A portable resuscitator/ventilator device especially intended for emergency use and powered by pressurized primary breathable gas such as oxygen or compressed air from a bottle comprises a control unit that outputs primary gas pulses to a patient valve that includes an entrainment mixer for diluting the primary gas with air. The entrainment mixer is selectively operable to that the patient valve delivers primary gas or air-diluted primary gas as required. The control unit includes a fixed value flow-control restrictor that passes a required tidal volume of primary gas for undiluted delivery to the patient and the impedance of the patient valve is arranged to increase when the entrainment mixer is operational so that flow of the primary gas is automatically reduced to provide the required tidal volume of air-diluted primary gas without wastage of primary gas or any adjustment of the control unit.

FIELD OF THE INVENTION 
This invention concerns resuscitator/ventilator devices of the type powered 
by pressurised breathable gas such as compressed air or oxygen and adapted 
to deliver pulses of this gas to the respiratory passages of a patient to 
accomplish forced ventilation of the lungs in cases of respiratory failure 
or impairment. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
Resuscitator/ventilator devices of this type, hereinafter termed, shortly, 
"gas-powered resuscitator/ventilator devices" typically include a control 
unit that generates the required pulses of breathable gas, and a so-called 
"patient valve" that is connected to the control unit by a flexible 
conduit or hose and that is associated with an oronasal mask or tracheal 
intubation device, this patient valve operating to connect the respiratory 
passages of the patient to the control unit during an inhalation phase, 
and to an exhaust outlet during the exhalation phase. Devices of this type 
in compact portable form are widely available to Emergency Services such 
as ambulance crews for resuscitation and short-term ventilation purposes, 
the devices in this form being almost invariably designed to deliver 
pulses of pure oxygen from a compressed oxygen source because not only is 
pure oxygen ventilation beneficial for short-term application such as in 
resuscitation, but its use in this way permits the control unit and 
patient valve to be very simple and robust devices, resistant to abuse and 
easily operated correctly by personnel with a minimum of training. Indeed 
it is these features of such devices that have led to their increasing use 
for longer term ventilation as when patients with impaired respiratory 
function are subject to extended transportation. However, medical opinion 
is not undivided about the merits of long-term ventilation with pure 
oxygen. Moreover such devices necessarily have a relatively high rate of 
oxygen usage so that their long-term use can lead to problems of oxygen 
source availability. 
There is therefore a need to provide a compact and portable gas-powered 
resuscitator/ventilator device with the facility to deliver to a patient, 
selectively, pure oxygen, oxygen diluted with air, or air. An objective of 
the present invention is to meet this need but without significantly 
affecting the standards of robustness, portability, resistance to abuse 
and ease of operation at present available in devices capable only of 
delivering pure oxygen. 
The type of gas-powered resuscitator/ventilator device here of interest 
divides into two main sub-types: the sub-type characterised by a low-force 
patient valve and that incorporates a control unit that generates pulses 
at a low pressure appropriate for direct delivery to the patient; and the 
sub-type characterised by a high-force patient valve and that incorporates 
a control unit that generates either high-pressure pulses or relatively 
low-pressure pulses that are only a small amount higher in pressure than 
the pulses to be delivered to the patient. The devices having a low-force 
patient valve use a low impedance (large bore conduit) connection between 
the control unit and the patient valve and can be vulnerable to 
malfunction in the presence of contamination, whereas the devices having a 
high-force patient valve can have a high impedance (small bore conduit) 
connection between the control unit and the patient valve. The high-force 
patient valve has a number of advantages from the point of view of 
reliability in addition to its ability to operate with a relatively high 
impedance connection to the control unit. U.S. Pat. No. 4,004,603 and its 
counterparts disclose a patient valve of this type. For convenience 
herein, devices having high-force patient valves will be called, shortly, 
"high-force devices". 
Traditionally, in ventilators designed for long-term use in, say, a 
hospital, dilution of oxygen to a desired breathable gas composition--for 
instance, a 30/70 oxygen/air mixture having therefore about 45% oxygen 
content--is accomplished by use of an entrainment mixer. However, the 
application of such an entrainment mixer to a gas-powered 
resuscitator/ventilator of the type of interest is not straightforward 
because such mixers can be designed to give either a high mixing ratio or 
high pressure recovery, but not both simultaneously. If, therefore, the 
mixer is designed to achieve the desired oxygen dilution the pressure 
recovery will generally be insufficient to allow of the use of a high 
impedance downstream connection: in other words, if the mixer is 
incorporated in the control unit, the latter will not be able to output 
pulses able to drive a high-force patient valve through a high-impedance 
conduit. In this context "high-impedance conduit" is to be understood as 
meaning a conduit that at the maximum flow therethrough imposes a pressure 
drop of more than about 3.5 kPa (0.5 psi). 
