U.S. patent number 3,669,108 [Application Number 04/867,804] was granted by the patent office on 1972-06-13 for ventilator.
This patent grant is currently assigned to Veriflo Corporation. Invention is credited to Louis A. Ollivier, Leif J. Sundblom.
United States Patent |
3,669,108 |
Sundblom , et al. |
June 13, 1972 |
VENTILATOR
Abstract
A ventilator capable of both pressure-cycled and volume-cycled
operation. A main valve connects a gas supply conduit to a
downstream conduit when the pressure in a command signal conduit
reaches a first predetermined pressure level and closes off the
downstream conduit from the gas supply conduit when the pressure in
the command signal conduit drops below a second predetermined
pressure level. In the expiratory cycle, the command signal conduit
and the downstream conduit are bled to atmospheric. The inspiratory
cycle may be initiated (1) by the patient breathing in and thereby
lowering airway pressure, or (2) after a time lapse following the
commencement of said expiratory phase, the duration of said time
lapse being determined as a set multiple of the time of the
preceding inspiratory phase. The expiratory phase may be initiated
(1) by the achievement of a predetermined airway pressure or (2)
upon the delivery of a predetermined volume of gas.
Inventors: |
Sundblom; Leif J. (Castro
Valley, CA), Ollivier; Louis A. (Menlo Park, CA) |
Assignee: |
Veriflo Corporation (Richmond,
CA)
|
Family
ID: |
25350487 |
Appl.
No.: |
04/867,804 |
Filed: |
October 20, 1969 |
Current U.S.
Class: |
128/204.26 |
Current CPC
Class: |
A61M
16/00 (20130101); A61M 16/0012 (20140204) |
Current International
Class: |
A61M
16/00 (20060101); A62b 007/02 () |
Field of
Search: |
;128/145.8,145.5-145.7,142-142.4,145 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Assistant Examiner: Mitchell; J. B.
Claims
We claim:
1. A ventilator for providing breathing gas to a patient during an
inspiratory phase and letting him exhale during an expiratory
phase, including in combination:
a gas supply conduit for supplying a breathable gas under
pressure,
a downstream conduit,
a command signal conduit,
an airway conduit suitable for connection to a patient,
means connecting said downstream conduit to said airway
conduit,
main valve means connected to said command signal conduit for
connecting said gas supply conduit to said downstream conduit
during each said inspiratory phase when the pressure in said
command signal conduit rises above a first predetermined pressure
level, and for closing off said downstream conduit from said gas
supply conduit during each said expiratory phase when the pressure
in said command signal conduit drops below a second, lower,
predetermined pressure level,
phase-actuation means connected to said command signal conduit for
terminating each said inspiratory phase and commencing a said
expiratory phase, by bleeding said command signal conduit to
atmosphere,
means connected to said command signal conduit for bleeding said
downstream conduit to atmosphere when said command signal conduit
pressure drops below said second predetermined pressure level at
the commencement of said expiratory phase,
ratio means connected to said command signal conduit, said
downstream conduit and said gas supply conduit for ending the
expiratory phase and initiating a new inspiratory phase by
increasing the pressure in said command signal conduit above said
first predetermined pressure level by supplying gas from said gas
supply conduit to said command signal conduit, after a lapse of
time following the commencement of said expiratory phase, said
ratio means having means for sensing the duration of each
inspiratory phase and for establishing a maximum duration of the
succeeding expiratory phase as a time ratio of the inspiratory
phase to the next succeeding expiratory phase, and
means for varying the setting of said time ratio.
2. The ventilator of claim 1 wherein said phase-actuation means is
connected to said airway conduit and is actuated by the pressure in
said airway conduit reaching a third predetermined pressure
level.
3. The ventilator of claim 2 having sensitivity control means
connected to said airway conduit for connecting said gas supply
conduit to said command signal conduit and thereby to raise the
pressure therein above said first predetermined pressure level when
the pressure in said airway conduit drops below a fourth
predetermined pressure level, due to the commencement by the
patient of an inspiratory phase, and to close off said command
signal conduit from said gas supply conduit when the pressure in
said airway conduit rises above said fourth predetermined pressure
level, said sensitivity control means thereby overriding said ratio
means whenever said patient initiates an inspiratory phase before
the time lapse following commencement of an expiratory phase has
not yet reached the time at which said ratio means would have acted
to initiate a said inspiratory phase.
4. The ventilator of claim 2 wherein said means for connecting said
downstream conduit to said airway conduit comprises means for
adjusting the pattern of the flow of gas from an initial peak flow
through a gradually decreasing flow to a minimal terminal flow,
including means for varying the initial peak flow independently of
said minimal terminal flow.
5. The ventilator of claim 4 wherein said means for adjusting the
pattern of flow of gas comprises
first flow means for providing a minimum constant flow from said
downstream conduit to said airway conduit,
second flow means for providing an adjustable initial peak flow
from said downstream conduit to said airway conduit, and
means responsive to the pressure in said airway conduit for
continually reducing the flow through said second flow means from
said peak flow as the pressure in said airway conduit
increases.
6. The ventilator of claim 5 wherein said first flow means includes
means for adjusting the amount of said constant flow.
7. The ventilator of claim 1 wherein the means for connecting said
downstream conduit to said airway conduit comprises
means for determining the volume of gas to pass from said
downstream conduit into said airway conduit during each inspiratory
phase,
means for determining the time over which said volume is to be
delivered, and
means for actuating said phase-actuation means at the conclusion of
that said time.
8. The ventilator of claim 7, wherein
said means for determining the volume comprises two relatively
rotatable conduit means having alignable orifices, a first said
conduit means being connected to said downstream conduit and a
second said conduit means being connected to said airway conduit,
and means for rotating said conduit means relative to each other
for varying the area of opening of the orifices that provide fluid
connection,
said means for determining the time comprises means for displacing
said conduit means axially relative to each other to vary the area
of opening of the orifices that provide fluid connection and flow
valve means connected to said downstream conduit, and sending gas
to said means actuating said phase-actuation means.
9. The ventilator of claim 8 wherein said downstream conduit is
connected to said first conduit means through a pressure regulator
having an orifice regulating the passage of gas from said
downstream conduit and pressure-control means regulating the size
of said orifice, said pressure control means being connected to
said flow valve means downstream thereof.
10. The ventilator of claim 8 wherein said means actuating said
phase-actuating means comprises pressure-operated means for
bleeding said command signal conduit when the amount of gas that
has passed through said flow valve means raises the pressure
exerted on said pressure-operated means to a predetermined
value.
11. The ventilator of claim 1 having manual valve means for passing
gas directly from said gas supply conduit to said command signal
conduit, for manual initiation of an inspiratory phase.
12. The ventilator of claim 1 wherein said main valve means
comprises
a housing divided into chambers by first and second diaphragms,
said first diaphragm being larger in effective area than said
second diaphragm, said first diaphragm having one side open to the
atmosphere,
a first chamber between said first and second diaphragms connected
to said command signal conduit,
a second chamber bounded by said second diaphragm and having an
inlet connected to said gas supply conduit and an outlet connected
to said downstream conduit,
valve means for opening and closing said inlet, said valve means
being connected to both said first and second diaphragms for
movement with them, and
spring means urging said valve means normally to close said
inlet,
said valve means opening said inlet when the pressure in said first
chamber rises to said first predetermined pressure level, said
valve means, upon commencement of its opening by the pressure on
said first diaphragm being rapidly opened by the pressure of the
gas entering said inlet from said gas supply conduit and acting on
said second diaphragm,
said valve means thereafter preventing closure until the pressure
on said first diaphragm drops below said second pressure level, at
which time said downstream conduit is being bled by its said
bleeding means, so that said valve means rapidly and positively
closes against said inlet, due to the lowering of pressure in said
second chamber able to act on said second diaphragm.
13. The ventilator of claim 1 wherein said ratio means
comprises
a reservoir,
a restricted orifice connecting said reservoir to said downstream
conduit, so that pressure in said reservoir builds up gradually
toward a value still somewhat less than that of said downstream
conduit during the time that said main valve means connects said
gas supply conduit to said downstream conduit, which is during the
entire inspiratory phase,
check valve means between said downstream conduit and said
reservoir, to prevent back flow from said reservoir to said
downstream conduit when said downstream conduit is bled to
atmosphere,
means sensitive to the pressure in said reservoir for opening and
closing off a connection between said gas supply conduit and said
command signal conduit, said connection being closed off so long as
the pressure in said reservoir remains above a predetermined level,
and
bleed means actuated by the drop in pressure in said downstream
conduit to atmospheric for bleeding said reservoir to atmosphere at
a predetermined flow rate during said expiratory phase, the time
for said bleed means to cause the pressure in said reservoir to
drop below the level where said command signal conduit is connected
to said gas supply conduit thereby depending on the length of
duration of said inspiratory phase, during which the pressure in
said reservoir is continually built up.
14. The ventilator of claim 1 having switch means for causing, in a
first position, the inspiratory phase to terminate when the
pressure in said airway conduit reaches a certain level and for
causing, in second position, the inspiratory phase to terminate
after a given volume has been delivered from said downstream
conduit to said airway conduit.
15. A ventilator for pressure-controlled operation with an
inspiratory phase and an expiratory phase, including in
combination:
a gas supply conduit for supplying a breathable gas under
pressure,
a downstream conduit,
a command signal conduit,
an airway conduit suitable for connection to a patient,
means connecting said downstream conduit to said airway
conduit,
main valve means connected to said command signal conduit for
connecting said gas supply conduit to said downstream conduit
during each said inspiratory phase when the pressure in said
command signal conduit rises above a first predetermined pressure
level and for closing off said downstream conduit from said gas
supply conduit during each said expiratory phase when the pressure
in said command signal conduit drops below a second, lower,
predetermined pressure level,
sensitivity control means connected to said airway conduit for
connecting said gas supply conduit to said command signal conduit
and thereby to raise the pressure therein above said first
predetermined pressure level when the pressure in said airway
conduit drops below a third predetermined pressure level due to the
commencement by a patient of an inspiratory phase, and to close off
said command signal conduit from said gas supply conduit when the
pressure in said airway conduit rises above said third
predetermined pressure level,
means for bleeding said command signal conduit to atmosphere
actuated by the pressure in said airway conduit reaching a fourth
predetermined pressure level, as upon commencement of an expiratory
phase,
means connected to said command signal conduit for bleeding said
downstream conduit to atmosphere when said command signal conduit
pressure drops below said second predetermined pressure level, as
at the beginning of said expiratory phase, and
ratio means connected to said command signal conduit, said
downstream conduit and said gas supply conduit for ending said
expiratory phase and initiating a new inspiratory phase by
increasing the pressure in said command signal conduit above said
first predetermined pressure level by supplying gas from said gas
supply conduit to said command signal conduit, if the patient fails
to initiate a new inspiratory phase for himself, after a time lapse
following the commencement of a said expiratory phase, said ratio
means having means for sensing the duration of each inspiratory
phase and for establishing automatically a maximum duration of the
succeeding expiratory phase as a time ratio of the inspiratory
phase to the next succeeding expiratory phase.
16. The ventilator of claim 15 having manual valve means for
passing gas directly from said gas supply conduit to said command
signal conduit, for manual initiation of an inspiratory phase.
17. The ventilator of claim 15 wherein said means for connecting
said downstream conduit to said airway conduit comprises a
two-position valve having a first position wherein said downstream
conduit is connected to said airway conduit through means for
adjusting flow, a restricted orifice, and a venturi in series, said
venturi having an air inlet from atmosphere and drawing in air
therefrom to dilute said gas to a desired dilution, said valve
having a second position wherein the connection is through means
setting the pattern of the flow of gas from an initial peak flow
and a gradually decreasing flow to a minimal terminal flow.
18. The ventilator of claim 15 wherein said means for connecting
said downstream conduit to said airway conduit comprises means for
adjusting the pattern of the flow of gas from an initial peak flow
and a gradually decreasing flow to a minimal terminal flow,
including means for varying said initial peak flow independently of
said minimal terminal flow.
19. The ventilator of claim 18 wherein said means for adjusting the
pattern of flow of gas comprises:
first flow means for providing a minimum constant flow from said
downstream conduit to said airway conduit,
second flow means for providing an adjustable initial peak flow
from said downstream conduit to said airway conduit, and
means responsive to the pressure in said airway conduit for
continually reducing the flow through said second flow means from
said peak flow as the pressure in said airway conduit
increases.
20. The ventilator of claim 19 wherein said first flow means
includes means for varying the minimum constant flow.
