U.S. patent application number 10/570352 was filed with the patent office on 2006-11-09 for valves.
Invention is credited to Jonathan Kevin Ben, Paul James Leslie Bennett.
Application Number | 20060249209 10/570352 |
Document ID | / |
Family ID | 29226513 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060249209 |
Kind Code |
A1 |
Ben; Jonathan Kevin ; et
al. |
November 9, 2006 |
Valves
Abstract
A gas-powered resuscitator includes an oscillatory timing valve
(14) having an outlet (23) connected via a manually-operable valve
assembly (16, 25) to a patient valve (41). The timing valve (14)
has a sealing rod (145) movable along a bore (141) between a
forward position in which it blocks flow through the valve and a
rear position in which it enables flow through the valve. The rear
end (151) of the rod (145) is mounted in a piston (146) and is
urged rearwardly to an open position by a spring (148). A flexible
diaphragm (149) is joined around its edge (158) to the housing
(140) of the valve, separating the rear end (159) of the valve from
the forward end (160) and extending over the rear end (146) of the
piston (146). The control inlet (34) of the valve (14) opens into
its rear part (159) so that gas pressure applied to the inlet acts
on one side of the diaphragm (149) to urge the piston (146) and rod
(145) forwardly to the closed position against the action of the
spring (148).
Inventors: |
Ben; Jonathan Kevin; (Bushey
Heath, GB) ; Bennett; Paul James Leslie; (Marston
Moretaine, GB) |
Correspondence
Address: |
LOUIS WOO;LAW OFFICE OF LOUIS WOO
717 NORTH FAYETTE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
29226513 |
Appl. No.: |
10/570352 |
Filed: |
September 3, 2004 |
PCT Filed: |
September 3, 2004 |
PCT NO: |
PCT/GB04/03758 |
371 Date: |
March 3, 2006 |
Current U.S.
Class: |
137/613 |
Current CPC
Class: |
A61M 16/201 20140204;
A61M 16/208 20130101; A61M 16/127 20140204; A61M 16/00 20130101;
Y10T 137/87917 20150401; A61M 16/107 20140204; A61M 16/20 20130101;
A61M 16/209 20140204; A61M 16/206 20140204 |
Class at
Publication: |
137/613 |
International
Class: |
G05D 16/06 20060101
G05D016/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2003 |
GB |
0320761.0 |
Claims
1. A gas-operated oscillatory timing valve including a gas inlet, a
gas outlet, a passage between the inlet and outlet, a movable
member displaceable between a first position in which gas can flow
along the passage and a second position in which gas is prevented
from flowing along the passage, a gas control inlet by which gas
can be supplied to the valve to cause the movable member to be
displaced between the first and second positions, characterized in
that the valve includes a flexible diaphragm exposed on one side to
gas pressure from the control inlet such as to be deflected
thereby, and that the diaphragm is arranged such that movement of
the diaphragm caused by pressure change at the control inlet is
operable to displace the movable member.
2. A valve according to claim 1, characterized in that the movable
member has a sealing portion, that one of the inlet and outlet
opens into the passage through a side opening, that the movable
member is movable axially along the passage between the first
position in which the sealing portion is on one side of the side
opening and the second position in which the sealing portion is on
the opposite side of the side opening.
3. A valve according to claim 2, characterized in that the valve
has two 0-ring seals in the passage one on either side of the side
opening, and that the movable member has an enlarged annular
portion movable between the two 0-ring seals.
4. A valve according to claim 1, characterized in that the valve
includes a spring operable to urge the movable member into the
first or second position.
5. A valve according to claim 1, characterized in that the movable
member includes a rod member and a piston member, that one end of
the rod is movable relative to the piston member, and that the
piston member includes a spring arranged to urge the rod member
into contact with the piston member.
6. A valve according to claim 1, characterized in that the
diaphragm extends across an end of the movable member.
