Title:
FLOW RESPONSIVE RESPIRATION APPARATUS
United States Patent 3817246


Abstract:
Respiration apparatus for IPPB therapy in which the inspiratory effort of the patient to initiate an inspiration phase is sensed by a flow sensor which operates by directing a laminar jet of gas across a conduit of the apparatus toward a receiver, to produce a normal pressure in the receiver when there is no flow in the conduit. A second receiver establishes a reference pressure, and the change in the pressure relationship between the receivers, resulting when the patient creates a cross-flow across the jet, is used as a pilot signal to operate an actuator for opening a flow control valve. Similarly, as the flow rate is reduced near the end of the inspiration phase, the pressure relationship is restored and the actuator closes the control valve. One embodiment uses a laminar jet that is directed into an aligned receiver to raise the pressure therein relative to a receiver spaced from the jet, and referenced to actual patient delivery pressure, until a cross-flow disturbance changes the jet to turbulent, thereby reducing the pressure in the aligned receiver. Another embodiment uses a turbulent jet directed between two longitudinally spaced receivers, disposed in close proximity to one another, to establish equal pressures therein until the jet is deflected longitudinally toward one of the receivers and away from the other in response to a cross-flow.



Inventors:
WEIGL J
Application Number:
05/313983
Publication Date:
06/18/1974
Filing Date:
12/11/1972
Assignee:
PURITAN BENNETT CORP,US
Primary Class:
Other Classes:
137/842
International Classes:
A61M16/00; G01F23/16; (IPC1-7): A61M16/00
Field of Search:
128/145
View Patent Images:
US Patent References:
3669108VENTILATOR1972-06-13Sundblom
3537449RESPIRATOR USING PURE FLUID AMPLIFIER1970-11-03Foxwell
3429323FLUID AMPLIFIER1969-02-25Mott
3428068TURBULENCE AMPLIFIER1969-02-18Howie
3413993Fluid device1968-12-03Ziemer
3385295Apparatus for use in administering intermittent positive pressure breathing therapy1968-05-28Beasley



Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Dunne G. F.
Attorney, Agent or Firm:
Fulwider Patton Rieber Lee & Utecht
Claims:
I claim

1. Flow responsive respiration apparatus for administering intermittent positive pressure breathing therapy to a patient from a source of gas under pressure and through delivery means into which the patient breaths to initiate an inspiration phase of a respiration cycle, said apparatus having, in combination:

2. Flow responsive respiration apparatus for administering intermittent positive pressure breathing therapy to a patient from a source of gas under pressure and through delivery means into which the patient breaths to initate an inspiration phase of a respiration cycle, said apparatus having, in combination:

3. Flow responsive respiration apparatus for administering intermittent positive pressure breathing thereapy to a patient from a source of gas under pressure and through delivery means into which the patient breathes to initiate an inspiration phase of a respiration cycle, said apparatus having, in combination:

4. Respiration apparatus for administering intermittent positive pressure breathing therapy to a patient from a source of gas under pressure and through delivery means into which the patient breathes to initiate a respiration cycle, said apparatus having, in combination;

5. In a respiration apparatus for administering intermittent positive pressure breathing therapy to a patient from a source of gas under pressure through delivery means into which the patient breaths to initiate a respiratory cycle, the combination of:

6. In a respiration apparatus for administering intermittent positive pressure breathing therapy to a patient, and including a source of gas under pressure, delivery means for administering the gas to the patient, conduit means connecting said source to the patient to carry the gas to the delivery means, and a selectively operable flow control valve for opening and closing said conduit means between said source and said delivery means, the combination of:

7. A respiration apparatus as defined in claim 6, in which said receiver means include a first receiver positioned across said portion of said conduit means in alignment with said jet, and in which said jet-directing means produces a jet which remains laminar at said first receiver as long as the jet is undisturbed, and changes to turbulent at said first receiver when disturbed by a cross-flow.

8. A respiration apparatus as defined in claim 7 further including a second receiver in said conduit means spaced from said first receiver to establish a reference pressure with respect to which said first and second levels are detectable in said means for opening said control valve.

