Dual mode fluidic ventilator
United States Patent 3905363

A ventilator employs a fluidic circuit which alternates between a control mode and a demand mode. The control mode provides oxygen to a non-breathing patient at a predetermined rate and volume. The demand mode provides oxygen to a breathing patient to assist the patient in his breathing. The fluidic circuit automatically switches between these modes in response to the patient's needs. A multiposition switch assembly provides different flow rates and volumes during the control mode depending upon the patient's size.

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International Classes:
A61M16/00; (IPC1-7): A61M16/00
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Other References:

"Logic Circuit of Artificial Respiration" Fourth Cranfield Fluidics Conference, Coventry, Gt. Britian, Belforte..
Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Recla, Henry J.
Attorney, Agent or Firm:
Stevens, Richard L.
Having described my invention, what I now claim is

1. A ventilator for controlling the flow of a fluid to a user, which comprises:

2. The ventilator of claim 1, wherein means responsive to the switching means includes a flip-flop actuatable between first and second states; and

3. The ventilator of claim 2, which includes a second fluid amplifier responsive to the switching means in its second mode, the second fluid amplifier adapted to provide a signal to the flip-flop while the switching means is in its second mode.

4. The ventilator of claim 3, wherein the flip-flop in its first state provides a signal to and opens the first fluid amplifier and in its second state stops the signal to and closes the first fluid amplifier.

5. The ventilator of claim 2, which includes a plurality of coordinated pairs of restrictors, each pair of restrictors of a different value to establish a plurality of BPM's and I/R ratios; and

6. The ventilator of claim 5, wherein the ventilator includes a plurality of tidal flow restrictors and the means to select a coordinated pair of restrictors includes means to select one of said tidal flow restrictors.

7. A ventilator for controlling the flow of fluid to a user, which comprises:

8. The ventilator of claim 7 wherein each of the restrictors of the pair is of a different value.

9. The ventilator of claim 8 which includes a plurality of coordinated pairs of restirctors, each pair of restrictors of different values whereby a plurality of BPM's and I/R ratios are established; and

10. The ventilator of claim 9 which includes at least one tidal flow restrictor downstream of the first fluid amplifier to control the flow rate of fluid to the user.

11. The ventilator of claim 10, which includes a plurality of tidal flow restrictors and the means to select a coordinated pair of restricotrs includes means to select one of said tidal flow restrictors.

12. The ventilator of claim 9, wherein the means to select which coordinated pair of restrictors is placed in communication with its associated time delay relay includes:


In the field of respirators or ventiltors, it is known to provide apparatus which can function without moving parts through the employment of fluidic circuits (see, for example, U.S. Pat. No. 3,736,949). Ventilators, whether or not employing fluidic circuits, generally control the duration of the inspiration and expiration phases (I/E ratio) and the flow rate, such as tidal volume.

In the use of ventilator there are two types of patient conditions which require separate modes of operation: controlled ventilation, that is, totally controlling the breathing of the patient; and demand ventilation, that is, aiding the patient in his breathing as a function of his demand. Ventilators currently available provide both modes of operation, and can switch from assisted ventilation to controlled ventilation automatically. However, if the patient recovers while on controlled ventilation, then, in most ventilators, an alarm is actuated and to place the respirator in the assisted ventilation mode, manual actuation is required.

In ventilators, there are ranges over which the apparatus must be capable of functioning to handle all situations. That is, there is a requirement to control the breaths per minute (BPM), the I/E ratio, and the tidal volume entering the patient's lungs. The BPM and I/E ratio and tidal volume vary depending upon patient condition and size. These conditions can be categorized whereby a plurality of defined operational parameters can be established to handle most situations. In some ventilators, multiposition switches are employed. Each position of the switch corresponds to a given set of conditions, i.e., BPM, I/E ratio, and tidal volume. However, these switches incorporated into the ventilator are electrically operable and increase the danger of an explosion based on the fluid used, and additionally do not allow the unit to be easily sterilized.


