U.S. patent number 3,756,229 [Application Number 05/097,933] was granted by the patent office on 1973-09-04 for ventilator.
This patent grant is currently assigned to Veriflo Corporation. Invention is credited to Louis A. Ollivier.
United States Patent |
3,756,229 |
Ollivier |
September 4, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
VENTILATOR
Abstract
A fully pneumatic ventilator capable of both pressure-cycled and
volume-cycled operation. A flow controller operates on the basis of
a difference between two control pressures, the lesser of which
gradually increases during each inspiratory phase of a breathing
cycle, to give a flow which starts out at a relatively high rate
and is gradually reduced until cut off. In volume-cycled operation,
the ventilator employs a cycle generator and a time-volume valve to
generate an inspiratory time, a ratio between the expiratory time
and the inspiratory time, and to set a volume to be delivered. The
time-volume valve enables independent setting of the volume and the
inspiratory time. The cycle generator and the time-volume valve
supply the flow controller with its control signals, and in turn
supplies the patient with the breathing gas. There is a relief
valve to avoid exerting too much pressure on the patient's airways,
and there is a vacuum relief preventing too great a suction upon
them. An override ends an expiratory phase and starts a new
inspiratory phase if the patient seeks to initiate inspiration. In
the pressure-controlled mode of operation an airway pressure sensor
and controller is employed, and the cycle generator and the time
portion of the time-volume valve are not used. Various safety
features are provided in both modes.
Inventors: |
Ollivier; Louis A. (Menlo Park,
CA) |
Assignee: |
Veriflo Corporation (Richmond,
CA)
|
Family
ID: |
22265831 |
Appl.
No.: |
05/097,933 |
Filed: |
December 14, 1970 |
Current U.S.
Class: |
128/204.26;
137/908 |
Current CPC
Class: |
A61M
16/00 (20130101); Y10S 137/908 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61m 016/00 () |
Field of
Search: |
;128/145.5,145.6,145.7,145.8 ;137/63R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Fourth Cranfield Fluidics Conference, Logic Circuit of Artifical
Respirators.
|
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Dunne; G. F.
Claims
I claim:
1. A volume-cycled fully pneumatically operated pneumatic
ventilator for connection to a supply of breathing gas, including
in combination:
pneumatically operated flow control means for providing breathing
gas during the inspiratory phase of each breathing cycle at a rate
dependent upon the difference between first and second control
pneumatic pressures, PC1 and PC2,
pneumatically operated ratio control means for generating said
pressure PC1 at a constant value and only during the inspiratory
phase, for delivering said pressure PC1 to said flow control means,
and for determining the ratio of inspiratory time to expiratory
time for each said cycle,
pneumatically operated time control means connected to said ratio
control means for determining an inspiratory time for each
breathing cycle, independently of the volume to be delivered, and
for generating said second control pneumatic pressure PC2 from said
pressure PC1 at a value always less than said pressure PC1 when the
pressure PC1 is present, and sending said pressure PC2 to said flow
control means,
said time control means increasing second control pressure PC2
during the inspiratory phase from a minimum value to a maximum
value, then decreasing it during the expiratory phase from said
maximum value to said minimum value, and
pneumatically operated volume control means connected to said time
control means and to said flow control means for determining,
independently of time, the volume of breathing gas delivered in
each inspiratory phase.
2. The ventilator of claim 1 having a patient airway conduit
connected to said flow control means for providing said breathing
gas to a patient, an exhalation valve in said patient airway
conduit, and control means for actuating said exhalation valve in
synchronization with said time control means, for opening said
exhalation valve during each said expiratory phase and closing it
during each said inspiratory phase.
3. The ventilator of claim 1 wherein said time control means is
connected to said ratio control means for receiving said pressure
PC1 by a parallel network of a check valve and a restriction, means
for opening said check valve during each inspiratory phase for
rapid flow of gas at said PC1 pressure and for closing it during
each expiratory phase, so that said PC2 pressure flows back only
through said restriction, said restriction being sized to be
effective at the shorter values of the time setting, said
ventilator also having means comprising a part of said ratio
control means for bleeding said pressure PC1 to atmosphere at the
beginning of each expiratory phase.
4. The ventilator of claim 1 having
a manually actuated sigh valve connected to said time control means
by a conduit into which said PC2 pressure is delivered, and
a sigh chamber to which gas from said conduit is admitted when said
manually actuated sigh valve is opened, thereby increasing the
capacity of the timing system and lengthening both the inspiratory
and expiratory phases proportionately, with proportional increase
in volume, while said manually actuated valve is held open.
5. The ventilator of claim 1 having pneumatically operated override
means for actuation by a patient able to initiate a new inspiratory
phase before completion of a controlled expiratory phase,
comprising
a patient airway conduit connected to said flow control means,
means connected to said patient airway conduit for sensing a
patient-induced vacuum of given value,
signal supply means for producing a pressure signal when said given
value is sensed, and
means for venting said PC2 pressure from its then pressure to its
minimum pressure upon application of said signal thereto.
6. A volume-cycled fully pneumatically operated pneumatic
ventilator, including in combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
pneumatically operated regulator means connected to said supply
means and having an outlet for said gas at a second, lower,
pressure P2,
pneumatically operated flow control means connected to said supply
means for providing breathing gas at a rate dependent upon the
difference between first and second control pneumatic pressures,
PC1 and PC2,
a patient airway conduit connected to said flow control means for
flow therethrough of said breathing gas, said conduit having an
exhalation valve,
pneumatically operated ratio control means connected to said
regulator means for generating from said pressure P2, the pressure
PC1 at a constant value, for delivering said pressure PC1 to said
flow control means, and for determining the ratio of inspiratory
time to expiratory time for each said cycle,
pneumatically operated time control means connected to said ratio
control means for determining an inspiratory time for each
breathing cycle, independently of the volume to be delivered, and
for generating said second control pneumatic pressure PC2 from said
pressure PC1 and sending it to said flow control means,
means in said ratio control means for causing said first control
pressure PC1 to be present only during the inspiratory phase and to
be constant during that phase, said second control pressure PC2
being always less than PC1 during the inspiratory phase and
increasing continually during that phase from a minimum value to a
maximum value,
means in said ratio control means for decreasing continually said
pressure PC2 during the expiratory phase from said maximum value to
said minimum value,
pneumatically operated volume control means connected to said time
control means and to said supply means at pressure P1 and to said
flow control means at a pressure P3 for determining, independently
of time, the volume of breathing gas to be delivered in each
inspiratory phase, and
pneumatically operated exhalation valve control means connected to
said time control means and said exhalation valve for synchronizing
the opening of the exhalation valve with said expiratory phase and
the closing thereof with said inspiratory phase.
