reservoir is connected to normally closed pilot valve 34. By periodically opening and closing valve 34 for a specified and controlled length of time, a known volume of gas termed "tidal volume" (T.V.) is allowed to leave the reservoir. The system provides for delivery of a constant volume of gas during each minute, the so called "minute volume" (M.V.) of gas, independent of changing input impedance or development of impedance in the system. The system automatically compensates for any changes in patient's input impedance by supplying an increased input pressure, great enough to provide the specified volume of gas to the patient in the given length of time. The tidal volume is established by the respirator cycle rate in accordance with the following equation: ##EQU1##
Should the patient input impedance build up suddenly, the first cycle thereafter would supply a slightly diminished tidal volume since the reservoir pressure would still be at the pre-build-up level. During the several following cycles the pressure would tend to increase in the reservoir, since with a constant gas flow into the reservoir, more gas would be entering than leaving. This would continue to occur until the increased pressure would be great enough to overcome the increased impedance and re-establish the equilibrium condition, namely, that in which the volume of gas leaving the reservoir is equal to the volume of gas entering the reservoir, thereby re-establishing the same constant minute volume. The maximum pressure supplied by the reservoir is controlled by a panel-mounted adjustable pressure relief valve 32. Adjustable relief valve 33 which can be set for the same pressure or slightly higher is redundant and is present for purposes of safety.
The maximum pressure reaching the patient's lungs is established by adjustable relief valve 38. Fixed maximum pressure relief valve 37 which is pre-set to about 100 cm of water serves as a second stage of protection. All relief valves re-seal automatically when the pressure is returned within the pre-established safe limit.
This method of intermittent pressure release makes unnecessary the use of a collapsible chamber such as a piston, bellows or bag as is used in other "volume cycled" respirators. It also does away with complex motive-device systems needed to move the collapsible chamber. Also, since the signal generator can be operated on ordinary compressed air, none of the valuable medicinal gas is wasted in operation of the system.
A single cycle of automatic mode operation consists of the following steps:
1. (see FIGS. 2 and 4) Pulse B on. This closes the port of patient exhaust valve B assuring that all gas supplied will go to the patient and not to the atmosphere.
2. After a small, pre-set delay time δ delta being large enough to allow complete closure of valve B, pulse A from the signal generator opens valve 34 allowing a "pressure release" from the reservoir and gas is supplied to the patient through line 42.
3. After t i (inspiratory time) signal A returns to zero and valve 34 closes, stopping flow to the patient and beginning pressure increase in the reservoir.
4. Valve B remains actuated for a pre-set length of time (t B ).
5. Plateau time (d) is the time during which valve 34 has already closed but signal B is still on, valve B still being actuated.
The plateau period is a period of zero flow so that equilibration takes place and the respirator pressure is equal to the internal pressure in the respiratory system of the patient, which in this case is the alveolar pressure. This period of zero flow allows equilibration of pressures and gas concentrations in the various compartments of the lungs, thus producing a more uniform distribution and more efficient transport and utilization of gases.
6. During time (d) signal C connects a pressure gauge 59 through three-way valves 58 to the system downstream of valve 34 thus making it possible to take a direct reading on the alveolar pressure of the patient.
7. Signal B off. This opens the patient exhaust valve to the atmosphere allowing expiration during a length of time t e (expiration time) lasting until the on-set of the next cycle.
The respirator of the present invention is designed so that it can also operate in the demand mode, namely, an attempt by the patient to inhale is used to trigger each cycle. FIG. 6 shows the pulse logic diagram for operation in the demand mode. In the period between digit 1 and digit 2 the respirator waits for the demand signal. The demand signal is shown in the diagram as starting at 2 and reaching full strength at 2 + ε.
The condition of the demand circuit and the oscillator circuit at time t = 1 is shown in FIG. 7. The connection between the demand circuit and the oscillator circuit takes place at gate 5 port 4 from which variable orifice R 2 and the connection to the pressurized gas supply have been removed. These items have been placed at gate 11 port 5 of the demand circuit. When the signal generator is operating in the demand mode, a shift signal, the operation of which will be described later, applies a permanent pressure to gate 11, port 1 so that port 5 of gate 11 is permanently closed. When the system is to be operated in the automatic mode, pressure is removed from gate 11, port 1 which places ports 5 and 3 of gate 11 in direct connection with port 4 of gate 5.
The way in which the system responds to a demand signal from the demand circuit is shown in Table 2.
TABLE 2 ____________________________________________________________ ______________ SIGNAL GENERATOR & DEMAND CIRCUIT (Demand mode operation) TIME Gate Central Port Input Port Output State Notes Port 3 ____________________________________________________________ ______________ t = 1 4 2 ON 5 OPEN ON 3 1 ON 5 CLOSED OFF 10 1 OFF 5 OPEN OPEN Quick dump 1 2 OFF 5 CLOSED OFF (A) 2 1 ON 4 OPEN ON 6 1 ON 5 CLOSED OPEN C 3 starts filling 7 2 OFF 5 CLOSED OFF Point Q OFF 8 1 OFF 5 OPEN ON (B) 9 1 ON 4 OPEN ON (C) 5 1 OFF 4 CLOSED TO ATM 1 + ε 7 2 ON 5 OPEN ON Point Q ON 8 1 ON 5 CLOSED OFF (B) 9 2 ON 4 CLOSED OFF (C) 5 1 ON 5 CLOSED OFF Gates 4, 3, 10, 1, 2, 6. unchanged CIRCUIT WILL REMAIN IN THIS CONDITION UNTIL A DEMAND SIGNAL IS RECEIVED. 2 14 1 ON 4 OPEN ON Demand SINGLE Signal 13 ON SHOT 2 12 1 ON 4 OPEN ON Flip Flop Demand Set Signal 11 1 ON 4 ON ON By Def. of Demand mode. Port 1 is ON 5 1 ON 4 OPEN ON C 1 filled. 4 1 ON 5 CLOSED OFF 3 1 OFF 5 OPEN ON 10 1 ON 5 CLOSED 1 2 OFF 5 CLOSED OFF (A) 2 1 OFF 4 CLOSED OFF 7 2 OFF 5 CLOSED OFF Point Q OFF 6 1 OFF 5 OPEN Quick dump 8 1 OFF 5 OPEN ON (B) 9 1 OFF 4 CLOSED OFF (C) 2 + ε 5 1 OFF 5 OPEN TO ATM THRU R 1 C 1 starts emptying All other gates unchanged 3 1 2 ON 5 OPEN ON (A) start of After inspiration t = δ 4 ti 5 1 OFF 5 OPEN TO ATM C 1 empty All others the same 4 + ε 5 1 OFF 5 OPEN TO ATM 4 1 OFF 5 OPEN ON 3 1 ON 5 CLOSED OFF 10 1 OFF 5 OPEN quick dump 4 + ε 1 2 OFF 5 CLOSED OFF (A) 2 1 ON 4 OPEN ON 6 1 ON 5 CLOSED Point Q 7 2 OFF 5 CLOSED OFF OFF 9 1 ON 4 OPEN ON (C) 5 7 2 ON 5 OPEN ON Point Q ON After 8 1 ON 5 CLOSED OFF (B) t = d 9 2 ON 4 CLOSED OFF (C) 5 1 ON 4 OPEN OFF 35 SINGLE SHOT 12 2 ON 4 CLOSED flip flop reset CIRCUIT REMAINS IN THIS CONDITION UNTIL DEMAND SIGNAL IS RECEIVED ____________________________________________________________ ______________
In the demand circuit, gate 12 is a flip-flop, gates 13 and 35 are single shots and gate 14 receives the demand signal to set the system in operation. Before showing how the system is put into demand mode operation, it is necessary that a contingency which must be guarded against be indicated. This contingency is that when the respirator is operating in the demand mode, the connected patient may become too feeble to inhale with sufficient strength to trigger the demand circuit. In this event, attendants must be called by means of appropriate alarm systems and the respirator must go over automatically to automatic mode cycling. These functions are carried out by the shift circuit of FIG. 8. It is also possible to put the system into demand mode operation by pushing the demand mode button, which is panel mounted, for an instant; this "sets" the flip-flop gate 17 and connects the supply port 4 of gate 18 with port 3 and supplies pressure to port 1 of gate 11 permanently closing port 5 of gate 11 so long as the signal generator is in the demand mode. The demand trigger signal from the patient manifold then activates diaphragm-operated-demand valve 63 which sends a signal to gate 14 of the demand circuit. At the same time, a signal is sent to gate 15 which connects the gas supply at port 4 of gate 15 with port 3 of gate 15, rapidly filling reservoir C 5 and blocking the supply gas pressure from gate 16. At the end of the demand signal from valve 63, port 5 of gate 15 opens and reservoir C 5 starts to empty slowly through orifice R 9 . If no further demand signal from valve 63 is received within a pre-set time, reservoir C 5 empties sufficiently so that port 5 of gate 16 opens and connects port 3 with a pressurized gas supply which is carried through line 72 to reset flip-flop 17 which throws the signal generator into the automatic mode of operation and at the same time sounds an alarm. However, if a demand signal is forthcoming from the patient before reservoir C 5 empties completely, the reservoir is refilled again and gate 17 stays in the position where supply port 4 is connected to output port 3.