Accordingly, to maintain the advantages of the high-force device sub-type, 
an entrainment mixer if used to accomplish oxygen dilution must be located 
at the patient valve. However this leads to control problems because of 
the basic requirement, in a resuscitator/ventilator device of the type of 
interest, to be able to deliver pure oxygen when necessary, e.g. for 
resuscitation purposes. Thus it must be possible to disable the 
entrainment mixer, or to substitute a patient valve not having such a 
mixer, to provide for delivery of pure oxygen when this is required. 
Selective disablement of an entrainment mixer at the patient valve, or the 
facility to exchange patient valves with and without entrainment mixers, 
respectively, leads to flow regulation problems because flow regulation is 
normally performed within the control unit by means of a high-impedance 
restriction that makes the output of the unit independent of the impedance 
characteristics both of the patient valve and of the conduit connecting 
the latter to the control unit, and also independent of patient 
compliance, over a wide range of values. If the flow regulation is set to 
deliver in accordance with the requirements of pure oxygen ventilation 
then, when a patient valve having an entrainment mixer is brought into 
operation to achieve dilution of oxygen delivered by the control unit, the 
oxygen delivery will be in excess of oxygen requirements and wastage will 
occur. That is to say, while the device in these circumstances delivers 
diluted oxygen as desired, its oxygen consumption will remain at the rate 
corresponding to usage of pure oxygen. 
Accordingly it would appear that provision must be made at the control unit 
for resetting the flow regulation in accordance with the absence or 
presence at the patient valve of an operative entrainment mixer. This is 
obviously undesirable in a device that must be used, perhaps under adverse 
emergency conditions, by personnel with little training and/or who are 
called upon to use the device infrequently. 
However, it has been discovered that it is in fact possible to avoid the 
apparent need for resetting of flow regulation arrangements at the control 
unit, by giving the patient valve impedance characteristics that affect 
the flow regulation function, appropriately to reduce oxygen delivery by 
the control unit, when there is an operative entrainment mixer at the 
patient valve. 
SUMMARY OF THE INVENTION 
The invention provides a gas-powered resuscitator/ventilator device of the 
type comprising a control unit having a high-impedance flow-regulation 
restriction adapted to output to a patient valve primary gas pulses 
appropriate for undiluted delivery to a patient. The patient valve 
includes an entrainment mixer than when operative dilutes primary gas 
pulses output by the control unit. The patient valve and the entrainment 
mixer, when this is operative, jointly provide a primary gas flow 
impedance so related to the impedance of the flow-regulation restriction 
of the control unit as to reduce primary gas flow therethrough. 
Thus by simple substitution of the relatively low-impedance patient valve 
that would be appropriate to deliver undiluted primary gas--e.g. pure 
oxygen--by the patient valve and operative entrainment mixer combination, 
the flow-regulation at the control unit is automatically overridden, 
conveniently to the extent necessary to compensate for the reduced primary 
gas requirement of the patient valve and operative entrainment mixer 
combination. 
The device of the invention may have two exchangeable patient valves--one 
of relatively low impedance and adapted to deliver to a patient undiluted 
primary gas pulses as received from the control unit, and another 
including a permanently operative entrainment mixer and of appropriately 
higher impedance--or the device may comprise a single patient valve 
incorporating an entrainment mixer that may be rendered operative or 
inoperative as required, by means that cause the impedance presented to 
primary gas flow to be appropriately raised when the entrainment mixer is 
rendered operative. 
Thus, in an embodiment of the invention, a gas-powered 
resuscitator/ventilator device comprises a control unit having a 
high-impedance flow-regulation restriction adapted to output to a patient 
valve primary gas pulses appropriate for undiluted delivery to a patient, 
the patient valve including an entrainment mixer and a series flow 
restrictor, a shunt circuit and ganged valve means oppositely controlling 
diluent flow to the entrainment mixer and primary gas flow in said shunt 
circuit respectively. 