7. A valve according to claim 6, characterized in that there is an
annular space between the housing of the valve and the outside of
the movable member at one end, and that the diaphragm extends
across the end of the movable member and is folded into a loop in
the annular space such that the loop rolls relative to the movable
member as the movable member moves relative to the housing.
8. A valve according to claim 1, characterized in that the natural
position of the movable member is such as to enable gas flow from
the inlet to the outlet, and that elevated pressure at the control
inlet is effective to move the movable member to prevent gas flow
from the inlet to the outlet.
9. A resuscitator including a timing valve according to claim
1.
10. A resuscitator according to claim 9 including a
manually-operable valve assembly, characterized in that the outlet
of the timing valve is connected to an inlet of the
manually-operable valve assembly, and that the control inlet of the
timing valve is connected to receive gas pressure from an outlet of
the manually-operable valve assembly.
Description
[0001] This invention relates to gas-operated oscillatory timing
valves of the kind including a gas inlet, a gas outlet, a passage
between the inlet and outlet, a movable member displaceable between
a first position in which gas can flow along the passage and a
second position in which gas is prevented from flowing along the
passage and a gas control inlet by which gas can be supplied to the
valve to cause the movable member to be displaced between the first
and second positions.
[0002] Resuscitators are used to supply breathing gas to a patient
who may not be breathing spontaneously. Portable resuscitators may
take the form of a resilient bag that is squeezed manually to
supply a volume of air to the patient, the bag refilling with air
when it is released so that a new volume of air can be supplied.
Alternatively, the resuscitator may be a mechanical device
including a gas-operated timing valve with O-ring sliding seals.
The resuscitator also includes various other controls and is
connected to an oxygen cylinder, which both provides the breathing
gas, or a part of this, and which may also provide the power to
drive the components of the resuscitator. Examples of such
resuscitators are described in GB 2174760, GB 2174609, EP 343818,
EP 342883, EP 343824, GB 2282542, EP 691137, GB 2284159 and GB
2270629. These resuscitators are arranged to supply gas in a cyclic
manner to the patient at a rate compatible with normal breathing.
Existing timing valves used in resuscitators suffer from various
problems and are not usually capable of operating reliably at low
temperatures where the valve is of a compact size.
[0003] It is an object of the present invention to provide an
alternative valve.
[0004] According to one aspect of the present invention there is
provided a valve of the above-specified kind, characterised in that
the valve includes a flexible diaphragm exposed on one side to gas
pressure from the control inlet such as to be deflected thereby,
and that the diaphragm is arranged such that movement of the
diaphragm caused by pressure change at the control inlet is
operable to displace the movable member.
[0005] The movable member preferably has a sealing portion, one of
the inlet and outlet opening into the passage through a side
opening, the movable member being movable axially along the passage
between the first position in which the sealing portion is on one
side of the side opening and the second position which the sealing
portion is on the opposite side of the side opening. The valve may
have two O-ring seals in the passage one on either side of the side
opening, the movable member having an enlarged annular portion
movable between the two O-ring seals. The valve preferably includes
a spring operable to urge the movable member into the first or
second position. The movable member may include a rod member and a
piston member, one end of the rod being movable relative to the
piston member and the piston member including a spring arranged to
urge the rod member into contact with the piston member. The
diaphragm preferably extends across an end of the movable member.
There may be an annular space between the housing of the valve and
the outside of the movable member at one end, the diaphragm
extending across the end of the movable member and being folded
into a loop in the annular space such that the loop rolls relative
to the movable member as the movable member moves relative to the
housing. The natural position of the movable member is preferably
such as to enable gas flow from the inlet to the outlet, elevated
pressure at the control inlet being effective to move the movable
member to prevent gas flow from the inlet to the outlet.
[0006] According to another aspect of the present invention there
is provided a resuscitator including a timing valve according to
the above one aspect of the invention. The resuscitator preferably
includes a manually-operable valve assembly, the outlet of the
timing valve being connected to an inlet of the manually-operable
valve assembly and the control inlet of the timing valve being
connected to receive gas pressure from an outlet of the
manually-operable valve assembly.
