05/113279

05/22/1973

02/08/1971

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U.S. Philips Corporation (New York, NY)

128/203.250

A61M16/16; A61M16/18; A61M16/10; A61M16/00

128/145.5,145.6,145.7,145.8,188 251/337,50 137/524

Gaudet, Richard A.

Dunne G. F.

What we claim is

1. In a medical respirator comprising a cylinder for containing patient gas at a storage pressure which is higher than atmospheric pressure, a piston having opposite end faces thereof of unequal areas movable within said cylinder and dividing said cylinder into first and second volumes, first connection means connected to a source of gas and to said first volume for supplying patient gas thereto during an expiratory period of said respirator, second connection means connected to said first volume for passing patient gas therefrom to a patient during an inspiration period of the respirator, switching means for connecting said first volume to said first or second connection means during expiration or inspiration periods, means connected to said switching means for cyclically operating said switch, means connected to said second volume for supplying gas thereto the pressure of which acts on said piston to expel the gas within said first volume, a liquid injector means for injecting an adjustably predetermined quantity of liquid into the patient gas to be passed to the patient comprising a variable volume container for the liquid, driving means connected to said variable volume liquid container and operable by said storage pressure of said gas to reduce the volume of said liquid container to cause liquid to be discharged therefrom into the said quantity of gas, means connecting said driving means to said switch for applying said gas at storage pressure to said driving means to cause operation thereof so that the quantity of liquid discharged is proportional to the said storage pressure of the gas, and a spring control means for adjustably controlling said driving means having increasing restitution force with increasing deflection from an unstressed position acting on the driving means in such a direction as to tend to oppose movement thereof, caused by the gas for reducing the volume of said liquid.

2. In the medical respirator according to claim 1 wherein the variable volume container comprises a piston in a cylinder.

3. In the medical respirator according to claim 2 wherein the driving means is a piston in the cylinder.

4. In the medical respirator according to claim 1 wherein the driving means is a bellows.

5. In the medical respirator according to claim 1 wherein the spring is a helical spring.

6. In the medical respirator according to claim 1 wherein the spring is a blade spring.

7. In the medical respirator according to claim 1 further comprising means for adjusting the increase of restitution force of the spring with increase of deflection.

8. In a medical respirator according to claim 1 further comprising flow rate controlling means connected to said liquid container for controlling the rate at which liquid is passed from the container into the said quantity of gas.

9. In the medical respirator according to claim 1 further comprising means connected to said liquid container for delivering the quantity of liquid which is discharged therefrom into the stored quantity of gas within said first volume during an expiratory period.

10. In the medical respirator according to claim 1 further comprising means connected to said liquid container for delivering said quantity of liquid which is discharged therefrom into the predetermined quantity of gas while the gas is being passed to the patient during an inspiratory period.

This invention relates to liquid injectors for medical respirators in which a predetermined quantity of patient gas is stored at higher than atmospheric pressure in a known volume during an expiratory period of a respiratory cycle and discharged to a patient during the next following inspiratory period of the cycle. In respirators of the type described, sometimes referred to as "tidal volume" respirators, the quantity of gas passed to a patient per respiratory cycle, i.e. the tidal volume, is proportional to the product of the gas pressure and the known volume. This quantity may therefore be varied by controlling the pressure of the patient gas fed to and stored in the known volume.

In medical respirators, it is sometimes required that a quantity of liquid be added to the patient gas in each respiratory cycle; this being effected by a liquid injector. The quantity of liquid normally used per cycle is very small in relation to the tidal volume and must be accurately controlled. The quantity per cycle is usually expressed as a ratio of liquid, or liquid vapor, to patient gas.

An object of the invention is the provision of a liquid injector for respirators of the type described in which alteration of the patient gas pressure to adjust the tidal volume also affects the quantity of liquid injected by the injector such that the liquid/gas ratio of the mixture discharged to the patient is held constant.

According to one aspect of the invention, the injector includes a movable member the displacement of which from a datum position controls the quantity of liquid injected into the patient gas in each cycle; the said displacement being directly proportional to the pressure of the stored patient gas.

According to a further aspect of the present invention, spring means are provided which control the displacement of the movable member by exerting a force tending to oppose the displacement.