By means of this arrangement, a required ventilation tidal flow of pure 
oxygen (the primary gas supplied by the control unit) can be obtained via 
both of the entrainment device and the shunt circuit in parallel, while 
the entrainment device is effectively disabled by the valve means 
preventing flow of diluent into the entrainment mixer. In this operating 
mode, the primary gas flow impedance of the patient valve will be low, 
relatively to the flow-regulation restriction, so that the output to the 
patient valve will be substantially independent of changes in downstream 
compliance. Alternatively, when the entrainment mixer is placed in its 
operative condition by setting said valve means to allow diluent to enter 
the entrainment mixer, the shunt circuit is closed by said valve means to 
prevent by-pass flow of primary gas (oxygen) therethrough, the impedance 
of the patient valve to primary gas flow being thereby raised to the 
extent necessary to limit the total flow of oxygen drawn from the control 
unit. 
The restrictor associated with the entrainment mixer may conveniently be 
constituted by the nozzle thereof, because this arrangement offers the 
highest available pressure recovery, it being understood that the 
impedance offered by this restrictor is preferably selected to provide, in 
combination with the flow-regulation restriction of the control unit, no 
more than the appropriate flow of primary gas (oxygen) to provide, with 
dilution, the total ventilation tidal flow volume required by the patient. 
Thus, the impedance of the shunt circuit and of the mixer and associated 
restrictor may be so chosen that when the mixer is operative the impedance 
at the patient valve exceeds that obtaining when the mixer is disabled by 
an amount such that the primary gas flow to the patient valve is reduced 
in correspondence with the dilution of the primary gas to maintain a 
selected delivered gas volume. 
While the invention is especially advantageously applicable to 
resuscitator/ventilator devices of the high-force sub-type to enable the 
reliability and other advantages of the high-force patient valve to be 
realized in conjunction with the ability to change, simply, from pure 
oxygen to diluted oxygen delivery, the invention may also be applied with 
advantage to devices of the low-force sub-type. 
It should be understood that when flow through the shunt circuit is 
prevented in the operative condition of the entrainment mixer, the 
effective additional restriction of the primary gas (oxygen) flow path 
downstream of the control unit not only reduces the oxygen flow to the 
required value but also raises the oxygen pressure upstream of the 
entrainment mixer during the passage of a gas pulse, thereby to optimise 
the operation of the entrainment mixer and to provide a pressure/flow 
characteristic such that different patient airway resistances and lung 
compliances will have minimal effect upon the tidal flow volume delivered 
to the patient's lungs. 
A resuscitator/ventilator embodying the invention has also the capability 
of delivering air pulses to a patient to assist breathing in circumstances 
in which oxygen enrichment of the delivered air is unnecessary or 
undesirable. Thus, by substituting a compressed air source for the normal 
oxygen source and using the entrainment mixer to "dilute" the air pulses 
thereby output by the control unit, air alone may be delivered. The 
compressed air source might, for instance, be a low power compressor. 
The entrainment mixer may be of any suitable type. However it is preferred 
to employ an entrainment mixer of the construction described in co-pending 
Application Ser. No. 857,912 that allows the mixer to be of compact format 
without significant prejudice to its pressure-recovery capabilities.

DESCRIPTION OF THE ILLUSTRATED PRIOR ART, AND OF EMBODIMENTS OF THE 
INVENTION 
Referring to the drawings, FIG. 1 shows the basic components of a 
gas-powered resuscitator/ventilator device intended to deliver undiluted 
breathable gas--typically medical oxygen--from a source thereof to a 
patient for short-term forced ventilation. The device consists of two main 
units, a control unit 1 and a patient valve 2 connected by a flexible 
conduit 3. The arrangement illustrated is that for a device having a 
control unit that delivers pulses of gas at suitable pressure to a 
high-force patient valve, the conduit 3 constituting a high impedance 
connection between the control unit 1 and the patient valve 2 and 
consisting, for instance, in a flexible small bore hose. 