21. The ventilator of claim 18 wherein said means for adjusting the
pattern of the flow of gas comprises
a housing divided by a diaphragm and a partition into first,
second, and third chambers,
said first chamber being open to the atmosphere and bounded by said
diaphragm,
said second chamber being between said diaphragm and said partition
and having an inlet connected to said downstream conduit through an
adjustable needle valve to deliver said minimal terminal flow, and
an outlet connected to said airway conduit,
said third chamber having an inlet connected directly to said
downstream conduit,
said partition having an opening therethrough connecting said
second and third chambers,
valve means for opening and closing said opening and connected to
and controlled by said diaphragm,
spring means in said housing for exerting pressure on said
diaphragm, and
compression means connected to said spring means for compressing
said spring means for varying its pressure on said diaphragm,
the pressure in said airway conduit and in said second chamber
acting on said diaphragm and tending to close said valve means.
22. The ventilator of claim 15 wherein said airway conduit includes
an exhalation valve having a housing divided into three chambers by
first and second diaphragms, so that there are a first chamber
bounded by said first diaphragm and having an inlet, a second
chamber between said diaphragms and open to the atmosphere, and a
third chamber bounded by said second diaphragm and connected to
said airway conduit,
first valve means opened and closed by said diaphragms for
connecting said third chamber to the atmosphere,
spring means normally urging said valve means toward a closed
position, and
an auxiliary conduit connected to said inlet and connected through
an adjustable valve providing a variable-size restricted orifice to
said airway conduit.
23. The ventilator of claim 22 provided with a pressure relief
valve having a housing divided by a diaphragm into two chambers,
one connected to atmosphere and having an inlet connected to said
auxiliary conduit, and the other connected to said downstream
conduit, and valve means connected to said diaphragm for opening
and closing said inlet, with spring means normally urging said
valve means to open said inlet.
24. The ventilator of claim 15 wherein said main valve means
comprises
a housing divided into chambers by first and second diaphragms,
said first diaphragm being larger in effective area than said
second diaphragm, said first diaphragm having one side open to the
atmosphere,
a first chamber between said first and second diaphragms connected
to said command signal conduit,
a second chamber bounded by said second diaphragm and having an
inlet connected to said gas supply conduit and an outlet connected
to said downstream conduit,
valve means for opening and closing said inlet, said valve means
being connected to both said first and second diaphragms for
movement with them, and
spring means urging said valve means normally to close said
inlet,
said valve means opening said inlet when the pressure in said first
chamber rises to said first predetermined pressure level,
said valve means upon commencement of its opening by the pressure
on the larger said first diaphragm being rapidly opened by the
pressure of the gas entering said inlet from said gas supply
conduit and acting on the smaller said second diaphragm,
said valve means thereafter preventing closure until the pressure
on said first diaphragm drops below said second pressure level, at
which time said downstream conduit is being bled to atmosphere by
its said bleeding means, so that said valve means rapidly and
positively closes against said inlet, due to the lowering of
pressure in said second chamber able to act on said second
diaphragm.
25. The ventilator of claim 15 wherein said sensitivity control
means comprises
a housing divided into three chambers by a diaphragm and a
partition,
a first chamber bounded by said diaphragm and connected to said
airway conduit,
a second chamber between said diaphragm and said partition and open
to the atmosphere, and
a third chamber bounded by said partition and having an inlet
connected to said gas supply conduit and an outlet connected to
said command signal conduit and valve means extending through said
partition and sealed thereto and actuated by said diaphragm for
opening and closing the connection between said inlet and said
outlet and
spring means urging said valve means to close said connection
between said inlet and said outlet so that when said inlet is
opened by creation of a vacuum in said first chamber, gas from said
gas supply conduit flows into said command signal conduit.
26. The ventilator of claim 25 having means for adjusting said
spring pressure.
27. The ventilator of claim 15 wherein said ratio means
comprises
a reservoir connected by a restricted orifice to said downstream
conduit, so that pressure in said reservoir builds up gradually and
continuously during the time when the pressure in said downstream
conduit is above atmospheric, that is, during the entire
inspiratory phase,
check valve means between said reservoir and said downstream
conduit preventing flow back from said reservoir to said downstream
conduit,
valve means sensitive to the pressure in said reservoir for
connecting said command signal conduit and said gas supply conduit
and for disconnecting them when the pressure in said reservoir is
above a predetermined level, and
bleed means actuated by the drop in pressure to atmospheric in said
downstream conduit, for bleeding said reservoir to atmospheric at a
constant flow rate during said expiratory phase.
28. The ventilator of claim 15 wherein said ratio means
comprises
first housing means divided into three chambers by first and second
diaphragms, said first diaphragm being smaller in effective area
than said second diaphragm, said first housing means having a first
chamber bounded by said first diaphragm and having a first inlet
connected to said gas supply conduit and a first outlet connected
to said command signal conduit, a second chamber between said first
and second diaphragms and connected to the atmosphere, a third
chamber bounded by said second diaphragm and having a second inlet
and a second outlet, first valve means connected to both said first
and second diaphragms for normally closing said first outlet,
except when the pressure in said third chamber drops below a
predetermined level,
check valve means connected to said downstream conduit and
connected through a restricted orifice to said second inlet, to
supply gas from said downstream conduit to said third chamber to
gradually build up pressure therein during each inspiratory phase,
while preventing flow back from said third chamber to said
downstream conduit,
a pressure relief valve comprising second housing means divided by
a third diaphragm into fourth and fifth chambers, said fourth
chamber being connected to said downstream conduit and said fifth
chamber having a third inlet connected to the second outlet and
connected to atmosphere through an adjustable needle valve, the
flow rate of which determines a limiting time ratio between the
expiratory phase and the inspiratory phase, third valve means
connected to said third diaphragm for opening and closing said
third inlet, and spring means urging said third valve means away
from closing said third inlet, said third inlet being held closed
by the pressure in said downstream conduit until said pressure
drops to atmospheric at the end of said inspiratory phase, said
third inlet being open during the expiratory phase.
29. A ventilator for pressure-controlled operation with an
inspiratory phase and an expiratory phase, including in
combination:
a gas supply conduit for supplying a breathable gas under
pressure,
a downstream conduit,
a command signal conduit,
an airway conduit suitable for connection to a patient,
main valve means connected to said command signal conduit for
connecting said gas supply conduit to said downstream conduit
during each said inspiratory phase when the pressure in said
command signal conduit reaches a first predetermined pressure level
and for closing off said downstream conduit from said gas supply
conduit during each said expiratory phase when the pressure in said
command signal conduit drops below a second, lower pressure
level,
sensitivity control means connected to said airway conduit for
connecting said gas supply conduit to said command signal conduit
and thereby to raise the pressure in said command signal conduit to
said first predetermined pressure level when the pressure in said
airway conduit drops due to the commencement by a patient of an
inspiratory phase, to a third predetermined pressure level, and to
close off said command signal conduit from said gas supply conduit
when the pressure in said airway conduit rises above said third
predetermined pressure level,
means, actuated by the pressure in said airway conduit rising to a
fourth predetermined pressure level, for bleeding said command
signal conduit to atmosphere, as upon commencement of said
expiratory phase,
means connected to said command signal conduit for bleeding said
downstream conduit to atmosphere when said command signal conduit
pressure drops below said second predetermined pressure level as at
the beginning of said expiratory phase, and
flow control means connecting said downstream conduit to said
airway conduit according to a predetermined flow pattern, with a
peak flow rate at the commencement of each said inspiratory phase
and a flow rate gradually diminishing to a lower terminal flow rate
according to said pattern.
30. The ventilator of claim 29 having means for varying said
predetermined flow pattern by changing the peak flow rate without
changing the terminal rate.
31. The ventilator of claim 29 wherein said flow control means
comprises:
first flow means for providing a minimum constant flow from said
downstream conduit to said airway conduit,
second flow means for providing an adjustable initial peak flow
from said downstream conduit to said airway conduit, and
means responsive to the pressure in said airway conduit for
continually reducing the flow through said second flow means from
said peak flow as the pressure in said airway conduit
increases.
32. The ventilator of claim 31 wherein said first flow means
includes means for varying the minimum constant flow.
33. The ventilator of claim 29 wherein said flow control means
comprises:
a housing divided by a diaphragm and a partition into first,
second, and third chambers,
said first chamber being open to the atmosphere and bounded by said
diaphragm,
said second chamber being between said diaphragm and said partition
and having an inlet connected to said downstream conduit through an
adjustable needle valve to deliver said minimal terminal flow, and
an outlet connected to said airway conduit,
said third chamber having an inlet connected directly to said
downstream conduit,
said partition having an opening therethrough connecting said
second and third chambers,
valve means for opening and closing said opening and connected to
and controlled by said diaphragm,
spring means in said housing for exerting pressure on said
diaphragm, and
compression means connected to said spring means for compressing
said spring means for varying its pressure on said diaphragm,
the pressure in said airway conduit and in said second chamber
acting on said diaphragm and tending to close said valve means.
34. A ventilator for providing breathing gas to a patient during an
inspiratory phase and letting him exhale during an expiratory
phase, including in combination:
a gas supply conduit for supplying a breathable gas under
pressure,
a downstream conduit,
a command signal conduit,
an airway conduit suitable for connection to a patient,
means connecting said downstream conduit to said airway
conduit,
main valve means connected to said command signal conduit for
connecting said gas supply conduit to said downstream conduit
during each said inspiratory phase when the pressure in said
command signal conduit rises above a first predetermined pressure
level, and for closing off said downstream conduit from said gas
supply conduit during each said expiratory phase when the pressure
in said command signal conduit drops below a second, lower,
predetermined pressure level,
phase-actuation means connected to said command signal conduit for
terminating each said inspiratory phase and commencing a said
expiratory phase, by bleeding said command signal conduit to
atmosphere,
means connected to said command signal conduit for bleeding said
downstream conduit to atmosphere when said command signal conduit
pressure drops below said second predetermined pressure level at
the commencement of said expiratory phase,
ratio means connected to said command signal conduit, said
downstream conduit and said gas supply conduit for ending the
expiratory phase and initiating a new inspiratory phase by
increasing the pressure in said command signal conduit above said
first predetermined pressure level by supplying gas from said gas
supply conduit to said command signal conduit, after a lapse of
time following the commencement of said expiratory phase, said
ratio means having means for sensing the duration of each
inspiratory phase and for establishing a maximum duration of the
succeeding expiratory phase as a time ratio of the inspiratory
phase to the next succeeding expiratory phase,
pneumatic timing means connected to said gas supply conduit,
and
sigh means connected to said phase actuation means and actuated by
said pneumatic timing means at intervals longer than the
inspiratory-expiratory cycle of the ventilator as controlled
without said pneumatic timing means by said phase actuation means
and said ratio means, for causing a longer inspiratory phase than
usual and a greater volume than usual.
35. The ventilator of claim 34 wherein said pneumatic timing means
comprises a needle valve connected to said gas supply conduit, a
pressure-actuated valve downstream of said needle valve and having
a fixed-capacity chamber wherein the pressure builds up from
atmospheric to the pressure for actuating said pressure-actuated
valve, and means for bleeding said chamber to atmosphere after
actuation of said pressure actuated valve.
36. The ventilator of claim 34 wherein said phase-actuation means
is connected to said airway conduit and is actuated by the pressure
in said airway conduit reaching a third predetermined pressure
level and means actuated by said pneumatic timing means for raising
said third predetermined pressure level to a fourth higher
predetermined pressure level for a single inspiratory phase.
37. The ventilator of claim 34 wherein
the means for connecting said downstream conduit to said airway
conduit comprises
means for determining the volume of gas to pass from said
downstream conduit into said airway conduit during each inspiratory
phase,
means for determining the time over which said volume is to be
delivered, and
means for actuating said phase-actuation means at the conclusion of
that said time, and
means actuated by said pneumatic timing means for continuing to
supply said gas to said airway conduit from said downstream conduit
for an additional time, thereby increasing the volume of a single
inspiratory phase by a predetermined percent.
38. The ventilator of claim 34 wherein
the means for connecting said downstream conduit to said airway
conduit comprises
means for determining the volume of gas to pass from said
downstream conduit into said airway conduit during each inspiratory
phase,
means for determining the time over which said volume is to be
delivered, and
means for actuating said phase-actuation means at the conclusion of
that said time, and
means actuated by said pneumatic timing means for increasing the
volume of a single inspiratory phase by a predetermined and
adjustable percent of the volume set by said means for determining
the volume.
39. The ventilator of claim 34 wherein
the means for connecting said downstream conduit to said airway
conduit comprises
means for determining the volume of gas to pass from said
downstream conduit into said airway conduit during each inspiratory
phase,
means for determining the time over which said volume is to be
delivered, and
means for actuating said phase-actuation means at the conclusion of
that said time, and wherein
said pneumatic timing means generates a trigger signal when the
sigh-frequency time is reached and said ventilator is in a said
expiratory phase,
means actuated by said trigger signal for resetting the sigh
frequency timer to zero,
time lengthening means actuated by said trigger signal for
lengthening the time set by said means for determining the time so
that the connection between said downstream conduit and said airway
conduit is maintained during the additional time, for maintaining
the trigger signal as the ventilator changes from its expiratory
phase to its inspiratory phase,
means for returning said trigger signal to a zero value as the
ventilator changes from that said inspiratory phase to its next
expiratory phase,
means actuated when said trigger signal returns to zero for
starting the sigh frequency timer on a new cycle and closing off
said time lengthening means from said means determining the
time.