According to a further aspect of the invention there is provided a liquid injector, for a medical respirator of the type described, in which patient gas at the said pressure is applied during the expiratory or inspiratory period to displace a movable member to transfer liquid from a reservoir to the predetermined quantity of patient gas, and in which spring means control the displacement of the movable member to hold the liquid/gas ratio in the mixture of liquid and gas fed to the patient constant with change of the said pressure.

The above and other features of the invention will be more readily understood by a perusal of the following description of exemplary embodiments thereof having reference to the accompanying drawings in which:

FIG. 1 is an explanatory diagram;

FIG. 2 shows one embodiment of the invention in which the injector and drive system operate in the inspiratory period of a Tidal Volume Respirator;

FIG. 3 shows an alternative to FIG. 2 in which liquid is delivered to stored patient gas during an expiratory period, the mixture of liquid and gas being delivered in the next following inspiratory period.

In FIG. 1 a pressure driven motor M, which may be a cylinder enclosing a piston or bellows, giving linear movement with applied pressure, is coupled by a mechanical link ML to an injector I of a type in which displacement of liquid is proportional to displacement of a movable member. An extension E of link ML is engaged with one end of a spring SP, whose other end is fixed. The motor input is connected by a line 11 to a switch SW, which, in the shown position, connects the input of the motor M to atmosphere as indicated by an arrowhead A. In the shown position spring SP is unstressed. A liquid reservoir LR supplies injector I via a line 12 and a one way valve D1, and liquid from injector I is passed to atmosphere, arrowhead A, via a second one way valve D2 and line 13.

Movement of switch SW to its alternative position connects gas at adjustable pressure in line 15, supplied from pressure regulator PR fed via line 14 from a source PS of gas at higher than atmospheric pressure, to the motor input, and motor M will be driven. Such drive will move link ML and the movable member of the injector by an amount depending on the gas pressure and the opposed force from the now compressed spring SP. Adjustment of gas pressure may therefore control the amount of liquid displaced from injector I.

Substitution of a spring of different rate, i.e. one in which the deflection for a given applied force is not the same as that for spring SP, will, at any gas pressure applied to motor M, result in a different liquid displacement per unit of gas pressure. For a fixed pressure, therefore, a means controlling the spring rate may be calibrated in terms of liquid delivered on each operation of switch SW.

As described above, a quantity of liquid will be delivered from injector I immediately after switch SW connects the motor M to gas pressure. The delivery may be prolonged by the inclusion of resistance to flow, as for example, by a flow control FC in line 13 from the outlet of the injector I.

In FIG. 2, the scale of which is not uniform, a pneumatically operated spool valve 60 is controlled by air pressure supplied by air lines connected to control ports 29 and 66, the arrangement being such that a pneumatic timing circuit supplies pressure to port 29, with port 66 vented to atmosphere, during an inspiration period, and supplies pressure to port 66, with port 29 vented, during an expiration period. A cylinder 50 contains a piston 54, having unequal area end faces 52 and 51 (the area of latter being greater than the former) which divides the cylinder into two volumes V1 and V2. During an expiratory period, with the spool or shuttle of valve 60 in its alternative position to that shown so that a passage is established between valve ports 47 and 48, gas in volume V2 is transferred to volume V1 via pipe lines 53, 46 and 49. Additional gas is provided from a pressure source (not shown) connected to port 43 at a pressure determined by a regulator 45 connected between ports 47 and 43 by pipe lines 46 and 44. During this expiratory period piston 54 moves towards the left to increase the capacity of volume V1 and the quantity of gas stored in volume V1, the tidal volume, is the product of pressure as determined by regulator 45 and the maximum capacity of volume V1 when in its extreme left hand position.

During an inspiratory period, valve 60 establishes a passage as shown between ports 48 and 55, and gas passes from volume V1 via pipe lines 49 and 56 to a flow control 57 and thence to a patient via line 58. During this period pressure in pipe line 56 is substantially constant due to the movement of piston 54 to the right under the influence of gas pressure from regulator 45 applied to volume V2 via pipe lines 46 and 53.