As aforenoted, the signal generator can be intentionally set to automatic mode operation by pressing switch 73 which connects port 2 of gate 17 to a pressurized gas supply thus resetting the flip-flop.
The construction of the Diaphragm-Operated Demand valve 63 and its associated fluidic circuitry for generating a pulse are shown in FIG. 9.
A function which can be added to the respirator to enhance its value in the treatment of patients is a volume compensated sigh circuit (periodic maximal inflation). The circuit is shown in FIG. 10 and consists of a sigh pulse generator and a sigh synchronizing circuit. Gate 119 is inserted between gates 5 and three-position valve 74. With the sigh control cut off by the three-position valve 74, reservoir C 1 (FIG. 5) empties through adjustable orifice R 1 and ports 3 and 5 in series of gate 119. When three-position valve 74 is put in the automatic sigh position, and a pressure signal is received at port 1 of gate 119, port 5 of gate 119 is closed and adjustable orifice R 26 is placed in series with adjustable orifice R 1 , increasing the time required for the emptying of reservoir C 1 . The sigh pulse generator circuit can be set so that a sigh signal is delivered only after a pre-set number of cycles. The adjustment as to the frequency of the sigh circuit signal is carried out by a selection of the sizes of tanks C 14 and C 15 and adjustable orifice R 23 which is panel mounted. The three-position valve 74 is also connected so that a sigh can be provided at any time at the discretion of an attendant. Synchronization between the sigh circuit and the phase of the signal generator is carried out by the sigh synchronizing circuit. Details of the operation of the sigh circuit are given in Table 3.
TABLE 3 ____________________________________________________________ ______________ SIGH CIRCUIT (Selector Switch In Auto Sigh Position) TIME Gate Control Input Output Port 3 Notes No. Port/State Port/State State ____________________________________________________________ ______________ Pulse Output- t =O Pulse 113 1 OFF 5 OPEN ON Starts filling Generator C 15 Circuit 111 1 OFF 5 OPEN TO ATM Power ON 112 1 OFF 4 CLOSED After 111 1 ON 4 OPEN ON C 14 fills t SP =Length of C 15 dumpted Sigh Pulse 112 1 ON 4 OPEN to ATM 113 1 ON 5 CLOSED OFF Pulse OFF Dumpted to ATM -t SP + ε 111 1 OFF 5 OPEN TO ATM C 14 starts emptying Where ε is a small time 112 1 OFF 4 CLOSED Interval 113 1 ON 5 CLOSED OFF Pulse still OFF After 113 1 OFF 5 OPEN ON C 14 Empty Pulse Output- T s = Interval 111 1 OFF 5 OPEN TO ATM C 15 starts Between filling Sighs 112 1 OFF 4 CLOSED Synchronizing 114 1 ON 4 OPENS ON flip-flop Circuit flip- switches On CASE I flop Pulse Gener- ator Signal 115 1 ON 4 OPEN ON Arrives When Q is ON 116 1 ON 4 OPEN ON flip-flop flip- switches ON flop 117 1 ON 5 CLOSED OFF 118 flip-flop flip-flop 1 OFF 5 OFF OFF remains OFF 119 1 OFF 5 OPEN TO ATM. After Short Time=ε 114 2 ON 4 CLOSED OFF RESET Q OFF 115 1 OFF 4 CLOSED OFF 117 1 OFF 5 OPEN ON 118 1 ON 4 OPEN ON Flip-flop Set(ON) 119 1 ON 4 OPEN TO ATM through ADD-ON Resistor 116 2 ON 4 CLOSED OFF RESET -Q ON 118 2 ON 4 CLOSED OFF RESET Synchronizing 114 1 ON 4 OPEN ON SET Circuit Case II 115 1 OFF 4 CLOSED OFF Pulse Genera- tor Signal 116 1 OFF 4 CLOSED OFF REMAINS Arrives when RESET (OFF) Q is off. 117 1 OFF 5 OPEN OFF 118 1 OFF 4 CLOSED OFF REMAINS RESET 119 1 OFF 4 CLOSED TO ATM Q ON 114 1 ON 4 OPEN ON SET 115 1 ON 4 OPEN ON 116 1 ON 4 OPEN ON SET 117 1 ON 5 CLOSED OFF 118 1 OFF 4 CLOSED OFF REMAINS RESET 119 1 OFF 4 CLOSED TO ATM After t=ε 114 2 ON 4 CLOSED OFF RESET Q OFF 115 1 OFF 4 CLOSED OFF 117 1 OFF 5 OPEN ON 118 1 ON 4 OPEN ON SET 119 1 ON 4 OPEN TO ATM THROUGH ADD-ON RESISTOR 116 2 ON 4 CLOSED OFF RESET Q ON 118 2 ON 4 CLOSED OFF RESET ____________________________________________________________ ______________
It has already been mentioned that failure to receive a trigger signal when the signal generator is operating in demand mode causes the activation of alarm signals. In general, this alarm is adjusted to sound if an interval of about 6 seconds passes without the arrival of another demand signal. Alarm circuits in addition to that associated with the shift circuit are shown in FIG. 11. Should the main power supply line be disconnected, supply disconnect indicator 77 will show this immediately, port 5 of gate 20 will be opened and the compressed gas stored in tank C 9 will pass through ports 5 and 3 of gate 20 to gate 22 where the combination of orifices R 14 and R 16 and tank C 11 with gate 16 acts as an oscillator to move diaphragm 78 of diaphragm-valve 79 back and forth to cause bell 81 to sound. The same alarm sounds when actuated by gate 21 of the shift circuit.
In the event of a disconnect at the patient manifold or a drop in pressure below a pre-set value, the drop is sensed during signal A by the sensitive snap sensor 82. The disconnect is visually indicated at the indicator 83. The drop in pressure at port 1 of gate 19 disconnects the main power supply therefrom and sets into motion the same train through tank C 9 etc. as described above.
The way in which the patient is connected to the patient supply tube 42 and demand valve 63 is shown in block-diagram form in FIG. 12. With this type of arrangement, four connections must be made from the respirator to the vicinity of the patient. Other types of arrangements are possible in which only three are necessary, but the arrangement shown in FIG. 12 is particularly advantageous in that the dead space between exhaust valve 44 and the patient and between emergency breathing port 57 and the patient is very small.
Valves 44 and valve 57 are both diaphragm valves. In valve 44 (FIG. 13) diaphragm 87 is in close proximity to the orifice of tube 88. Consequently, any attempt by the patient to inhale causes the diaphragm to seal against the tube and causes a slight drop in pressure in tube 42 which is transmitted through demand port 89 to the demand valve.