The present invention is directed to a method and apparatus for controlling the flow rate of a fluid into an enclosure. More particularly, the method and apparatus of the invention are directed to a ventilator which may alternate between a controlled ventilation mode and a demand ventilation mode. The control mode insures that an enclosure is filled intermittently with a fluid in uniform cycles of duration including a first phase for delivering the fluid to the enclosure and a second phase for interrupting the flow to the enclosure.

In another aspect of the invention, a manually operative pneumatic switch is provided, which is devoid of electrical dependence, and which provides the capability of switching from one of a plurality of positions corresponding to pre-established sets of conditions.

In the preferred embodiment of the invention, a ventilator is provided which automatically alternates between a damand ventilation mode and a controlled ventilation mode. This alternation between modes is controlled solely by the patient's needs. A fluid supply is provided and communicates with the ventilator. The ventilator includes a fluidic integrated circuit necessary to control the demand ventilation mode, the controlled ventilation mode, and the alternation between these modes and is solely responsive to the level of pressure in the conduit which communicates with the patient. When the patient only requires assistance, the demand ventilation mode functions. If the patient requires full control, then the ventilator automatically switches to the controlled ventilation mode. If the patient subsequently requires only assistance, then the ventilator automatically switches to the demand ventilation mode.

More particularly, the invention is directed to a ventilator to control the flow of fluid to a patient in at least two modes, and means responsive to the pressure variations in the ventilating conduit to alternate between a first demand ventilation mode to a second controlled ventilation mode. Further, the invention includes a switch which controls the BPM, I/E ratio, and tidal volume during the controlled ventilation mode.

The method of the invention comprises measuring the pressure in an enclosure, providing a first fluid flow to the enclosure in response to the measured pressure at a first level, and providing a second fluid flow to the enclosure at a second pressure level in response to a change in the pressure level in the enclosure, and alternating between the first and second modes solely in response to the pressure in the enclosure.

Another aspect of the invention is directed to a multiposition switch to function in combination with the fluidic integrated circuit. A switch assembly is provided which comprises a plurality of mechanical switches or buttons, each switch in communication with at least one valve, the valve in communication with a fluidic circuit. Actuation of the button opens its corresponding valve and deactivates all other valves.

More particularly, the switch assembly comprises a push button selector and a valve assembly. The selector includes a plurality of valves associated therewith. The valves communicate with the fluidic integrated modular circuit and correspond to a set of conditions of operation: BPM, I/E ratio, and tidal volume. Actuation of a push button will insure the desired conditions are met for the ventilator.


FIG. 1 is a block diagram of a ventilator, which embodies the invention;

FIG. 2 is a schematic illustration of a circuit employed in the ventilator;

FIG. 3 is a perspective telescopic view of the push button selector;

FIG. 4 is a side sectional view of a valve block assembly, engaged to the push button selector; and

FIG. 5 is a perspective view of the switch assembly.


In FIG. 1, a ventilator 10 which embodies the invention is shown in block diagram form and includes a fluidic integrated circuit module 12 mated to a switch assembly 14. A delivery line or conduit 16 places a patient in communication with the ventilator 10 and includes any of the well-known devices adapted for such purpose, such as masks or mouthpieces (not shown). A pressure-relief valve 18 to insure that the pressure developed does not reach a level which would be injurious to the patient and an indicator 20 to demonstrate visibly the operating pressure of the ventilator are secured to the line 16.

Referring to FIG. 2, the fluidic integrated modular circuit 12 is shown in detail and includes a fluid amplifier 22 disposed upstream of the indicator 20 and downstream of the fluid power or air source and a switching circuit 24. A control mode circuit 30 is shown in communication with the amplifier 22 and a control mode amplifier 26. The circuit 30 also includes restrictors R3A-R3E; R4A-R4E; and R5A-R5E.

The switching circuit 24 comprises a Schmitt trigger ST1 in combination with a time-delay relay TDR-1. The Schmitt trigger ST1 includes a resistor R1, a reference control port C1, a control port C2 which is downstream of all circuits and in direct communication with the patient, and output ports 0-2 and 0-1. The output 0-2 communicates directly with a control port CV-2 of the fluid amplifier 26. The power supply PS flows to the Schmitt trigger ST-1 as shown and through restrictor R-1 which sets the level of ST-1 and to the reference control port 0-2. The output port 0-1 provides a signal to the time-delay relay TDR-1. The time-delay relay includes a restrictor R2 to control the duration of the delay of the output signal of the relay, as will be described in the operation of the invention.