[0007] A resuscitator including a timing valve according to the
present invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
[0008] FIG. 1 is a circuit diagram of the resuscitator;
[0009] FIG. 2 is a perspective view of the outside of the
resuscitator;
[0010] FIG. 3 illustrates cam profiles on the manual control
button; and
[0011] FIG. 4 is a cross-sectional view of the oscillator/timing
valve in greater detail.
[0012] With reference first to FIGS. 1 and 2 there is shown the
various components of the resuscitator and their interconnections.
All the components are contained within a common housing 1, which
is sufficiently compact and light to be hand held and connected at
its patient outlet 2 directly to a face mask 3. The inlet 4 of the
resuscitator is connected via flexible tubing 5 to a source of
oxygen, such as a cylinder 6 or, for example, a hospital pipeline,
delivering pressure between 40 and 150 psi. This arrangement
enables single-handed operation, the same hand holding the face
mask 3 and controlling the resuscitator. Alternatively, however,
the resuscitator could be located adjacent the oxygen cylinder and
its patient outlet connected to a face mask or breathing tube via
flexible tubing.
[0013] The inlet 4 is provided by a pressure regulator 10 including
a filter 11 and an outlet 12, which connects oxygen to various of
the other components in the resuscitator. The oxygen splits into
five paths. It is supplied to an inlet 13 of an oscillator/timer
14, the inlet 15 of a manual or momentary valve 16, an inlet 17 of
a demand detector 18, an inlet 19 of a demand valve 20 and an inlet
21 of a spontaneous breathing valve 22.
[0014] Gas supplied to the oscillator/timer 14 flows to its outlet
23 when the oscillator is open or on and from there passes to an
inlet 24 of a bi-stable valve 25 the operation of which is
controlled by the manual valve 16. The manual valve 16 and the
bi-stable valve 25 can be considered together as forming a manual
valve assembly. More particularly, operation of the bi-stable valve
25, and hence supply of gas to the patient, is controlled by gas
pressure at its pilot inlet 50, which is connected to the outlet 51
of the manual valve 16.
[0015] The manual valve 16 includes a spool 60 movable up and down
a vertical bore 61 by the action of either a button 62 or a toggle
63. The inlet 15 and outlet 51 open into the bore 61 at locations
spaced along its length and the spool 60 has seals that can be
positioned to permit or prevent flow of gas from the inlet 15 to
the outlet 51 via the bore. In its normal position, as illustrated,
a spring 64 urges the button 62, and hence the spool 60, upwards to
a position where flow of gas between the inlet 15 and outlet 51 is
prevented, so the valve 16 and hence the bi-stable valve 25 is off
or closed.
[0016] When the button 62 is depressed, the spool 60 moves down and
allows pressurised gas at the inlet 15 to pass to the outlet 51 to
pilot the piston 65 of the bi-stable valve 25. Alternatively, any
movement of the toggle 63 beyond a certain angle, will also pull
down the spool 60, via a follower bobbin 66 and crank 67.
[0017] When the button 62 or toggle 63 is released, the spool 60
moves upwardly and pressurised gas piloting the piston 65 escapes
to atmosphere via a vent 68 at the bottom of the manual valve 16.
The manual valve 16 and the bi-stable valve 25 are arranged so that
it is not possible to control the ventilation frequency or flow
rate by slight operations of either the button 62 or the toggle 63.
The output pressure provided by the bi-stable valve 25 is,
therefore, either fully on or fully off.
[0018] The outlet 26 of the bi-stable valve 25 connects to a pilot
inlet 27 of a patient dump valve 28, mounted with the spontaneous
breathing valve 22. While the bi-stable valve 25 is open, that is,
during the patient inspiratory phase, pressurised gas exiting at
the outlet port 26 pilots the patient dump valve 28 at its inlet 27
to cause it to close so that gas cannot escape via the valve. The
outlet 26 of the bi-stable valve 25 also connects to two inlets 30
and 31 of a variable restrictor device 32, which is manually
adjustable to vary both the tidal volume and the frequency of
delivery of gas cycles to the patient.