So long as the respirator is connected to a source of pressurized gas, signal D will be received at port 91 of valve 57 to hold diaphragm 92 in closed position against the urging of spring 86. In the event of failure of signal D, spring 86 forces and maintains diaphragm 92 into open position and connects the patient directly to the ambient air.
It is desirable that it be possible to measure the alveolar pressure in the lungs of a patient at the end of inspiration. When signal C is received (FIG. 14) from the oscillator circuit by gate 30, damping tank C 13 is connected with the patient manifold through ports 4 and 3 of gate 30 and the alveolar pressure can be measured by turning valve 58 to the proper position. The pressure is read on pressure gauge 59. When signal C is not received, valve 58 may be rotated into position so that the pressure in the patient manifold can be measured.
In certain cases, it is desirable that the pressure in the patient's lungs be above atmospheric pressure at the end of expiration, for this purpose, a transparent vessel 93 is shown in FIG. 15 containing water or a sterilizing solution into which dips an open-ended graduated tube 94 which is adjustable vertically through a seal ring 96. Exhaust from the vessel takes place through a filter 97 which may be either disposable or sterilizable.
In other cases, it is desirable that the pressure in the patient's lungs at the end of expiration be below atmospheric pressure. A venturi 98 as shown in FIG. 16 is fitted into exhaust port 99 of patient valve 44. A jet of gas from the pressurized gas supply is supplied to the venturi 98 through adjustable orifice R 24 . The orifice is adjustable over a range to give a pressure drop ranging from between zero and 20 cm of water.
If it is desired to introduce resistance to exhalation without influencing the pressure at the end of exhalation, a flexible cap may be placed over the end of exhaust port 99 with an orifice of selected size in the end thereof (not shown).
As is obvious, the pneumatic logic gates and the passive elements such as orifices and reservoirs of the signal generator could be connected by tubing of appropriate diameter. However, a preferred embodiment of connections between the various elements is one in which the interconnections are formed as grooves in plates, which, most suitably, are of moldable plastic. If three plastic plates, each about 6 millimeters in thickness are stacked together, two interfaces are formed. Grooves can be formed at either face of the two interfaces. In FIG. 17, circuit plate 101 is shown as having grooves formed therein in a perpendicular pattern. Holes which are perpendicular to the face of the circuit plate penetrate the plate and connect channels on opposite faces. It is necessary to have grooves at both interfaces so that lines can cross each other. Closed channels are formed when top cover plate 102 and bottom cover plate 103 are sealed to circuit plate 101. Logic gates or passive elements are then connected to circuit channels 104 through ports (not shown) in top cover plate 102. The analogy to printed circuits as used in electronic devices is obvious, so that the system of connections of the device of FIG. 17 may be appropriately termed printed pneumatic circuitry.
Suitably placed ports 106 in bottom cover plate 103 are used as mounting holes, exhaust ports, for making connections to passive elements (R and C) and to receive input and send output signals.
Since respirators are to be used with a series of patients, protection against cross-infection must be provided. Filters 24 and 39 are designed to protect the respirator itself from dust particles and liquid droplets. Protection of the patient is provided by filter 39 (FIG. 1) which is ultra-fine in porosity. A preferred form is the so-called micro-port filter which may be sterilized. Filter 97 (FIG. 15) may be of the same type. The purpose of filter 97 is to prevent contamination of the air in the vicinity of the patient. The primary purpose of humidifier 41 is to add moisture to the air being supplied to the patient. However, medication can also be incorporated in the humidifier to be carried with the air stream to the patient. The design of the humidifier is not critical except that it must not alter tidal volume.
A simplified signal generator is shown in FIG. 18 in the state corresponding to time = 1 (FIG. 4). The operation of this circuit is clear from Table 4.
TABLE 4 ____________________________________________________________ ______________ SIMPLIFIED OSCILLATOR CIRCUIT OUTPUT GATE CONTROL INPUT PORT 3 TIME NO. Port/State Port/State STATE NOTES ____________________________________________________________ ______________ 1 41 1 off 4 open OFF C 14 filled and starts emptying through R 25 42 1 on 5 closed OFF 43 1 off 5 closed OFF (A) C 15 empty 44 1 off 4 closed ON (B) C 16 starts emptying through R 28 45 1 off 5 open ON (C) 2 41 1 off 4 closed OFF C 14 still emptying 42 1 on 5 closed OFF 43 1 off 5 open OFF (A) 44 1 off 4 closed OFF (B) C 16 empty 45 1 off 4 closed OFF (C) 3 42 1 off 5 open ON C 14 empty 43 1 on 5 closed OFF (A) C 15 starts filling 44 1 on 4 open ON (B) 45 1 on 5 closed OFF (C) 41 1 on 4 open ON C 14 starts filling 4 41 1 on 4 open 3 ON C 14 starts filling 42 1 off 5 open 3 ON 43 1 on 5 closed (A) OFF 44 1 on 4 open 3 ON (B) 45 1 on 5 closed 3 OFF (C) 5 41 1 on 4 open 3 ON C 14 still filling 42 1 off 5 open 3 ON 43 1 on 5 closed (A) ON C 15 full 44 1 on 4 open 3 ON (B) ON 45 1 on 5 closed 3 OFF (C) OFF ____________________________________________________________ ______________
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above article without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
The use of a respirator is indicated in a wide variety of medical conditions such as chronic pulmonary emphysema, chronic bronchitis, pulmonary edema, dyspnea, pneumoconiosis, pulmonary arteriosclerosis, bronchial asthma, among others. It is also applicable for use during surgery as an anesthesia ventilator, for postoperative support, in treatment of a patient who is comatose or in shock, and, in short, in support of any patient unable to maintain normal autonomous respiration.
In the design of a respirator, it must be taken into account that the respirator may be used in a hospital or in surroundings where no electrical power is available, and, moreover, the respirator must be suitable for use with patients of any age from infancy through adulthood to geriatric.
Respirators fall into two categories, either (1) pressure cycled or (2) volume cycled. In the first category, medicinal gas, which includes filtered air, oxygen and mixtures containing oxygen is supplied to the patient until a fixed pressure is reached. In the second type, medicinal gas is supplied to the patient until a fixed volume has been transferred. Pressure cycled respirators, up to now, have been more popular because of the fact that the mechanism involved is relatively simple and the cost, consequently, is relatively low. The principle control device in such a respirator is some type of pressure-actuated valve having various combinations of diaphragms, springs, magnets, etc. which switch from supply to exhaust when a pre-set pressure is reached. They have the additional advantages of being small, light-weight and consequently easily portable. In general, they have means for allowing triggering of the supply of gas by means of an attempt by the patient to inhale. The principle disadvantage of this type of respirator is that it cannot maintain delivery of a pre-set volume of gas to the patient if resistance to gas flow develops either in the air-way to the patient or in the patient himself.
The volume-cycled respirator has the important advantage of being able to deliver a constant tidal volume independent of a change in the patient's compliance and resistance developing in the air-way. Moreover, it is possible to include accessory features with a volume cycled respirator. Such features are periodic maximal inflation (sigh), effective humidification of the medical gas, multiple alarm systems informing the operator of various types of difficulties which may occur and simple adjustment of the quantity of medical gas to be supplied to the patient.
Volume-cycled respirators of the prior art have been high in cost, and of large size and weight, as the result of which they have not been truly portable. Moreover, they have involved a large number of components and moving parts, resulting in the need for frequent maintenance and presenting problems of reliability. Also, in common with pressure cycled respirators it has not been possible to vary the amount of gas delivered over a sufficiently wide range so that a single unit could be used in the treatment of both pediatric and adult patients. Finally, no unit is available which can be powered by pressurized gas alone.
