Closed Circuit Medical Respirators

Abstract

A closed circuit medical respirator provided with a face mask for applying patient gas to a patient and for transmitting exhaled gas to the respirator. A closed path extends from the face mask to a gas purifier, a bellows and back to the face mask. Appropriate drive means are connected with the bellows for causing flow of gas to and from the patient so as to create a positive pressure in the path during one part of the respiratory cycle and a negative pressure during the other part. A gas flow sensor is provided in the path and is connected to a controller for operating the drive means of the bellows. Changeover switches connected with a multi-vibrator are provided for connection with the controller and inspiratory and expiratory valves so as to alternately operate the flow of gas in accordance with the required respiratory cycle.

Description

The present invention relates to medical respirators having closed circuit operation.

Medical respirators are frequently used on "closed circuit" and when so used, gas exhaled by a patient is purified and returned to the input of the machine to be retransmitted to the patient. To replace any loss that may occur due to leakage and/or absorption by the patient over a period of time it is customary to introduce a small bleed of patient gas into the closed circuit formed by patient and respirator, the bleed frequently being inserted in the return path so that additional gas may augment that from the patient during an expiratory period. The gas may be passed to and from the patient by, for example, the variation in volume of a driven bellows, or by other similar means, a reservoir being provided in the circuit to allow for the differences in volume of the circuit during a respiratory cycle. With such circuits it is difficult to obtain any negative pressure to extract all gas from the patient or to provide any resistance to the flow of gas from the patient during an expiration period, either of which may be desirable in certain circumstances.

The invention provides a respirator that follows a flow rate/time curve, during the expiratory period of a respiratory cycle to give more natural rhythm to the breathing of the patient.

The invention also provides a gas circuit for a respirator which, on closed circuit, requires a minimum volume of reservoir and provides negative or positive resistance to gas flow during the expiratory period as required.

The various features and advantages of the present invention will be apparent from the following description of an exemplary embodiment thereof, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of part of the closed gas circuit of a respirator embodying the invention, and

FIG. 2 shows the parts of FIG. 1 included in a block schematic diagram of the patient and drive gas circuits of a pneumatically operated respirator.

Referring now to FIG. 1, a pipe line 6 forms a gas connection between a patient (not shown) and a bellows P, the bellows being operated by a mechanical link T driven by a driving element U/V. Power for operating the driving element is supplied from line 7 via a controller 8 and thence by line 9. A sensor 10, having a bias or operating point (i.e. the input level at which an output signal is available) which may be varied and having an output proportional to the difference in input pressure in lines 6 and a regulating pressure determined by the bias is connected to line 6 and may have a connection from the power supply as shown by broken line 11. A line 12 carries any output signal from the sensor 10 to an amplifier 13 supplied with power over line 7A, the output from the amplifier being applied via line 14 to the controller 8.

In operation, gas in line 6 causes the sensor 10 to produce an output signal which is enlarged by amplifier 13 and passed to the controller 8 so as to apply power from the supply to the driving element U/V which then controls the operation of the bellows P in such a manner that the bellows movement assists, follows, or resists the flow of gas in line 6 according to the adjustment of the bias of sensor 10. If gas is being received by the bellows P from the patient via pipeline 6 and the bias of sensor 10 is adjusted so that no output is immediately produced, movement of the bellows P will create a positive resistance to the flow of gas from the patient. On the other hand, if an output signal is produced by the sensor 10 during a period when no gas is being passed from the patient, the bellows P will be driven by the driving element U/V to lead gas from the patient and a negative resistance to gas flow will be produced, i.e. negative pressure is established, tending to draw gas from the patient. Further, the bias adjustment may be set to zero in which case the movement of the bellows will follow the natural expulsion rate curve of gas from the patient.

In FIG. 2, the closed patient gas circuit comprises a patient (not shown) connected to port S of an expiratory valve R associated with a face mash FM, line 6 connected to a second port of valve R, a non-return valve NR3, a gas purifier 15, a non-return valve NR1, port P1, bellows P, port P3, non-return valve NR2, line 3 and a third port of expiratory valve R. Patient gas to charge the system and make up losses is applied to a port N which, if the gas is substantially at atmospheric pressure, may be connected directly with the junction of non-return valve NR1 and purifier 15. With patient gas supplied at above atmospheric pressure, inspiratory valve R2 may be used as shown or it may be replaced by a spring loaded valve. The purpose of the non-return valves NR1, 2 and 3 is to prevent gas circulation in the wrong direction and valve NR3 is essential when patient gas is supplied at pressure and when expiratory valve R is of the type that does not at any time prevent gas flow from bellows to patient.