The gas supply, that may for instance be from a cylinder of compressed 
oxygen and at a pressure in the range 250-600 kPa and typically 400 kPa 
(2.5-6 bar, typically 4 bar) is conventionally represented at 4 and is 
connected to a pressure regulator 5 that maintains a suitable output 
pressure (for instance 250 kPa (2.5 bar)) that is unaffected by variations 
in the gas supply pressure. The pressure regulator 5 may be external or, 
as represented, incorporated in the control unit. In either case, the 
control unit includes a timing unit 6 and associated valve 7 that when the 
control unit is in operation release suitably timed pulses of gas to a 
flow control valve 8. The timing unit 6 may for instance be a gas-powered 
oscillator, e.g. as disclosed in British Pat. No. 1,533,550. 
The patient valve 2 may take a variety of forms, its function being to 
respond to the arrival of a gas pressure pulse over the conduit 3 to duct 
this pulse to the patient via an oronasal mask or intratracheal tube, 
while in the interval between such pulses the patient valve establishes 
communication between the patient and an exhalation port. The particular 
arrangement conventionally represented is that of a high-force patient 
valve of the construction described in U.S. Pat. No. 4,004,603, the 
restrictor shown at 9 being the internal flow path restriction that 
maintains a pressure differential between the gas pulse inlet and the gas 
pulse outlet of the valve while gas is flowing through the valve to the 
patient, thereby reliably to maintain the valve in the condition in which 
this flow path is open. 
In a typical form of the system diagrammatically represented in FIG. 1, and 
in which the control unit 1 is intended to produce relatively low-pressure 
pulses, the flow control valve 8 is set to produce, at the required oxygen 
flow rate to deliver a pulse of the required tidal volume, a pressure 
drop, typically about 150 kPa (1.5 bar), that is a high percentage of the 
output pressure of the pressure regulator 5 so that minor impedance 
changes downstream of the valve 8, e.g. arising from variations in patient 
airway resistance and lung compliance, can have very little effect on the 
overall impedance downstream of the pressure regulator 5 and, hence, on 
the gas flow to the patient. 
FIG. 2 illustrates an embodiment of the invention in which the control unit 
10 may correspond in construction and arrangement with that of the device 
shown in FIG. 1, comprising a pressure regulator 15 providing, e.g., an 
output pressure of about 250 kPa (2.5 bar) as in the prior art arrangement 
of FIG. 1, a timing unit 16 and associated valve 17 together with a flow 
control valve 18. This control unit is intended to draw oxygen from a 
suitable source conventionally represented at 14 and to output pulses of 
oxygen via a conduit 13 that may conveniently be a high impedance conduit 
constituted by a flexible hose of relatively small bore. 
In the system of FIG. 2, the patient valve represented at 12 includes an 
entrainment mixer 20 having an associated restrictor 21 in series and 
conveniently constituted by the nozzle of the mixer 20. The entrainment 
mixer 20 and restrictor 21 are bridged by a shunt circuit comprising a 
restrictor 22 and a valve 23 that is ganged with a valve 24 controlling a 
diluent inlet 25 for the entrainment mixer 20. 
The ganged valves 23, 24 are so arranged that when valve 23 is open, valve 
24 is closed, and vice versa. 
FIG. 3 shows, on a larger scale, the theoretical circuit of the patient 
valve 12 of FIG. 2. As in the case of FIG. 1, the illustration is that 
applicable to a patient valve of the high-force form and, depending on the 
operating condition, either the entrainment mixer 20 and its associated 
restrictor 21 (nozzle) constitute the flow path restriction between the 
gas pulse inlet and the gas pulse outlet of the valve of these devices 
with the restrictor 22 in parallel therewith constitute the said flow path 
restriction, for the purpose described. 
In operation of the embodiment of FIGS. 2 and 3, when the 
resuscitator/ventilator device is to deliver pure oxygen pulses for forced 
ventilation of a patient, the ganged valves 23, 24 are set so that the 
valve 23 is open and the valve 24 is closed. Closure of the valve 24 
prevents the entry of diluent (air) to the entrainment mixer 20 so that 
the pure oxygen pulses from the control unit 10, arriving at the gas pulse 
inlet 26, divide and flow through the shunt circuit with its restrictor 22 
and through the entrainment mixer 20 and its associated restrictor 21 to 
the patient connection 27. The restrictors 21 and 22 are so sized, in 
relation to the impedance offered by the flow control valve 18 of the 
control unit 10, as to provide the requisite small pressure drop for 
holding the patient valve in its pulse-transmitting condition while 
passing the required ventilation tidal flow volume of oxygen to the 
patient. Because the impedance offered by the parallel restrictors 21 and 
22 is small compared with that of the valve 18, and because of the 
non-linearity of the pressure drop/flow relationship of the restrictors 
21, 22 and of the valve 18, it is the setting of the latter that 
effectively regulates the oxygen flow in this operating mode. 