For injection of liquid during an inspiratory period the pressure in pipe line 56 is utilized by applying it to a piston 20, within a cylinder 20A, via a pipe line 21; the resulting movement of piston 20 under the influence of the pressure being transferred by a piston rod 20B to a plunger 22, working within a cylinder 22A, which together comprise an injector. Piston 20 is preferably of larger diameter than plunger 22 and of much smaller diameter than piston 54. A recessed collar 20C is secured to piston rod 20B and engages one end of a spring blade 23 attached to an anchoring bar 23A. The position of another bar 23B, slidable on bar 23A, determines the point at which flexure of spring blade 23 may commence, the arrangement of bars 23A, 23B and collar 20C being such that, with no pressure in cylinder 20A, the spring blade 23 is substantially unstressed and the volume defined by piston 20 and cylinder 20A is substantially zero.

Fluid, from a reservoir not shown, is supplied to the injector cylinder 22A via a fluid line 24 and a one way valve D1 and may leave the injector by way of fluid line 25 having a one way valve D2 therein. Valve D2 is very lightly spring loaded so that the head of fluid within the reservoir and injector does not of itself cause liquid to flow beyond it. A liquid flow control 26 receives liquid from line 25 and passes it to a patient via a line 27 joined to the patient gas line 58.

Movement of bar 23B relative to bar 23A may be by any conventional control means, and, as such movement alters the spring rate and therefore the deflection for a given applied force, the control may be calibrated in terms of liquid ejected. Alteration of pressure, by regulator 45, not only alters the deflection and amount of liquid ejected for a given position of bar 23B, but also the quantity of gas stored per expiratory period; the tidal volume of gas being delivered to a patient in the next following inspiratory period. The control for movement of bar 23 may therefore be calibrated in terms of the ratio of liquid to patient gas per respiration or, for a given temperature and with a volatile liquid, in terms of the ratio or percentage of liquid vapor to patient gas, such ratios remaining constant during changes of tidal volume caused by alteration of gas pressure.

Certain small disadvantages are apparent in such a system:

a. The volume of gas in cylinder 20A discharges substantially exponentially to the patient through flow control 57 after piston 54 has reached its extreme right hand position and/or valve 60 has operated to terminate an inspiratory period. This advantage may be made negligible by arranging that the maximum volume within cylinder 20A and piston 20 is small and also small relative to the maximum capacity of volume V1. As the maximum quantity of liquid to be injected is small, this is readily achieved.

b. Liquid flow control 26 must be adjusted, in addition to the pneumatic timing controls and gas flow control 57 of the respirator, so that transfer of liquid from the injector to line 58 and the patient occurs within the set inspiratory period.

c. Deflection, and therefore liquid ejected, is proportional to the cube of the effective length of spring blade 23, making difficult the provision of a linear scale for the control means.

The above disadvantages are overcome, either completely or partially, in the injection system shown in FIG. 3 in which gas within a storage volume is injected with liquid during an expiratory period, the mixture of gas and liquid being passed to the patient in the next following inspiratory period.

In FIG. 3, in which the scale employed is not uniform, walls 74, 75 and 76 contain two rigid diaphragms 70 and 72, connected by a spacing member 79 fixed thereto and having respective flexible surrounds 71 and 73, to define two volumes V1 and V2 with respective entry ports 83, 83A and 82.

Parts concerned with liquid injection are a bellows 30, sealed in a container 30A to define a volume V3, which drives a plunger 32 within a cylinder 32A by means of a linking piston rod 30B when gas pressure is introduced into volume V3 by a pipe line 31C; plunger 32 and cylinder 32A forming at least part of an injector.

Liquid for the injector is supplied from a reservoir, not shown, via liquid pipe line 34 containing a one way valve D1, and leaves the injector by line 35 containing a second one way valve D2 which is lightly spring biased to the closed position.

A spring 33 has one end attached to an anchoring member 33A which carries, in slidable engagement, a fulcrum member 33B. Pivoted on fulcrum 33B is a bar 33C to one end of which is attached the other end of spring 33. The other end of bar 33C is bifurcated to embrace piston rod 30B, a pin 30C therein engaging the upper surface of bar 33C. Two pairs of rods 33D, mounted on anchorage 33A, act as guides for bar 33C during movement. Guides, not shown, on bar 33C prevent horizontal movement of the bar relative to pin 30C.

In this expiratory period injection system it is essential that the pressurized area of bellows 30, corresponding to the area of piston 20 in FIG. 2, is greater than the working area of plunger 32.