9. A respiration apparatus as defined in claim 7 further including a disturbance amplifier in said portion of said conduit means, having an edge alongside the path of said jet, adjacent said first receiver.

10. A respiration apparatus as defined in claim 9 further including a plurality of flow-straightening vanes in said portion of said conduit means for directing the cross-flow perpendicular to said jet.

11. A respiration apparatus as defined in claim 6 in which said portion of said conduit is a first restricted conduit communicating with said delivery means, and further including a second, larger conduit also communicating with said delivery means around said first conduit, and having check means therein for directing said cross-flow through said first conduit and passing the flow of gas from said source to said delivery means.

12. A respiration apparatus as defined in claim 6 in which said receiver means comprise two receivers spaced apart on opposite sides of the path of said jet to be pressurized equally thereby when there is no cross-flow in said portion of said conduit means, one of said receivers being positioned to be pressurized to a higher level as said jet is deflected by said cross-flow.

13. A respiration apparatus as defined in claim 12 in which said portion of said conduit means is a tube adjacent said delivery means through which the patient breathes and through which all of the gas is supplied to the patient.

Description:
BACKGROUND OF THE INVENTION

This invention relates to respiration apparatus, and more particularly to apparatus for administering intermittent positive pressure breathing (IPPB) therapy to a patient.

In such therapy, air, oxygen or oxygen-enriched air under pressure is supplied to a patient cyclically through delivery means such as a face mask or the like. Each inspiration phase is initiated in response to a slight inspiratory effort by the patient, and begins with a peak flow rate which inflates the patient's lungs, the flow rate then being reduced to a relatively low level at which all flow is terminated. Following the inspiration phase, the lungs are vented to atmosphere during an expiration phase, which terminates when the next inspiratory effort by the patient initiates the next cycle.

Examples of prior IPPB apparatus are shown in U.S. Pat. No. 3,362,404 and No. 3,368,555, illustrating two different approaches to the manner in which inspiration may be initiated and terminated. In U.S. Pat. No. 3,362,404, the patient draws air through the delivery means to create a pressure drop in the diaphragm chamber of a triggering valve, and this pressure drop is used to open a flow responsive valve which initiates the inspiration phase and eventually terminates inspiration in response to a selected low terminal flow level. In U.S. Pat. No. 3,368,555, a similar inspiratory effort by the patient is applied as a biasing signal to a control fluid amplifier of the monostable, lock-on type to switch a fluid flow therein from a preferred channel to another channel, thereby switching the flow through a main fluid amplifier of the bistable, lock-on type to initiate an inspiration cycle. The flow in the control amplifier switches back to the preferred channel automatically when the biasing signal is removed, and this switches the main amplifier to terminate inspiration at a selected low terminal flow rate.

Both of these approaches are effective to initiate inspiration in response to slight inspiratory efforts, but both utilize the actual reduction of pressure caused by the patient's inspiratory effort as the source of an actuating pressure signal, with the result that there is a perceptible resistance to inspiratory effort at the beginning of inspiration until the machine overcomes its internal delays and begins to flow gas through the delivery means. A primary object and advantage of the present invention is the reduction of this resistance to an almost imperceptible level, to increase the comfort of the patient during IPPB therapy, in a novel manner that does not detract in any way from other performance characteristics of the apparatus.

SUMMARY OF THE INVENTION

The present invention resides in a respiration apparatus of the foregoing general character in which the inspiratory phase of each respiration cycle is initiated by a flow-sensing device that does not require the patient to create a pressure drop any greater than that required to produce a slight flow of air within the conduits of the apparatus. In other words, the sensing device of the present invention is capable of initiating the inspiration phase in response to an inspiratory effort by the patient that is virtually the same as the normal effort during involuntary breathing, and is effective to initiate the inspiration phase with an open air circuit through the apparatus, preferably through a filter for mixing air with the primary flow of gas from the source.

This is accomplished by incorporating a fluidic flow sensor in one of the conduits of the apparatus, including means on one side of one of the conduits for directing a jet of gas under pressure across the conduit and receiver means in the path of the jet reference pressure relationship between two receivers of the receiver means, in the absence of any flow in the conduit. When a very low threshold flow is created in the conduit by the inspiratory effort of the patient, for example, a flow as low as 2 to 4 liters per minute, or even less, this cross-flow disturbs the air jet, changes the reference pressure relationship between the receivers, and produces a pressure signal that is used to initiate the inspiration phase of the apparatus. A pressure-actuated control valve responds to the signals of the flow sensor to initiate the supply of respiration gas, and a conventional regulator controls the flow rate to the patient.