7. A volume-cycled pneumatic ventilator, including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
regulator means connected to said supply means and having an outlet
for said gas at a second, lower, pressure P2,
flow control means connected to said supply means for providing
breathing gas at a rate dependent upon the difference between first
and second control pneumatic pressures, PC1 and PC2,
a patient airway conduit connected to said flow control means for
flow therethrough of said breathing gas, said conduit having an
exhalation valve,
ratio control means connected to said regulator means for
generating from said pressure P2, the pressure PC1 at a constant
value, for delivering said pressure PC1 to said flow control means,
and for determining the ratio of inspiratory time to expiratory
time for each said cycle,
time control means connected to said ratio control means for
determining an inspiratory time for each breathing cycle,
independently of the volme to be delivered, and for generating said
second control pneumatic pressure PC2 from said pressure PC1 and
sending it to said flow control means,
means in said ratio control means for causing said first control
pressure PC1 to be present only during the inspiratory phase and to
be constant during that phase, said second control pressure PC2
being always less than PC1 during the inspiratory phase and
increasing continually during that phase from a minimum value to a
maximum value,
means in said ratio control means for decreasing continually said
pressure PC2 during the expiratoy phase from said maximum value to
said minimum value,
volume control means connected to said time control means and to
said supply means at pressure P1 and to said flow control means at
a pressure P3 for determining, independently of time, the volume of
breathing gas to be delivered in each inspiratory phase, and
exhalation valve control means connected to said time control means
and said exhalation valve for synchronizing the opening of the
exhalation valve with said expiratory phase and the closing thereof
with said inspiratory phase,
said flow control means comprising
a diaphragm assembly of three diaphragms,
namely, first and second outer diaphragms of equal effective area
and a central diaphragm of smaller effective area,
a seat at one end of said diaphragm assembly,
a first chamber at one end of said diaphragm assembly closed by
said first outer diaphragm and having an outlet orifice toward and
away from which said seat moves, flow through said outlet orifice
being varied according to the position of said seat, said first
chamber having an inlet connected to said volume control means at
said pressure P3,
a second chamber between said first outer diaphragm and said
central diaphragm connected to said time control means at pressure
PC2,
a third chamber between said central diaphragm and said second
outer diaphragm connected to said ratio control means at pressure
PC1, and
a fourth chamber at the opposite end of said diaphragm assembly
from said first chamber and connected to said supply pressure
P1,
compression spring means in said fourth chamber bearing on said
diaphragm assembly, and
means for setting the degree of compression of said compression
spring means,
whereby as said pressure PC2 increases during the inspiratory phase
and said pressure P1 remains constant, the outflow from said
orifice decreases during said inspiratory phase from a maximum to a
minimum, and
whereby the outflow is shut off during said expiratory phase, as
said pressure PC1 is then atmospheric and PC2 is greater than
PC1.
8. The ventilator of claim 6 having pneumatically operated override
means for actuation by a patient able to initiate a new inspiratory
phase before completion of a controlled expiratory phase,
comprising
pneumatically operated means connected to said patient airway
conduit for sensing a patient-induced vacuum of given value,
pneumatically operated signal supply means for producing a pressure
signal when said given value is sensed, and
pneumatically operated means for venting said PC2 pressure from its
then pressure to its minimum pressure upon application of said
signal thereto.
9. A volume-cycled pneumatic ventilator including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
regulator means connected to said supply means and having an outlet
for said gas at a second, lower, pressure P2,
flow control means connected to said supply means for providing
breathing gas at a rate dependent upon the difference between first
and second control pneumatic pressures, PC1 and PC2,
a patient airway conduit connected to said flow control means for
flow therethrough of said breathing gas, said conduit having an
exhalation valve,
ratio control means connected to said regulator means for
generating from said pressure P2, the pressure PC1 at a constant
value, for delivering said pressure PC1 to said flow control means,
and for determining the ratio of inspiratory time to expiratory
time for each said cycle,
time control means connected to said ratio control means for
determining an inspiratory time for each breathing cycle,
independently of the volume to be delivered, and for generating
said second control pneumatic pressure PC2 from said pressure PC1
and sending it to said flow control means,
means in said ratio control means for causing said first control
pressure PC1 to be present only during the inspiratory phase and to
be constant during that phase, said second control pressure PC2
being always less than PC1 during the inspiratory phase and
increasing continually during that phase from a minimum value to a
maximum value,
means in said ratio control means for decreasing continually said
pressure PC2 during the expiratory phase from said maximum value to
said minimum value,
volume control means connected to said time control means and to
said supply means at pressure P1 and to said flow control means at
a pressure P3 for determining, independently of time, the volume of
breathing gas to be delivered in each inspiratory phase,
exhalation valve control means connected to said time control means
and said exhalation valve for synchronizing the opening of the
exhalation valve with said expiratory phase and the closing thereof
with said inspiratory phase,
override means for actuation by a patient able to initiate a new
inspiratory phase before completion of a controlled expiratory
phase, comprising
means connected to said patient airway conduit for sensing a
patient-induced vacuum of given value,
signal supply means for producing a pressure signal when said given
value is sensed, and
means for venting said PC2 pressure from its then pressure to its
minimum pressure upon application of said signal thereto,
said means for sensing comprising
a first diaphragm assembly in a housing and having a first
large-area diaphragm and a second small-area diaphragm, with a
first chamber between them connected to said airway conduit, the
other side of said first large-area diaphragm being vented to the
atmosphere, the other side of said second small-area diaphragm
being open to a second chamber vented to the atmosphere, and a seat
supported by said first diaphragm assembly, spring means in said
first chamber, and sensitivity control means for setting the
pressure exerted by said spring means against said first diaphragm
assembly, and
a detector assembly having
a second diaphragm assembly open at one end to said second chamber
and having a tubular extension that provides an axial conduit and
is opened and closed by said seat, spring means acting on said
second diaphragm assembly to urge it to open said axial conduit,
and a third chamber on the opposite end of said second diaphragm
asembly,
means for limiting the motion of said second diaphragm assembly to
a fixed amount, and
passage means through said second diaphragm assembly into said
third chamber from said axial conduit, said third chamber having an
inlet with a restricted orifice leading into said third chamber and
connected to said regulator at the pressure P2, and a port
connecting said third chamber to said signal supply means.