Driving gas for the pneumatically operated and timed respirator shown in the example is applied to ports C, L2, L3, 16 and 17; 7: the gas at these various ports not necessarily being of equal pressure. Conveniently, the driving gas is compressed air. Driving gas from port 16 passes via line 7A to pneumatic ampifier 13 and from port 17 to an adjustable pressure regulator PR4 and thence by line 11 to a pressure sensor 10, which may be a valve operated by differential pressure, whose input port 10A is connected to line 6 between valves R and NR3.

A pneumatic timing circuit 18, conveniently of the fluid multi-vibrator type operates changeover valves CO2 and CO3 alternately in accordance with the required respiratory cycle, the feeds to ports V1 and V2 of a double-acting bellows driving cylinder V being alternately energized, via ports E3 and D2, from inlet ports L3 and L2 respectively. The feed to the actuating cylinders Z and Z2 of valves R and R2 are simultaneously alternately de-energized by these same changeover valves. The feed to port V2 is direct from port D2 of valve CO2, but that to port V1 from port E3 of valve CO3 is taken via line 7 to the input of the controller 8 and thence by line 9 to port V1 of the cylinder V.

Sensor 10 in this embodiment comprises a differential pressure operated valve which, when pressure at its port 10A has a predetermined relationship with that set by regulator PR4 the bias control, produces an output signal in line 12 which is then applied to the input of amplifier 13, which may also be a pressure differential operated valve. The output from amplifier 13 is passed over line 14 to open the controller 8, also a pressure controlled valve, an so permit driving gas from port L3 to drive the piston U of cylinder V in a direction that expands the bellows P, the piston and bellows being linked by the piston rod T.

FIG. 2 shows the position at the commencement of the expiratory stroke, with solid lines indicating a gas passage then available within valves CO2 and CO3. The broken lines within the valves show the available gas passages in the alternative positions of the valves. Valve R and the piston of actuating cylinder Z are in their upper position connecting port S to line 6 (port Z being vented to atmosphere via ports D3 and F3). Valve R2 and the piston of cylinder Z2 are in their lower position because driving gas is supplied to the cylinder Z2 from inlet L2 via port E2; so connecting patient gas from port N to the closed circuit. Piston U of cylinder V is free to move downwards, since port V2 is vented to atmosphere via ports D2 and F2 of valve CO2. Driving gas from port L3 is applied to controller 8 via port E3 and line 7, and the drive to the piston U via line 9 and port V1 will be controlled as previously described by the sensor 10.

As during the first portion of the expiratory period gas flow from a patient is high, the signal from sensor 10 will be large, thereby opening controller 8 towards its full extent and thereby expanding the bellows rapidly. At a later period in the expiratory period the gas flow from the patient is at a lower level resulting in a smaller signal from the sensor 10, a smaller amount of opening of controller 8 and a slower expansion of the bellows. The natural variation of tidal volume (the amount of patient gas passed to the patient during an expiratory period) with time is thus followed by the respirator to produce a more natural rhythm of the respiratory cycle.

If desired another sensor, with associated pressure regulator, amplifier and controller, may be similarly arranged to control the inspiratory period in a more natural manner, the other sensor input then being connected to line 3 and the other controller being inserted in the line between ports D2 and V2.

The sensor 10, amplifier 13 or controller 8 may be such that there is a non-linear relationship between the input signal applied to the sensor and the movement of the bellows.

The sensor 10 is not restricted to a type operated by pressure differential but may be operated by other means, e.g. rate of flow of gas. In such a case a restriction may be placed in the line 6 with the two inlet ports of a differential pressure sensor connected to a line 6, one on each side of the restriction. Bias, mechanical or pneumatic, may be applied to the sensor and/or controller to provide the previously mentioned lag or lead of the bellows movement and correction operation of the system.