On the other hand, with the ganged valves 23, 24 set so that the valve 23 
is closed and the valve 24 is open, the entrainment mixer 20 is enabled to 
receive diluent through diluent inlet 25, to be entrained in and mixed 
with the oxygen that passes through the mixer 20 and associated restrictor 
21 (only) upon the arrival of an oxygen pressure pulse at the pulse inlet 
26. 
In this operating mode, because there is no flow in the shunt circuit 
comprising the restrictor 22, the effective impedance of the flow path 
between the pulse inlet 26 and the patient connection 27 is raised 
relative to that obtaining in the same flow path in the operating mode for 
delivery of pure oxygen to the patient connection 27. The consequence of 
this is that the oxygen flow in this operating mode is reduced, the 
non-linearity of the pressure drop/flow relationship for the restrictor 21 
and for the valve 18 making the pressure drop at the restrictor 21 the 
more significant at this reduced flow rate and thus sharply transferring 
flow control from the valve 18 to the mixer 20 and restrictor 21 
combination. By appropriate choice of impedance values for the mixer 20 
and its associated restrictor 21, at the reduced flow rate required when 
the mixer 20 is operative, therefore, it can be arranged that in this 
operating mode the effective impedance at the patient valve so exceeds 
that of the flow control valve 18 as predominantly to control the flow 
rate at an amount such as to cause the oxygen flow in this mode to be 
approximately one-third of that in the operating mode in which the device 
delivers pure oxygen to the patient, while the mixer dilutes this oxygen 
with about twice its own volume of air to produce the same tidal flow 
volume as when delivering pure oxygen. 
The valve 18 in a typical operational setting is equivalent to a throttle 
having a diameter of about 1.2 mm: in such configuration the restrictor 21 
when constituted by the nozzle of the entrainment mixer would have a 
diameter of about 0.65 mm and the restrictor 22 a diameter of about 1.5 
mm. 
Thus, merely by suitable choice of impedance values, at the relevant flow 
rates, for certain components, the ventilation tidal flow volume required 
by a patient can be provided either wholly by oxygen or by a mixture of 
air and oxygen, with the oxygen flow and consumption being automatically 
reduced in the latter case merely as a consequence of bringing the 
entrainment mixer 20 into operation by actuation of the ganged valves 23, 
24. That is to say, no adjustment of the flow control valve 18 at the 
control unit 10 is required on switching between delivery of pure oxygen, 
on the one hand, and delivery of diluted oxygen, on the other hand. 
Moreover the components providing this selectable gas composition facility 
are either static (entrainment mixer 20, restrictors 21, 22) or of such 
simple mechanical form (ganged valves 23, 24) as to impose no reliability 
or other penalties upon the construction and use of the device in 
comparison with the equivalent device not having this additional facility. 
As noted, the invention is also applicable to devices having low-force 
patient valves and FIG. 4 illustrates the theoretical circuit of the 
switchable entrainment mixer as applied to such a patient valve. In FIG. 4 
the low-force patient valve is represented at 30 with its pulse inlet 31, 
patient connection 32 and exhalation port 33. In applying the invention, 
an entrainment mixer 34 with associated restrictor 35 and bridged by a 
shunt circuit 36 is arranged upstream of the pulse inlet 31. The 
entrainment mixer 34 has a diluent gas inlet 37 controlled by a valve 38 
that is ganged with a valve 39 in the shunt circuit 36 so that when the 
valve 38 is open, the valve 39 is closed, and vice versa. 
When the valve 39 is open there is effectively no impedance in the oxygen 
path to the pulse inlet 31 so that all gas flow control is exercised at 
the control unit in much the same way as in the arrangements illustrated 
in FIGS. 1 and 2. However, when the valve 39 is closed and the valve 38 is 
open, the impedance of the restrictor 35 appears in the oxygen flow path 
to the pulse inlet 31 and thus both reduces the oxygen flow while raising 
the upstream pressure to a value appropriate for correct functioning of 
the entrainment mixer 34. 