40. The ventilator of claim 34 wherein said sigh means
includes:
sigh volume control means for determining the additional volume
delivered during said longer inspiratory phase,
a main control valve connected to said pneumatic timing means and
initiated thereby, and connected to said gas supply conduit and
delivering a limited supply of gas directly therefrom when
initiated,
a communication control valve actuated when said main control valve
delivers said gas from said gas supply conduit upon said
initiation, said communication control valve being connected to
phase-actuation means and acting when actuated to delay the
termination of the next said inspiratory phase, and
reset valve means connected to said main control valve and to said
communication control valve for resetting them upon completion of
said next inspiratory phase to the position and pressure they had
prior to said initiation, and connected to said pneumatic timing
means for initiating a new timing interval thereby upon completion
of said next inspiratory phase.
41. The ventilator of claim 40 wherein said main control valve is
connected to said downstream conduit and is biased thereby against
initiation so long as the pressure in said downstream conduit is
above atmospheric, thereby preventing the master control valve from
being initiated during an inspiratory phase.
42. A ventilator for pressure-controlled operation with an
inspiratory phase and an expiratory phase, including in
combination:
a gas supply conduit for supplying a breathable gas under
pressure,
a downstream conduit,
a command signal conduit,
an airway conduit suitable for connection to a patient,
means connecting said downstream conduit to said airway
conduit,
main valve means connected to said command signal conduit for
connecting said gas supply conduit to said downstream conduit
during each said inspiratory phase when the pressure in said
command signal conduit rises above a first predetermined pressure
level and for closing off said downstream conduit from said gas
supply conduit during each said expiratory phase when the pressure
in said command signal conduit drops below a second, lower
predetermined pressure level,
sensitivity control means connected to said airway conduit for
connecting said gas supply conduit to said command signal conduit
and thereby to raise the pressure therein above said first
predetermined pressure level when the pressure in said airway
conduit drops below a third predetermined pressure level due to the
commencement by a patient of an inspiratory phase, and to close off
said command signal conduit from said gas supply conduit when the
pressure in said airway conduit rises above said third
predetermined pressure level,
means for bleeding said command signal conduit to atmosphere
actuated by the pressure in said airway conduit reaching a fourth
predetermined pressure level, as upon commencement of an expiratory
phase,
means connected to said command signal conduit for bleeding said
downstream conduit to atmosphere when said command signal conduit
pressure drops below said second predetermined pressure level, as
at the beginning of said expiratory phase,
ratio means connected to said command signal conduit, said
downstream conduit and said gas supply conduit for ending said
expiratory phase and initiating a new inspiratory phase by
increasing the pressure in said command signal conduit above said
first predetermined pressure level by supplying gas from said gas
supply conduit to said command signal conduit, if the patient fails
to initiate a new inspiratory phase for himself, after a time lapse
following the commencement of a said expiratory phase, said ratio
means having means for sensing the duration of each inspiratory
phase and for establishing automatically a maximum duration of the
succeeding expiratory phase as a time ratio of the inspiratory
phase to the next succeeding expiratory phase,
pneumatic timing means connected to said gas supply conduit,
and
sigh means connected to said means for bleeding said command signal
conduit and actuated by said pneumatic timing means at intervals
longer than the inspiratory-expiratory cycle of the ventilator as
controlled without said pneumatic timing means by said phase
actuation means and said ratio means, for raising the actuating
pressure level of said means for bleeding said command signal
conduit above said fourth predetermined pressure level, to a higher
fifth pressure level.
43. The ventilator of claim 42 wherein said pneumatic timing means
comprises a needle valve connected to said gas supply conduit, a
pressure-actuated main sigh control valve downstream of said needle
valve and having a fixed-capacity chamber wherein the pressure
builds up from atmospheric to the pressure for actuating said main
sigh control valve, and means for bleeding said chamber to
atmosphere after actuation of said main sigh control valve.
44. The ventilator of claim 43 wherein said sigh means comprises a
communication control valve connected to said main sigh control
valve and actuated thereby when downstream pressure therefrom is
above atmospheric for connecting said airway conduit to said means
for bleeding said command signal conduit to supply the pressure to
raise said pressure from said fourth level to said fifth level, and
means, actuated by said means for bleeding said downstream conduit,
for de-actuating said communication control valve, disconnecting it
from said airway conduit, and for bleeding to atmospheric the
connection therefrom to said means for bleeding said command signal
conduit.
45. The ventilator of claim 43 wherein said main sigh control valve
is connected to and biased by said downstream conduit to prevent
its actuation when said downstream conduit is above atmospheric
pressure.
Description
This invention relates to an improved ventilator capable of both
pressure-cycled and volume-cycled operation.
Can be either Pressure-Cycled or Volume-Cycled
Ventilators heretofore on the market have either been
pressure-cycled or volume-cycled and have not been capable of
shifting from one form of operation to the other, as is the device
of the present invention, where simple movement of a selector
handle accomplishes the shift. Hence, prior-art ventilators were
strictly limited to one of these two types of operation and extra
machines were required. The present invention enables a single
machine to become very versatile and to be adapted to the needs of
the patient and to the desires of the doctor. Moreover, as will be
seen, the ventilator of this invention also gives greater
versatility within each type of operation than has been available
from prior-art machines.
Flow Pattern Adjustable
Another difficulty with the ventilators heretofore on the market
has been that their flow pattern of delivery has been capable of
little, if any, adjustment; each has had a basically fixed flow
pattern. It is desirable to have a large initial flow at the
beginning of the inspiratory phase and to have the flow gradually
diminish toward a predetermined minimum flow at the end of the
inspiratory phase.
The ventilator of the present invention enables a wide range of
adjustment of the flow pattern, and any such flow pattern is
reproducible independently of the time setting of the cycle. The
maximum initial flow can be adjusted to a desired amount, the
smaller terminal flow at the end can be adjusted to what is
desired, and the change from one to the other adjusted too.
Automatic Ratio of Inspiratory Time to Expiratory Time
The ventilator of this invention also provides for setting a ratio
between the inspiratory time and either the maximum or the actual
expiratory time in the breathing cycle. This adjustment, once set,
is maintained until purposely reset, but a wide range of such
ratios is readily obtainable. Thus, this ratio setting enables full
control of the patient's breathing cycle on the basis that the
longer it takes to inhale, the longer it takes to exhale, and each
inspiration controls the succeeding expiration, and a new
inspiratory phase is initiated at the right time. This same ratio
setting can be used as a backup expedient when a patient normally
initiates each inspiratory phase himself but if he fails to do so
within a time bearing the set ratio to his previous inspiration,
the machine will itself begin the new inspiratory phase.
Independent Setting of Inspiratory Time and Tidal Volume
In its volume-cycled mode the ventilator of this invention is also
capable of a separate noninteracting adjustment of the total volume
and the inspiratory time, so that either the time or the volume can
be changed without changing the other, whereas heretofore
adjustment of one would require adjustment of the other, each time
a change is made. In this invention there is a novel interaction of
parts that automatically cares for these adjustments.
Pressure Sensitivity and Safety
When the device is used in its pressure-cycled mode, the airway
pressure is employed to sense a patient's initiation of a new
inspiratory phase and then to feed the breathing gas to him at a
doctor-set rate and manner. In addition, the airway pressure is
used to terminate the inspiratory phase and commence an expiratory
phase. Furthermore, in both the pressure-cycled and volume-cycled
modes of operation, patient safety is assured by a
pressure-activated safety release that terminates the inspiratory
phase before a dangerous airway pressure is reached.
Manual Override
In both volume-cycled and pressure-cycled operation the doctor can
readily override and initiate a new inspiratory phase manually
simply by pressing a button provided for that purpose.
Supply Pressure and Gas Mixture Versatility
A significant object of the invention is to provide a ventilator
that can be used with relatively low pressures, such as 25 psig
supply pressure, instead of requiring a supply at 50 psig, or
higher.
Many optional features are also available in this ventilator, such
as a change from pure oxygen to air-diluted oxygen, the use of
so-called "negative pressure" where that is desirable and the
elimination of it where it is not, and the adjustment of many other
factors.
The ventilator of this invention is supplied with a compressed gas
such as oxygen, air or a premix of air and oxygen at a regulated
pressure, typically of approximately 50 psi, though that may be
varied. When using oxygen as the supply gas the ventilator of this
invention will deliver pure oxygen or an oxygen-air mixture in the
"pressure-cycled" mode. In the volume-cycled mode, the ventilator
will deliver pure oxygen only. When using air as the supply gas,
the ventilator will deliver air in both the pressure-cycled and
volume-cycled modes. When using mixture obtainable from an oxygen
ratio controller, the ventilator will deliver the same oxygen-air
mixture as that supplied in either pressure-cycled or volume-cycled
modes.
Sigh
In normal breathing, from time to time a person will take an
exceptionally deep breath and then exhale that deep breath. This
sigh is quite useful in maintaining healthy conditions. Most
breathing machines make no provision for other than consistent
uniformity. The device of the present invention makes it possible
for the doctor to cause a sigh at suitable intervals,
super-imposing the sigh on the regular cycle without upsetting
subsequent regular cycling until the next sigh.
Other objects and advantages of the invention will appear from the
following description of a preferred form of the invention.
In the drawings:
FIGS. 1A, 1B, and 1C comprise a pneumatic circuit diagram of a
ventilator embodying the principles of the present invention. The
three views fit together and comprise a single diagram.
FIG. 2 is a view in perspective of the exterior of a ventilator
unit embodying the principles of the invention.
FIG. 3 is a view on an enlarged scale and in front elevation of a
preferred embodiment of the main control valve from the circuit of
FIG. 1B, being a component of the unit of FIG. 2.
FIG. 4 is a view in rear elevation of the valve of FIG. 3.
FIG. 5 is a view section taken along the line 5--5 in FIGS. 3 and
4.
FIG. 6 is a view in elevation and in section, on an enlarged scale,
of a preferred embodiment of the initiator or sensitivity control
valve used in the circuit of FIG. 1B.
FIG. 7 is a view in elevation and in section, on an enlarged scale,
of a preferred embodiment of the pressure controller of the circuit
of FIG. 1B.
FIG. 8 is a view in elevation and in section, on an enlarged scale,
of a preferred embodiment of the volume profile regulator of FIG.
1A.
FIG. 9 is a top view, partly broken away and shown in section, on
an enlarged scale, of a preferred embodiment of the volume control
unit of FIG. 1A.
FIG. 10 is a view in section taken along the line 10--10 in FIG.
9.
FIG. 11 is a view in section taken along the line 11--11 in FIG.
10.
FIGS. 12A, 12B, 12C, and 12D are diagrammatic views showing the
operation of the compensator port with respect to the volume port
at extreme settings of the volume and inspiratory time control
shafts, all for the unit of FIGS. 9 to 11.
FIG. 13 is a view in section taken along the line 13--13 in FIGS. 9
and 10.
THE SELECTOR VALVE ASSEMBLY 12 (FIG. 1B)
In FIG. 1B a supply 10 of oxygen at some desired pressure is
provided. The supply 10 may include a regulator or other device to
provide the desired pressure, and the oxygen supplied may be pure
oxygen or air or a mixture of oxygen and air. For that matter,
other gases may be used if desired. The supply 10 is connected by a
conduit 11 to a manually operated valve assembly 12 at an inlet 13.
The valve assembly is operated by a valve control lever or selector
12a shown in FIG. 2.
The valve assembly 12 is preferably provided with five valves, each
of which has three positions, an "off" position, a
"pressure-cycled" position, and a "volume-cycled" position. Thus,
the assembly 12 includes a valve 14 connected to the inlet 13,
which either shuts off the supply of oxygen from the conduit 11 or,
in the volume-cycled mode, sends it to a "volume-cycled" outlet 15
or, in a pressure-cycled mode, sends it to a "pressure-cycled"
outlet 16. The outlets 15 and 16 are connected to a main internal
supply conduit 20. Since the outlets 15 and 16 are connected
together, the valve 14 acts substantially as an "off-on" valve,
either passing the full supply of oxygen or cutting it off
completely, but the structure shown is preferred in order to
provide a simple ganged assembly 12, --that is, the valve 14 is
ganged with valves 17, 18, 19, and 29 for movement of all of them
together between these three positions; either all of valves 14,
17, 18, 19, and 29 are in "off" position, or all of them are in the
"pressure-cycled" position, or all of them are in the
"volume-cycled" position.
The second valve 17 of the valve assembly 12 has an inlet 21 which
is always connected to the main conduit 20 and which is connected
alternately to a "volume-cycled" outlet 22 or a "pressure-cycled"
outlet 23 or is blocked in an "off" position. Like the first valve
14, the second valve 17 is operative in both the pressure-cycled
and volume-cycled modes.