10. The ventilator of claim 9 having a relay for said detector
assembly comprising
a third diaphragm assembly having a pair of diaphragms of equal
effective areas defining a fourth chamber on one side of said third
diaphragm assembly, connected to the third chamber for maintaining
the same pressure as in said third chamber,
a fifth chamber between said diaphragms and vented to atmosphere,
and
a sixth chamber on the other side of said third diaphragm assembly,
said third diaphragm assembly having an axial opening and a
passageway opening from said sixth chamber into said fifth
chamber,
a seventh chamber joined to said sixth chamber by a port,
a poppet for opening and closing said port and having an extension
for engaging said axial opening and closing it when engaged by said
third diaphragm assembly, said third diaphragm assembly operating
when in contact with said poppet to open said port, said seventh
chamber having an inlet connected to said P2 pressure, and
a signal conduit connecting said sixth chamber to said means for
venting said PC2 pressure.
11. The ventilator of claim 6 having a manually adjustable
pneumatically operated pressure relief valve connected to said
patient airway conduit for venting pressure to atmosphere when it
exceeds a preset value.
12. The ventilator of claim 6 having a vacuum release valve
connected to said patient airway conduit for admitting air to said
airway conduit if the vacuum therein exceeds a predetermined
value.
13. The ventilator of claim 6 having a manually actuated sigh valve
connected to said pressure PC2 and a sigh chamber to which gas at
pressure PC2 is admitted when said manually actuated valve is
opened, thereby increasing the capacity of the timing system and
lengthening both the inspiratory and expiratory phases
proportionately, with proportional increase in volume, while said
manually actuated valve is held open.
14. The ventilator of claim 6 having
a control conduit connecting said exhalation valve to said patient
airway conduit through a restriction and connecting exhalation
valve to said exhalation valve control means and
wherein said exhalation valve control means is connected to said
pressure PC1 and comprises
a diaphragm valve biased by a spring for venting said control
conduit to atmosphere during said expiratory phase,
said diaphragm valve being closed by said pressure PC1 overcoming
said bias spring when said pressure PC1 is present during said
inspiratory phase.
15. The ventilator of claim 6 having
pneumatically operated means for operating humidifying, nebulizing,
and high-pressure exhalation means through an operating conduit,
comprising
pneumatic relay means connected to said pressure PC1 and to said
pressure P3 for generating a pressure equal to PC1 and for
conducting it to said operating conduit during said inspiratory
phase and for bleeding said operating conduit to atmosphere during
said expiratory phase.
16. A fully pneumatic volume-cycled ventilator, providing
inspiratory phases alternating with expiratory phases, including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
regulator means connected to said supply means and having an outlet
for said gas at a second, lower, pressure P2,
pressure generating means connected to said regulator means for
generating from said pressure P2 a first control pneumatic pressure
PC1 upon the initiation of each inspiratory phase and holding said
pressure at a constant value until the end of said inspiratory
phase,
time control means connected to said pressure generating means for
determining an inspiratory time for each breathing cycle,
independently of the volume to be delivered, by generating a second
pneumatic pressure PC2 from said pressure PC1, said second control
presssure PC2 being always less than PC1 during the inspiratory
phase and increasing during that phase from a minimum value to a
maximum value, and for determining an expiratory time for the
breathing cycle by bleeding said first control pressure PC1 to
atmosphere upon the termination of each said inspiratory phase and
decreasing said second control pressure PC2 during the expiratory
phase from said maximum value to said minimum value,
ratio control means connected to said time control means for
determining the ratio of inspiratory time to expiratory time for
each breathing cycle,
flow control means connected to said supply means and to said
pressures PC1 and PC2 for providing breathing gas at a rate
dependent upon the difference between first and second control
pneumatic pressures, PC1 and PC2,
a patient airway conduit connected to said flow control means for
conducting said breathing gas and having exhalation valve
means,
exhalation valve control means connected to said exhalation valve
means and to said time control means for synchronizing said
exhalation valve with said inspiratory and expiratory phases,
and
volume control means connected to said supply means, said time
control means and to said flow control means at a pressure P3 for
determining, independently of time, the volume of breathing gas
delivered in each inspiratory phase by (1) varying the flow rate
whenever the time is varied so that the volume delivered during the
set time remains unchanged and by (2) enabling additional variation
of the flow rate for any one time setting for changing the volume
delivered while the time remains unchanged.
17. The ventilator of claim 16 having
a control conduit connecting said exhalation valve means to said
patient airway conduit through a restriction and connecting said
exhalation valve to said exhalation valve control means and
wherein said exhalation valve control means comprises
a diaphragm valve biased by a spring for venting said control
conduit to atmosphere during said expiratory phase,
said diaphragm valve being connected to said pressure PC1 and being
closed by said pressure PC1 overcoming said bias spring when said
pressure PC1 is present during said inspiratory phase.
18. The ventilator of claim 16 having
means for operating humidifying, nebulizing, and high-pressure
exhalation means through an operating conduit, comprising
relay means connected to said pressure PC1 and to said pressure P3
for generating a pressure equal to PC1 and for conducting it to
said operating circuit during said inspiratory phase and for
bleeding said operating conduit to atmosphere during said
expiratory phase.