The fluid amplifier 22 includes a control port CV-1, in communication with the output, port L, of time-delay relay TDR-1. The fluid amplifier 22 also includes the inlet port IV-1, downstream of the power supply PS and an outlet port OV-1, which provides a signal to the control circuit 30.

The control circuit 30 includes a flip-flop FF1 in communication with the outlet port OV-1 of the fluid amplifier 22. The flip-flop FF1 includes control ports C1 and C2, and outlet ports 0-2 and 0-1, which communicate with the time-delay relays TDR-2 and TDR-3, respectively. The time cycle of each leg of the flip-flop FF1 is determined by a combination of the time-delay relay and the restrictive device, e.g. R3A, R4A in which it is in combination with. The time-restrictive device is calibrated to establish both the I/E ratio and the BPM. This is determined by selection of the appropriate button on the switch assembly 14 as will be described in detail in the description of FIGS. 3 and 4, and the operation of the invention. The inlets E of the time-delay relays TDR-2 and TDR-3 are in communication with both the control ports C1 and C2 of the flip-flop FF1 and the control port CV-2 of the fluid amplifier 22.


The switch assembly comprises two sections: the push-button selector and the valve block assembly.

The switch assembly may, in addition to being used with the fluidic integrated circuit 12 of the present invention, be used with other pneumatic or fluidic circuits. The switch assembly shown in detail in FIGS. 3 and 4 is a 7-position switch and includes an off button which prevents operation of the entire unit and a CPR switch, which must remain manually depressed to function and provides fluid to the patient at a rate of 60 slpm for cardioarrest victims. The remaining five buttons control, in combination with the restrictors shown in FIG. 2, predetermined conditions for tidal volume, BPM and I/E ratio. Push-buttons are identified as OFF, 30-50, 50-100, 100-150, 150-200, 200 up, and CPR.

Referring to FIG. 3, the push-button selector of the switching assembly is shown in perspective telescopic view. The assembly comprises a dowel pin 50 received in an aperture 50 of a button-slide 54. The dowel pin 50 is disposed in the button slide 54 by pressure fit such that an approximately equal length, say for example 11/32 of an inch protrudes from both the top and the bottom of the button slide 54. For purposes of clarity, only one button slide-dowel assembly is shown in FIG. 3. However, it should be understood that matching assemblies are provided for each of the buttons.

A spring 56 is received in the button slide 54 between the two protruding tails 58(a) and (b) and extends beyond the upper and lower surfaces of the slide 54.

A dowel pin 60 is received securely by pressure fit in an aperture 62 in the end of a valve button housing 64. A valve interlock bar 66, having L-shaped slots therein 68, 70(a-e) and 72, and a tab 74 at one end thereof is disposed in the valve button housing 64. A spring 76 is disposed about the dowel pin 60 extends therebeyond to engage the tab 74 of the valve interlock bar 66 such that it biases the valve interlock bar 66 rightwardly as shown in FIG. 3.