The third valve 18 of the valve assembly 12 has an inlet 24 which
is either connected to a "pressure-cycled" outlet 25 or is blocked
off in both its "off" position and its "volume-cycled" position. In
other words, the valve 18 is operative only in the pressure-cycled
mode.
The fourth valve 19 of the valve assembly 12 has an inlet 26, a
"volume-cycled" outlet 27 and a "pressure-cycled" outlet 28, and
the fourth valve is operative in both the pressure-cycled and
volume-cycled modes.
The fifth valve 29 of the valve assembly 12 has an inlet 85
connected in the volume-cycled mode alone to an outlet 86 that
leads directly to the atmosphere. There are no inlets in the "off"
position or the pressure-cycled mode; so the fifth valve 29 is
operative only in the volume-cycled mode.
It is stressed that all of the valves in the assembly 12 are linked
together for simultaneous operation, so that all of them are either
off, are in the "volume-cycled" position, or in the
"pressure-cycled" position. It has been noted that the valves 14,
17, and 19 are operative in both modes, the valve 19 operative only
in the pressure-cycled mode and the valve 29 operative only in the
volume-cycled.
THE MAIN VALVE 30 (FIGS. 1B and 3-5)
The internal supply conduit 20 leads to a main valve 30 at a
normally closed inlet 31; when a closure member 32 is retracted
from an opening 33, oxygen from the conduit 20 can pass via an
outlet 34 to a downstream conduit 35.
The closure member 32 is secured to two diaphragms 36 and 37, which
cooperate with the housing assembly 38 to divide the interior of
the main valve 30 into three chambers 39, 40, and 41. The housing
38 (FIG. 5) is so constructed that the diaphragm 36 has a
significantly smaller area exposed to the gas than does the
diaphragm 37. The chamber 39 lies between the smaller area
diaphragm 36 and the inlet 31 and outlet 34; this chamber 39 is
used for the passage of the supply gas. In between the two
diaphragms 36 and 37, the chamber 40 is provided with a port 42
that communicates with a command signal conduit 43. The third
chamber 41 is kept at atmospheric pressure by an atmospheric bleed
port 44 and contains a spring 45 which urges the diaphragms 36 and
37 and the closure member 32 toward the closed position. As shown
in FIGS. 3 to 5, bolts 46 may be used both to hold the housing
assembly 38 together and to mount the valve 30 to a support member
47, shown in phantom lines.
The spring 45 acts to keep the closure member 32 against the inlet
port 31 until the pressure in the chamber 40 and the command signal
conduit 43 rises above a predetermined value (e.g., 18 psig), well
above atmospheric pressure. Then, the fact that the pressure in the
chamber 40 acts on a larger area on the diaphragm 37 than on the
diaphragm 36, causes the diaphragm 37 to move toward the chamber 41
and thereby move the closure member 32 away from the inlet 31. As
soon as the high-pressure gas from the conduit 20 begins entering
the inlet 31 and flowing into the chamber 39, it acts on the
diaphragm 36, and thus both the diaphragm 36 and 37 are then
causing the closure member 32 to open. The result is that once the
critical pressure in the chamber 40 and command signal conduit 43
is reached, the main valve 30 opens the inlet very quickly in what
is, in effect, a snap action. The inlet 31 then sends gas from the
main conduit 20 into the downstream conduit 35.
In order for the closure member 32 to close off the inlet 31, the
pressure in the chamber 40 and in the command signal conduit 43
must drop to a predetermined level well below the pressure that
opens the inlet 31, e.g., 9 psig. As will be seen the conduit 43 is
bled to atmosphere, and when the pressure level does fall below
this second, lower, critical level, the closure member 32 does
close the inlet 31. Subsequently, as will be seen, the pressure in
the downstream conduit is bled toward atmospheric.
THE DOWNSTREAM CONDUIT 35 (FIGS. 1A and 1B)
The downstream conduit 35 communicates directly with the valve 19
at its inlet 26. The effects of this connection, which accomplish
one of the main functions of the downstream conduit 35, are
explained later. The downstream conduit 35 also communicates
directly, as by branch conduits, with a check valve 48 and a first
pressure relief valve 50, both to be described later. Further, as
shown in FIG. 1A, the conduit 35 communicates with a second
pressure relief valve 51, the function of which is also explained
later. Still further, the conduit 35 communicates by an inlet 53
with a chamber 54 in a "negative-pressure" control valve 55; the
internal supply conduit 20 also communicates with the "negative
pressure" control valve 55 through an inlet port 56 leading into a
chamber 57 on the opposite side of a diaphragm 58 from the chamber
54. This valve, too, is dealt with further below. Finally, the
downstream conduit 35 also communicates with a sigh device 300
(FIG. 1C).
THE AUTOMATIC RATIO EXPIRATORY TIMER (FIG. 1B)
The command signal conduit 43 and the internal supply conduit 20
are connected to an automatic ratio expiratory timer 60. The
purpose of this device is to conclude the expiratory phase of
operation quite positively and to initiate a new inspiratory phase,
in the event the patient does not do so himself by actuating the
initiator 90 discussed in the next section. In other words, the
expiratory phase is either terminated in every cycle by this timer
60 or at least it is always there to set a maximum time limit for
the expiratory phase. This time, moreover, is not a time constant,
since it takes longer to exhale after a long-drawn breath than to
exhale a shorter-drawn breath. Hence, the timer determines the
maximum length of each expiratory phase as a set ratio to the
length of the immediately preceding inspiratory phase. The set
ratio is, itself, set by the physician and can be changed at his
order.
The automatic ratio expiratory timer 60 (FIG. 1B) comprises a
principal valve 61, the check valve 48, the relief valve 50 and a
needle valve 62, regulated by the control 62a in FIG. 2.
The valve 61 has three chambers 63, 64, and 65 provided by two
diaphragms 66 and 67, the diaphragm 67 having a much larger exposed
area than the diaphragm 66 (compare the valve 30). The first
chamber 63 is connected by an inlet 68 to the main inlet conduit
20. The two diaphragms 66 and 67 are both rigidly connected to a
closure member 70, which a spring 69 normally urges to close a port
71. When the port 71 is opened, it connects the chamber 63 to the
command signal conduit 43. The smaller area diaphragm 66 which
closes the chamber 63 cooperates with the larger area diaphragm 67
to provide the central chamber 64, which is bled to atmosphere at
all times through a port 72. On the opposite side of the large
diaphragm 67, is the chamber 65 which has two ports 73 and 74. The
port 73 is connected to the check valve 48 through a restricted
orifice 75.
The port 74 is connected to an inlet 76 of the pressure relief
valve 50, on the opposite side of a diaphragm 77 from a port 78
that is connected to the downstream conduit 35. The diaphragm 77
and a spring 79 normally keep the inlet 76 open, except when the
pressure at the port 78 is large enough to overcome the pressure of
the spring 79 and the pressure on the other side of the diaphragm
77 in the chamber 80. The diaphragm 77 divides the valve 50 into
chambers 80 and 81, and a bleed line 82 leads by a port 83 in the
chamber 80 to an adjustable needle valve 62, which is used to set
the ratio in the timing operation, as will be described
subsequently.
During inspiration, gas from the downstream conduit 35 flows
through the check valve 48, and the restricted orifice 75 into the
chamber 65 and builds up pressure there, for the inlet 76 is then
shut off by the full pressure of the downstream conduit 35 acting
through the inlet 78 on the diaphragm 77. The orifice 75 is small,
but as pressure builds up and becomes great enough, it closes the
closure member 70 against the port 71 and disconnects the command
signal conduit 43 from the main gas supply conduit 20.
When the inspiratory phase ends and expiration begins, the
downstream conduit 35 and the command signal conduit 43 are back
bled to the atmosphere (how will be explained below), and then the
inlet 76 is opened and the chamber 65 is bled slowly to atmosphere
at a controlled rate through the needle valve 62. Backflow from the
chamber 65 to the downstream conduit is prevented by the check
valve 48. Depending on the amount of gas in the chamber 65 -- which
depends on the duration of the inspiratory phase -- the time for
the chamber 65 to drop to a predetermined pressure will vary. At
that pressure, the closure member 70 is opened, and gas flows via
the chamber 63 from the main gas supply conduit into the command
signal conduit 43. The command signal conduit 43 then raises the
pressure in the chamber 40 of the main valve 30 and opens the inlet
31 to start a new inspiratory phase.
While different values can be used, the springs may be set to close
off the port 71 when the pressure in the chamber 65 is about 7
psig. The orifice 75 may be set so that in the maximum time for
inspiration, the pressure in the chamber 65 will reach about 35
psig.
THE INITIATOR OR SENSITIVITY CONTROL 90 (FIGS. 1B and 6)
The command signal conduit 43 is also connected by a branch to an
initiator or sensitivity control device 90. This initiator 90 is
used in the pressure-cycled mode to initiate the inspiratory phase,
by overriding the automatic ratio expiratory timer 60, which thus
performs a backup function. The patient's own termination of his
expiratory phase is used to trigger the passing of gas from the
main gas supply conduit 20 into the command signal conduit 43,
thereby actuating the main valve 30. The initiator 90 may also be
used in the volume-cycled mode, if desired, though normally it is
not so used. In fact, if desired the volume port 22 of the valve 17
may simply be shut off.
The initiator 90 has three chambers 91, 92, and 93 provided by a
housing 94, a diaphragm 95, and a rigid partition 96, as shown in a
preferred embodiment in FIG. 6. The chamber 92 between the
diaphragm 95 and the rigid partition 96 is kept at atmospheric
pressure by an atmospheric bleed port 97. The chamber 93 between
the rigid partition 96 and the housing 94 is provided with an inlet
98 that is connected to or disconnected from a port 104 by a
closure member 100 which is connected to and is actuated by the
diaphragm 95. An adjustable spring 101 exerts pressure on the
diaphragm 95, urging the closure member 100 toward a position
disconnecting the inlet 98 from the port 104. This inlet port 98 is
connected by a conduit 102 and the pressure port 23 of the valve 17
to the main gas supply conduit 20. It may also, through an on-off
valve 103, be connected to the volume port 22 of the valve 17, so
that the volume-cycled mode may or may not use the sensitivity
control device 90, whereas the pressure-cycled mode always uses
this device 90. The command signal conduit 43 is connected to the
chamber 93 by a port 104. There is also a very important port 105
for the chamber 91, discussed in the next section.
In the preferred structure shown in FIG. 6, the diaphragm 95 has a
bracket 99 secured thereto in engagement with a rod or shaft 106.
An O-ring 109 provides both a seal where the rod 106 passes through
the partition 96 and a pivot for it to swing about. The closure
member 100 comprises a disc threaded adjustably to the shaft 106
and provided with an annular gasket 108, effective in all
rotational positions of the disc to close the outlet port 104
except when the diaphragm 95 causes the rod 106 to tilt and pivot
on the O-ring 107. The spring 101 is of the leaf type with a
right-angle portion 109 attached to the rod 106, in a way to enable
some relative movement, such as sliding. A screw 87 enables
adjustment of the spring pressure, thereby setting the pressure
requested for the diaphragm 95 to open or close the port 104. There
is a stop 88 for the shaft 106 and a set-screw 89 for the
disc-valve 100. The spring 101 can be adjusted to set the
patient-actuated pressure over the range between about 1 centimeter
of water and 15 centimeters of water.
THE FACE MASK 110 AND THE AIRWAY CONDUIT 113 (FIGS. 1A and 1B)
The patient typically wears a face mask 110 (FIG. 1A), which is
connected by a conduit 111 to an exhalation valve 112. From the
exhalation valve 112, a conduit 113 at airway pressure is connected
(FIG. 1B) to the sensitivity control device 90 at the port 105 on
the opposite side of the diaphragm 95 from the central chamber 92
and on the same side as the spring 101. When the pressure in the
airway 113 drops, the diaphragm 95 is moved by the pressure of the
spring 101, to tilt the rod 106 and open the port 104, as will be
seen subsequently in the explanation of the operation of the
ventilator.
THE PRESSURE SAFETY VALVE 120 (FIG. 1B)
The airway conduit 113 is also connected to an inlet 119 of a
pressure s safety valve 120 leading in between two diaphragms 121
and 122 that divide the valve 120 into chambers 123, 124, and 125.
The idea here is to prevent the buildup of any dangerous pressure
in the lungs. The effective area of the diaphragm 121 is larger
than that of the diaphragm 122. On the opposite side of the larger
diaphragm 121 is a spring 126, and (like the structure of the main
valve 30) the smaller diaphragm 122 and the larger diaphragm 121
are both connected to a valve closure member 127 which closes an
inlet 128 that is connected to the command signal conduit 43. When
the port 128 is open the command signal can flow to atmospheric
pressure through the chamber 125 a bleed port 129. The chamber 123
is also bled to atmospheric pressure. If the pressure in the airway
113 becomes excessive (i.e., rises above a predetermined pressure,
such as 70 centimeters water, set as a limit by the spring 126), it
acts on the diaphragm 121, overcomes the pressure of the spring 126
and opens the inlet 128, bleeding the command signal conduit 43 to
atmosphere and thereby terminating the inspiratory phase.