19. A volume-cycled fully pneumatically operated pneumatic
ventilator for connection to a supply of breathing gas, including
in combination:
pneumatically operated pressure generating means for generating
from said supply a first control pneumatic pressure PC1 upon the
initiation of each inspiratory phase and holding said pressure at a
constant value until the end of said inspiratory phase,
pneumatically operated time control means connected to said
pressure generating means for determining an inspiratory time for
each breathing cycle, independently of the volume to be delivered,
by generating a second pneumatic pressure PC2 from said pressure
PC1, said second control pressure PC2 being always less than PC1
during the inspiratory phase and increasing during that phase from
a minimum value to a maximum value, and for determining an
expiratory time for the breathing cycle by bleeding said first
control pressure PC1 to atmosphere upon the termination of each
said inspiratory phase and decreasing said second control pressure
PC2 during the expiratory phase from said maximum value to said
minimum value,
pneumatically operated ratio control means connected to said time
control means for determining the ratio of inspiratory time to
expiratory time for each breathing cycle,
pneumatically operated flow control means connected to said supply
and to said pressures PC1 and PC2 for providing breathing gas at a
rate dependent upon the difference between first and second control
pneumatic pressures, PC1 and PC2,
a patient airway conduit connected to said flow control means and
including exhalation valve means,
pneumatically operated control means connected to said exhalation
valve means and to said time control means for synchronizing said
exhalation valve means with said inspiratory and expiratory phases,
and
pneumatically operated volume control means connected to said
supply, said time control means, and to said flow control means for
determining, independently of time, the volume of breathing gas
delivered in each inspiratory phase by (1) varying the flow rate
whenever the time is varied so that the volume delivered during the
set time remains unchanged and by (2) enabling additional variation
of the flow rate for any one time setting for changing the volume
delivered while the time remains unchanged.
20. The ventilator of claim 19 wherein said time control means is
connected to said pressure generating means for receiving said
pressure PC1 by a parallel network of a check valve and a
restriction, said check valve being opened during each inspiratory
phase for rapid flow of gas at said PC1 pressure and closed during
each expiratory phase, so that back flow to decrease said second
control pressure PC2 is only through said restriction, which is
sized to be effective at the shorter values of the time
setting.
21. A volume-cycled, completely pneumatically operated pneumatic
ventilator for connection to a supply of breathing gas, including
in combination:
pneumatic time control means for determining the inspiratory time
for each breathing cycle, independently of the volume of breathing
gas to be delivered, by generating from said supply a first control
pneumatic pressure PC1 upon the initiation of each inspiratory
phase and by generating a second control pneumatic pressure PC2
from said pressure PC1,
said first control pressure PC1 being present only during the
inspiratory phase and constant during that time and dropping to
atmospheric at the beginning of the expiratory phase, said second
control pressure PC2 being always less than PC1 during the
inspiratory phase and increasing during that phase from a minimum
value above atmospheric to a maximum value, then decreasing during
the expiratory phase from said maximum value to said minimum
value,
pneumatically operated ratio control means connected to said time
control means for determining the ratio of inspiratory time to
expiratory time for each breathing cycle,
a patient airway conduit having exhalation valve means,
pneumatically operated flow control means connected to said supply,
said ratio control means, said time control means, said volume
control means and said patient airway conduit, for providing
breathing gas from said supply to said patient airway conduit at a
rate dependent upon the difference between said first and second
control pneumatic pressures PC1 and PC2,
pneumatically operated control means connected to said exhalation
valve means and to said time control means for synchronizing the
operation of said exhalation valve means with said inspiratory and
expiratory phases, and
pneumatically operated volume control means connected to said
supply and said time control means for determining, independently
of time, the volume of breathing gas delivered in each inspiratory
phase.
22. The ventilator of claim 21 wherein said time control means is
connected to said ratio control means for receiving said pressure
PC1 by a parallel network of a check valve and a restriction, said
check valve being opened during each inspiratory phase for rapid
flow of gas at said PC1 pressure and closed during each expiratory
phase, so that back flow from said pressure PC2 during the
expiratory phase is only through said restriction, which is sized
to be effective at the shorter values of the time setting, said
ventilator also having means comprising part of said ratio control
means for bleeding said pressure PC1 to atmosphere at the beginning
of said expiratory phase.
23. The ventilator of claim 21 having
a manually actuated sigh valve connected to said time control means
by a conduit into which said PC2 pressure is delivered, and
a sigh chamber to which gas from said conduit is admitted when said
manually actuated sigh valve is opened, thereby increasing the
capacity of the timing system and lengthening both the inspiratory
and expiratory phases proportionately, with proportional increase
in the volume of breathing gas during said lengthened inspiratory
phase, while said manually actuated valve is held open.