[0019] The restrictor 32 includes a manually-displaceable control
member in the form of a rotary plate 70 mechanically coupled with a
lever 90 on the casing 1 so that the plate can be rotated through a
limited angle by displacing the lever. The restrictor 32 has three
tapering grooves one of which 71 connects the inlet 30 with an
outlet 33; the second groove 72 connects the inlet 31 with an
outlet 37; and the third groove 73 connects an inlet 38 with an
outlet 39. Rotating the plate 70 relative movement between the
inlets 30, 31 and 38, the outlets 33, 37 and 39 and the grooves 71
to 73 so as to alter the restriction to flow between the respective
inlets and outlets. The first groove 71 controls the timing rate of
the oscillator/timer 14. The outlet 33 connects to the control or
timing inlet 34 of the timer 14 so that rotating the plate 70 such
as to produce a higher flow of gas to the timer control inlet
increases its frequency of operation, in a manner described in
greater detail later.
[0020] Gas supplied to the other inlet 31 of the restrictor 32
flows via the second groove 72 to a second outlet 37. The second
outlet connects both to the third inlet 38 of the restrictor 32 and
to an inlet 40 of a patient valve assembly 41, via an Air Mix/No
Air Mix valve 42. The third inlet 38 connects with the third outlet
39 via the third groove 73, which in turn connects to the nozzle
inlet 80 of an air entrainment device 81 opening into the patient
valve assembly 41.
[0021] The second and third grooves 72 and 73 taper in an opposite
sense from the first groove 71 so that when the plate 70 is rotated
to cause an increased flow at the outlet 33 it causes a reduction
in gas flow from the other outlets 37 and 39. Thus, if the user
moves the lever 90 to demand an increased frequency of ventilation
cycles, this rotates the plate 70 and automatically, simultaneously
produces a reduced flow rate or tidal volume of gas. A lower
operating frequency is used with children who also require a lower
tidal volume.
[0022] Instead of the tapering slots 71 to 73 it would be possible
for the restrictor to have rows of holes of increasing sizes.
[0023] Operation of the Air Mix/No Air Mix valve 42 connected
between the outlet 33 and the patient valve assembly 41 is
controlled by a rotary knob 142 on the casing 1. The knob 142 can
be moved between one of two different positions, marked 100% and
50% respectively. The valve 42 controls whether the patient
receives pure oxygen (100%), that is, No Air Mix, or whether this
is mixed with air to give an oxygen content of about 50%, that is,
Air Mix. When the knob 142 is in the 100% position, the valve 42 is
fully open and gas from the outlet 37 flows substantially entirely
directly to the inlet 40 of the patient valve assembly 41 because
this route presents a lower resistance to flow. If, however, the
knob 142 is turned to the 50% position, it turns the valve 42 off
completely so that all gas emerging from the outlet 37 now flows
via the inlet 38, the groove 73 and the outlet 39 to the inlet 80
of the air entrainment device 81. The high velocity jet of oxygen
produced within the entrainment device 81 draws in air from an air
inlet 82, which has an oxygen concentration of about 21%. The
resultant gas mixture has a nominal oxygen content of 50% and this
enters the patient valve assembly 41.
[0024] The patient valve assembly 41 has the demand valve 20 at its
upper end and a patient valve 43 at its lower end opening into the
resuscitator outlet port 2. The patient valve 43 includes a
non-return valve 45 of conventional kind, such as described in U.S.
Pat. No. 4,774,941. The valve 43 includes a duck-bill valve,
arranged to permit flow of gas from the valve assembly 41 to the
patient but to prevent flow in the opposite direction into the
interior of the assembly. The valve 45 is supported centrally on a
flexible diaphragm 46, which bears against the upper end of the
outlet port 2. The outlet port 2 is supported coaxially within an
outer ring 47 to provide an annular space 48 closed by
non-entrainment flap valves 49. Thus, when the patient exhales, the
non-return valve 45 closes and the diaphragm 46 lifts off the
outlet port 2 to allow the exhaled gas to flow into the annular
space 48 and thereby vent to atmosphere via the flap valves 49. The
flap valves 49 allow gas to flow out of the annular space 48 but
prevent flow in the opposite direction.