In a convenient configuration for such an arrangement, the control unit 
would be arranged similarly to that of FIGS. 1 and 2 but with a flow 
control valve adapted to provide pulses at a pressure of about 0.5 kPa (5 
mbar) when the valve 39 is open (and valve 38 closed) for delivery of pure 
oxygen to the patient. With the valve 39 closed (and valve 38 open) for 
delivery of diluted oxygen, the impedance of the mixer 34 and restrictor 
35 (preferably constituted by the nozzle of the mixer) results in the 
pressure upstream of the restrictor 35 rising to approximately the 
delivery pressure of the pressure regulator of the control unit--say 250 
kPa (2.5 bar) in the typical case. 
FIGS. 5 to 7 illustrate a practical realisation of the invention, in the 
form of a selectable output patient valve for a resuscitator/ventilator 
and conforming with the principles described in relation to FIGS. 2 and 3. 
As shown in FIGS. 5 to 7, this realisation comprises a valve body part 50 
defining a cylinder closed at a gas supply end by a cap 51 having an inlet 
port 52 for connection to a control unit that outputs pulses of primary 
gas, usually oxygen, in the manner described in relation to FIGS. 1 and 2. 
At the opposite, or exhalation end, the body part 50 has its cylinder 
closed by an annular plug 53 that provides an exhalation port 54 and a 
seating for a spring 55 within an annular valve seat 56. 
The body part 50 is further comprised of a lateral gas transfer stub 57 and 
a patient connection stub 58 to receive a connecting tube for an oronasal 
mask or the like (not shown). 
A waisted valve piston 59 is reciprocable within the cylinder of body part 
50, being engaged by the spring 55 to be urged towards the gas supply end 
of the cylinder (to the right as seen in FIG. 5) and away from the valve 
seat 56. 
The gas supply end of the cylinder accommodates a pilot assembly comprising 
a sleeve 60 located in a stepped bore portion of the cylinder and secured 
to the periphery of a flexible diaphragm 61 the central portion of which 
is secured to an operating plunger 62 having a spigot portion 63 engaged 
in a central recess in the piston 59. 
The stubs 57 and 58 are interconnected within the body part 50, externally 
of the cylinder therein. The stub 57 has a connection to the cylinder via 
a port 64 in the wall of the cylinder and positioned to align with the 
waist of the piston 59 when the latter has moved to the left, as seen in 
FIG. 5, to engage the valve seat 56. The stub 58, on the other hand, 
connects with the cylinder via a port 65 positioned to be uncovered by the 
piston 59 when this is in the position illustrated, thereby to provide 
communication between the patient connection stub 58 and the exhalation 
port 54 in this position of the piston. 
As so far described, the patient valve is functionally equivalent to the 
patient valve described in U.S. Pat. No. 4,004,603, differing in detail 
from the latter in that the piston 59 is driven by the pilot assembly 
diaphragm 61 in response to a gas pulse at the inlet port 52, rather than 
by gas acting directly on the piston, and in that gas entering the body 
part at port 52 reaches the patient connection stub by a restricted flow 
path external of the piston and cylinder, rather than through a restricted 
passage in the piston. 
Thus, when a gas pulse arrives at port 52, the piston 59 is driven to the 
left as seen in the drawing, against the thrust of spring 55, to occlude 
the port 65 and to engage the valve seat 56 so as to isolate the patient 
connection stub 58 from the exhalation port 54. Under these conditions the 
gas pulse passes, by a route to be described, to the gas transfer stub 57 
and thence to the stub 58 to flow to the patient and cause forced 
inhalation by the latter. When gas pulse pressure at the port 52 decays, 
the spring 55 returns the piston to the illustrated position to 
re-establish communication between the stub 58 and the exhalation port 54 
so that the patient may exhale. 
In accordance with the present invention, the gas flow path between the 
port 52 and the gas transfer stub 57 comprises an entrainment mixer that 
may be brought selectively into operation in such manner as automatically 
to adapt the primary gas flow to the required tidal volume of total 
supplied breathing gas. 
Thus the patient valve further comprises a second body part 70 in the form 
of a plate that is secured to the body part 50 by bolts, one of which is 
shown at 71 (FIG. 6) and the other of which is not shown but is located to 
transfix and secure in place the jet block 72, described below, of the 
entrainment mixer by passing through a bore 73 in the jet block. The body 
part 70 has a plenum 74 that engages the gas transfer stub 57, being 
sealed thereto by an O-ring 75. 