THE PRESSURE CONTROLLER 130 (FIG. 1B AND 7)
Normally, however, the inspiratory phase in the pressure-cycled
mode is terminated by a pressure controller 130. If the sigh
function is to be omitted, the pressure controller may be built
just like the pressure safety valve 120, but set for lighter
pressure to provide the normal pressure control for the ventilator.
When the sigh function (see below, re FIG. 1C) is incorporated, a
preferred embodiment of the pressure controller 130 may be as shown
in FIG. 7. This unit 130 has a diaphragm 131 of larger effective
area than either diaphragm 132 or diaphragm 133, between which it
lies, and these diaphragms 131, 132, and 133 cooperate with a
housing 114 to provide chambers 115, 116, 117, and 118, a spring
134 being in the atmospheric chamber 118. The diaphragms 131 and
132 and 133 are secured together and to a closure member 135 and
normally urge it against an inlet port 136,which joins the end
chamber 115 to the command signal conduit 43. When the closure
member 135 is moved away from the port 136, the command signal
conduit 43 is bled to atmosphere through a port 137. The chamber
117 between the two diaphragms 131 and 133 has a port 140 connected
by a conduit 141 to the pressure outlet 25 from the valve 18, and
thereby, to the airway 113. The spring 134 is adjusted by a handle
or shaft 142 to give a desired pressure on the closure member 135.
A guide pin 143 engages a groove 143a in a nut 143b to guide the
nut 143b without rotation when the shaft 142 is turned. Since the
valve 18 has its inlet 24 connected to the airway pressure conduit
113, when and only when the valve assembly 12 is in the
pressure-cycled mode, the airway pressure is then conducted to the
central chamber 116 of the pressure controller 130. The chamber
117, which lies between the diaphagms 131 and 133 is connected by a
port 138 to a conduit 139 leading to the sigh device 300.
Omitting for the present the effect of the sigh apparatus 300, the
main function of the pressure controller 130 is to terminate the
inspiratory phase when the pressure in the airway 113 reaches a
predetermined pressure. At this pressure, since the pressure in the
airway 113 is also the pressure in the line 141 and in the chamber
116 during the pressure-cycled mode, the pressure in the chamber
116 and the pressure of the spring 134 are overbalanced, and the
command signal line is bled to atmospheric pressure through the
inlet 136, chamber 115, and port 137. The command signal conduit 43
bleeds away the pressure in the chamber 40 of the main valve 30,
and the port 31 is therefore closed. The operating point of the
pressure controller can be set over a range of about 5 to 50 cm
water.
THE AIR SWITCH 145 AND PROFILE FLOW CONTROLLER 150 (FIG. 1A)
In the pressure-cycled mode, the valve 19 is used to connect the
downstream pressure conduit 35 leading from the main valve 30 to a
conduit 144 leading to an air switch 145 (FIGS. 1A and 2). The air
switch 145 is a manually operated valve which sends the oxygen from
the conduit 144 through a flow-rate controller 150 to provide a
controlled flow of the pure oxygen or sends it through a venturi
149, at which air is picked up to dilute the oxygen. It determines
whether the patient gets 100 percent oxygen (if that is the gas
supplied at the supply 10) or one of various dilutions thereof.
Thus, the air switch 145 in one position connects the conduit 144
to a conduit 146 leading to a variable needle valve 147 and thereby
through a restrictor orifice 148 to the venturi 149, and thence to
the airway conduit 113 to send oxygen-enriched air to the mask 110
therethrough.
In its other position, the air switch 145 connects the conduit 144
to a conduit 151 which leads to the profile flow controller 150,
comprising a valve unit 152 with three chambers 153, 154, and 155.
Two of the chambers 153 and 154 are divided from each other by a
diaphragm 156 with a spring 157 in the chamber 153. The chamber 153
is kept at atmospheric pressure through a bleed port 158. The third
chamber 155 is divided from the central chamber 154 by a poppet
valve 160 and opening 161. The poppet valve 160 is normally urged
into the opening 161 to close it by a spring 162 and is also
actuated by the diaphragm 156. An inlet conduit 163 into the third
chamber 155 is connected to the conduit 151 by a conduit 159 and
conducts oxygen into the central chamber 154 when the poppet valve
160 is open, at a rate determined by the amount by which the poppet
valve 160 is open. The gas may then pass through an outlet port 164
and from thence to the airway pressure conduit 113. A by-pass is
provided through a conduit 165 and a needle valve 166 to give a
much smaller flow rate of gas from the conduit 151 to an inlet port
167 into the central chamber 154. This is the terminal or minimum
flow.
A pressure relief valve 168 may be incorporated to bleed the airway
113 to atmosphere if the pressure introduced from the port 154
should become excessive.
The pressure flow controller 150 sends gas to the patient at a
regulatable large initial amount and at a flow rate that gradually
reduces toward or to a set minimum rate. The pattern of reduction,
the rate at which the flow rate decreases, is determined by the
pressure on the spring 157, which is adjustable to the patient's
requirements or to the prescribed treatment. The maximum or initial
flow rate is set by the spring 157, and the minimum or terminal
flow is set by the needle valve 166. Typically, the terminal flow
is adjustable in the range of 1 to 10 liters per minute, and the
peak flow is adjustable in the range of 60 to 100 liters per
minute.
THE NEBULIZER 170 (FIG. 1A)
Preferably, the downstream conduit 35 is also connected to a
nebulizer 170 (FIG. 1A) through a restricted valve 171 to give a
small flow of high-pressure gas to atomize the liquid added to the
main flow into the airway pressure conduit 113. Also, a pressure
gauge 172 (FIGS. 1A and 2) may be connected to the airway pressure
conduit 113 to give a reading of airway pressure.
THE NEGATIVE PRESSURE DEVICE AND THE EXHALATION VALVE
112(FIG.1A),
WITH ITS ASSOCIATED PRESSURE RELIEF VALVE 200 (FIG. 1B)
The negative pressure device 55, when used, connects the chamber 57
by a port 174 to a conduit 175 through an adjustable needle valve
176 (with control 176a in FIG. 2) and into the exhalation valve 112
at an inlet 177. A closure member 178 in the negative pressure
device 55 is connected to the diaphragm 58, and the diaphragm 58
and a spring 179 normally keep the port 174 closed.
The negative pressure port 177 of the valve 112 leads into a
venturi 180 in a chamber 181, into which the conduit 111 and 113
also open through ports 182 and 183; the flow from the venturi 180
passes to an outlet valve 184, the outlet port 185 of which is
normally kept closed by the pressure of a spring 186 (or similar
device, such as a bladder) on interconnected diaphragms 187 and
188, and by the pressure from a conduit 190. This conduit 190 is
connected by a restrictor orifice 191(FIG. 1B) to the airway
pressure conduit 113. The conduit 190 is a small-diameter line so
that it is very responsive, and the action will be described later.
This line 190 and its restrictor conduit 191 are connected by an
inlet 192 into a chamber 194 of the valve 112.
The line 190 is also connected to a pressure relief valve 200 at an
inlet 201 (FIG. 1B). The pressure relief valve 200 has a single
diaphragm 202 dividing the valve 200 into a chamber 203 having a
port 204 to atmosphere on one side, and a chamber 205 having a port
206 connected to the downstream conduit 35. A spring 207 aids the
diaphragm 202 in keeping the port 201 open, and when it is open,
the auxiliary line 190 is bled to atmosphere.
THE PRESSURE RELIEF VALVE 51 (FIG. 1A)
The conduit 43 also leads to the pressure relief valve 51 (FIG.
1A), which is a secondary valve for the main valve 30 and is used
in both modes. The valve 51 has a single diaphragm 195 with a
chamber 196 on one side connected by a port 197 to the command
signal conduit 43. A valve 198 connected to the diaphragm 195 is in
the other chamber 199 and normally acts to close an inlet port 207a
connected to the downstream conduit 35. A bleed port 208 to
atmosphere is provided from the chamber 199, and a spring 209 tends
to help open the valve 198.
The pressure relief valve 51 is closed so long as there is a
predetermined amount of pressure in the command signal conduit 43;
otherwise it is open. When the valve 51 is closed, the pressure in
the downstream conduit 35 is monitored; when the valve 51 is
opened, the downstream conduit 35 is bled to atmospheric. Thus,
when the command signal conduit 43 has enough pressure to open the
main valve 30, the same pressure closes the relief valve 51. And
when the command signal conduit 43 is bled to atmosphere through
either the pressure controller 130 or through the pressure safety
valve 120, at the end of the inspiratory phase, the valve 51 is
opened and the downstream conduit 35 is at once bled to the
atmosphere.
THE MANUAL TRIGGER VALVE 210 (FIG. 1B)
For manual operation in both modes there is provided a manual
trigger valve 210 (FIG. 1B) comprising a valve body 211 having an
inlet 212 connected to the internal supply conduit 20 and having a
valve 213 normally urged by a spring 214 to a closed position at a
port 215. When the valve 213 is opened by depressing a manual stem
219, the air can flow from the conduit 20 through the trigger valve
210 from the chamber 216 to the other chamber 217 and thence by a
port 218 to the command signal conduit 43, whence it flows to the
chamber 40 and opens the valve 40. Thus the valve 210 enables the
physician manually to monitor the ventilator, to initiate the
inspiratory phase.
All of the parts so far described are used in the pressure-cycled
mode of operation, and some of them are also used in the
volume-cycled mode of operation. The ones next to be described are
used only in the volume-cycled mode.
VOLUME MODE: VOLUME PROFILE REGULATOR 225 (FIGS. 1A AND 8)
As stated, in the volume-cycled mode of operation the sensitivity
control 90 may or may not be used, depending on whether the valve
103 is open or closed. In either event, however, the valve 19 (FIG.
1B) is set so that the downstream gas flows from the conduit 35
into a conduit 220 leading by two branch conduits 221 and 222 to a
volume profile regulator 225 and an inspiratory time regulator
240.
The volume profile regulator 225 is used to enable the flow to the
patient in this mode to start at a large initial flow and then to
decrease as the inspiratory phase continues until the end of the
cycle. In this respect it resembles -- but is different from -- the
pressure flow controller 150.
The volume profile regulator 225 (see especially FIG. 8) comprises
a housing 226 having a larger area diaphragm 227, a smaller-area
diaphragm 228, and a rigid partition 229. One side of the diaphragm
227 is open to the atmosphere, as by a port 226a in the housing
226. A poppet valve 230 is urged by the diaphragms 227 and 228 and
springs 231 and 231a toward a position away from an opening 232
which the poppet valve 230 sometimes closes. Gas from the conduit
221 enters by an inlet port 224 into a chamber 233 and goes through
the opening 232 controlled by the poppet valve 230 to a chamber
234, and from thence by an outlet 235 to a conduit 236 leading to a
control valve 237 and thence to the airway pressure conduit 113.
The control valve 237 with indicator 237a in FIG. 2, enables
adjustment of the volume in a manner subsequently to be explained.
The control valve 237 is an integral part of a time-volume control
unit 275 which is given more attention below.
The volume profile flow regulator 225 also has a chamber 238
between the diaphragm 227 and 228 with a port 239. As will be seen,
during the inspiratory phase, pressure builds up in the chamber 238
and gradually reduces the flow out through the port 235 by moving
the poppet valve 230 toward the opening 232. The pressures of the
springs 231 and 231a, the stiffness of the diaphragms 227 and 228,
and their areas relative to each other, cooperate with the variable
pressure of gas into the chamber 238 to determine the profile of
the inspiratory phase.
THE INSPIRATORY TIMER 250 AND ASSOCIATED ELEMENTS (FIGS. 1A)
The oxygen from the conduit 222 enters the inspiratory time
regulator 240 through a flow-reducing restricted orifice 241 and an
inlet port 242. The purpose of the inspiratory time regulator is to
provide a supply of gas at a regulated pressure to the inspiratory
timer 250. A diaphragm 243 is loaded by a spring 242 to close off a
vent port 248 to atmosphere. The gas entering the inlet port 242
flows to an outlet port 245 via an annular chamber 249, except for
gas that is vented to atmosphere from the chamber 249 by the vent
port 248. This venting serves to keep the gas supplied to the
outlet port 246 at a constant pressure, for as the pressure
increases in the chamber 249, the diaphragm 243 is moved up to
increase the bleed flow through the vent port 248; since a small
motion of the diaphragm 243 will create a large change in bleed
flow, the pressure will remain practically constant.