A plurality of separate button interlocks 79(a-f), shown side by side, have U-shaped slots 80 at one side thereof. The reduced section of each button interlock when aligned side by side defines with the reduced section of the button lock it is contiguous to V-shaped slots 82. The button interlocks 79(a-e) are placed in the valve button housing 64 below the interlock bar 66 such that the V-shaped slots 82 register with aligned upper and lower control slots 65 and 67, of the housing 64, and the L-shaped slots of the interlock bar 66. The back wall of the housing 64 is characterized by a plurality of uniformly spaced rectangular openings 84 each opening adapted to receive in a slidable manner a button slide 54. The button slide 54 is received in the rectangular opening at the rear of the housing 84, the spring 56 contacting the inner surface of the back wall, and the dowel pin 50 is received in a slidable manner in the slots 65 and 67 of the housing 64 in the slot 70(a) of the interlock bar 66 and in the V-shaped slot of the interlock bar 78. A valve button guide 90 having a plurality of parallel equally spaced slots 91 on its upper surface 92 and a plurality of equally spaced apertures 93 on the front thereof is secured, such as by screws, to the valve button housing 64 and the extended ends of the button slide 54 pass through the openings 93. The buttons, identified as OFF, 30-50, etc., are then secured by pressure fit to the elongated end of the button slide 54. When assembled, the upper and lower surfaces 92 and 95 of the button guide are within the housing 64 such that the valve interlock bar is slidably secured between the top surface of the button guide 90 and the bottom surface of the top ledge of the housing 64. The interlocks 79 are slidably secured between the bottom surface of the button guide 90 and the upper surface of the lower ledge of the housing 64. The slide 54 is between the shelves of the button guide 90. Slots 65, 70, 91, 82, and 67 are all in register such that the dowel pin 50 of the buttons 30-50, etc., passes through all. There are no corresponding slots 82 for the OFF and CPR buttons, and the dowel pins 50 engage the L-shaped slots 68 through 72 of the valve interlock bar 66 respectively.

In the preferred embodiment of the invention, fifteen valve assemblies are required for the buttons 30-50, etc. Three assemblies each are stacked in series and function as one unit as will be described to provide the input and output apertures for the openings required, as shown in FIG. 2 and identified as A(1-5) through E(1-5). One valve assembly is required for the CRT button and no valve assemblies are required for the OFF button.

Referring to FIG. 4, the valve block assembly is shown, a first valve schematically, the second valve in cross-section, and the third valve in partial section partial perspective.

The valve 100 includes a valve block 122 and a valve stem 101 shown in closed position having a rear shoulder portion 102 and a forward conical-shaped portion 104. The rear-shaped and forward-shaped portions terminate in rear and front stems 108 and 106. A spring 110 is received about the stem 108 and engages the shoulder 102 at one end and engages a spring retainer 112 at the other end. The spring retainer 112 is secured into the inner shoulder 113 of valve block 122 by press fit. A diaphragm 114 is secured in non-movable sealing engagement by press fit in the outer shoulder 115 of the valve block 122. The seal retainer 116 is received in a slidable manner in the apertures of the retainer 112 and diaphragm 114.

The central section of the valve block 122 has a chamber in which the valve stem 101 reciprocates between its open and closed positions, input and output conduits A1 -A2, A3 -A4, and A5 -A6 respectively; a shoulder 124, a conduit 132 and an outer ring portion 133. A ring-like shoulder 126 on the forward portion of each valve mates with a corresponding recess 128 at the rear of each valve block 122. The first valve 100 includes a section 140 through which the seal retainer 116 passes. The section 140 includes a rectangular recess 142 which receives the rear portion of the button slide 54 shown in FIG. 3.

Referring to the second valve 100, the conical section 104 of the stem 101 sealingly engages the shoulder 124, preventing fluid flow between the ports A3 and A4. The stem is biased to to this closed position by the spring 110. The stem 101 is partially received in conduit 132 where it contacts retainer 116. Movement of the button slide 54 initially engages retainer 116 which moves rearwardly effecting movement of the subsequent valve stems 101 and retainers 116.

Keyways 150 maintain the entire assembly in line and provide mounting holes for screws to clamp the valve assembly to the switching assembly.

FIG. 5 illustrates the entire assembly with the 30 ports corresponding to the ports of FIG. 2. It being understood that for each button, except OFF and CRT these are the corresponding valves in series which provide six ports. Specifically, the following relationship is provided: button 30-50, ports A(1-6); button 50-100, ports B(1-6); button 100-150, ports C(1-6); button 150-200, ports D(1-6); and button 200 up, ports E(1-6). As shown in FIG. 1, the power supply at 40-90 psig flows directly to the single valve 130 associated with the CPR button and the output flows directly to the patient by passing the entire fluidic integrated circuit.

The physical interface between the circuit 12 and the switch assembly 14 is accomplished by clamping the fluidic integrated circuit module 12 to the top of the valve assembly 14, such as by screws being threaded into the holes in the valve assembly 14. The sealing is accomplished by O-rings which fit into the standard counterboard holes in the fluidic integrated circuit module and actually seal against the valve assembly when the two parts are clamped together.