The body part 70 defines both a by-pass passage 76 and a mixer bore 77, 
both of which communicate with the plenum 74. The by-pass passage breaks 
tangentially into a chamber housing a poppet valve assembly 79 to be 
described below. 
The mixer bore 77 houses the entrainment mixer that is constituted by the 
jet block 72, a receiver 80 and a pressure recovery section 81 comprising 
an insert 82 in the receiver body and having a substantially constant 
clear bore with steps defined by a succession of sharp-edged grooves. The 
mixer bore 77 is stepped near the plenum 74 to locate the end of the 
receiver body and the latter is sealed in the bore 77 by an O-ring 83. The 
receiver 80 is defined by an axial bore in the receiver body, 
communicating with an entrainment chamber 84 defined between wings 85 at 
the end of the receiver body and that serve to locate, by abutment, the 
jet block 72. The jet block 72 is also sealed in the mixer bore by a pair 
of O-rings 86 in grooves in the block 72. An axial jet passage 87 in the 
jet block extends to intercept a cross bore 88 in a waisted portion of the 
jet block 72 between the O-rings 86. As noted above, the jet block 72 is 
secured in the mixer bore 77 by a fixing bolt for the body part 70 
extending through the bore 73 in the jet block. This fixing of the jet 
block also secures in place the receiver body that is effectively trapped 
between the jet block and a step in the mixer bore. 
As best seen in FIG. 6, the waisted portion and cross bore 88 of jet block 
72 communicate with a primary gas passage 89 formed partly in the body 
part 70 and partly in the end cap 51, this passage 89 communicating with 
the primary gas inlet port 52. An O-ring 90 provides a seal at the 
junction between the cap 51 and the body part 70. 
The poppet valve assembly 79 comprises, as shown in FIG. 6, a valve 
constituted by a body 91 housed partly in the body part 70 and partly in 
the cap 51. The body 91 has an inlet 92 at one end and an outlet 93 at the 
other and houses a ball 94 and spring 95 controlling flow through the body 
91. The inlet 93 communicates in the cap 51 with the primary gas inlet 
port 52. 
The poppet valve assembly further comprises an actuating poppet 96 slidable 
in a guide 97 and sealed by O-rings. The poppet 96 has a spigot that 
extends into the outlet 93 of the valve body 91 to engage the ball 94 to 
unseat the latter when the poppet is moved to the right as seen in FIG. 6. 
When the ball 94 is so unseated, the by-pass passage 76 is placed in 
communication with the primary gas inlet port 52 via the chamber 78. 
The patient valve further comprises a setting assembly (FIG. 6) comprising 
a barrel 100 secured to the body part 70 so that its axis is offset from 
that of the poppet valve assembly 79, the axis of the latter being near to 
the internal wall of the barrel 100. The barrel 100 houses a valve sleeve 
101 having a ring of ports 102 and is slidable in the barrel to bring the 
ports 102 into and out of register with corresponding ports 103 in the 
barrel. The sleeve 101 is restrained from rotation by a pin 104 in the 
barrel running in a slot in the sleeve. A spring 105 acts to urge the 
sleeve 101 to the left, as see in the drawing, towards the position in 
which the ports 102 register with the ports 103. 
The end of the sleeve 101 abuts the poppet 96 and the arrangement is such 
that when the sleeve is in the position shown, in which the ports 102 are 
out of register with the ports 103, the poppet is shifted to unseat the 
ball 94 of the poppet valve assembly. Conversely, when the sleeve 101 is 
positioned to register its ports with those of the barrel 100, the ball 94 
is allowed to seat to interrupt communication between the primay gas inlet 
port 52 and the by-pass passage 76. 
The setting assembly further includes a knob 106 rotatable with respect to 
the barrel 100 and carrying a cam 107 that acts on a cross pin 108 on the 
valve sleeve 101 to shift this against the thrust of the spring 105. The 
cam 107 is shaped to provide detent action to retain the knob in one or 
other of two relatively rotated positions, corresponding with the two 
required axially shifted positions of the valve sleeve 101. 