The regulator 240 is set to deliver to the outlet port 245 and a
conduit 246 regulated pressure at a desired level, and the conduit
246 is connected through a needle valve 247 to an inspiratory timer
250, with indicator 250a of FIG. 2. The needle valves 247 and 237
are interacting and form part of the time-volume control device 275
discussed below, by which the inspiratory volume and time can be
changed.
The outlet from the needle valve 247 leads to a port 251 in a
fixed-capacity center chamber 252 of the inspiratory timer 250
between two diaphragms 253 and 254, a larger diaphragm 253 and a
smaller diaphragm 254. To both diaphragms 253 and 254 is connected
the stem 255 of a closure valve 256 for an inlet 257 which is
connected to the command signal conduit 43 and normally holds that
inlet 257 closed. From the chamber 258 with the inlet 257 is a
bleed 259 to atmosphere, and the spring chamber 260 of the larger
diaphragm 253 also has a bleed port 261 to atmosphere, as well as a
spring 262 bearing on the diaphragm 253.
Thus, the gas that passes through the pressure regulator 240 and
the control valve 247 gradually builds up pressure in the timer 260
during the inspiratory phase, starting from atmospheric pressure at
the beginning of each inspiratory phase. When a predetermined time
has elapsed, the pressure in the chamber 252 reaches a
predetermined level that opens the closure member 256, uncovering
the inlet port 257. As this inlet port 257 is uncovered, the rush
of pressure of the gas flowing in from the command signal conduit
43 helps to snap open the valve, and the command signal conduit 43
is quickly bled to atmosphere, ending the inspiratory phase by
resulting in closure of the main valve 30.
In order to prepare the inspiratory timer 250 for the next phase,
by bleeding the pressure in the chamber 252 to atmospheric, the
inspiratory timer 250 is connected by conduits 263 and 264 to
another pressure relief valve 265 at an inlet 266. The pressure
relief valve 265 has a single diaphragm 267 with a spring 268 in
one chamber 269, urging a valve closure member 270 normally to open
the inlet 266. The chamber 269 is bled to atmosphere by a port 271
so that when the valve 270 is in open position, the gas from the
conduit 263 is vented to the atmosphere. A chamber 272 on the other
side of the diaphragm 267 is connected by a port 273 to the
downstream air conduit 35.
Thus, when the inspiratory timer ends the inspiratory cycle by
bleeding the command signal conduit 43 to atmosphere, the drop in
pressure in the conduit 43 opens the valve 51 and the downstream
conduit 35 is bled to atmosphere. The resultant reduction in
pressure of the conduit 35 enables the spring 268 to open the
closure member 270 away from the inlet port 266, and the conduit
263 and the chamber 252 are bled to atmosphere. The valve 256 is
then closed by the spring 262. When the next inspiratory phase
begins, the surge of pressure in the downstream conduit 35 closes
the valve 265, and the flow of gas through the needle valve 247 can
build up pressure in the chamber 252.
The diaphragms 253 and 254 and the bias spring 262 are sized so
that the valve seat 256 is closed when the pressure in the
intermediate chamber 252 is atmospheric and opens when the pressure
reaches a nominal value of 5 psig (at the end of the inspiratory
phase), the pressure being created by the flow of supply gas
through the needle valve 247 into the fixed capacity chamber 252.
The time that it takes to build up the pressure, say, of 5 psi,
represents the inspiratory time. It may be adjusted from 0.5 to 4
seconds by setting the needle valve opening 247. At the end of the
inspiratory phase, the pressure is returned to atmospheric by the
action of the pressure release valve 265.
The pressure increase from 0 to 5 psig is proportional to the total
volume which passes through the needle valve 247. This volume is
proportional to area x time. The total volume being a constant in
the calibration, the valve opening is therefore proportional to the
reciprocal of time; hence, the non-linearity of the time scale
graduation.
The inspiratory timer 250 is also connected by the conduit 263 and
the port 239 to the chamber 238 of the volume profile regulator 225
which lies in between the two diaphragms 227 and 228. Thus, during
the inspiratory phase, the pressure builds up there and gradually
moves the poppet valve 230 closer to its opening 232, shaping the
flow profile of the inspiratory phase.
As the pressure in the chamber 238 increases, it creates a force
opposing the force of the spring 231, and the regulator setting is
decreased. As a result, the output pressure of the regulator
decreases progressively as the pressure in the chamber 238
increases. Typically, the output pressure goes from 30 psig to 5
psig as the inspiratory timer pressure goes from 0 to 5 psig.
THE VOLUME-TIME CONTROLLER 275 (FIGS. 1A and 9-13)
A housing 276 is provided with an inlet 277 and an outlet port 278.
A variable area opening is created by moving a slot 280 (preferably
rectangular in cross section) of an adjustable sleeve 281 relative
to a slot 283 in the stationary housing 276, the slot 283 also
being preferably rectangular in cross section. A maximum size of
opening is obtained when the two openings 280 and 283 coincide
(FIG. 12C). Reduction from that maximum condition is done in two
modes: a rotation and an axial displacement of the adjustable
sleeve 281.
The rotation of the sleeve 281 is directly related to the volume
setting (V); the axial displacement is proportional to the
reciprocal of inspiratory time (1/t). The net area of the opening
in then proportional to: Volume x (1/Time). Since the flowrate is
directly proportional to the area, we have:
Flowrate = Volume x (1/time)
or the fundamental relationship:
Volume = Flowrate x time.
The settings of volume and inspiratory time are thus independent
and noninteracting. A change in volume setting modifies the opening
area, and therefore the flowrate, in a direct relationship. A
change in the inspiratory time setting modifies the opening area in
an inverse ratio; an increase in time decreases the flowrate, in
order to maintain the same total volume in a longer time.
The axial movement of the sleeve 281 is the axial displacement of a
screw 284 actuated directly, by an inspiratory time knob 285, the
sleeve 281 being spring loaded by a spring 286 against the screw
284 to assure cooperation between the screw 284 and the sleeve 281.
The knob 285 drives, through a step-up gear train 287, 288 the
needle valve 247 of the inspiratory timer. The rotation of the
sleeve 281 is obtained by a gear train 290, 291, in which the
driven gear segment 291 is attached to the sleeve shaft 292 (FIG.
10), and the driving gear 290 is actuated by a volume knob 237 a
(FIGS. 2 and 10).
FIGS. 12A through 12D show four extreme positions of the two
orifices 280 and 283:
FIG. 12A shows the small overlap in area of the rectangular
orifices 280 and 283 when the time shaft is in its full clockwise
position to give the maximum time interval, while the volume shaft
is in its full counterclockwise position to give minimum volume.
The orifices 280 and 283 are in different planes and at minimum
overlap in both directions. FIG. 12B shows the larger overlap, with
both orifices on the same plane but at extreme opposite angles.
This setting gives both minimum time and minimum volume, for both
the time shaft and the volume shaft are in their full
counterclockwise positions.
In FIG. 12C, the maximum volume is obtained, with the orifices 280
and 283 coinciding, while the time is again at minimum. The time
shaft is fully counterclockwise, while the volume shaft is fully
clockwise.
In FIG. 12D the volume shaft is again fully clockwise to give
maximum volume, while maximum time is also obtained by having the
time shaft fully clockwise.
In a typical instance, the area of the full overlap--i.e., the area
of each of the orifices 280 and 283,-- is 0.01 square inch (FIG.
12C). In FIGS. 12B and 12D, the area of overlap is then 0.001
square inch, and in FIG. 12A the area of the overlap is only 0.0001
square inch.
INTERRELATIONSHIPS AND GENERAL FUNCTIONING OF THE ASSEMBLY (FIGS.
1A AND 1B)
Now that the elements other than the sigh device 300 have been
described and their individual operation indicated, some general
relationships and functioning will be noted before the detailed
operation is given.
As noted earlier, the selector valve assembly 12 has three
positions: "pressure-cycled," "volume-cycled" and "off." In the
"off" position, the regulated gas supply 10 is shut off from the
entire device. In the "pressure-cycled" position, (1) The internal
supply conduit 20 to the main valve 30 is connected to the
regulated gas supply 10, (2) The downstream conduit 35 leading from
the main valve 30 is connected to the air switch 145. (3) The
connecting line 141 between the patient supply line or airway
conduit 113 and the pressure controller 130 is open. (4) The supply
line 102 between the internal supply conduit 20 and the initiator
90 is open. In the "volume-cycled" position, (1) The internal
supply conduit 20 to the main valve 30 is connected to the
regulated gas supply 10, and (2) The downstream conduit 35 leading
from the main valve 30 to the volume control unit 275 is open.
The two-position main valve 30 is either fully open or fully
closed, depending on the command signal from the conduit 43. If the
command signal, i.e., the pressure in the conduit 43 increases
beyond a predetermined value, such as 20 psig, the main valve 30
opens and remains open. If the signal decreases to a lower
predetermined value (such as approximately 10 psig), the main valve
30 closes.
The relief valve 51 exhausts the downstream pressure in the conduit
35 to atmosphere when the main valve 30 closes.
On a command signal from the airway conduit 113, typically a slight
vacuum, the initiator 90 sends high-pressure gas from the conduits
20 and 102 to the command signal conduit 43, causing the main valve
30 to open. The reader will recall that the initiator 90 has a
diaphragm 95 that is subjected to a differential pressure;
atmospheric pressure on one side in the chamber 92 and, at this
time, a slight vacuum on the other side in the chamber 91 generated
by the patient and sent there by the airway conduit 113. The effort
created by the differential pressure opens the valve closure 100 in
the compartment 93, and the port 104 then supplies the
high-pressure gas from the conduit 102 to the command signal
conduit 43. The magnitude of the vacuum required to generate the
control signal is adjustable by the loading spring 101.
The pressure controller 130 also senses the pressure in the airway
conduit 113, with a desired set pressure, and when the two become
equal, generates a signal to shut off the main valve 30, by
bleeding the command signal conduit 43 to atmosphere.
The airway pressure, which is the patient's breathing pressure,
starts at atmospheric pressure or at a slight vacuum at the
beginning of each inspiration,then gradually increases during the
inspiratory period to the preset value; this may be a value from a
minimum of 5 cm. water to a maximum about 60 cm. water. When the
pressure in the airway conduit 113 has reached the preset value,
the gas in the command signal conduit is exhausted to atmosphere,
causing a pressure drop, which, in turn causes the main valve 30 to
close, shutting off the gas supply to the patient.
The pressure safety valve 120 also senses the airway pressure,
compares it with a preset maximum (approximately 70 cm. water)
pressure. If the pressure in the airway conduit 113 exceeds the
preset maximum pressure, a signal is generated to shut off the main
valve 30, by exhausting the command signal conduit 43 to
atmosphere. Again, this pressure drop causes the main valve 30 to
close.
When a desired expiratory time has elapsed, the expiratory timer 60
initiates a new inspiratory phase by connecting the high-pressure
gas supply conduit 20 to the command signal conduit 43, which opens
the main valve 30. During the inspiratory phase, the expiratory
timer 60 is recharged. The intensity or pressure of the recharge is
directly proportional to the inspiratory time. At the end of the
inspiratory phase and the beginning of the expiratory phase, the
expiratory timer 60 starts discharging (bleeding off air pressure)
at a preset rate. When the discharge reaches a reference low level,
a new inspiratory phase is initiated. If the rate of discharge is
set at a value such that the discharge time is twice as long as the
recharge time, the respirator is known to operate on a 1:2
inspiratory/expiratory ratio. This ratio is maintained even though
the inspiratory time varies from one breath to another. The
automatic ratio expiratory timer 60 is effective in both
pressure-cycled and volume-cycled modes.
The air switch 145 is connected to the downstream side of the main
valve 30 by the conduits 35 and 144. If is effective in the
pressure-cycled mode only, when it provides a selection of
delivering pure oxygen through the profile flow controller 150 or
an oxygen-air mixture through the venturi 149.
The flow controller 150 provides the patient with a suitable flow
pattern during the inspiratory period. The demand of gas is
greatest at the start of the inspiratory phase; then it gradually
diminishes. The flow controller operates on the basis of creating a
variable orifice 160, 161 as a function of the difference between a
spring-set pressure and the patient's airway pressure. The flow is
then determined by the area of the orifice. By adjusting manually
the magnitude of the differential pressure, a higher or lower flow
rate can be obtained. A manual setting limits the maximum opening
of the variable orifice 160, 161. The initial high flow,
corresponding to this maximum opening, constitutes the "peak flow,"
and the manual setting is the flow rate control. An adjustable
by-pass flow through the valve 166 provides a "terminal flow"
control.
In the alternate position of the selector switch 145, the profile
function is by-passed, and the gas supply is applied to the nozzle
of the venturi 149. The flow from the nozzle draws in air,
producing an air-gas mixture. The flow rate is then controlled by
the needle valve 147, which is actuated by the control knob of the
profile flow controller 150, thus providing a single common control
knob for both operations.