As long as there is flow through the flow sensor, the changed pressure relationship is maintained to maintain the apparatus in the inspiration phase. As flow rate is reduced during inflation of the patient's lungs, however, the cross-flow through the jet is reduced to a low rate which falls below the threshold level for the flow sensor, the reference pressure signal is restored to the reference relationship, and the inspiratory phase is terminated by the control valve.

In one form of flow sensor disclosed, a turbulent jet is directed between two receivers disposed in close proximity to each other, to establish equal pressures therein until the jet is deflected longitudinally by a cross-flow, and all flow passes through the sensor, which may have a relatively high flow area capable of handling the peak flow rate of the apparatus. In another, more sensitive form, a normally laminar jet is directed into an aligned receiver, and a reference receiver is spaced from the jet to establish a reference pressure, the jet being converted to turbulent by a cross-flow, thereby dropping the pressure in the aligned receiver sharply. The flow area in this form is restricted, and a by-pass is provided around the sensor, for carrying peak flow rates to the patient.

Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of a respiration apparatus constructed in accordance with the present invention;

FIG. 2 is a similar schematic view of an alternative embodiment of the invention;

FIG. 3 is an enlarged longitudinal cross-sectional view of a flow sensor incorporated in the apparatus of FIG. 2;

FIG. 4 is an enlarged cross-sectional view of a flow sensor incorporated in the apparatus of FIG. 1, the view being taken in a plane indicated by line 4--4 of FIG. 5;

FIG.5 is a cross-sectional view taken along line 5--5 of FIG. 4; and

FIG. 6 is an enlarged cross-sectional view of a pilot-operated flow control valve suitable for use in both embodiments of the invention.

DETAILED DESCRIPTION

As shown in the drawings for purposes of illustration, and with particular reference to FIG. 1, the invention is embodied in an IPPB respiration apparatus 10 for delivering an intermittent flow of air under pressure to a patient from a compressor 11, through the various conduits and control components of the apparatus and delivery means 12 such as a face mask adapted to be worn over the patient's mouth and nose. The compressor draws outside air in through a filter 13 and a silencer 14, and pumps the air through a second filter 15 into a main flow conduit 17 in which the pressure is controlled by a regulator 18.

From this conduit 17, the air is passed intermittently through a selectively operable control valve 19 and through a conduit 20 to a conventional pressure-responsive relief valve 21 for reducing the flow rate to the patient as back pressure in the system indicates that the patient's lungs are approaching full inflation. The outlet 22 of this relief valve is connected through two conduits 23 and 24 to the delivery means 12. The entrance into the relief valve 21 is shown as a jet 25 for directing the gas into a venturi section 27, thus creating a pressure drop for drawing outside air through a filter 28 and entraining this air with the primary air flow from the valve 21.

Thus, the opening and closing of the control valve 19 initiates and terminates the inspiration phases of successive respiratory cycles of the apparatus 10, and the relief valve 21 controls the flow rate during each such phase. The relief valve initially passes a relatively high peak flow, and then reduces this flow to a relatively low terminal flow rate before the valve 19 is closed to terminate inspiration. A gauge 29 preferably is provided to indicate system pressure.

After termination of inspiration, the patient is permitted to exhale naturally through the delivery means 12 and an exhalation valve 30 in the conduit 24 adjacent the delivery means, this valve comprising an exhalation port 31 which is closed during inspiration by a pressure-actuated closure 32, herein an inflatable "mushroom" or "balloon" closure connected through a conduit 33 and a pressure divider formed by two restrictors 34, to the conduit 35 that is pressurized during inspiration. When air is being supplied to the patient, the closure is inflated and the exhalation valve is closed. During exhalation, the pressure in the closure is relieved, and the valve opens to allow exhaled gas to escape.