SUMMARY OF THE INVENTION
Pressurized medicinal gas is supplied at a constant flow rate to a rigid tank. An air supply tube runs from the rigid tank to a means for connecting the tube to a patient. The means may be a face mask, a nose mask or even a tube inserted into the trachea of the patient. Intermediate of the rigid tank and the patient are a normally closed valve, a fine filter and a humidifier.
A signal generator using pneumatic logic, powered either by the source of medicinal gas or by an auxiliary source of compressed air which need not be as pure as the medicinal gas, opens a normally closed valve in the main air-way to the patient for a fixed period. Close to the end of the main air-way connecting with the patient is a side tube at the end of which is a normally open valve. The normally open valve on the side tube is held in closed position by a signal from the signal generator when medicinal gas is being supplied to the patient. At the end of the fixed period which is adjustable, the valve and the main air-way are closed, and shortly thereafter the signal to the valve in the side tube is cut off. At this point the side-tube valve opens and the patient exhales through the side tube. It should be noted that the system is fail-safe in that disconnection of the signal generator from its source of pressurized gas allows the exhaust valve to open so that the patient can breath through the side tube.
As aforenoted, medicinal gas is supplied to the rigid tank at a fixed rate. During inhalation, the pressure in the rigid tank drops and during exhalation the pressure in the rigid tank rises to its original value. In the event that the compliance of the patient increases or resistance in the main air tube increases, the volume of air delivered to the patient will decrease on the first cycle after the resistance develops. As a consequence, the pressure in the rigid tank will not drop as far as it normally would during inspiration, and on the next expiration the pressure will rise to a value higher than normal. Since the rigid tank is being supplied with gas at a constant rate, the pressure in the tank will rise until the volume delivered to the patient on each cycle will equal the volume delivered to the tank during each cycle, thus restoring the conditions under which the patient is fed with the desired quantity of medicinal gas on each cycle.
In the event that the patient is too weak to make any attempt to inhale, the signal generator logic operating the medicinal gas supply under the conditions described is said to be operating in "automatic mode." However, it is possible to modify the logic so that each cycle of inspiration and exhalation is initiated or triggered by an attempt of the patient to inhale. Under such conditions, the respirator is said to be operating in the "demand mode." This method of operation is preferable when the patient is strong enough to attempt to breath. However, it carries with it the dangers that the patient may become enfeebled and too weak to attempt to inhale. The present invention includes a shift circuit which changes the mode of operation from demand to automatic in the event that the patient fails to attempt to inhale within a pre-set number of seconds subsequent to the end of exhalation.
The logic includes a maximal inflation circuit termed a "sigh" circuit which provides for a deeper inhalation after a preset number of inhalations of normal volume.
Where a respirator is being used in a region such as a hospital where a supply of compressed air is usually available, the compressed air, if properly filtered, can be used both for the main source of medicinal gas and as the power for the logic circuit. An automatic substitution circuit is provided in the present invention so that if the main supply of compressed air fails, connection is automatically made to an auxiliary tank which may contain either compressed air or medicinal gas. In this way, the patient is protected against failure of the main supply.
An object of the present invention is to provide an improved volume cycled respirator which is powered by pressurized gas alone and which is portable.
Another object of the present invention is to provide an improved volume cycled respirator utilizing a rigid tank instead of the usual bellows or bag.
A further object of the present invention is to provide an improved volume cycled respirator in which a rigid tank is supplied with a medical gas at a fixed controlled rate.
Still another object of the present invention to provide an improved volume cycled respirator including control by a signal generator consisting of fluidic logic elements and which may be powered either with medical gas or with clean compressed air.
Another object of the present invention is to provide an improved volume cycled respirator which is simple in construction, inexpensive, highly reliable, easy to operate and requiring virtually no maintenance.
Yet another object of the present invention is to provide an improved volume cycled respirator which is sufficiently portable and simple to operate so that it can be used while a patient is in transit in a vehicle such as an ambulance, a police car or a fire engine.
Yet a further object of the present invention is to provide an improved volume cycled respirator suitable for treatment of pediatric, adult and geriatric patients.
Still a further object of the present invention is to provide an improved volume cycled respirator which automatically switches over to an emergency source of medical gas in the event that the main power supply fails.
Yet a further object of the present invention is to provide an improved volume cycled respirator in which provision is made for connecting the patient directly to the ambient atmosphere in the event of complete system failure.
A particularly significant object of the present invention is to provide an improved volume cycled respirator having both visible and audible alarms to indicate any anticipated type of malfunction, including failure of a gas supply and loss by the patient of the ability to attempt to inhale.
A still further object of the present invention is to provide an improved volume cycled respirator which may be used as an anesthesia ventilator.
A further object of the present invention is to provide an improved volume cycled respirator with means for an automatically volume compensated periodic maximal inflation (sigh) wherein the periodic sigh does not change the average rate of supply of medical gas to the patient.
A still further object of the present invention is to provide an improved volume cycled respirator having a cycle in which is present a plateau period at the end of inspiration to allow equilibration of the various compartments of the patient's lungs and during which patient's alveolar pressure may be measured.
A further object of the present invention is to provide an improved volume cycled respirator having means for accurately mixing a plurality of gases to form a desired medical gas composition.
Yet a further object of the present invention is to provide an improved volume cycled respirator having means for controlling both the inspiratory time and the expiratory time.
Yet another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the expiratory resistance thus providing means for retarding the rate of expiratory flow.
Still another object of the present invention is to provide an improved volume cycled respirator having means for adjusting the end expiratory pressure so that it is either above or below ambient pressure.
Another object of the present invention is to provide means for interconnecting fluidic logic elements without the use of tubing.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 is a block diagram showing the principle components of a volume cycled respirator in accordance with the present invention;
FIG. 2 is a block diagram of a volume cycled respirator in accordance with the present invention indicating how gases are mixed to form a suitable feed to a patient, and giving a diagrammatic key to components;
FIG. 3 contrasts essential components of the present invention with analogous components of the prior art;
FIG. 4 is a diagram of the signals emitted by a pneumatic logic system in accordance with the present invention where the respirator is to operate in automatic mode;
FIG. 5 is a schematic diagram of the basic oscillator circuit of the logic system for operating the respirator in automatic mode;
FIG. 6 is a diagram of the signals necessary for operating the respirator in demand mode;
FIG. 7 is a diagram of a signal generator system showing how a demand circuit is coupled with the basic oscillator circuit;
FIG. 8 is a shift circuit which renders the demand circuit inoperative in the event that the patient becomes too feeble to inhale;
FIG. 9 is a diaphragm-operated demand valve in section with a diagrammatic representation of a signal generator for supplying a triggering pulse;
FIG. 10 is a sigh circuit which can be connected to the basic oscillator circuit to cause a deeper inhalation than usual at controlled intervals;
FIG. 11 shows how failure of the system or enfeeblement of the patient causes alarms to sound and become visible;
FIG. 12 is a block diagram of the portion of the respirator adjacent to the patient using same;
FIG. 13 shows diagrammatically the valve through which exhalation normally takes place and a redundant valve for connection of the patient to the ambient air in case of total system failure;
FIG. 14 is a diagrammatic representation of a circuit which makes it possible to measure the alveolar pressure in the patient's lungs at the end of inhalation and alternatively to measure continuous system pressure.