Claims

What is claimed is:

1. A closed circuit medical respirator comprising a face mask for applying patient gas to a patient, an expiratory valve within said face mask and having an inlet port and an outlet port, a gas purifier having an inlet and an outlet connected on the inlet side thereof to the outlet port of said expiratory valve, a gas container connected to the outlet of said gas purifier, said container being connected to said inlet port of said expiratory valve to thereby complete a closed path, a source of patient gas to replenish losses in the system connected to said path, sensor which produces an outlet signal in response to a predetermined fluidic property connected with said path at a point between said expiratory valve and said gas purifier, a bias control means connected to said sensor, a source of driving gas connected to said bias control, a controller connected to and operated by the output signal of said sensor, a driving means linked to said container for driving same, a source of driving gas connected to said controller so as to be passed therethrough and connected to said driving means, a pneumatic timing circuit operated by a source of driving gas connected thereto, and a pair of changeover valves connected to said timing circuit and operated thereby so as to alternately provide a source of driving gas to the driving means operating the flow of gas from said container in accordance with the required respiratory cycle, said sensor operating to vary the amount of driving gas allowed to pass through said controller as determined by the phase of the respiratory cycle.

2. The closed circuit medical respirator according to claim 1 wherein said container comprises an expandable bellows.

3. The closed circuit medical respirator according to claim 2 further comprising a first non-return valve located in said closed path between the outlet port of said expiratory valve and the inlet of said gas purifier, a second non-return valve located in said closed path between the outlet of said gas purifier and said bellows, and a third non-return valve located in said closed path between said bellows and the inlet port of said expiratory valve, said non-return valves being provided so as to prevent circulation of gas in the wrong direction.

4. The closed circuit medical respirator according to claim 3 wherein said source of patient gas for replenishing losses is substantially at atmospheric pressure and is connected directly to said path at a point between said second non-return valve and the outlet of said gas purifier.

5. The closed circuit medical respirator according to claim 3 further comprising an inspiratory valve having the source of patient gas for replacing losses connected thereto, said inspiratory valve being connected to said closed path at a point between said second non-return valve and the outlet of said gas purifier.

6. The closed circuit medical respirator according to claim 5 further comprising a first actuating cylinder for said expiratory valve and a second actuating cylinder for said inspiratory valve, said actuating cylinders being connected through one of said changeover valves to a source of driving gas so as to be alternately energized in accordance with the required respiratory cycle.

7. The closed circuit medical respirator according to claim 6 further comprising an amplifier connected between the output of said sensor and said controller.

8. The closed circuit medical respirator according to claim 7 wherein said sensor is a differential pressure operated valve.

9. A closed circuit medical respirator comprising a flexible bellows forming a gas container for receiving and supplying gas to a patient, means for coupling said container to a patient, a driving means connected to said container for operating the flow of gas therefrom, said driving means comprising a piston within a cylinder connected to the container, a sensing means connected between said coupling means and said container, said sensing means having adjustable bias means applied thereto and output means controllable by the level of said bias, controller means for controlling said driving means so that the difference between the flow of gas as determined by said driving means and a flow of gas from said patient is substantially constant, a piston rod connected between said piston and said bellows so that movement of the piston within the cylinder produces a change of volume within the bellows thereby controlling the flow of gas to and from the patient, and a source of driving gas connected to the cylinder for operating same, said output means of said sensing means being connected to said controller means so as to control the pressure of gas passing therethrough, said sensing means being arranged to detect said difference between flow rates and said difference being controlled by the bias applied to the sensor.

10. The closed circuit medical respirator according to claim 9 further comprising first and second changeover valves connected to said expiratory and said inspiratory valves and to said means for controlling said driving means and said cylinder respectively for controlling movement of the piston within the cylinder in alternate directions in accordance with the respective periods of the respiratory cycle, and a fluid operated multi-vibrator having a source of driving gas connected thereto, said multi-vibrator being connected to said first and second changeover switches.

11. The closed circuit medical respirator according to claim 10 wherein said means for controlling said driving means comprises a controller device connected between said sensing means and said piston carrying cylinder, a source of driving gas and means connected between said source of driving gas and said controller for passing driving gas therethrough to the cylinder, whereby said sensor controls the amount of driving gas passed by said controller to said cylinder.

12. The closed circuit medical respirator according to claim 11 further comprising an amplifier connected between the output of said sensing means and said controller for amplifying the output signal to the controller so that said controller controls the pressure of the drive gas fed to the cylinder.

13. The closed circuit medical respirator according to claim 12 wherein said means for coupling said supply of gas to a patient is a face mask having housed therein a respiratory valve controlled by alternate operation of said multi-vibrator so that the respiratory valve allows patient gas to flow from the bellows via one part of the closed circuit to the face mask during each inspiratory period of the respiratory cycle and from the face mask back to the bellows via the other part of the closed circuit during each expiratory period.