If medication is to be administered to the patient as an incident to the IPPB therapy, a conventional nebulizer 36 may be included with the delivery means and supplied with nebulizing air under pressure through the conduit 35, a one-way check valve 37, and a needle valve 38. Nebulizing air also may be supplied during the expiration phase by means of a conduit 39 connected to the conduit 17 ahead of the control valve 19 and having a flow restrictor 40 therein, this conduit being connected to the conduit 35 between the check valve 37 and the needle valve 38.

In accordance with the present invention, the inspiration phases are initiated and terminated by a fluidic flow sensor 42 in which a jet 43 is directed across one of the conduits of the apparatus, herein the conduit 23, toward receiver means which establish a reference pressure relationship and maintain that relationship as long as there is no disturbance in the conduit. When a disturbance occurs, as a result of inspiration by the patient through the delivery means 12 and the conduits of the apparatus, the pressure relationship departs from the reference, and this change is used to open the control valve 19 and initiate an inspiration phase of the apparatus. Similarly, when the flow rate is reduced to the low terminal flow rate, the pressure relationship is restored to the reference level, and this change is used to close the control valve and terminate the inspiration phase of the apparatus.

More specifically, as shown schematically in FIG. 1 and in detail in FIGS. 4 and 5, the flow sensor 42 comprises a jet tube 44 opening into one side of the conduit 23 and shaped and positioned to direct a controlled laminar jet of gas (herein air from a conduit 45 connected through a restrictor 47 to the conduit 17) across the conduit 23 and across the path of air drawn through the conduit when the patient begins to breathe through the respiration apparatus.

Directly across the conduit and aligned with the jet tube 44 to receive the air jet 43 is a first receiver tube 48, the pressure in which is a function of the laminarity (as opposed to turbulence) of the air jet. Such a jet remains laminar for a considerably distance downstream from the orifice of the jet tube, and then breaks up into turbulence. The receiver tube is positioned closer to the jet orifice than the distance to the point of turbulence, and thus normally receives a laminar flow.

Spaced along the conduit from the first receiver tube 44 is a second receiver tube 49, or reference tube, in which the pressure is essentially unaffected by the jet flow. Thus, a predetermined pressure differential normally exists between the two receiver tubes 48 and 49, the difference being the pressure increase in the tube 48 produced by the jet 43, as long as it remains laminar in character at the entrance to the tube.

When a patient begins to breathe through the apparatus, the external influence on the pressures at the two receiver tubes 48 and 49 is the same, but the disturbance of the air jet by the cross-flow of air in the conduit substantially reduces the distance to the point of turbulence. The receiver tube 48 is farther from the jet orifice than the reduced distance to the point of turbulence, and thus receives turbulent, rather than laminar, flow. The result is a marked decrease in the pressure in the receiver tube 48, relative to original pressure. This decrease serves as a pilot pressure signal to actuate the control valve 19 and initiate the inspiration phase, herein through a pressure-operated actuator 50.

Similarly, as the flow to the patient is reduced by the relief valve 21 near the end of the inspiration phase and the rate of flow through the conduit 23 declines, the disturbance of the air jet 43 is terminated, and the flow again becomes laminar at the entrance to the receiver tube 48. When this occurs, the pressure in the tube increases markedly, and this increase serves as a pilot-pressure signal which acts through the actuator 50 to close the valve 19.

Shown in FIGS. 4 and 5 is a specific embodiment of a suitable flow sensor 42, in a form which may be injection molded as a small and inexpensive part, in two pieces, with the jet tube 44, the receiver tubes 48 and 49, and the conduit 23. Basically, the sensor comprises two flat plates 51 and 52 fitted together as shown in FIG. 5 and having adjacent recessed sides defining the tubes and the conduit.

The patient end of the conduit 23 is a port 53 in the plate 52, and the inlet end is a similar port 54 in the same plate. The air jet tube 44 is formed by an elongated channel in the plate 52, which channel may be rectangular in transverse cross-sectional shape for convenience of manufacture. The two receiver tubes 48 and 49 may be similar channels, permissibly of shorter length. When the upper plate 51 is clamped over the lower plate, the recesses, which may be in one or both plates, define the various ports.