FIG. 15 is a device for maintaining the pressure in the patient's lungs above atmospheric at the end of exhalation;
FIG. 16 is a device for lowering the pressure in the patient's lungs below atmospheric at the end of exhalation;
FIG. 17 shows schematically how interconnections may be made between fluidic circuit components by means of grooves molded or otherwise formed in flat plates; and
FIG. 18 is a schematic diagram of a simplified signal generator for operating the respirator in automatic mode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principle of operation of the present invention is exemplified in FIG. 1 where a medical gas supply 21 which may consist of relatively clean compressed air, or oxygen, or an anesthetic is connected to a patient through a quick disconnect 22, a check valve 23, a filter 24, where the filter is fine enough to remove relatively coarse particles and droplets of oil, a pressure regulator 27, an on-off valve 26, a flow meter 28, an adjustable flow control valve 29, a rigid tank 31 having pressure relief valves 32 and 33, a remote-operated normally-closed valve 34, a patient manifold 36 fitted with a fixed maximum pressure relief valve 37 and an adjustable pressure relief valve 38, an ultra-fine filter 39 for preventing infection of the patient, a humidifier 41 which may also be used for medication of the patient and a tube 42 leading to the patient and fitted with connecting means (not shown) which may consist of a face or a nose mask or a tube inserted into the trachea of the patient. Adjacent to the patient is a side tube 43 leading to a normally-open valve 44 through which the patient can exhale. The signals which open normally-closed valve 34 and close normally-open valve 44 are delivered by signal generator 46. Signal generator 46 consists entirely of fluidic-logic elements powered by pressurized gas supply 47. It is possible to use medical gas supply 21 for powering signal generator 46 but in general it is wasteful of relatively expensive medical gas. The signal from the signal generator which operates normally-closed valves is termed A for convenience and the signal which operates normally-open valve 44 is termed signal B for convenience.
Further detail, particularly with respect to the medical gas supply, is shown in FIG. 2, where, in the example shown, each source has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. The usual medical gas supply, is supplemented with an emergency supply, usually of oxygen. Emergency supply 48 has its own quick disconnect 22, check valve 23, filter 24, and regulator 27. In the event of failure of the regular supply, the pressure in supply line 49 becomes inadequate to hold normally-open valve 51 in closed position whereupon valve 51 opens and the emergency supply 48 of oxygen becomes available to the system. Check valve 52 prevents backward flow of oxygen in the event of failure of the normal medical gas supply. It is convenient to use a single switch for 4 on-off valves 53 which are used in starting up and shutting down the system, three of these being in the medical gas supply lines and the fourth shutting off an audible alarm signal. Flow control valves 54 control the rate of flow of each of the components of the medical gas, the rate of flow being shown by flow meters 56. The medical gas components flowing through the flow control valves 54 are mixed in rigid tank 31 and then passed through the air-way as aforenoted. Line 60 connects the patient manifold to a snap sensor (FIG. 11) in the fluidic logic circuitry 46 the function of which will be detailed below. Valve 57 is normally open and is held closed whenever power is supplied to the signal generator 46. In the event of failure of power to the signal generator, valve 57 opens and furnishes an additional connection between the patient and the ambient atmosphere.
Three-way valve 58 connects pressure gauge 59 either to the patient directly through the main air-way so that continuous system pressure may be measured or to the air-way through signal sampling circuit so that the patient's alveolar pressure can be measured.
As aforenoted, the principal differences between the respirator of the present invention and those of the prior art lie in the fact that a rigid tank is used instead of the previous bellows or piston or bag and in the fact that the present system is operated completely by means of pressurized gas so that the assembly is much simpler than those of the prior art. The differences are indicated schematically in FIG. 3.
The wave shapes sent to normally-closed valve 34 and normally-open valve 44 by signal generator 46 are shown in FIG. 4 wherein zero on the ordinate axis indicates the absence of a signal and a one indicates the presence of a signal. The C-pulse is put out by the signal generator in addition to A- and B-pulses, the purpose of the C-pulse being to make it possible to measure alveolar pressure in the lungs of the patient at the end of inhalation. The alveolar pressure is measured in the interval between the end of inhalation which is indicated by time 1 on the abscissa of the diagram and the beginning of exhalation at time 2. The period of time between 1 and 2 is indicated by the letter d. An interval between the end of exhalation and the beginning of inhalation is also introduced between times 3 and 4 to allow sufficient time to elapse for exhaust valve 44 to close before inlet valve 34 opens. The time interval between numerals 3 and 4 is indicated by the Greek letter delta in FIG. 4. It should be noted that inhalation takes place on the output of the signal whereas exhalation takes place in the absence of a signal from the signal generator due to the fact that valve 34 is normally closed and valve 44 is normally open. The basic oscillator circuit in the signal generator is shown in FIG. 5. The circuit in this form, that is, without accessory circuits, operates in what is termed "automatic mode." In this mode, it is assumed that the patient is too feeble to attempt to breath by himself so that medical gas is supplied in selected volume and at a selected frequency to the patient and the elasticity of the patient's chest and thorax are relied upon for exhalation over a period which again is adjustable subject to the discretion of an attendant. The pneumatic circuit of FIG. 5 consists of 10 pneumatic gates numbered from 1 to 10 each having a control chamber with ports 1 and 2 therein and an output chamber with ports 3, 4 and 5 therein. Each control chamber is separated from the output chamber by a diaphragm as shown schematically, and each diaphragm with the exception of that in gate 4 is biased toward port 1 by a spring. Movement of the diaphragm toward port 1 closes port 4 and opens port 5; movement of the diaphragm toward port 2 opens port 4 and closes port 5. Port 3 is always open and is regarded as the output port. The triangles in the Figure indicate connections to what is in general a single source of pressurized gas. The circles labelled C 1 to C 3 are gas reservoirs and the facing arcs labelled R 1 through R 8 are orifices. The orifices with an arrow therethrough are adjustable. The combination of C 2 and R 5 acts as a delay line and the delay is indicated by the Greek letter delta. Similarly the combination of R 6 and C 3 acts as a delay line and the combination is labelled with d. The arrows labelled A through D at the right hand edge of the diagram indicate the destinations of the output signals of the basic oscillator circuit. The letter N indicates that the point designated is pressurized; the letter F indicates that the point is unpressurized. A=F indicates that a signal in the form of pressurized gas is being sent to the appropriate valve (34), and similarly for B, C and D.
As aforenoted, port 3 is generally but not necessarily the output port for transfer of pressure to another logic element. One of the other ports in the output chamber may be used to vent pressure and is termed a "dump port." Where the vented gas need not traverse a flow-rate-restricting orifice, the venting is termed "quick-dumping."
The operation of the oscillator circuit will be understood from Table 1 which shows the condition of the circuit at each stage and from the explanation which follows. In the table and in FIG. 4, t i is the period during which the patient inhales and t e is the period during which the patient exhales. The total period during which valve B (44) is closed is labelled t B .
The state of the Basic Oscillator Circuit operating in Automatic mode, i.e., without demand signal from the patient is shown in FIG. 5 for t=3. The state corresponds to the circled points in FIG. 4.