[0025] Operation of the oscillator/timer 14 will now be described
in more detail with reference to FIG. 4. The oscillator/timer 14
has an outer tubular housing 140 into which the control inlet 34
and outlet 23 open axially. The outlet 23 opens into the left-hand
end of a relatively small diameter axial bore or passage 141, which
opens at its right-hand end into a larger diameter cavity 142. The
inlet 13 of the oscillator/timer 14 opens laterally into the bore
141 about midway along its length. Inside the bore 141 there are
two O-ring seals 143 and 144, one being located between the inlet
13 and the outlet 23 and the other being located between the inlet
13 and the opening of the bore into the cavity 142. Within the
cavity 142 are mounted a sealing rod 145, a cap or piston 146, two
helical springs 147 and 148 and a diaphragm 149. The sealing rod
145 is mounted axially and extends with its left-hand end 150
located in the bore 141 and its right-hand end 151 retained within
the cap 146. The left-hand end 150 of the rod 145 has an enlarged
annular bead 152 set back a short distance from its end and
positioned between the two O-rings 143 and 144. The rod 145 extends
through the right-hand O-ring 144, which makes a sliding, sealing
engagement with the outside of the rod. The right-hand end of the
rod 145 has an enlarged flange 153 spaced a short distance from its
end, which is engaged on its right-hand side by the left-hand end
of the spring 147. The spring 147 extends axially and abuts the
inside, closed, right-hand end 246 of the cap 146. The left-hand
side of the flange 153 abuts the right-hand side of a flange 154
projecting inwardly of the cap 146 about midway along its length.
The left-hand end 155 of the cap 146 is open and enlarged to form
an internal shoulder 156 and it is a loose, non-sealing, sliding
fit within the cavity 142. The shoulder 156 is contacted by the
right-hand end of the second helical spring 148, which is of larger
diameter than the first spring 147 and extends axially around the
sealing rod 145. The left-hand end of the second spring 148 abuts
an end wall 157 at the left-hand end of the cavity 142.
[0026] The oscillator/timer 14 is completed by the diaphragm 149,
which is made of a flexible, impervious, low stiffness fabric and
silicone rubber material. The diaphragm 149 is circular in shape
with a thickened circumferential lip 158, which is trapped and
sealed between two parts of the housing 1 such that the diaphragm
extends transversely of the cavity 142 and seals a rear part 159 of
the cavity from a forward part 160. The central part of the
diaphragm 149 is moulded with a mesa formation 161 projecting into
the rear part 159 of the cavity 142 and closely embracing the
external surface of the rear, closed end of the cap 146. Between
the mesa formation 161 and the lip 158 the diaphragm 149 curves
forwardly around a curved annular lip 162 on the inside of the
housing 140 and is formed into a U-shape rolling loop 163 in the
annular space 164 between the inside of the housing and the outside
of the rear part 246 of the cap 146.
[0027] In the natural position of the oscillator/timer 14, the
spring 148 pushes the cap 146, and hence the sealing rod 145,
rearwardly to a position where the annular bead 152 on the rod is
rearwardly, that is, to the right of the opening of the inlet 13
into the bore 141. The passage between the inlet 13 and the outlet
23 is, therefore, unobstructed so that gas can flow through the
oscillator/timer 14 and it is on or open. Movement of the sealing
rod 145, therefore controls flow of gas along a passage through the
oscillator/timer between the inlet 13 and the outlet 23.