It should be evident that it is very important for the jet tube 44 to be smooth-walled, to avoid premature transition to turbulent flow. Suitable connectors 55 are formed on the plate 52 with passages 57 to carry the jet flow into the jet channel 44 and for connection of signal lines to the receiver channels 48 and 49.

It will be seen in FIG. 4 that a plurality of elongated parallel fins 58, 59 and 60 are formed in the left-hand portion of the conduit 23, perpendicular to the path of the jet 43 across the conduit. These fins serve as flow straighteners, and also reduce the cross-sectional flow area of the conduit, to concentrate the cross-flow on the air jet. The flow area in the opposite end portion is greater by an amount equal to that occupied by the fins, and also is increased by widening of the conduit 23, the resulting restriction being indicated schematically at 61 in FIG. 1.

In addition, it will be seen in FIG. 4 that the upper fin 60, farthest from the orifice of the jet tube 44, has a downstream end 62 which is closely adjacent the normal path of the jet 43 when the flow is laminar. This fin is intended to intercept and amplify the eddy currents along the edge of the jet that are created by cross-flow, and thus to promote crisp switching of the sensor.

The sensitivity of the flow sensor 42 may be adjusted to different threshold flow rates by moving the disturbing cross-flow either closer to or farther from the jet orifice along the axis of jet flow. Accordingly, the inspiration phase can be initiated and terminated at different flow rates through the conduit 23. For example, for high sensitivity, at a threshold flow rate on the order of 1 to 2 liters per minute, the cross-flow is directed at the jet at a location relatively close to the supply jet orifice. For a lower degree of sensitivity, at a threshold rate of 2 to 4 liters per minute, the cross-flow is directed at the jet at a location farther away from the jet orifice and closer to the receiver orifice.

While high sensitivity is desirable for ease in initiation of inspiration, lower sensitivity can be desirable for termination at a somewhat higher terminal flow rate. Thus, a comprise may be made between these two considerations, or a by-pass may be provided so that only a portion of the flow is passed through the flow sensor 42.

The illustrative pressure-operated actuator 50, shown in FIG. 1, includes two inflatable members 63 and 64, which may be of the "mushroom" type comprising freely flexible, hollow plastic bodies. These members are disposed on opposite sides of a lever 65 to urge the lever back and forth relative to an orifice 67 through which air under pressure from a conduit 68 escapes when the lever is spaced from the orifice. The member 63 on the left-hand side is connected by a conduit 69 to the receiver tube 48, and thus will be inflated when there is no flow through the conduit 23, to urge the lever 65 toward the orifice 67 into a blocking position. The member 64 on the right-hand side of the lever is connected by a conduit 70 to the receiver tube 49, to be subjected to the lower patient delivery pressure, and tending to swing the lever to an open position. A light spring 71 is positioned to exert an opening force on the lever, and to cooperate with the member 64 in developing an opening force moment that is less than the closing moment when jet flow is undisturbed, but greater than the closing moment when the jet flow is disturbed.

A manual control 72 is shown in FIG. 1 for shifting the lever 65 into and out of its blocking position, independently of the forces exerted by the members 63 and 64. This is simply a yoke 73 that is pivotally mounted on a pin 74 above the free end of the lever, with the legs of the yoke straddling the lever and a knob 75 projecting upwardly therefrom and normally held in the centered position shown, by two springs 77. The knob can be shifted in either direction to cause the yoke to pick up the lever and shift it into a selected position.

Air under pressure is continuously supplied to the signal conduit 68 through the control valve 19 to escape through the orifice 67 when it is unblocked by the lever 65, and to build up an actuating back-pressure signal in the conduit when the orifice is blocked. This back-pressure signal from the normally blocked orifice holds the control valve in a closed condition, indicated by the dotted-line arrow 78 in FIG. 1, and permits the valve to open when the orifice is unblocked, as indicated by the arrow 79.

Various control valves are available to serve this function, one suitable valve construction being shown in detail in FIG. 6. This valve has a body 80 formed with two internal diaphragm chambers 81 and 82 with diaphragms 83 and 84 therein, the upper diaphragm 83 serving normally to close a passage 85 through a partition 87 between the chambers, and the diaphragm 84 serving normally to close a passage 88 extending out through the lower end of the body and connected to the conduit 20 leading to the relief valve 21.