24. A fully pneumatic volume-cycled pneumatic ventilator, providing
inspiratory phases alternating with expiratory phases, including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
regulator means connected to said supply means and having an outlet
for said gas at a second, lower, pressure P2,
a PC1 conduit,
a PC2 conduit,
a cycle generator having a housing with an inlet connected to the
outlet from said regulator means and having a first diaphragm
assembly with two diaphragms of different effective areas, with
atmospheric pressure between them, a first seat at one end bounded
by the smaller area diaphragm of said first diaphragm assembly,
adapted to close said inlet or to open it to a first chamber, said
first chamber having an outlet, a second chamber at the other end
bounded by the larger area diaphragm of said first diaphragm
assembly and having a port connected to said PC2 conduit, a
compression spring in said second chamber urging said first
diaphragm assembly to close said inlet, and an
inspiratory-time-to-expiratory-time ratio determining screw
assembly for regulating the compression of said spring,
a fixed-orifice bleed connected to the outlet of said first
chamber,
said cycle generator also having a second diaphragm assembly with
two diaphragms of different effective areas and a second seat, a
third chamber at one end bounded by the larger area diaphragm of
said second diaphragm assembly and having an inlet connected to the
outlet from said first chamber and an outlet leading to said PC1
conduit via a spring-urged check valve which transmits the pressure
of said first chamber to said PC1 conduit during each inspiratory
phase and prevents back flow from said PC1 conduit into said third
chamber at end of each expiratory phase, when said first seal
closes said inlet to said cycle generator and while said third
chamber bleeds to atmosphere through said fixed orifice bleed, a
fourth chamber between the diaphragms of said second diaphragm
assembly having a port connected to said PC2 conduit, and a fifth
chamber at the other end bounded by the smaller area of diaphragm
of said second diaphragm assembly having an inlet connected to said
PC1 conduit, normally closed by said second seat and an outlet
vented to atmosphere, for venting said PC1 conduit during each said
expiratory phase,
an inspiratory-time-determining valve, having an inlet connected to
said PC1 conduit and an outlet connected to said PC2 conduit, for
supplying said PC2 conduit with the gas at a varying pressure PC2
always lower than the pressure PC1 during each inspiratory phase,
said time-determining valve having a logarithmically shaped stem
and orifice and time-setting means for determining the position of
said stem relative to said orifice and therefore the flow rate from
said PC1 conduit to said PC2 conduit, said PC2 pressure building up
continuously during each said inspiratory phase to a maximum value
set by said ratio-determining screw assembly, and continuously
decreasing during said expiratory phase by bleeding through said
PC1 conduit to atmosphere until it reaches a minimum value which is
a set amount lower than said maximum value, the set amount being
determined by the ratio of the effective areas of the two
diaphragms of said first diaphragm assembly,
an inspiratory volume-determining valve, having an inlet connected
to said supply means, an outlet at a reduced pressure P3 and at a
flow determined by the relative position of a plug within an
orifice, the plug being shaped so that its position sets the area
of passage according to a logarithmic function, first flow-setting
means determining the position of said plug relative to its orifice
entirely independently of said time-setting means and second
flow-setting means also determining the position of said plug
relative to its orifice in inverse ratio to the setting of said
time, so that the volume delivered by said volume-determining valve
remains the same when the time determining means alone is
varied,
a flow controller having a third diaphragm assembly of three
diaphragms including two outer diaphragms of equal effective area
and a central diaphragm of smaller effective area and having a
third seat at one end, a sixth chamber at one end of said third
diaphragm assembly having an outlet orifice toward and away from
which said third seat moves, flow through said outlet orifice being
varied according to the position of said third seat, said sixth
chamber having an inlet connected to the outlet from said
volume-determining valve at said pressure P3,
said flow controller also having a seventh chamber adjacent to said
sixth chamber, between said first outer diaphragm and the central
diaphragm with a port connected to said PC2 conduit, an eighth
chamber adjacent to said seventh chamber between the central
diaphragm and the second outer diaphragm with a port connected to
said PC1 conduit, and a ninth chamber at the opposite end of said
diaphragm assembly from said sixth chamber with a port connected to
said supply pressure P1, a compression spring in said ninth chamber
bearing on said third diaphragm assembly, and means for setting the
compression of said compression spring,
whereby as said pressure PC2 increases during the inspiratory phase
and said pressure PC1 remains constant, the outflow from said
outlet orifice decreases from a maximum at the start of the
inspiratory phase to a minimum at the end of the phase, and
whereby the flow is shut-off during the expiratory phase as PC1 is
at atmospheric pressure and PC2 is greater than PC1,
a patient airway conduit connected to said outlet orifice of said
flow controller,
an exhalation valve in said patient airway conduit, and
exhalation valve control means for said exhalation valve connected
thereto and to said cycle generator for synchronizing the opening
and closing of said exhalation valve with the initiation,
respectively, of said expiratory and inspiratory phases.
25. The ventilator of claim 24 having
a control conduit connecting said exhalation valve to said patient
airway conduit through a restriction and connecting said exhalation
valve to said exhalation valve control means and
wherein said exhalation valve control means is connected to said
PC1 conduit and comprises
a diaphragm valve biased by a spring for venting said control
conduit to atmosphere during said expiratory phase,
said diaphragm valve being closed by said pressure PC1 overcoming
said bias spring when said pressure PC1 is present during said
inspiratory phase.
26. The ventilator of claim 24 having
means for operating humidifying, nebulizing, and high-pressure
exhalation means through an operating conduit, comprising
relay means connected to said PC1 conduit and to the outlet of said
inspiratory volume-determining valve at said pressure P3 for
generating a pressure equal to PC1 and for conducting it to said
operating conduit during said inspiratory phase and for bleeding
said operating conduit to atmosphere during said expiratory
phase.
27. The ventilator of claim 24 wherein the inlet to said
inspiratory-time-determining valve is connected to said PC1 conduit
by a parallel network of a check valve and a restriction, said
check valve being opened during each inspiratory phase for rapid
flow of gas and closed during each expiratory phase, so that back
flow is only through said restriction, the restriction being sized
to be effective at the shorter expiratory times for which the
ventilator can be set.
28. The ventilator of claim 24 having an adjustable pressure relief
valve connected to said airway conduit for venting pressure to
atmosphere when it reaches a preset value.
29. The ventilator of claim 24 having a vacuum release valve
connected to said airway conduit for admitting air to said airway
conduit if the vacuum therein exceeds a predetermined value.
30. The ventilator of claim 24 having a manually actuated sigh
valve connected to said PC2 conduit and a sigh chamber to which gas
from said PC2 conduit is admitted when said manually actuated valve
is opened, thereby increasing the capacity of the timing system and
lengthening both the inspiratory and expiratory phases
proportionately, with proportional increase in volume, while said
manually actuated valve is held open.
31. The ventilator of claim 24 having override means for actuation
by a patient able to initiate a new inspiratory phase before
completion of a controlled expiratory phase, comprising means
connected to said patient airway conduit for sensing a
patient-induced vacuum of given value, signal supply means for
producing a pressure signal when said given value is sensed, and
means for venting said PC2 pressure conduit from its then pressure
to its minimum pressure upon application of said signal
thereto.