The interior of the barrel 100 communicates, via a passage (not shown) in 
the body part 70, with the entrainment chamber 84 of the entrainment 
mixer. Thus, when the knob 106 is rotated to the position in which the 
valve sleeve ports 103 register with the barrel ports 102, the entrainment 
chamber 84 is placed in communication with the ambient atmosphere to 
enable diluent air to be drawn into the chamber 84 by entrainment action 
of the primary gas jet that issues from the nozzle 87 when a primary gas 
pulse is applied to the inlet port 52. In this setting of the knob 106, 
the poppet valve ball 94 is seated to prevent primary gas flow to the 
by-pass passage 76. Thus the primary gas is diluted en route to the plenum 
74 and thence to the patient. 
In this realisation of the invention, as compared with the theoretical 
diagrams of FIGS. 2 and 3, the nozzle 87 of the entrainment mixer 
corresponds with the restrictor 21 of FIGS. 2 and 3; the poppet valve 
assembly 79 corresponds with the valve 23; and the barrel 100 and sleeve 
101, with their respective ports 102, 103, correspond with the valve 24. 
The restrictor 22 of FIGS. 2 and 3 has no direct counterpart but its 
function of providing, in parallel with the nozzle 87, a flow path 
impedance between the primary gas inlet port 52 and the plenum 74 
sufficient to produce the pressure drop required to shift the piston 59 to 
close the exhalation port 54, against the action of spring 55, is 
accomplished by the flow path impedance attributable to the poppet valve 
assembly 79. 
For certain purposes a device that can assist a patient to breathe air of 
normal oxygen content can be preferred to a device capable only of 
delivering oxygen or oxygen-enriched air. A resuscitator/ventilator 
embodying the invention can be adapted very simply to provide for delivery 
of pulses of air for such purposes. Thus, by substituting a source of 
compressed air for the described source of compressed oxygen, the control 
unit of such a resuscitator/ventilator would output air pulses, instead of 
oxygen pulses, to the patient valve. While such air pulses might be 
delivered direct to the patient, by the patient valve, in the same way as 
pure oxygen pulses would be delivered to the patient in one of the 
operating modes previously described, it is more advantageous to use the 
entrainment mixer to "dilute" the air delivered by the control unit, to 
provide the total breathable gas volume required, thereby minimising use 
of the compressed air source. In practice this means that a bottle of 
compressed air could provide for assisted breathing for a significant 
period, the air bottle supplying only about one third of the total 
breathing air required by the patient. 
Moreover, because of the low demand on the compressed air source in such an 
operating mode, the compressed air source could be constituted by, for 
istance, a lightweight compressor capable of operation by a low power 
(e.g. 50 watt) electric motor drawing energy from a battery pack or 
umbilical lead to a vehicle battery to provide both portability and long 
term operation in the absence of bottled compressed air availability. 
A resuscitator/ventilator embodying the invention can also provide other 
useful facilities, based upon its capability of inducing the admixture of 
a gas at ambient pressure with a primary gas supplied at pressure to power 
the device. 
Thus, for instance, the gas made available for entrainment may be oxygen or 
oxygen-enriched air supplied, e.g., by an oxygen concentrator such as a 
molecular sieve concentrator. Accordingly the device may be caused to 
deliver to a patient a breathing gas consisting of oxygen-enriched air by 
being powered by compressed air as the primary gas and mixing this with 
oxygen or oxygen-enriched air, at about ambient pressure, supplied to the 
entrainment mixer of the patient valve. In a practical realisation of this 
operational possibility, and using a patient valve of the configuration 
described with reference to FIGS. 5 to 7, the ports 102 in the barrel 100 
could be enclosed in a shroud fed with oxygen or oxygen-enriched air of 
suitable oxygen content output by, say, a molecular sieve oxygen 
concentrator. 
In like manner, a primary gas constituted by compressed air or oxygen might 
be "diluted" at the patient valve with an anaesthetic gas or vapour 
supplied in suitable form to be entrained in the primary gas. 
Thus, in principle a resuscitator/ventilator device embodying the invention 
may be powered by any suitable primary gas available under the required 
pressure and, with the aid of the entrainment mixer of the patient valve, 
deliver to the patient that primary gas "diluted" with any other "diluent" 
gas or vapour available at ambient pressure or thereabouts: the diluent 
being, for example, one or more of air, oxygen, water vapour, anaesthetic 
gas or vapour.