Patient gas at pressure is applied to a port 36 of the tidal volume respirator and is passed on line 37 to a pressure regulator 38 from whence it issues on a line 31 to port 82 of volume V2. Branches 31A and 31B of line 31 respectively feed ports A of two spool valves 39 and 40. Valves 39 and 40 work in unison and may be driven either mechanically or by other means. Their operation from the shown beginning of an inspiratory period terminates such period and starts an expiratory period which, in turn, is terminated by reverting the valves to the shown position. The drive and timing means for these valves are not shown.

During an inspiratory period gas pressure applied to port 82 expands volume V2 and drives the contents of volume V1 out of port 83A, via a line 41, ports B and C of valve 40, a line 56, a flow control 57 and a line 58, to a patient connected thereto. During this period volume V3 is reduced to a minimum, which may be substantially zero, due to the passage within valve 39 to atmosphere, indicated by an arrowhead issuing from port C, established from port B to which line 31C is connected. With a minimum volume V3 established the arrangement is such that neither bellows 30, which may be of metal, or spring 33, are stressed but pin 30C is in contact with bar 33C.

On change over of valves 39 and 40 to their expiratory position, communication to the patient is closed at port C of valve 40 and gas at pressure is passed to volume V1 via ports A and B of that valve, driving the diaphragm assembly towards the position shown. At the same time a path is established in valve 39 between ports A and B, applying pressure to volume V3, so contracting bellows 30 and moving plunger 32. The amount of such movement and of liquid ejected thereby is governed by forces acting in opposition to the pressure in volume V3 which comprise the tension in the now elongated spring 33 multiplied by any mechanical advantage given by the position of fulcrum 33B plus pressure from volume V1 acting on plunger 32 and any force exerted by compressed bellows 30.

Pressure in volume V1 may be regarded as substantially constant at the pressure set by regulator 38, which pressure is also applied to volume V3, so that movement of plunger 32 is proportional to the pressure determining tidal volume for any position of fulcrum 33B, which may therefore be calibrated, as for FIG. 2, in terms of the ratio of liquid to patient gas.

Movement of fulcrum 33B may be controlled, as for FIG. 2, by known means, e.g. threaded rod and nut, rack-and-pinion gears or cam and spring. As the opposing force exerted by the spring 33 is proportional to Ds/Dp, where Ds is the distance between spring and fulcrum and Dp is the distance between fulcrum and pin 30C, the movement calibration of fulcrum 33B departs from linearity less than in the case of the cantilever spring blade of FIG. 2. Where cam movement means are employed to linearize the scale a less steep profile is required.

In FIGS. 2 and 3 a simple type of plunger operated injector is shown. It may be replaced in both figures by a more complex type as described and shown in FIG. 3 of copending U.S. application Ser. No. 6,846 in which piston 72 corresponds to plunger 22 or 32. In FIG. 3 of the present application a broken line 31D represents a source of driving pressure for the cylinder 66 of FIG. 3 of U.S. application 6,846, broken line rectangles shown in both lines 31C and 31D indicating means e.g. restrictions and/or one way valves to control the required sequential action of the two moving parts of the more complex injector. With such an injector, one way valve D1 becomes superfluous and one way valve D2 is incorporated in the injector.

Gas from volume V3 discharged to atmosphere from port C of spool valve 39 represents wastage which may be small due to the small maximum capacity of volume V3. Such wastage may be eliminated by connecting port C of valve 39 to line 58 and so to the patient.

Other forms of construction of the various parts of the injection system of FIG. 3 are possible. The bellows 30 and container 30A may be replaced by the piston and cylinder of FIG. 2, as may be the tension spring arrangement by the equivalent cantilever or quarter elliptic spring system. Where a simple type of injector such as shown in FIGS. 2 and 3 is employed, cylinder 32A may be within a wall of volume V1, e.g. wall 75 in FIG. 3.

Other modifications are also possible. For example, in FIG. 2, to avoid using the liquid flow control 26, liquid pipe line 25 may be taken instead to gas pipe line 56 downstream of the junction with line 21. In such case piston 20 must be of greater diameter than plunger 22 and preferably a third one way valve is inserted in line 56 between the junctions of lines 21 and 25 to prevent liquid passing into line 21. Spring blade 23 also may have nonuniform dimensions throughout its length or be comprised of more than one blade to assist in obtaining a linear scale to the control for movement of bar 23B.