32. The ventilator of claim 31 wherein said means for sensing
comprises a housing, a fourth diaphragm assembly in said housing
having two diaphragms, one large area diaphragm and one small area
diaphragm, with a tenth chamber between them connected to said
airway conduit, the end with large area diaphragm of said fourth
diaphragm assembly being vented to the atmosphere, the other end
being open to an eleventh chamber and having a fourth seat, spring
means in said tenth chamber, and sensitivity control means for
setting the pressure exerted by said spring means against said
diaphragm assembly,
a detector assembly having a fifth diaphragm assembly open at one
end to said eleventh chamber and having a tubular extension that
provides an axial conduit and is opened and closed by said fourth
seat, spring means acting on said fifth diaphragm assembly to urge
it to open said axial conduit, twelfth chamber on the opposite end
of said fifth diaphragm assembly, the motion of said fifth
diaphragm assembly being limited to a fixed amount by internal
configuration of said eleventh and twelfth chambers, a port venting
said eleventh chamber to atmosphere, a passage through said fifth
diaphragm assembly into said twelfth chamber from said axial
conduit, an inlet connected to said P2 conduit and having a
restricted orifice leading into said twelfth chamber, and a port
connecting said twelfth chamber to said signal supply means.
33. The ventilator of claim 32 having a relay for said detector
assembly, comprising a sixth diaphragm assembly having a pair of
diaphragms of equal effective area defining a thirteenth chamber on
one side of said sixth diaphragm assembly, connected to the twelfth
chamber for maintaining the same pressure as in said twelfth
chamber, a fourteenth chamber between said diaphragms and vented to
atmosphere, and a fifteenth chamber on the other side of said sixth
diaphragm assembly, said sixth diaphragm assembly having an axial
opening and a passageway opening from said fifteenth chamber into
said fourteenth chamber, a sixteenth chamber joined to said
fifteenth chamber by a port, a poppet for opening and closing said
port and having an extension for engaging said axial opening and
closing it when engaged by said sixth diaphragm assembly, said
sixth diaphragm assembly operating when in contact with said poppet
to open said port, and an inlet into said sixteenth chamber
connected to said P2 pressure, and a signal conduit connecting said
fifteenth chamber to said means for venting PC2.
34. A fully pneumatic pressure-cycled ventilator including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure
regulator means connected to said supply means and having an outlet
for said gas at a second, lower, pressure P2,
an airway pressure sensor and controller comprising a housing, a
first diaphragm assembly in said housing having a large first
diaphragm, a smaller diaphragm, a first chamber between them having
a port, a second chamber on the other side of said large first
diaphragm, vented to the atmosphere, a third chamber on the other
side of said second diaphragm, a seat on said first diaphragm
assembly in said third chamber, a first spring in said first
chamber bearing against said first diaphragm assembly, and a
second, lighter, spring bearing on said large diaphragm in said
second chamber,
sensitivity control means for varying the pressure of said first
spring against said first diaphragm assembly,
a second diaphragm assembly having a pair of diaphragms of
different effective areas and open at one end to said second
chamber, with a third spring in said second chamber urging said
second diaphragm assembly away from said first diaphragm assembly,
a fourth chamber between said pair of diaphragms having a port, the
other end of said second diaphragm assembly being open to
atmospheric pressure,
said first and second diaphragm assemblies each having extensions
causing said second diaphragm assembly to exert force on said first
diaphragm assembly when pressure in said fourth chamber is
sufficient to overcome the force of said third spring and the
pressure in said first chamber,
a detector assembly having a third diaphragm assembly open to said
third chamber and carrying a tubular extension that provides an
axial conduit having an end facing said seat and opened and closed
by said seat, a fourth spring acting on said third diaphragm
assembly to urge it to open said axial conduit away from said seat,
a fifth chamber on the opposite side of said third diaphragm
assembly from said third chamber, the motion of said third
diaphragm assembly being limited to a fixed amount by internal
configurations of said third and fifth chambers, a port venting
said third chamber to atmosphere, a passage through said third
diaphragm assembly into said fifth chamber from said axial conduit,
an inlet connected to the outlet from said regulator means at
pressure P2 and having a restricted orifice leading into said fifth
chamber, and an outlet port from said fifth chamber,
a control conduit having its pressure controlled by and identical
to that of said outlet port of said fifth chamber,
a second pressure regulator for setting the pressure applied to
said fourth chamber, having an inlet connected to said control
conduit and having an outlet,
a conduit connected to said outlet of said second pressure
regulator having a fixed bleed to atmosphere and connected to the
port to said fourth chamber,
a flow valve, having an inlet connected to said supply means at
said pressure P1, a plug, an orifice, an outlet for gas at a
reduced pressure P3 and at a flow determined by the relative
position of said plug and said orifice, and flow-setting means
determining the position of said plug relative to said orifice,
a flow controller having a fourth diaphragm assembly having three
diaphragms including two outer diaphragms of equal effective area
and a central diaphragm of smaller effective area and having a
second seat at one end, a sixth chamber at one end of said fourth
diaphragm assembly having an outlet orifice toward and away from
which said second seat is moved, flow through said outlet orifice
being varied according to the position of said second seat, said
sixth chamber having an inlet connected to the outlet from said
flow valve at said pressure P3,
said flow controller also having a seventh chamber adjacent to said
sixth chamber, between said first outer diaphragm and the central
diaphragm of said fourth assembly with a port connected to
atmosphere, an eighth chamber adjacent to said seventh chamber
between the central diaphragm and second outer diaphragm with a
port connected to said control conduit, and a ninth chamber at the
opposite end of said fourth diaphragm assembly from said sixth
chamber, with a port connected to said supply pressure P1, a
compression spring in said ninth chamber bearing on said fourth
diaphragm assembly, and means for setting the compression of said
compression spring,
a patieairway conduit connected to said outlet orifice of aid flow
controller and connected to the port of said first chamber,
an exhalation valve in said patient airway conduit, and
exhalation valve control means connected to said control conduit
for opening said exhalation valve during each said expiratory phase
and closing it during each said inspiratory phase.
35. The ventilator of claim 34 having
a second control conduit connecting said exhalation valve to said
patient airway conduit through a restriction and connecting said
exhalation valve to said exhalation valve control means, and
wherein said exhalation valve control means comprises
a diaphragm valve biased by a spring for venting said second
control conduit to atmosphere during said expiratory phase,
said diaphragm valve being closed by said control pressure
overcoming said bias spring when said control pressure PC1 is above
atmospheric during said inspiratory phase.