The manual trigger 210 enables manual initiation of the ventilator
into an inspiratory phase by connecting the gas supply conduit 20
to the command signal conduit 43, thus causing the main valve 30 to
open.
A slight vacuum created at the exhalation valve 112 by the
ventilator during the expiratory phase known as "negative
pressure," (see U. S. Pats. Nos. 3,191,596 and 3,265,061). The
driving gas supplied from the gas supply conduit 20 upstream of the
main valve 30 passes through the pneumatically controlled valve 55
and then through the adjustable needle valve 176 to the venturi 180
located in the exhalation valve 112. The control valve 55 is
actuated by the pressure from the downstream side of the main valve
30 by the conduit 35. The needle valve 176 enables adjustment of
the value of the negative pressure.
The volume control is obtained by the volume selector 275, the
inspiratory timer 250, and the volume profile regulator 225.
The volume selector 275 enables selection of a desired volume to be
delivered, by setting a dial. The dial may be graduated in volume
units or have reference marks. The input of the unit is connected
to the downstream conduit 236 from the volume profile regulator
225. The output of the unit is connected to the patient's breathing
circuit.
The inspiratory timer 250 controls the time that it takes to
deliver the selected volume. The supply pressure for the timer 250
is regulated to an intermediate value (e.g., approximately 25 psig)
to minimize the effect of pressure variations in the main supply
line 20. The gas is then metered through a needle valve 247 into
the fixed-capacity chamber 252, where the pressure increases as a
function of time. When the pressure reaches a reference value
(e.g., 5 psig), the timer 250 exhausts the command signal conduit
43 to atmosphere which, in turn, shuts off the main valve 30 and
the gas supply to the patient. Its dial may be graduated in seconds
or have other reference marks.
The actions of the volume selector 275 and the inspiratory timer
250 are combined in such a way that the settings of the volume and
the inspiratory time are noninteracting. Changing the volume
setting does not affect the time setting; similarly, changing the
inspiratory time does not affect the volume setting.
The volume profile regulator 225 supplies the gas to the volume
selector 275. It regulates the gas pressure to a maximum of, e.g.,
30 psig, at the beginning of the inspiratory period and gradually
reduces it to a minimum of, e.g., 5 psig at the end of the period.
As a direct result of the variable pressure, the flow rate is
reduced accordingly, providing a controlled pattern.
The decrease in the regulated pressure is synchronized with the
control pressure of the inspiratory timer 250. This provides a
reproducible flow pattern independently of the inspiratory time
setting.
The pressure release valve 51 is open to atmosphere when the
pressure in the command signal conduit 43 is low (near
atmospheric). During the inspiratory phase, this pressure is high,
and it closes the port 207a. At the end of the inspiratory phase
and the start of the expiratory phase, the pressure in the conduit
43 is bled to atmospheric, causing the pressure release valve 51 to
open and bleed the downstream conduit 35 to atmosphere.
The exhalation valve 112 provides the means of opening the
patient's airway to atmosphere during the expiratory period, and
conversely of closing the communication with atmosphere during the
inspiratory period. A plastic bladder or diaphragm 187 works in
cooperation with the exhalation port 185 to control the opening.
When the bladder is inflated, (or the diaphragm 187 is under
pressure) there is no communication with atmosphere. When it is
deflated, the communication is established. The operation of the
bladder or diaphragm 187 is automatically controlled by the
ventilator through the auxiliary line 190.
OPERATION: PRESSURE-CYCLED MODE
The pressure-cycle mode of operation will be described first in its
use as an assist type of ventilator, with the patient supplying
part of the operation through his being able to breathe. The
selector 12a of the manual valve assembly 12, is set to the
pressure cycle mode.
A slight vacuum through the airway pressure conduit 113 of
approximately 2 centimeters of water is created by the patient, and
this is transmitted through the main airway 113 to the sensitivity
control 90. Here, this vacuum signal actuates the valve 100, which
therefore applies high pressure gas from the conduit 102 to the
command signal conduit 43, through the port 104. The command signal
conduit 43 transmits this pressure to the port 42 and chamber 40 of
the main valve 30, where it acts on the diaphragm 37 and opens the
closure member 32. Gas is then delivered from the internal supply
conduit 20 to the main valve chamber 39 and from there by the port
34 to the downstream conduit 35. This gas is delivered by the valve
19 and the conduit 144 to the air switch 145. Thence it passes
either through the venturi 149 or through the profile flow
controller 150 to the airway pressure conduit 113 and thence to the
mask 110 and hence to the patient.
The airway pressure conduit 113 is connected by the valve 18 and
the conduit 141 to the pressure controller 130, and when the
breathing pressure reaches a value, which is preset by the setting
of the spring 134 of the pressure controller 130, the command
signal conduit 43 is vented and exhausted to the atmosphere through
the inlet 136 and the port 137. When this command signal conduit 43
is exhausted to the atmosphere, the main valve 30 is closed by the
pressure of the spring 45, and the upstream conduit 20 is isolated
from the downstream conduit 35, and at the same time the supply to
the airway pressure 113 is cut off, thereby terminating the
inspiratory phase. Then the downstream conduit 35 is bled to
atmosphere through the valve 51.
At this time the auxiliary line 190 connected to the exhalation
valve 112 is opened to atmosphere through the pressure relief valve
200, controlled by the pressure in the downstream conduit 35. A
differential pressure is created by the restrictor 191 between the
main airway conduit 113 and the auxiliary conduit 190. This
difference in pressure causes the exhalation valve 112 to open to
the atmosphere. The differential pressure is created by the action
of the restrictor 191 in combination with the pressure relief valve
200.
During this time the patient is breathing out, and if he then
breathes in again, he will start another cycle. However, if the
spontaneous expiratory phase extends beyond the normally expected
duration, the ventilator, instead of being a mere assist device,
will both assist and control the patient's breathing, for the
automatic ratio expiratory timer 60 then takes over and initiates
an inspiratory phase by applying high pressure gas from the conduit
20 to the command signal conduit 43.
If a doctor should wish to override a patient's spontaneous
breathing and also override the autoratio expiratory timer 60, he
may start the ventilator into an inspiratory phase by operating the
manual trigger 210 to send regulated gas supply from the conduit 20
to the command signal conduit 43, causing the main valve 30 to
open.
During the inspiratory phase, the downstream line 35 is connected
to the nebulizer 170 and is supplied with correctly regulated gas
and a constant rate of flow is kept. This is, of course, shut off
during the expiratory phase, since the supply to the downstream
conduit 35 is then shut off.
OPERATION: VOLUME-CYCLED MODE
Operation in the volume-cycled mode employs the auto-ratio
expiratory timer 60, but it does not employ the conduit 144 or the
air switch 145, nor need it employ the pressure controller 90. In
this mode of operation, the conduit 220 is connected by the valve
19 to the downstream conduit 35 and leads to the profile flow
regulator 225 and the inspiratory time regulator 240, which both
act to send a regulated supply of gas to their respective conduits
236 and 246 and their respective valves 237 and 247. The
interconnected valves 237 and 247 are adjusted to give the desired
volume and the desired time, the time depending on the time it
takes to build up enough pressure in the inspiratory timer 250 to
act to shut off the main valve 30 by exhausting the command signal
conduit 43 to atmosphere, upon opening of the valve 256.
It is important that the setting of the volume by the control valve
237 and the setting of the inspiratory timer 250 by the needle
valve 247 be interrelated, and that the selector 275 automatically
compensate for a change in the setting of one to assure that the
effective value of the other is not affected. Even in this phase of
operation, if the pressure in the airway 113 should reach a
dangerously high value, the pressure safety valve 120 operates to
terminate the inspiratory phase, as it also does in the
pressure-cycled mode of operation.
In the volume-cycled mode, once the inspiratory time is selected,
the expiratory time automatically follows, in accordance with the
selected inspiratory-expiratory ratio set in the expiratory timer
60.
As the main valve 30 opens, gas is delivered from the downstream
side of the main valve 30 by the conduits 35 and 220 through the
volume control device 275 to the patient, without regard to airway
pressure. The pressure line between patient airway conduit 113
pressure and the pressure controller 130 unit is shut off, making
the pressure controller 130 unit inoperative.
The valves 237 and 247 are interrelated in such a way that volume
setting and inspiratory time setting are noninteracting and may be
set independently.
If the resistance of the restriction 191 in the auxiliary line 190
is decreased, a smaller differential pressure will result,
preventing the exhalation valve 112 from opening its port 185
fully. This will retard the exhaust of the airway pressure. By
making the restriction or orifice 191 adjustable, any desired
"expiratory resistance" can be obtained.
In either mode of operation the negative pressure device 55 may be
used, though of course it will not be normally used but only upon
special situations. In those special situations, during the
inspiratory phase the pressure in the downstream conduit 35 of the
main valve 30 shuts off the supply to the negative pressure unit
55. At the end of the inspiratory phase, as the main valve 30
closes, the pressure in the downstream conduit 35 drops to zero,
and the supply valve 174 to the negative pressure device opens.
With the negative pressure control dial or needle valve 176
partially open, a small flow goes through the venturi 180, and a
negative pressure is created at the exhalation valve 112. The value
of this pressure is determined by the setting of the control
dial.
In either mode of operation, if additional expiratory resistance is
desirable, the resistance in the restriction in the auxiliary line
190 may be decreased, and a smaller differential pressure results
which prevents the exhalation valve 112 from fully opening.
SIGH FUNCTION (FIG. 1C)
As stated earlier, the present invention makes it possible to
induce a sigh artificially from time to time, causing the patient
to inhale very deeply and exhale very deeply. The sigh mechanism
enables the determination of sigh frequency, the volume of the
sigh, and its synchronization in the inspiratory phase.
The sigh mechanism 300 is designed to be used in either of the two
modes of ventilation, volume-cycled or pressure-cycled. It has
different functions in these two modes, the independent functions
of the sigh device 300 in respective modes being established
automatically by the turning of the ventilator manual valve control
selector 12a. In the volume-cycled mode, the sigh volume is
adjustable from a zero to a one hundred percent increase in gas
volume, over and above the normal volume setting. In the
pressure-cycled mode, the airway pressure is automatically
increased by a fixed factor of the setting; it is not adjustable.
In both modes the sigh frequency is adjustable.
The sigh device 300 includes a sigh frequency control 301, a sigh
volume control 320, a main control valve 310, two communication
control valves 330 and 340, one for pressure-cycled operation and
one for volume-cycled operation. There are also two reset valves
350 and 380, a check valve 360, and a pressure relief valve
370.
THE SIGH FREQUENCY CONTROL 301 (FIG. 1C)
By sigh frequency is meant how often a sigh is imposed upon the
normal ventilator breathing cycle. The sign frequency control 301
may be a needle valve supplied by the regulated supply gas conduit
20, and the downstream side of the valve 301 feeds, via a conduit
302 and a port 303, a control chamber 311 of the main sigh control
valve 310, the combination constituting a pneumatic timer. When the
valve 310 is actuated by the pressure in a chamber 311 reaching a
predetermined value, a sigh is initiated. The sigh frequency is
thus directly proportional to the opening of the needle valve 301.
The more open the valve 301, the more often sighs will occur.
PRESSURE CONTROL IN THE PRESSURE-CYCLED MODE, BY THE PRESSURE
CONTROLLER 130. THE COMMUNICATION CONTROL VALVE 330 (FIGS. 1B AND
1C)
In the pressure-cycled mode, as noted before, the pressure
controller 130 senses the pressure in the airway conduit 113,
compares it with a desired set pressure and when the two become
equal, generates a signal to shut off the main valve 30. During the
sigh cycle, the pressure setting is automatically raised to a
proportionally higher fixed value, preferably approximately 60
percent higher. This is accomplished by introducing the airway
pressure to the chambers 116 and 117 on both sides of the main
diaphragm 131. The pressure at which the inspiratory phase is
terminated is now determined by the smaller diaphragm 133; since it
has a smaller effective area than the larger diaphragm 131, it
shuts off the main valve 30 at a higher airway pressure. The
pressure controller 130 is connected to the sigh unit 300 by the
conduit 139.
In this pressure-cycled mode, a communication control valve 330
provides the communication between the two pressure chambers 116
and 117 in the pressure controller 130 during a sigh cycle. The
valve 330 also vents the pressure line 139 to atmosphere after each
cycle. The valve 330 has a large-area diaphragm 331 and a
small-area diaphragm 332, defining chambers 333, 334 and 335. The
chamber 333 is vented to the atmosphere by a port 390 and has a
port 336 to which is connected the conduit 139 coming from the
pressure controller 130. The chamber 335 has two ports 337 and 338.