[0028] When gas pressure is supplied to the control inlet 34,
pressure within the rear part 159 of the cavity 142 increases. This
causes pressure to be applied to the right-hand side of the
diaphragm 149 forcing it against the cap 146 and moving the cap
forwardly like a piston, to the left against the action of the
spring 148. Air within the left-hand part of the cavity 142 can
escape to atmosphere through a small vent hole 165 in the housing
140. As the cap 146 moves to the left, the diaphragm 149 flexes and
the loop 163 rolls between the cap and the housing 140, peeling off
the outside of the cap and folding against the inside of the
housing. Pressure in the bore 141 initially prevents the rod 145
moving so that the spring 147 is compressed as the piston moves
forwards. When the rear end 151 of the rod 145 bottoms on the rear
end 246 of the piston, the rod is moved forwardly along the bore
141 moves until its rear end The spring 147 within the cap 146
bears against the flange 153 on the sealing rod 145 to keep it in
contact with the flange 154 on the cap, thereby moving the sealing
rod forwardly, along the bore 141. As the rod 145 moves forwardly
its annular bead 152 moves to the left of the inlet 13 and the
forward end 150 of the rod starts to enter the forward O-ring 143.
Pressure across the bead 152 is now equalized and the force of the
spring 147 is sufficient to push the rod forwardly so that its bead
is in full sealing contact with the left-hand O-ring 143. It can be
seen that this blocks flow of gas from the inlet 13 to the outlet
23 and thereby turns the oscillator/timer 14 off. This terminates
the inspiratory phase of gas delivery to the patient and starts the
expiratory phase.
[0029] When the timer/oscillator 14 turns off, all gas in the
charging circuit between the outlet 23 of the timer 14 and the
inlet 30 of the restrictor 32 escapes to atmosphere through the
patient valve assembly 41, either directly via the inlet 40 or via
the entrainment device 81. This releases pressure on the patient
dump valve 28, allowing it to open, which, in turn, allows the
patient circuit pressure to quickly vent to atmosphere via ports in
the patient dump valve.
[0030] When pressure at the control inlet 34 falls, the spring 148
starts to move the sealing rod 145 back to the open position. Gas
in the rear part 159 of the cavity 142 escapes via the inlet 34
back to the restrictor 32 and, in particular, flows to the inlet 30
via the groove 71. The rate of decay of gas pressure is, therefore,
determined by the timer setting of the restrictor 32. Once the
oscillator/timer 14 is open again a new inspiratory phase starts
and the ventilation cycles continue.
[0031] It can be seen that the diaphragm 149 provides a complete
seal between the two parts 159 and 160 of the cavity 142 and does
not rely on moving, wiping seals or this like. Conventional
pneumatic pistons use an O-ring to produce a seal. The present
construction enables the timing valve 14 to operate with lower
friction and stiction forces and hence enables the valve to operate
reliably at lower switching pressures. It is important to keep the
switching pressures as low as possible in order to ensure that the
tidal volume of the first inspiratory breath delivered is not
unduly increased. When the manual button 62 is first actuated, the
timing valve 14 is open so gas can flow to the patient until
pressure at the control inlet 34 has risen to the closing switching
pressure. If this pressure were relatively high, gas would flow to
the patient for a longer time and the tidal volume delivered could
be unduly high. If lower switching pressures are used in
conventional, O-ring valves, there is a higher risk of failure
especially at very low temperatures of down to -18.degree. C. and
especially if the valve is of a small size. The arrangement
described can have low friction and stiction forces in a small
oscillator over a wide range of temperatures between -18.degree. C.
and +50.degree. C.
[0032] When using the manual control button 62 or toggle 63, the
inspiratory period of the resuscitator lasts for as long as the
button is depressed or the toggle is deflected, up to the point of
a maximum inspiratory time, as determined by the oscillator/timer
14 and the setting of the variable restrictor 32. With this method
of operation it is possible to deliver any volume less than the
full tidal volume by releasing the button or lever before complete
delivery. By cutting the delivery short, another inspiratory cycle
can be delivered proportional to the incomplete volume not
delivered and to the time elapsed (the expiratory time) before
button 62 is next pressed or the toggle 63 is deflected. It is not
possible to deliver two or more full breaths in very close
succession, thereby avoiding the possibility of creating stacked
breaths and over inflating the patient. If a full 100% tidal volume
is delivered, the circuit will lockout until the full expiratory
time has passed. After which time, another inspiratory time can be
delivered under control.