The conduit 17 from the compressor 11 is connected to a port 89 on one side of the body, and delivers compressed air through this port to a cross-passage 90 in the body, feeding the air into the lower chamber 82 beneath the diaphragm 84, through a passage 91, and also through restrictors 92 and 93 into two vertical passages 94 and 95. The upper ends of these passages have venting restrictors 97 and 98 therein, which cooperate with the restrictors 92 and 93 in maintaining selected reduced pressures in the vertical passages 94 and 95. For example, when 10 psi air is supplied to the cross-passage 90, the restrictors 93 and 98 may be equal in size to maintain 5 psi in the passage 95, while the vent restrictor 97 is sufficiently larger than the restrictor 92 to maintain about one-third of 1 psi in the passage 94.

It will be seen in FIG. 6 that a conduit 99 leads from the passage 94 to the upper diaphragm chamber 81, above the diaphragm 83, to hold this diaphragm down to close the upper central passage 85 when the signal conduit 68 is blocked at the orifice 67. At the same time, 5 psi pressure from the vertical passage 95 is applied to the lower diaphragm chamber 82, above the diaphragm 84, through a passage 100. The resulting force, plus a light spring 101 above the diaphragm, holds the latter down to close the lower passage 88. This is the closed, or "off," condition of the valve 19 in which no flow is delivered from the "in" port 89 to the "out" passage 88.

When the orifice 67 is unblocked by the lever 65 in response to disturbance of the air jet 43 by the patient's breathing through the conduit 23, pressure above the upper diaphragm 83 is relieved, and the higher pressure from the chamber 82 below, acting through the central passage 85, lifts the diaphragm and is vented through a conduit 102. This relieves the pressure above the lower diaphragm 84, so that the lifting force of the pressure beneath it overcomes the spring 101 to raise the diaphragm and open the "out" passage 88, connecting this passage to the supply conduit 17 through the lower chamber 82, beneath the diaphragm 84, and through the cross-passage 90 and the "in" port 89.

Accordingly, air flows through the valve 19 to the relief valve 21, and thus to the patient, as long as the orifice 67 is unblocked by the lever 65. When the lever is returned to the blocking position, pressure is restored above the upper diaphragm 83, closing the central passage 85 and thereby restoring the pressure above the lower diaphragm 84 to close the "out" passage 88. This shuts off the flow out of the valve 19.

It has been stated that the pressure relief valve 21 may be of conventional construction, the valve illustrated being of the type sold by Bennett Respiration Products, Santa Monica, Calif., as the No. 1694 A Relief Valve. As will appear subsequently, the same function may be accomplished by a Bennett Respiration Products No. 0666 Diluter Regulator, which is preferred when the source supplies oxygen rather than air.

In general, the relief valve 21 defines a chamber 103 into which the primary flow of air is injected through a venturi device where room air is entrained past the outside-air filter 28, one side of this chamber being formed by a diaphragm 104 adjustably loaded by a spring 105 and adjusting screw 107 for setting the pressure control range. When ambient pressure exists in the chamber 103, a closure 108 carried by the diaphragm covers a "dump" port 109 opening out of the chamber, thus preventing escape of air except through the normal outlet 22 leading to the conduits 23 and 24.

As back pressure builds up in the chamber 103 as a result of inflation of the patient's lungs, the diaphragm 104 is raised away from the "dump" port 109, lifting the closure 108 to allow air to escape from the chamber. The action of the relief valve is progressive, and eventually results in dumping of almost all of the supply flow, and delivery of only a low terminal flow to the patient.

The entrance 110 of conduit 24 is closed during initiation and termination of the inspiration phase, by a flexible leaf-type check valve 111 which is closed initially to pass all of the flow from the patient's breathing to the sensor 42, and opens in response to delivery of the peak flow of air through the relief valve 21, thus increasing the flow capacity far beyond the practical flow through the restriction 61 in the flow sensor 42. This leaf valve closes again as the flow rate is reduced by the relief valve 21, for example, when the rate drops within the range of 10 to 20 liters per minute, and thereby routes all of the flow through the sensor as the inspiration phase nears completion.