The port 338 is also connected to the conduit 139 from the pressure
controller, while the port 337 is connected to a conduit 304 that
leads from the "pressure-cycled" outlet 25 of the valve 18 and is
thereby connected to the airway conduit 113. A single closure
system 339 either opens the port 336 and closes the port 337, or
else opens the port 337 and closes the port 336, depending on the
pressure in the chamber 334. When the pressure in the chamber 334
is well above atmospheric, the port 336 is closed, and the conduit
139 is connected by the ports 338 and 337 to the conduit 304 and
thereby to the airway conduit 113. When the pressure in the chamber
334 is low, near or at atmospheric, the port 337 is closed and the
conduit 139 is vented to atmosphere through the port 336 and
chamber 333. The chamber 334 is connected by a port 305 to a
conduit 306.
THE SIGH VOLUME CONTROL 320 FOR THE VOLUME-CYCLED MODE (FIGS. 1A,
1C, 9, AND 10)
The sigh volume control 320 is used only in the volume-cycled mode,
and it is connected to the ventilator's inspiratory timer system,
i.e., to the conduit 263 that leads to and from the pneumatic timer
250, which operates by metering a flow of gas into the
fixed-capacity chamber 252. By introducing the additional capacity
of the sigh volume control 320, the inspiratory time is increased
proportionately. In effect, the chamber of the sigh volume control
320 becomes a part of the chamber 252. This additional capacity is
adjustable within a range of, for example, 0 to 100 percent of the
originally set volume by means of the sigh volume control 320,
which, by increasing the time during which gas is delivered to the
patient, gives a corresponding increase in the volume delivered to
the patient.
The sigh volume control 320 may be a part of the volume-time
controller 275 and in the same housing 276 (FIGS. 9 and 10).
Basically, it may comprise a cylinder 321 with an adjustable piston
322. The cylinder 321 may have an open-end construction mounted
against a manifold 323 (FIG. 10) to enable capacity adjustment from
zero to a maximum value. An adjustment shaft 324 is secured to the
housing 276 by a retaining ring 325, and a threaded portion 326
extending into the piston 322 provides for the manual sigh
adjustment. The piston 322 may be sealed against leakage
therearound by an O-ring 327. Because of the friction to be
overcome in moving the piston 322, a multi-turn adjustment shaft
324 is desirable. A dial 328, which may, if desired, be driven
through a gear reducer (not shown) indicates the number of turns
(FIG. 2).
In the volume-cycled mode, the communication control valve 340
provides communication between the inspiratory timer 250 and the
sigh volume control 320. It also vents the sigh volume control 320
to atmosphere after each cycle. This valve 340 has a large-area
diaphragm 341 and a small-area diaphragm 342, defining chambers
343, 344, and 345. The chamber 343 has a port 346 and is vented to
atmosphere by a port 391. The port 346 is connected to the manifold
conduit 323. The chamber 345 has two ports 347 and 348. The port
348 is connected to the manifold conduit 323, and the port 347 is
connected by the conduit 263 to the chamber 252 of the inspiratory
timer 250. A single closure system 349 either opens the port 346
and closes the port 347 or else opens the port 347 and closes the
port 346, according to the pressure in the chamber 344, which is
connected to the conduit 306 by a port 307. When the pressure in
the chamber 344 is high, the port 346 is closed and the port 347 is
open to connect the inspiratory timer chamber 252 to the cylinder
321 via the conduits 263 and 323. When the pressure in the chamber
344 is low, the port 347 is closed and the conduit 323 is bled to
atmosphere via the inlet 346 and the port 391.
THE MAIN SIGH CONTROL VALVE 310
The control valve 310, which may be identical to the main valve 30,
is normally closed. It opens when the applied control pressure at
the port 303 is approximately 10 psig. The control valve 310 has a
large-area diaphragm 312 and a small-area diaphragm 313 defining
chambers 314, 311 and 315, and there is a port 316 in the chamber
315 opened and closed by a diaphragm-actuated closure member 317.
The port 316 is connected to the main gas supply conduit 20. An
open port 308 in the chamber 315 is connected to the conduit 306. A
port 318 in the chamber 314 is connected to the downstream conduit
35. A spring 319 helps bias the diaphragms 312 and 313 and the
closure member 317. In addition to the spring 319, pressure from
the downstream conduit 35 is applied to the chamber 314 during the
inspiratory phase to oppose the control pressure in the chamber
311, thus preventing the valve 310 from opening during the
inspiratory phase.
When the pressure in the chamber 311 rises above its critical level
(say, 10 psig) by virtue of a certain time during which gas passes
from the main supply conduit through the sigh frequency control
valve 301, the port 316 is opened, and gas at high pressure flows
from the main gas supply conduit 20 by the port 316, chamber 315,
and port 308, into the conduit 306. As a result, the chambers 334
and 344 are pressurized and the valves 339 and 349 are moved.
Depending upon whether the valve 12 is in "pressure-cycled" or
"volume-cycled" position, either the "pressure-cycled"
communication control valve 330 will connect the conduit 139 from
the pressure controller 130 to the airway conduit 113, or the
"volume-cycled" communication control valve 340 will connect the
conduit 263 to the conduit 323, thereby adding the capacity of the
chamber in the cylinder 321 to the capacity of the chamber 252.
Thus, a sigh is produced in either volume-cycled or pressure-cycled
operation.
THE RESET VALVES 350 AND 380 (FIG. 1C)
In order to reset everything in the sigh device, a series of
additional valves is used.
First, the valve 380 is used to reset the main control valve. The
valve 350 may be substantially identical to the main valve 30. It
has a large-area diaphragm 381 and a small-area diaphragm 382,
defining chambers 383, 384, and 385. The chamber 385 has an inlet
port 386 connected to the conduit 302, and the port 386 is normally
closed by a diaphragm-actuated valve 387. The chamber 384 has a
port 388 connected to the conduit 306, and the chamber 383 is kept
at atmospheric pressure and contains a spring 389 that bears on the
diaphragm 381 to bias the valve 387 to a normally closed
position.
When the valve 310 opens its port 316 and gas flows from the main
gas supply conduit 20 into the conduit 306, the port 387 is opened,
and the conduit 302 and chamber 311 are bled to atmospheric
pressure. The pressure in the chamber 314 then closes the port 316.
Thus the control valve 310 is open only briefly, but its closure
leaves pressure in the conduit 306. The valve 380 remains open
until the pressure in the conduit 306 is reduced.
The control valve 350, also like the valve 30, is normally closed.
The valve 350 has a large-area diaphragm 351 and a small-area
diaphragm 352 providing chambers 353, 354 and 355. The chamber 355
has a port 356 connected to the conduit 306 that is opened and
closed by a closure member 357, and is bled to atmosphere when a
net pressure of 10 psig is created in the chamber 354 to oppose the
force of a biasing spring 359. The chamber 353 is connected to the
conduit 35, and the chamber 354 is connected to a conduit 358.
During the inspiratory phase, the pressure from the downstream
conduit 35 is applied to both sides of the main diaphragm 351,
directly to one side and through a check valve 360 to the other
side. Since there is no differential pressure, no force is created
at that time to oppose the spring 359.
A check valve 360 passes flow from the downstream conduit 35 main
valve into the conduit 358 and thence to the control chamber of the
control valve 350. It prevents back flow when the pressure in the
downstream conduit 35 drops.
The pressure release valve 370, which is like the valve 51, is
normally open. Control pressure supplied from the downstream
conduit 35 closes the valve 370 during the inspiratory phase. The
valve 370 has a diaphragm 371, dividing it into chambers 372 and
373. The chamber 372 is bled to the atmosphere and has a port 374
connected to the conduit 358 and closed by a valve 375 when the
pressure in the chamber 373 is high enough to overcome the bias of
a spring 376. The chamber 373 is connected by a port 377 to the
downstream conduit 35. In the inspiratory phase only, therefore,
the valve 375 is closed; otherwise the conduit 358 is bled to
atmosphere.
At the start of the expiratory phase, the pressure in the chamber
353 is released, as the main valve 30 is shut off and the
downstream conduit 35 bled to atmosphere. The pressure in the
chamber 354 is released gradually through the valve 370, when the
pressure release valve 370 opens. As a result, at the start of the
expiratory phase a differential pressure exists initially across
the diaphragm 351, this pressure opposes the spring force 359 and
opens the valve 350, bleeding the conduit 306 to atmosphere. As the
pressure on this side of the diaphragm 351 is completely released,
the valve 350 returns to a zero differential pressure condition and
closes. This completes the re-setting operation: the conduits 302,
306, and 358 are all at atmospheric pressure and all are shut off
from the atmospheric bleed in ready condition. A new interval
begins as pressure builds up in the chamber 311.
RELATION OF THE SIGH DEVICE 300 TO THE VALVE ASSEMBLY 12 (FIGS. 1B
AND 1C)
In the pressure-cycled mode, the manually operated valve 18
provides a communication between the pressure controller 130 and
the communication control valve 330, by the conduits 139 and 304,
the valve outlet 25, and the conduit 141. In the volume-cycled
mode, the communication line 139 between the pressure controller
130 and the communication control valve 330 is vented to atmosphere
by the inlet 336 and the port 390. The conduit 304 is at this time
vented to atmosphere through the inlet 85 of the valve 29 and its
outlet 86.
OPERATION OF THE SIGH DEVICE 300: PRESSURE-CYCLED (FIGS. 1B AND
1C)
In operation, in the pressure-cycled mode, the valve assembly 12 is
set to the pressure-cycled mode. A sigh is initiated when gas,
supply by the main internal supply conduit 20, is metered past the
sigh frequency control valve 301 into the control chamber of the
control valve 310, causing it to open at a predetermined pressure.
To assure that valve 310 stays in phase with the operation and
opens only during an expiratory phase, gas supplied by the
downstream conduit 35 is introduced to the opposite side of the
large diaphragm 312, preventing the valve 310 from opening during
the inspiratory phase.
When the valve 310 opens, gas supplied by the conduit 20 passes
into the control chambers 334, 344, and 384 of the valves 330, 340,
and 380 causing all three valves to open. When the valve 330 opens,
communication is established between the two chambers 116 and 117
of the pressure controller 130, activating the smaller diaphragm
133. When the valve 340 opens, it establishes communication between
the inspiratory timer 250 and the sigh volume control 320; but with
the supply pressure of the inspiratory timer 250 shut off at the
valve assembly 12, the effect of opening this communication is
void. However, opening the valve 380 releases the control pressure
of the valve 310 to atmosphere, causing the valve 310 to close.
After the valve 310, closes, the pressure in the control chambers
of the valves 330, 340, and 380 remains until the completion of the
inspiratory phase.
At the end of the inspiratory phase, the differential pressure
created in the valve 350 by a pressure drop in the downstream
conduit 35 causes the valve 350 to open and the control pressure in
the valves 330, 340 and 380 and the conduit 306 is exhausted to
atmosphere. Further decrease of pressure in the downstream line
causes the pressure release valve 370 to open, and the pressure in
the control chamber 354 of the valve 350 is gradually exhausted to
atmosphere. After release of pressure in the control chamber 354 of
the valve 350, the valve 350 returns to its closed position. Now a
new period of the sigh frequency starts.
In this mode, the sigh frequency control 301 is the only control
used. It provides for an "off" position, and a graduation of 2, 4,
6, 8 and 10 sighs per hour. During a sigh cycle, the pressure is
increased by 60 per cent of its setting.
OPERATION OF THE SIGH DEVICE 300: VOLUME-CYCLED MODE
In the volume-cycled mode, the valve assembly 12 is set to the
volume-cycled mode. The operation of the sigh device 300 is similar
to that described in the pressure-cycled mode with the following
exceptions:
1. The control chamber 252 of the inspiratory timer 250
communicates with the sigh volume control 320 through the
communication control valve 340.
2. The communication line 139 between the two chambers 116 and 117
in the pressure controller 130 is vented to atmosphere through the
valve 29.
The sigh volume control 320 is adjustable within a range of zero to
one hundred per cent increase of the tidal volume setting. The
increase in tidal volume is obtained through a proportional
increase of the inspiratory time.
In the volume-cycled mode, the sigh frequency control 301 is used
in the same way as in the pressure-cycled mode. Thus, the sigh
frequency control 301 pneumatically:
1. Generates a trigger signal when the sigh-frequency cycle time is
reached and the ventilator is in the expiratory phase;
2. The trigger signal resets the sigh frequency timer to zero;
3. The trigger signal
a. opens the circuit to an additional capacity in the inspiratory
timer 250, and
b. maintains the circuit open as the ventilator switches to the
inspiratory phase;
4. The trigger signal returns to zero as the ventilator switches to
the next expiratory phase;
5. This last action, in turn,
a. starts the sigh frequency timer,
b. closes the circuit to the additional capacity in the inspiratory
timer 250, and
c. opens the additional capacity to atmosphere.
To those skilled in the art to which this invention relates, many
changes in construction and widely differing embodiments and
applications of the invention will suggest themselves without
departing from the spirit and scope of the invention. The
disclosures and the description herein are purely illustrative and
are not intended to be in any sense limiting.
* * * * *