The operation of the invention will be described in reference to the use of the ventilator as an emergency unit, wherein a patient of from 30 to 50 lbs. requires artificial ventilation. Referring to FIG. 1, a power supply of fluid supply such as oxygen tank is turned on and its output controlled at 3-10 lb. per square inch gauge pressure by pressure regulator 13 which is all that is required to operate the fluidic devices of the circuit 12. Upstream of the pressure regulator 13, the line branches and is connected to the input side of the valve 130 in combination with the CPR button. This flow of oxygen to the patient will hereinafter be referred to as the signal. Under operating conditions, the fluid supply will be at 50 standard liters per minute at the reference gauge pressure. A mask or tracheal tube, as is well known in the art, is placed about or in the patient's mouth and/or nose as appropriate. The pressure relief valve 18 insures that an injurious amount of pressure in the event of malfunction is not transmitted to the patient, and for example, would insure that no pressure above 50 CMH2 O reaches the patient.

The ventilator is activated by power turn on, and based on the size of the patient, the 30-50 button is actuated. This insures that a defined BPM and I/E ratio will be provided for the patient as required during the controlled ventilation mode. The restrictor R5A (ports A1, A2) is placed on line downstream of amplifier 22 and upstream of the delivery line 16. As long as the button 30-50 is actuated, R5A will control the flow rate whether the ventilator is in the demand or controlled ventilation mode.

Referring to FIGS. 3 and 4, as the 30-50 button is pushed, the button slide 54 is forced rearwardly against the bias of the spring 56, which spring engages the inside wall of the back of the housing 64 and the slide 54. Assuming no other button is engaged at the time, the dowel pin 50 travels in the slots 64 and 67 in the housing 64, cams against the angular surface 69a of the L-shaped slot 70a in the valve interlock bar 66. The dowel 50 will also travel in the slots 91 upper and lower of the valve button guide 90. The action will cam the interlock bar 66 to the left against the bias of the spring 76. At the same time, the dowel pin also cams against the inclined surfaces of the button interlocks 79b and 79c. It should be understood that the button interlocks in this embodiment comprises six separate pieces and, as shown, they are simply lying side by side. The left outer edge of interlock 79a is spaced apart from the left inner side wall of the housing 64 and the right outer edge of the interlock 79f is spaced apart from the right inner side wall of the housing. The movement of the button interlocks 79b and 79c by the action of the dowel pin 90 cause interlock 79a to move to the left and interlocks 79b, c, d, e, and f to move to the right such that the other buttons cannot be activated at the same time.

The button slide 54 travel is terminated when the dowel pin has traveled or cammed to the L-shaped portion of the slot 70a. After the dowel has cammed over the surface of the L-shaped slot 70a, it is received in the leg portion of the slot and the action of the spring 76 biasing the valve interlock bar 66 rightwardly locks the dowel pin into position and thereby locks the button 30-50 into position.

The rectangular section on the back of the slide now protrudes approximately one-fourth inch from the back side of the housing 64, and is received in the recess 142 and activates the corresponding valves in the valve assembly with this displacement. Specifically, the end of slide 54 contacts and moves the retainer 116. The length of the stem 101 is designed such that there is a small gap, say for example 0.15 inches, between the back of one valve stem and the front of the succeeding valve stem, insuring that when in the closed position each valve can properly close by the action of its own spring and not be interfered with by the positions of the other valves in the line. As the 30-50 button is pushed, in the selector section, the back of the button slide 54 pushes the corresponding valve stem back against the action of the spring 110, thereby providing communication between the input and output ports A1 -A2, A3 -A4, and A5 -A6 of the first, second and third valves, only the action of the first and second valves being shown in section, it being understood that all valves are identical. The design of the valve assembly and fluidic integrated modular circuit permits only one pair of paths for air flow for each valve to be opened at one time, or three sets of air paths for each button selection. Therefore, with the button 30-50 now actuated, the passageways for the restrictors R3A, R4A, and R5A are now available for operation during the controlled mode of the respirator.