TABLE I ____________________________________________________________ ______________ AUTOMATIC MODE CYCLING TIME Control Input Output (FIG. 4) Gate No. Port/State Port/State State (Port 3) Notes ____________________________________________________________ ______________ 1. Initial 4 1 off 5 open ON 3 1 on 5 open OFF 10 1 off 5 open OPEN Quick dump 1 2 off 5 closed OFF (A) 2 1 on 4 open ON 7 2 off 5 closed OFF 8 1 off 5 open ON (B) 9 1 on 4 open ON (C) 5 1 off 5 open OFF Through Orifice 6 1 on 5 closed OPEN 2. d 7 2 on 5 open ON 8 1 on 5 closed OFF (B) 9 2 on 4 closed OFF (C) 5 1 on 4 open ON 3. t e 4 1 on 5 closed OFF 3 1 off 5 open ON 10 1 on 5 closed OPEN 1 2 off 5 closed OFF 2 1 off 4 closed OFF 6 1 off 5 open OPEN Quick Dump 7 2 off 5 closed OFF 3. t e 8 1 off 5 open ON (B) 9 2 off 4 closed OFF 5 1 off 4 closed To Through Atmosphere R 1 4. δ 1 2 on 5 open ON (A) 5. t i 4 1 off 5 open ON 3 1 on 5 closed OFF 10 1 off 5 open OPEN Quick Dump 1 2 off 5 closed OFF (A) 2 1 on 4 open ON 6 1 on 5 closed OPEN C 3 Filling 7 2 off 5 closed OFF 8 1 off 5 open ON (B) 9 1 on 4 open ON (C) ____________________________________________________________ ______________
At time 3 signal B should be on, signal A should be off and signal C should be off. Now, referring to Table 1, we see that on gate 4, port 1 is marked on indicating that there is pressure at this point. Consequently, port 5 is closed and port 3 is unpressurized or as is designated here, off. Gate 3, port 1 is off, supply port 5 is open, port 3 is on, and consequently, port 1 of gate 10 is also on. This closes gate 10, port 5 and reservoir C 2 starts filling through R 5 . Gate 1, port 2 is off so gate 5 is closed and there is no A signal, which is as it should be according to FIG. 4. At gate 2, port 1 is off, port 4 is closed and port 3 is off. Consequently, gate 6, port 5 is open so that reservoir C 3 is connected to the outside atmosphere through port 3 and must be empty. At gate 7 port 2 is off, so supply 5 port is closed and port 3 is off. Gate 8, port 1 is therefore off connecting the supply at port 5 to port 3 so signal B is on, which again corresponds to FIG. 4. It should be noted that gate 8 is an inverter, giving a signal at port 3 when port 1 is unpressurized and vice versa.
At gate 9 both ports 1 and ports 2 are unpressurized, so the biasing spring in the control compartment moves the diaphragm to close supply port 4 as the result of which there is no signal coming through port 3 and signal C is off, again corresponding to the diagram. The signal D is always on when the system is connected to a supply of pressurized gas. Failure of the gas supply, turns off signal D, opens valve 57 to connect the patient with the external air, and causes alarms to become audible and visible. Orifices R 7 and R 8 are introduced in order to lower the pressure of signal D.
As can be seen from FIG. 5, all of the gates with the exception of gate 4 have biasing springs in the control chamber. This spring is omitted in gate 4 in order that the supply pressure at gate 5 should be adequate to move the diaphragm in gate 4 when both ports 1 and 2 are unpressurized. The supply pressure at gate 4, port 5 is reduced by orifices R 3 and R 4 in order that pressurizing port 1 will move the diaphragm against the pressure coming from port 5 without the aid of the usual biasing spring. The principle of operation of the volume cycle respirator can now be presented in terms of automatic mode cycling. Medical gas flows at a constant rate into a rigid tank 31. The output from the reservoir is connected to normally closed pilot valve 34. By periodically opening and closing valve 34 for a specified and controlled length of time, a known volume of gas termed "tidal volume" (T.V.) is allowed to leave the reservoir. The system provides for delivery of a constant volume of gas during each minute, the so called "minute volume" (M.V.) of gas, independent of changing input impedance or development of impedance in the system. The system automatically compensates for any changes in patient's input impedance by supplying an increased input pressure, great enough to provide the specified volume of gas to the patient in the given length of time. The tidal volume is established by the respirator cycle rate in accordance with the following equation: ##EQU1##
Should the patient input impedance build up suddenly, the first cycle thereafter would supply a slightly diminished tidal volume since the reservoir pressure would still be at the pre-build-up level. During the several following cycles the pressure would tend to increase in the reservoir, since with a constant gas flow into the reservoir, more gas would be entering than leaving. This would continue to occur until the increased pressure would be great enough to overcome the increased impedance and re-establish the equilibrium condition, namely, that in which the volume of gas leaving the reservoir is equal to the volume of gas entering the reservoir, thereby re-establishing the same constant minute volume. The maximum pressure supplied by the reservoir is controlled by a panel-mounted adjustable pressure relief valve 32. Adjustable relief valve 33 which can be set for the same pressure or slightly higher is redundant and is present for purposes of safety.
The maximum pressure reaching the patient's lungs is established by adjustable relief valve 38. Fixed maximum pressure relief valve 37 which is pre-set to about 100 cm of water serves as a second stage of protection. All relief valves re-seal automatically when the pressure is returned within the pre-established safe limit.
This method of intermittent pressure release makes unnecessary the use of a collapsible chamber such as a piston, bellows or bag as is used in other "volume cycled" respirators. It also does away with complex motive-device systems needed to move the collapsible chamber. Also, since the signal generator can be operated on ordinary compressed air, none of the valuable medicinal gas is wasted in operation of the system.
A single cycle of automatic mode operation consists of the following steps:
1. (see FIGS. 2 and 4) Pulse B on. This closes the port of patient exhaust valve B assuring that all gas supplied will go to the patient and not to the atmosphere.
2. After a small, pre-set delay time δ delta being large enough to allow complete closure of valve B, pulse A from the signal generator opens valve 34 allowing a "pressure release" from the reservoir and gas is supplied to the patient through line 42.
3. After t i (inspiratory time) signal A returns to zero and valve 34 closes, stopping flow to the patient and beginning pressure increase in the reservoir.
4. Valve B remains actuated for a pre-set length of time (t B ).
5. Plateau time (d) is the time during which valve 34 has already closed but signal B is still on, valve B still being actuated.
The plateau period is a period of zero flow so that equilibration takes place and the respirator pressure is equal to the internal pressure in the respiratory system of the patient, which in this case is the alveolar pressure. This period of zero flow allows equilibration of pressures and gas concentrations in the various compartments of the lungs, thus producing a more uniform distribution and more efficient transport and utilization of gases.
6. During time (d) signal C connects a pressure gauge 59 through three-way valves 58 to the system downstream of valve 34 thus making it possible to take a direct reading on the alveolar pressure of the patient.
7. Signal B off. This opens the patient exhaust valve to the atmosphere allowing expiration during a length of time t e (expiration time) lasting until the on-set of the next cycle.
The respirator of the present invention is designed so that it can also operate in the demand mode, namely, an attempt by the patient to inhale is used to trigger each cycle. FIG. 6 shows the pulse logic diagram for operation in the demand mode. In the period between digit 1 and digit 2 the respirator waits for the demand signal. The demand signal is shown in the diagram as starting at 2 and reaching full strength at 2 + ε.
The condition of the demand circuit and the oscillator circuit at time t = 1 is shown in FIG. 7. The connection between the demand circuit and the oscillator circuit takes place at gate 5 port 4 from which variable orifice R 2 and the connection to the pressurized gas supply have been removed. These items have been placed at gate 11 port 5 of the demand circuit. When the signal generator is operating in the demand mode, a shift signal, the operation of which will be described later, applies a permanent pressure to gate 11, port 1 so that port 5 of gate 11 is permanently closed. When the system is to be operated in the automatic mode, pressure is removed from gate 11, port 1 which places ports 5 and 3 of gate 11 in direct connection with port 4 of gate 5.
The way in which the system responds to a demand signal from the demand circuit is shown in Table 2.