[0033] The automatic cycle mode is achieved by holding down the
spool 60 by some releasable, mechanical means. In the present
example, this is achieved by a rotatable ring 262 surrounding the
button 62. When the ring 262 is rotated to its "Automatic"
position, two cam pins 263 projecting radially inwardly of the ring
engage an inclined portion 264 of two cam profiles 265 (as shown in
FIG. 3) formed diametrically opposite one another on the outside of
the button 62, thereby pushing down the button. In this way, the
button 62 is held in the actuated position and the resuscitator
delivers repeated timed ventilation cycles one after the other at a
frequency and tidal volume determined by operation of the
oscillator/timer 14 and the setting of the restrictor 32. When the
ring 262 is rotated back to its "Manual" setting, the cam pins 263
align with vertical sections 266 of the cam profiles 265 so that
movement of the button 62 is not impeded.
[0034] During any phase of the ventilation cycle, if the patient
takes a demand breath, a demand flow will be provided by the demand
valve 20. If the demand breath exceeds a pre-set tidal volume and
frequency combination, the automatic cycling, if being used, will
be temporarily inhibited. During this operation the pressure in the
patient circuit drops a few mbar below atmospheric pressure,
drawing down a diaphragm 170 in the demand valve 20. Pressure
already supplied to the demand valve 20 at the inlet port 19 will
have equalized above and below a flexible seal 171 and will have
piloted one side of the demand detector 18 via a port 172. Movement
of the diaphragm 170 acts on a valve lever 173 and allows pressure
above the seal 171 to flow out from a port 174. This action creates
a pressure drop across seal 171, which allows gas, at a flow rate
demanded by the patient, to enter the patient circuit.
Simultaneously, the drop in pressure above the seal 171 allows a
diaphragm 175 of the demand detector 18 to move to the left and
opens a path for gas through the demand detector 18 from the inlet
17 to the outlet 176. The gas then passes through a non-return
valve 177 to pressurize the timer/oscillator circuit at its control
inlet 34. This pressurisation moves the cap 146 and the sealing rod
145 until the path of gas between the inlet 13 and 23 stops, thus,
temporarily inhibiting the automatic cycling. When the patient's
demand breath has finished, pressure above and below the seal 171
equalizes again and the diaphragm 175 of the demand detector 18
returns back, stopping the path of gas to the outlet 176. At this
stage, gas trapped in the oscillator circuit escapes via the normal
route and the automatic cycle, in time, will recommence, if in this
mode, unless another demand breath is taken. The level of the
demand breath dictates the time allowed to charge the oscillator
circuit and thus the expiration time available.
[0035] In order to limit the maximum patient circuit pressure, the
resuscitator further incorporates a pressure relief valve 180
connected to the interior of the patient valve assembly 41. This
opens to atmosphere to relieve excess flow when a pre-determined
pressure is exceeded.
[0036] The spontaneous breathing valve 22 includes a piston 181
acted on by a spring 182 to move it to a position where the valve
is open to air. The piston 181 is also acted on by gas supply
pressure from the regulator 10 such that it is normally held
closed. However, if the supply pressure should drop, the valve 22
will open to enable a spontaneously breathing patient to breathe to
atmosphere. This provides an alternative breathing path if the
supply gas pressure should fall below the input pressure
requirements of the demand valve 20.
[0037] The circuit may include adjustable restrictors at locations
A and B in FIG. 1 by which operation of the resuscitator can be
tuned. In particular, a restrictor at position A, between the inlet
172 of the demand detector 18 and the demand valve 20, would be
used to control the response of the diaphragm 175 in the demand
detector. The other restrictor at position B, between the outlet
176 of the demand detector 18 and the inlet 34 of the
timer/oscillator 14, would be used to control the rate at which the
timer/oscillator is filled when a patient demand breath has
triggered the demand detector.
* * * * *