Design criteria for the flow sensor 42 can be worked out in accordance with known principles in the art, examples of existing reference literature being the book "Fluidics--Components and Circuits," by Foster and Parker, published by Wiley-Interscience, and specifically pages 301-308 thereof. Other reference works are Siwoff, "Improve-of the Static and Dynamic Behaviour of the Turbulence Amplifier (etc.)," Third Cranfield Fluidics Conference (1968), Paper -2; Verhelst, "On the Design, Characteristics and Production of Turbulence Amplifiers," Second Cranfield Fluidics Conference (1967), Paper F2; Siwoff, "A Method for Dimensioning the Turbulence Amplifier," Fourth Cranfield Fluidics Conference (1970), Paper A5; and "The Turbulence Amplifier in Control Systems" by R. N. Auger of Fluid Logic Control Systems, New York, N.Y.

A flow sensor 42 specifically designed for the system shown in FIG. 1, and constructed in the manner shown in FIGS. 4 and 5, uses a jet tube 44 about 1 inch in length and about 0.018 of an inch square, with the receiver tube 48 spaced 0.31 of an inch from the jet orifice. The effective flow area of the wider end portion of the conduit 23 is about 0.5 of a square inch, and the effective flow area of the restricted end portion is about 0.02 of a square inch.

With this sensor, a jet flow rate of about 0.3 of a liter per minute, at a pressure of 0.5 of one psi, can be used, and a pressure drop on the order of 0.05 of one centimeter H2 O at the port 53 creates enough flow through the conduit to trigger the sensor. In contrast, prior turbulence amplifiers have required a relatively large triggering pressure drop on the order of 1 centimeter H2 O, utilizing substantially smaller passages.

It bears emphasis that the flow sensor 42 is a highly sensitive type which is simple and inexpensive, easy to maintain, and stable in operation, and can operate with a low-pressure jet of low flow rate, sensitive to low cross-flow disturbances. This sensor can be characterized as a switching type, in which the pressure drop in the receiver tube 48 is sharp, when the normal laminar flow at the entrance to the receiver is changed to a turbulent flow. Because its effective flow area is small, however, high peak flow rates are by-passed around the sensor through the conduit 24.

Shown in FIG. 2 is an alternative form of the respiration apparatus 112 with a flow sensor 113 of the fluid jet deflection type (FIGS. 2 and 3). In this case, all of the patient flow during the inspiration phase passes through the sensor, eliminating the need for a by-pass conduit such as the conduit 24 of FIG. 1. This type of sensor may be somewhat less sensitive and stable, however, than the type shown in FIGS. 1, 4 and 5, but is effective to control inspiration in substantially the same manner, while having the advantageous capability noted above.

In this case, the sensor 113 has a tubular body 114, and a jet tube 115 opens into the body on one side thereof to direct a jet 117 of air across the conduit 118 defined by the body. This jet may travel, for example, about 0.5 inches and is directed toward a receiver formed by two tubes 119 and 120 (e.g., about 0.020 inches in internal diameter) spaced a short distance apart (e.g., about 0.040 of an inch) on opposite sides of the jet's path, preferably equidistant therefrom so that the jet creates equal pressures into the two receiver tubes.

A relatively high-pressure jet is used, for example, at 10 psi, delivering about 3 liters per minute, and the reference pressure relationship established comprises equal pressures in the two receiver (e.g. about 60 centimeters H2 O) rather than different pressures as in the first embodiment.

As the patient breaths air through the delivery means 121 and the sensor 113, the flow of air deflects the jet 117 toward the receiver 119, increasing the pressure linearly in this receiver, relative to the pressure in the receiver 120, as the flow rate in conduit 118 increases. The pressure change is applied to an actuator 122, through signal conduits 123 and 124, to operate a control valve 125 that may be the same as the valve 19 in FIGS. 1 and 6.

In this case, the actuator 122 is responsive to a preselected pressure differential, including an increase in the pressure at the receiver tube 119 produced by a given degree of deflection of the jet 117 toward the delivery means 121. The change in the pressure differential is proportional to the deflection of the jet and therefore the cross-flow, and the actuator 122 can be set to operate the valve 125 at a selected level. For background information regarding a fluid jet deflection device of this general type, reference is made to a report of J. W. Tanney, "An Anemometer for Very Low Velocities," File M49--7--82, February, 1967, Low Speed Aerodynamics Section, National Aeronautical Establishment, National Research Council of Canada.