TABLE 2 ____________________________________________________________ ______________ SIGNAL GENERATOR & DEMAND CIRCUIT (Demand mode operation) TIME Gate Central Port Input Port Output State Notes Port 3 ____________________________________________________________ ______________ t = 1 4 2 ON 5 OPEN ON 3 1 ON 5 CLOSED OFF 10 1 OFF 5 OPEN OPEN Quick dump 1 2 OFF 5 CLOSED OFF (A) 2 1 ON 4 OPEN ON 6 1 ON 5 CLOSED OPEN C 3 starts filling 7 2 OFF 5 CLOSED OFF Point Q OFF 8 1 OFF 5 OPEN ON (B) 9 1 ON 4 OPEN ON (C) 5 1 OFF 4 CLOSED TO ATM 1 + ε 7 2 ON 5 OPEN ON Point Q ON 8 1 ON 5 CLOSED OFF (B) 9 2 ON 4 CLOSED OFF (C) 5 1 ON 5 CLOSED OFF Gates 4, 3, 10, 1, 2, 6. unchanged CIRCUIT WILL REMAIN IN THIS CONDITION UNTIL A DEMAND SIGNAL IS RECEIVED. 2 14 1 ON 4 OPEN ON Demand SINGLE Signal 13 ON SHOT 2 12 1 ON 4 OPEN ON Flip Flop Demand Set Signal 11 1 ON 4 ON ON By Def. of Demand mode. Port 1 is ON 5 1 ON 4 OPEN ON C 1 filled. 4 1 ON 5 CLOSED OFF 3 1 OFF 5 OPEN ON 10 1 ON 5 CLOSED 1 2 OFF 5 CLOSED OFF (A) 2 1 OFF 4 CLOSED OFF 7 2 OFF 5 CLOSED OFF Point Q OFF 6 1 OFF 5 OPEN Quick dump 8 1 OFF 5 OPEN ON (B) 9 1 OFF 4 CLOSED OFF (C) 2 + ε 5 1 OFF 5 OPEN TO ATM THRU R 1 C 1 starts emptying All other gates unchanged 3 1 2 ON 5 OPEN ON (A) start of After inspiration t = δ 4 ti 5 1 OFF 5 OPEN TO ATM C 1 empty All others the same 4 + ε 5 1 OFF 5 OPEN TO ATM 4 1 OFF 5 OPEN ON 3 1 ON 5 CLOSED OFF 10 1 OFF 5 OPEN quick dump 4 + ε 1 2 OFF 5 CLOSED OFF (A) 2 1 ON 4 OPEN ON 6 1 ON 5 CLOSED Point Q 7 2 OFF 5 CLOSED OFF OFF 9 1 ON 4 OPEN ON (C) 5 7 2 ON 5 OPEN ON Point Q ON After 8 1 ON 5 CLOSED OFF (B) t = d 9 2 ON 4 CLOSED OFF (C) 5 1 ON 4 OPEN OFF 35 SINGLE SHOT 12 2 ON 4 CLOSED flip flop reset CIRCUIT REMAINS IN THIS CONDITION UNTIL DEMAND SIGNAL IS RECEIVED ____________________________________________________________ ______________
In the demand circuit, gate 12 is a flip-flop, gates 13 and 35 are single shots and gate 14 receives the demand signal to set the system in operation. Before showing how the system is put into demand mode operation, it is necessary that a contingency which must be guarded against be indicated. This contingency is that when the respirator is operating in the demand mode, the connected patient may become too feeble to inhale with sufficient strength to trigger the demand circuit. In this event, attendants must be called by means of appropriate alarm systems and the respirator must go over automatically to automatic mode cycling. These functions are carried out by the shift circuit of FIG. 8. It is also possible to put the system into demand mode operation by pushing the demand mode button, which is panel mounted, for an instant; this "sets" the flip-flop gate 17 and connects the supply port 4 of gate 18 with port 3 and supplies pressure to port 1 of gate 11 permanently closing port 5 of gate 11 so long as the signal generator is in the demand mode. The demand trigger signal from the patient manifold then activates diaphragm-operated-demand valve 63 which sends a signal to gate 14 of the demand circuit. At the same time, a signal is sent to gate 15 which connects the gas supply at port 4 of gate 15 with port 3 of gate 15, rapidly filling reservoir C 5 and blocking the supply gas pressure from gate 16. At the end of the demand signal from valve 63, port 5 of gate 15 opens and reservoir C 5 starts to empty slowly through orifice R 9 . If no further demand signal from valve 63 is received within a pre-set time, reservoir C 5 empties sufficiently so that port 5 of gate 16 opens and connects port 3 with a pressurized gas supply which is carried through line 72 to reset flip-flop 17 which throws the signal generator into the automatic mode of operation and at the same time sounds an alarm. However, if a demand signal is forthcoming from the patient before reservoir C 5 empties completely, the reservoir is refilled again and gate 17 stays in the position where supply port 4 is connected to output port 3.
As aforenoted, the signal generator can be intentionally set to automatic mode operation by pressing switch 73 which connects port 2 of gate 17 to a pressurized gas supply thus resetting the flip-flop.
The construction of the Diaphragm-Operated Demand valve 63 and its associated fluidic circuitry for generating a pulse are shown in FIG. 9.
A function which can be added to the respirator to enhance its value in the treatment of patients is a volume compensated sigh circuit (periodic maximal inflation). The circuit is shown in FIG. 10 and consists of a sigh pulse generator and a sigh synchronizing circuit. Gate 119 is inserted between gates 5 and three-position valve 74. With the sigh control cut off by the three-position valve 74, reservoir C 1 (FIG. 5) empties through adjustable orifice R 1 and ports 3 and 5 in series of gate 119. When three-position valve 74 is put in the automatic sigh position, and a pressure signal is received at port 1 of gate 119, port 5 of gate 119 is closed and adjustable orifice R 26 is placed in series with adjustable orifice R 1 , increasing the time required for the emptying of reservoir C 1 . The sigh pulse generator circuit can be set so that a sigh signal is delivered only after a pre-set number of cycles. The adjustment as to the frequency of the sigh circuit signal is carried out by a selection of the sizes of tanks C 14 and C 15 and adjustable orifice R 23 which is panel mounted. The three-position valve 74 is also connected so that a sigh can be provided at any time at the discretion of an attendant. Synchronization between the sigh circuit and the phase of the signal generator is carried out by the sigh synchronizing circuit. Details of the operation of the sigh circuit are given in Table 3.
TABLE 3 ____________________________________________________________ ______________ SIGH CIRCUIT (Selector Switch In Auto Sigh Position) TIME Gate Control Input Output Port 3 Notes No. Port/State Port/State State ____________________________________________________________ ______________ Pulse Output- t =O Pulse 113 1 OFF 5 OPEN ON Starts filling Generator C 15 Circuit 111 1 OFF 5 OPEN TO ATM Power ON 112 1 OFF 4 CLOSED After 111 1 ON 4 OPEN ON C 14 fills t SP =Length of C 15 dumpted Sigh Pulse 112 1 ON 4 OPEN to ATM 113 1 ON 5 CLOSED OFF Pulse OFF Dumpted to ATM -t SP + ε 111 1 OFF 5 OPEN TO ATM C 14 starts emptying Where ε is a small time 112 1 OFF 4 CLOSED Interval 113 1 ON 5 CLOSED OFF Pulse still OFF After 113 1 OFF 5 OPEN ON C 14 Empty Pulse Output- T s = Interval 111 1 OFF 5 OPEN TO ATM C 15 starts Between filling Sighs 112 1 OFF 4 CLOSED Synchronizing 114 1 ON 4 OPENS ON flip-flop Circuit flip- switches On CASE I flop Pulse Gener- ator Signal 115 1 ON 4 OPEN ON Arrives When Q is ON 116 1 ON 4 OPEN ON flip-flop flip- switches ON flop 117 1 ON 5 CLOSED OFF 118 flip-flop flip-flop 1 OFF 5 OFF OFF remains OFF 119 1 OFF 5 OPEN TO ATM. After Short Time=ε 114 2 ON 4 CLOSED OFF RESET Q OFF 115 1 OFF 4 CLOSED OFF 117 1 OFF 5 OPEN ON 118 1 ON 4 OPEN ON Flip-flop Set(ON) 119 1 ON 4 OPEN TO ATM through ADD-ON Resistor 116 2 ON 4 CLOSED OFF RESET -Q ON 118 2 ON 4 CLOSED OFF RESET Synchronizing 114 1 ON 4 OPEN ON SET Circuit Case II 115 1 OFF 4 CLOSED OFF Pulse Genera- tor Signal 116 1 OFF 4 CLOSED OFF REMAINS Arrives when RESET (OFF) Q is off. 117 1 OFF 5 OPEN OFF 118 1 OFF 4 CLOSED OFF REMAINS RESET 119 1 OFF 4 CLOSED TO ATM Q ON 114 1 ON 4 OPEN ON SET 115 1 ON 4 OPEN ON 116 1 ON 4 OPEN ON SET 117 1 ON 5 CLOSED OFF 118 1 OFF 4 CLOSED OFF REMAINS RESET 119 1 OFF 4 CLOSED TO ATM After t=ε 114 2 ON 4 CLOSED OFF RESET Q OFF 115 1 OFF 4 CLOSED OFF 117 1 OFF 5 OPEN ON 118 1 ON 4 OPEN ON SET 119 1 ON 4 OPEN TO ATM THROUGH ADD-ON RESISTOR 116 2 ON 4 CLOSED OFF RESET Q ON 118 2 ON 4 CLOSED OFF RESET ____________________________________________________________ ______________
It has already been mentioned that failure to receive a trigger signal when the signal generator is operating in demand mode causes the activation of alarm signals. In general, this alarm is adjusted to sound if an interval of about 6 seconds passes without the arrival of another demand signal. Alarm circuits in addition to that associated with the shift circuit are shown in FIG. 11. Should the main power supply line be disconnected, supply disconnect indicator 77 will show this immediately, port 5 of gate 20 will be opened and the compressed gas stored in tank C 9 will pass through ports 5 and 3 of gate 20 to gate 22 where the combination of orifices R 14 and R 16 and tank C 11 with gate 16 acts as an oscillator to move diaphragm 78 of diaphragm-valve 79 back and forth to cause bell 81 to sound. The same alarm sounds when actuated by gate 21 of the shift circuit.