36. The ventilator of claim 34 having
means for operating humidifying, nebulizing, and high-pressure
exhalation means through an operating conduit, comprising
relay means connected to said control pressure and to said pressure
P3 for generating a pressure equal to said control pressure and for
conducting it to said operating conduit during said inspiratory
phase and for bleeding said operating conduit to atmosphere during
said expiratory phase.
37. The ventilator of claim 34 having
pneumatic means connected to said control pressure for determining
a constant time interval,
means for beginning said time interval at the beginning of each
said expiratory phase, and
means actuated upon completion of said time interval for initiating
a new said inspiratory phase unless said inspiratory phase has
already been started by patient effort during said time
interval,
said new inspiratory phase being subject to the stated conditions
of the control pressure generating means.
38. The ventilator of claim 34 having an adjustable pressure relief
valve connected to said airway conduit for venting pressure to
atmosphere when it reaches a preset value.
39. The ventilator of claim 34 having a vacuum release valve
connected to said airway conduit for admitting air to said airway
conduit if the vacuum therein exceeds a predetermined value.
40. The ventilator of claim 34 having a relay for said detector
assembly, comprising
a fifth diaphragm assembly having a pair of diaphragms of equal
effective area defining a tenth chamber on one end, connected to
said fifth chamber for maintaining the same pressure as in said
fifth chamber, an eleventh chamber between said diaphragms and
vented to atmosphere, and a twelfth chamber on the other end, said
fifth diaphragm assembly having an axial opening in said twelfth
chamber leading to a passageway opening into said eleventh chamber,
and
a patient airway chamber joined to said twelfth chamber by said
port, a poppet for opening and closing said port and having an
extension for engaging said axial opening and closing it when
engaged by said fifth diaphragm assembly, said fifth diaphragm
assembly operating when in contact with said poppet to open said
port, and
an inlet into said thirteenth chamber connected to said P2
pressure, and an outlet connecting said twelfth chamber to said
control conduit.
41. A ventilator operated solely by pneumatics and capable of both
pressure-cycled and volume-cycled operation, including in
combination:
supply means for supplying a breathing gas at a first regulated
pressure P1,
pneumatically operated regulator means connected to said supply
means and having an outlet for said gas at a second, lower,
pressure P2,
pneumatically operated pressure reduction and flow-rate determining
means having an inlet connected to said supply means at the
pressure P1 and having an outlet for gas at pressure P3,
pneumatically actuated flow control means having an inlet connected
to said flow-rate determining means and having an outlet and
pneumatically controlled means for opening said outlet only when a
first control pressure PC1 is above a second control pressure PC2
and for then supplying said outlet with breathing gas from its said
inlet at a flow rate dependent on the instantaneous difference
between said first and second control pressures,
a patient airway conduit connecting said outlet of said flow
control means to a patient to be ventilated,
a master operations switch connected to said regulator means and
having a first "volume-cycled" position and a second
"pressure-cycled" position,
first pneumatically operated pressure generating means connected to
said master operations switch for generating from said pressure P2
the pressure PC1 at a constant value, for delivering said pressure
PC1 to said flow control means as said first control pressure when
said switch is in "volume-cycled" position,
pneumatically operated time control means connected to said first
pressure generating means for determining an inspiratory time for
each breathing cycle, independently of the volume to be delivered,
by generating the pressure PC2 from said pressure PC1 at a value
lower than PC1 during said inspiratory phase and sending it to said
flow control means as said second control pressure PC2 by causing
said pressure PC1 to be present only during the inspiratory phase
and to be constant during that phase, said pressure PC2 increasing
continually during that phase from a minimum value to a maximum
value, always less than said pressure PC1 during said inspiratory
phase and for determining an expiratory time for a breathing cycle,
by bleeding said first control pressure PC1 to atmosphere upon the
termination of each said inspiratory phase and by decreasing
continually said pressure PC2 during the expiratory phase from said
maximum value to said minimum value,
pneumatically operated ratio control means connected to said time
control means for determining the ratio of inspiratory time to
expiratory time for each breathing cycle,
pneumatically operated volume-control means connected to said time
control means and to said flow-rate determining means for
determining, independently of time, the volume of breathing gas to
be delivered in each inspiratory phase of said volume-cycled
mode,
second pneumatically operated pressure generating means connected
to said regulator means and to said switch when said switch is in
"pressure cycled" position, for generating a pressure PC3 when the
pressure in said patient airway conduit drops below a first
predetermined level, indicating an attempt by the patient to
initiate an inspiratory phase of a breathing cycle,
pnuematically operated means for ceasing generation of said
pressure PC3 and for bleeding it to atmosphere when the pressure in
said airway conduit attains a second predetermined level well above
said first predetermined level,
said operations switch acting in said "pressure-cycled" position to
connect said pressure PC3 to said flow control means as said first
control means and for bleeding said pressure PC2 to atmospheric and
for disconnecting said pressure PC1 from said flow control means,
said operations switch acting in said "volume-cycled" position to
disconnect said pressure PC3 from said flow control means.
42. The ventilator of claim 41 having
an exhalation valve in said patient airway conduit, and
exhalation valve control means for opening said exhalation valve
during each said expiratory phase and closing it during each said
inspiratory phase.
43. The ventilator of claim 42 having
a control conduit connecting said exhalation valve to said patient
airway conduit through a restriction and connecting said exhalation
valve to said exhalation valve control means and
wherein said exhalation valve control means is connected by said
switch to said PC1 in the "volume-cycled" position and to said PC3
in the "pressure-cycled" position and comprises
a diaphragm valve biased by a spring for venting said control
conduit to atmosphere during said expiratory phase,
said diaphragm valve (a) being closed, when said master operations
switch is in "volume-cycled" position, by said pressure PC1
overcoming said bias spring when said pressure PC1 is present
during said inspiratory phase and (b) being closed, when said
master operations switch is in "pressure-cycled" position by said
pressure PC3 overcoming said bias spring when PC3 is above
atmospheric during said inspiratory phase.