When any of the buttons with the exception of the OFF and CPR buttons, are actuated, the following ports open and restrictors are made operable: button 30-50, ports A1-2, restrictor R5A; ports A3-4, restrictor R3A; ports A5-6, restrictor R4A. Correspondingly, for button 50-100, ports B1-2, restrictor R5B; ports B3-4, restrictor R3B . . . 200 up, ports E3-4, restrictor R3E; and ports E5-6, resistor R4E. The tidal volume restrictors shown in FIG. 2 are such that they provide the following flow rates:

Restrictor Flow(SCC/M) Flows(L/M) ______________________________________ R5A 2600 2.6 R5B 3000 2.0 R5C 7500 2.5 R5D 10,000 10.0 R5E 10,500 10.5 ______________________________________ For the controlled ventilation mode to establish the BPM and I/E ratio at 1:2 one pair of restrictors (4 ports) is operated at one time. This is achieved by setting the time lapse before resetting flip-flop FF1.

______________________________________ Restricted Coordinated Frequency of Breath I/E Ratio Pair ______________________________________ R3A-R4A 40 BPM 1:2 R3B-R4B 30 BPM 1:2 R3C-R4C 25 BPM 1:2 R3D-R4D 20 BPM 1:2 R3E-R4E 15 BPM 1:2 ______________________________________

Referring to FIG. 2, the restrictors control the duration of the time-delay relays TDR 2 and 3, which in turn allow actuation of the flip-flop FF1 between its first and second states. For the valve position 30-50, the volume through the tidal restrictor R5A, ports A1-2 open, is 65 cc. with an I/E ratio of 0.5 to one seconds. Correspondingly, for the remaining four positions, the volume, BPM, and I/E ratios are 100 cc., 40 BPM, 0.8 seconds to 1.6 seconds; 200 cc., 30 BPM, 0.67 seconds to 1.33 seconds; 300 cc., 25 BPM, 0.80 seconds to 1.60 seconds; 500 cc., 20 BPM and 1.0 to 2.0 seconds; and 70 cc., 15 BPM, 1.33 to 2.67 seconds.

After the ventilator is activated, referring to FIG. 2, there is a signal immediately present at one side of the restrictor R1, and at the input ports of the Schmitt trigger ST1 and the time-delay relay TDR-1 at the input port IV-1 of the amplifier 22. Also, there is a signal present at the input port IV-2 of the amplifier 26. The Schmitt trigger ST1 functions in its normal manner such that its input will switch between first and second states depending upon control signals.

The signal at control port C1 is set by the restricting device R1. A signal appearing at control port C2 greater than the signal at C1 will shift the output of the Schmitt trigger to output port O1. Conversely, when the input signal at C2 is less than that at C1, the output will shift to the O2 port. It should be noted that the control port C2 is directly in communication with the patient at a point downstream of all devices.

If the patient is breathing, as he inhales he will cause the signal at C2 to decrease, shifting the output of the Schmitt trigger to O2. Port O2 is connected to control port CV2 of amplifier 26, which amplifier is activated when the O2 port is activated, causing the normally closed amplifier 26 to open and permit the supply to pass through the valve through the tidal volume restrictor R5A and to the patient.

If the patient is not breathing, the rise in signal at C2 switches the output of the Schmitt trigger to O1, shutting off the supply to the patient by closing amplifier 26 (no signal from O2 of ST1) and causes the signal to be present at the input port E of the time-delay relay, TDR-1. TDR-1 delays the signal for a preset time, e.g., 15 seconds, before it allows the signal to exit at port L. If the patient inhales before the time delay elapses, the signal at C2 decreases and then the Schmitt trigger switches to its O2 state and the amplifier 26 is opened. The time-delay relay TDR-1 is disabled. As long as the patient is breathing, the fluidic circuit remains in its first or demand ventilation mode, namely through activation of the fluid amplifier 26 allowing the flow of supply to the patient based on the patient's control (pressure in the respiratory system).