In the event of a disconnect at the patient manifold or a drop in pressure below a pre-set value, the drop is sensed during signal A by the sensitive snap sensor 82. The disconnect is visually indicated at the indicator 83. The drop in pressure at port 1 of gate 19 disconnects the main power supply therefrom and sets into motion the same train through tank C 9 etc. as described above.
The way in which the patient is connected to the patient supply tube 42 and demand valve 63 is shown in block-diagram form in FIG. 12. With this type of arrangement, four connections must be made from the respirator to the vicinity of the patient. Other types of arrangements are possible in which only three are necessary, but the arrangement shown in FIG. 12 is particularly advantageous in that the dead space between exhaust valve 44 and the patient and between emergency breathing port 57 and the patient is very small.
Valves 44 and valve 57 are both diaphragm valves. In valve 44 (FIG. 13) diaphragm 87 is in close proximity to the orifice of tube 88. Consequently, any attempt by the patient to inhale causes the diaphragm to seal against the tube and causes a slight drop in pressure in tube 42 which is transmitted through demand port 89 to the demand valve.
So long as the respirator is connected to a source of pressurized gas, signal D will be received at port 91 of valve 57 to hold diaphragm 92 in closed position against the urging of spring 86. In the event of failure of signal D, spring 86 forces and maintains diaphragm 92 into open position and connects the patient directly to the ambient air.
It is desirable that it be possible to measure the alveolar pressure in the lungs of a patient at the end of inspiration. When signal C is received (FIG. 14) from the oscillator circuit by gate 30, damping tank C 13 is connected with the patient manifold through ports 4 and 3 of gate 30 and the alveolar pressure can be measured by turning valve 58 to the proper position. The pressure is read on pressure gauge 59. When signal C is not received, valve 58 may be rotated into position so that the pressure in the patient manifold can be measured.
In certain cases, it is desirable that the pressure in the patient's lungs be above atmospheric pressure at the end of expiration, for this purpose, a transparent vessel 93 is shown in FIG. 15 containing water or a sterilizing solution into which dips an open-ended graduated tube 94 which is adjustable vertically through a seal ring 96. Exhaust from the vessel takes place through a filter 97 which may be either disposable or sterilizable.
In other cases, it is desirable that the pressure in the patient's lungs at the end of expiration be below atmospheric pressure. A venturi 98 as shown in FIG. 16 is fitted into exhaust port 99 of patient valve 44. A jet of gas from the pressurized gas supply is supplied to the venturi 98 through adjustable orifice R 24 . The orifice is adjustable over a range to give a pressure drop ranging from between zero and 20 cm of water.
If it is desired to introduce resistance to exhalation without influencing the pressure at the end of exhalation, a flexible cap may be placed over the end of exhaust port 99 with an orifice of selected size in the end thereof (not shown).
As is obvious, the pneumatic logic gates and the passive elements such as orifices and reservoirs of the signal generator could be connected by tubing of appropriate diameter. However, a preferred embodiment of connections between the various elements is one in which the interconnections are formed as grooves in plates, which, most suitably, are of moldable plastic. If three plastic plates, each about 6 millimeters in thickness are stacked together, two interfaces are formed. Grooves can be formed at either face of the two interfaces. In FIG. 17, circuit plate 101 is shown as having grooves formed therein in a perpendicular pattern. Holes which are perpendicular to the face of the circuit plate penetrate the plate and connect channels on opposite faces. It is necessary to have grooves at both interfaces so that lines can cross each other. Closed channels are formed when top cover plate 102 and bottom cover plate 103 are sealed to circuit plate 101. Logic gates or passive elements are then connected to circuit channels 104 through ports (not shown) in top cover plate 102. The analogy to printed circuits as used in electronic devices is obvious, so that the system of connections of the device of FIG. 17 may be appropriately termed printed pneumatic circuitry.
Suitably placed ports 106 in bottom cover plate 103 are used as mounting holes, exhaust ports, for making connections to passive elements (R and C) and to receive input and send output signals.
Since respirators are to be used with a series of patients, protection against cross-infection must be provided. Filters 24 and 39 are designed to protect the respirator itself from dust particles and liquid droplets. Protection of the patient is provided by filter 39 (FIG. 1) which is ultra-fine in porosity. A preferred form is the so-called micro-port filter which may be sterilized. Filter 97 (FIG. 15) may be of the same type. The purpose of filter 97 is to prevent contamination of the air in the vicinity of the patient. The primary purpose of humidifier 41 is to add moisture to the air being supplied to the patient. However, medication can also be incorporated in the humidifier to be carried with the air stream to the patient. The design of the humidifier is not critical except that it must not alter tidal volume.
A simplified signal generator is shown in FIG. 18 in the state corresponding to time = 1 (FIG. 4). The operation of this circuit is clear from Table 4.
TABLE 4 ____________________________________________________________ ______________ SIMPLIFIED OSCILLATOR CIRCUIT OUTPUT GATE CONTROL INPUT PORT 3 TIME NO. Port/State Port/State STATE NOTES ____________________________________________________________ ______________ 1 41 1 off 4 open OFF C 14 filled and starts emptying through R 25 42 1 on 5 closed OFF 43 1 off 5 closed OFF (A) C 15 empty 44 1 off 4 closed ON (B) C 16 starts emptying through R 28 45 1 off 5 open ON (C) 2 41 1 off 4 closed OFF C 14 still emptying 42 1 on 5 closed OFF 43 1 off 5 open OFF (A) 44 1 off 4 closed OFF (B) C 16 empty 45 1 off 4 closed OFF (C) 3 42 1 off 5 open ON C 14 empty 43 1 on 5 closed OFF (A) C 15 starts filling 44 1 on 4 open ON (B) 45 1 on 5 closed OFF (C) 41 1 on 4 open ON C 14 starts filling 4 41 1 on 4 open 3 ON C 14 starts filling 42 1 off 5 open 3 ON 43 1 on 5 closed (A) OFF 44 1 on 4 open 3 ON (B) 45 1 on 5 closed 3 OFF (C) 5 41 1 on 4 open 3 ON C 14 still filling 42 1 off 5 open 3 ON 43 1 on 5 closed (A) ON C 15 full 44 1 on 4 open 3 ON (B) ON 45 1 on 5 closed 3 OFF (C) OFF ____________________________________________________________ ______________
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above article without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.