As before, the actuator 122 has two inflatable actuating members 127 and 128 that are pressurized through the conduits 123 and 124, a lever 129 between these members, an orifice 130 positioned to be blocked and unblocked by the lever, and a spring 131 for assisting the member 128 in urging the lever toward the blocking position. An adjusting screw 132 is provided to vary the spring force, thereby to set the actuator for operation at a selected output pressure level of the signal produced by the sensor 113.

When the orifice 130 is blocked, a back-pressure signal is applied through a conduit 133 to the control valve 125 to maintain it in the closed condition, as described in connection with FIG. 6, thereby preventing any flow of primary gas through the main flow conduits of the system. In this embodiment, a main flow conduit 134 connects a pressure-regulated source 135 to the valve 125, which is connected through another main conduit 137 to a flow-rate regulating valve 138, from which gas flows to the sensor 113 and the patient through a conduit 139, the conduit 118 of the sensor being a section of this conduit. A conduit 136 connects the source to the jet tube 115.

In this instance, the source 135 supplies oxygen, which may be diluted in the regulating valve 138. For this purpose, the valve 138 is a diluter/regulator of the type sold by Bennett Respiration Products as No. 0666, previously mentioned.

When the patient starts to withdraw air from the apparatus 112, the flow control valve 125 is opened in response to the increased pressure in the receiver tube 119, resulting in the unblocking of the orifice 130. Then oxygen flows through the valve from the conduit 134 to the conduit 137, and thus to the diluter/regulator. Initially, the flow enters a control chamber 140, from which it flows through a conduit 141 through a venturi device 142 where outside air is drawn in through a filter 143. Then the mixture is delivered through a conduit 144 to a pressure chamber 145 in the diluter/regulator, and passes out through the conduit 139 leading to the sensor 113 and the delivery means 121.

In the pressure chamber 145, the back pressure in the system is sensed by a diaphragm 147 that is backed by a spring 148 adjusted by a screw 149 to set the pressure range of the device. As the back pressure increases during the inspiration phase, the diaphragm bulges upwardly, and acts through a linkage 150 to shift a flow-restricting plunger 151 towards an orifice 152 forming the inlet to the control chamber 140. The plunger is moved progressively closer to the orifice, thereby progressively reducing the flow rate as the back pressure increases.

As the flow drops to a selected low flow rate, the jet 117 of the sensor 113 returns toward its normal position between the two receivers 119 and 120, and the pressure differential declines to the threshold level, whereupon the lever 129 is returned to its blocking position to close the valve 125 and terminate inspiration. The expiration phase then occurs in the same manner as in the apparatus of FIG. 1, the exhalation valve being formed by a port 154 adjacent the delivery means 121, and an inflatable closure 155 pressurized during inspiration through a conduit 157 that communicates with the main flow conduit 137 through a restrictor 158. A restricted bleed passage 159 relieves pressure in the closure 155 when the inspiration flow in the conduit 137 is terminated, so the patient can exhale through the port 154.

From the foregoing, it will be evident that the present invention provides an improved respiration apparatus that is truly flow responsive, being operable in response to a flow on the order of 1 to 4 liters per minute that can be drawn through an open system of conduits, without need for a positively operated check valve for isolating the patient from the air supply openings in the relief valve 21 or the diluter/regulator 138. The result in an apparatus that can be much more comfortable in use, since the resistance of the apparatus to the initial breath is almost imperceptible, and the opening of the control valve 19, 125 supplies gas for pressure breathing as a smooth continuation of the patient's first slight effort.

Sensitivity is high, particularly in the apparatus 10, and is easily varied, and low pressure, low quantity jet flows can be used, again particularly the form 10, in which the flow sensor can be made as relatively inexpensive, easy-to-clean, molded plastic part.

It also will be evident that, while two specific embodiments have been illustrated and described, various modifications and changes may be made without departing from the spirit and scope of the invention.