If the patient does not breath during the delay, then the signal appears at the output port L of TDR-1 and the control port CV1 of the fluid amplifier 22. When the signal is present at the control port CV1 of the fluid amplifier 22, the valve opens and permits a signal to pass through and to be introduced to the PS control ports of the flip-flop FF1 and the two time-delay relays TDR-2 and TDR-3, as well as one side of each of the two restrictive devices R3A and R4A, ports A3-4, A5-6 being open, button 30-50 being actuated.

FF1 immediately and indiscriminately assumes either its O2 or O1 output state. Assuming that it takes the O2 state, then the signal exits through O2 and enters port E on TDR-2. The delay network in the device in conjunction with the restrictive device R3A permits exit of the signal at port L after the time set has elapsed, which is 0.5 seconds the flip-flop then switches to its O1 state, providing a signal at E of TDR-3 and CV-2 of amplifier 26. The fluid amplifier 26 remains open the period of time that it takes for the delay restrictive circuit of the TDR-3 and the restrictor R4A to emit the signal at port L of the relay and at the control port C2 of the flip-flop. When this occurs, the flip-flop changes to its O2 state and the entire cycle is repeated until the patient starts spontaneous breathing or the machine is shut off. Thus, if the patient does not start spontaneous breathing, then the apparatus continues in its controlled mode cycle. The fluid amplifier 26 also allows the tidal volume to flow through the restrictor R5A, ports A5-A6 being open.

The time cycle of each leg is set by a combination of time-delay relay and restrictive device calibrated to establish both the I/E ratio and the BPM. Once in the controlled mode, as soon as the patient commences spontaneous breathing, then the inhalation will cause the Schmitt trigger at input port C1 to switch, allowing the fluid amplifier 26 to open to assist the patient in breathing. If the patient does not continue spontaneous breathing within the fixed period of time, then the Schmitt trigger, in combination with the time-delay relay TDR-1 will switch to the controlled mode, employing the fluid amplifier 22 and the combination of restrictors as described.

Referring to FIGS. 3 and 4, if a different set of conditions are required for a patient, when another button is pushed, say for example the 150-200 button, the same action initially takes place as when the 30-50 button is pushed, and the corresponingly dowel pin of the 150-200 button moves forward in its slots, it cams the interlock bar 66 to the left prior to engaging and separating the button interlocks 97d and e, permitting the 30-50 button that was previously activated to return to its inactive position forced by the action of the spring 56 between the housing 64 and the button slide 54. More specifically, as the interlock bar 66 moves to the left, the dowel 50 of the slide 54 is moved closer to the longer leg of the L-shaped slot 70a. When the movement of the dowel associated with the 150-200 button completes its camming action but prior to its entry into the short leg of the slot 70d, the action of the spring 56 forces the slide 54 back to its closed position. The button 150-200 does not slide back, of course, because of the manual pressure being applied. The portion of the dowel which extends below the slide does not engage the interlocks 79d and e until the dowel is pressed into the short leg portion of the slot 70d. At that time, the bar 66 moves rightwardly locking the 150-200 button into position, and opening its corresponding valves, and the button interlocks 79d and e are separated. The movement of the button interlock as before prevents the actuation of two buttons at the same time.

The OFF button will not act to open any valve and is only used to disconnect all other positions when desired. The CPR button is momentary, providing the same action on the button interlocks 79, but can only be held in place manually, as is apparent from its corresponding slot in the interlock bar 66. This button operates a single valve, two ports, identical to those previously described, which supplies oxygen to the patient at a rate of 60 slpm directly from the source by passing the fluidic circuit entirely as long as the button is held in place providing the ventilation requirements for cardiopulmonary resuscitation for cardiac arrest victims.

Although my invention has been described with reference to particular values as far as I/E ratios, BPMs and tidal volumes, it is obvious that these may be varied by those skilled in the art. Also, it is apparent that additional or fewer valves may be stacked in serial relationship to allow for the opening or closing of other ports as desired. Further, the valve assembly may be used either alone or in combination with the above-described fluidic circuit or other pneumatic circuits. Additionally, any structure which would control the alternation of modes of operation, such as a demand valve and fluidic control arrangement, may be employed; for example, a demand valve may replace the Schmitt Trigger.