44. The ventilator of claim 41 having
pneumatically operated means for operating humidifying, nebulizing,
and high-pressure exhalation means through an operating conduit,
comprising
pneumatic relay means, connected by said switch, when in the
"volume-cycled" position to said pressure PC1 and, when in the
"pressure-cycled" position to said pressure PC3, said relay means
in both modes being connected to said pressure P3, for generating a
pressure equal to PC1 or PC3, according to the position of said
switch, and for conducting it to said operating conduit during said
inspiratory phase and for bleeding said operating conduit to
atmosphere during said expiratory phase.
45. The ventilator of claim 41 having
pneumatic means connected to said pressure PC3 for determining a
constant time interval,
pneumatically operated means for beginning said time interval at
the beginning of each said expiratory phase, and
pneumatically operated means actuated upon completion of said time
interval for initiating a new said inspiratory phase unless said
inspiratory phase has already been started by patient effort during
said time interval, said new inspiratory phase being subject to the
stated conditions of the second pressure generating means.
46. The ventilator of claim 41 having an adjustable pressure relief
valve connected to said patient airway conduit for venting pressure
to atmosphere, when it reaches a preset value.
47. The ventilator of claim 41 having a vacuum release valve
connected to said patient airway conduit for admitting air to said
airway conduit if the vacuum therein exceeds a predetermined
value.
48. The ventilator of claim 41 having a manually actuated sigh
valve connected to said PC2 conduit and a sigh chamber to which gas
from said PC2 conduit is admitted when said manually actuated valve
is opened, thereby increasing the capacity of the timing system and
lengthening both the inspiratory and expiratory phases
proportionately, with proportional increase in volume, while said
manually actuated valve is held open in said "volume-cycled"
mode.
49. The ventilator of claim 41 having pneumatically operated
override means for actuation in the "volume-cycled" mode by a
patient able to initiate a new inspiratory phase before completion
of a controlled expiratory phase, comprising a signal conduit for
transmitting a pressure signal from said second pressure generating
means at pressure PC3 when the pressure in said patient airway
conduit drops below said first predetermined level and means
connected to said signal conduit for venting said PC2 pressure
conduit from its then pressure to its minimum pressure upon receipt
of said signal.
50. A fully pneumatically operated ventilator of the type free from
electric circuits and supplying breathing gas to a patient via an
airway conduit during an inspiratory phase and stopping the supply
during an expiratory phase,
characterized by incorporating two modes of operation, (a) a
volume-cycled mode in which the ventilator supplies a predetermined
volume of breathing gas to the airway conduit over a predetermined
time during the inspiratory phase and then is actuated to the
expiratory phase for a predetermined time, and (b) a pressure
cycled mode in which the ventilator supplies the breathing gas to
the airway conduit whenever the pressure in the airway conduit
drops below a predetermined level and stops the supply whenever a
predetermined higher pressure is attained in the airway conduit,
said ventilator comprising
gas inlet means shared by both said modes,
gas regulator means connected to said inlet means and shared by
both said modes,
pneumatically operated flow control means shared by both said modes
and separately connected to said inlet means and to said gas
regulator means for controlling the rate of flow of gas to the
patient,
gas outlet means connected to said flow control means and shared by
both said modes,
a pneumatically operated exhalation valve shared by both said
modes, in said airway conduit,
pneumatically actuated pneumatic control switch means shared by
both said modes and separately connected to said inlet means and to
said regulator means and connected to said exhalation valve for
operating said exhalation valve,
pneumatically operated pressure sensing means shared by both said
modes and connected to said outlet means and to said regulator and
to said flow control means for changing said ventilator from an
expiratory phase to an inspiratory phase when the patient makes an
effort of a predetermined negative pressure sensed by said sensing
means, and
a two-position manually operated master operation switch for
selecting which of said two modes is to be used at any one time,
said master operation switch having a single handle for switching
from one mode to the other by a single simple movement.
51. The ventilator of claim 50 characterized by said
pressure-cycled mode comprising
a flow-rate-determiner and pressure-reducer means having an inlet
connected to the supply of breathing gas,
said flow control means having an inlet connected to said
flow-rate-determiner and pressure-reducer means and having
pneumatic control means for opening its outlet when the control
pressure is above a predetermined minimum pressure and for closing
it when the control pressure drops below the predetermined minimum
pressure,
said patient airway conduit connecting the outlet of the flow
control means to the patient to be ventilated through said outlet
means, and
control pressure generator means connected directly to the supply,
to the flow control means, and to the patient airway conduit, for
generating the control pressure when the pressure in said airway
conduit drops below a first predetermined level, indicating an
attempt by the patient to initiate an inspiratory phase of a
breathing cycle, and for ceasing generation of the control pressure
and for bleeding said control pressure to atmosphere when the
pressure in said airway conduit attains a second predetermined
level well above the first predetermined level, thereby initiating
the expiratory phase of the breathing cycle.
52. The ventilator of claim 51 characterized in that said control
pressure generator means includes
a first sensor for sensing the first predetermined level,
a lock actuated by said first sensor for locking the control
pressure generator means in generating position upon attainment of
the first predetermined level,
a second sensor for sensing the second predetermined pressure,
and
an unlocker actuated by the second sensor for unlocking said lock
upon attainment of the second predetermined level.
53. The ventilator of claim 51 characterized by
a pneumatic timer connected to the control pressure for determining
a constant time interval,
a first initiator for beginning the constant time interval at the
beginning of each expiratory phase, and
a second initiator actuated upon completion of the time interval
for initiating a new said inspiratory phase unless the inspiratory
phase has already been started by patient effort during said time
interval,
the new inspiratory phase being subject to the stated conditions of
the control pressure generator means.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved ventilator capable of both
volume-cycled and pressure-cycled operation.
Heretofore, the ventilators on the market have been either cycled
by pressure or cycled by volume, and they have not been capable of
shifting from one form of operation to the other, as is the
ventilator of the present invention, where a simple rotation of a
selector knob accomplishes the shift. Hence, whereas prior-art
ventilators were strictly limited to one of these two types of
operation, the present is able to do both. It therefore eliminates
the need for an extra machine. Moreover, it is very compact, --
more compact than any of the volume-cycled ventilators heretofore
in use. The present invention enables a single machine to be very
versatile and to be adapted to various needs of patients and to the
desires of doctors.
A difficulty with ventilators heretofore on the market has been
that their flow pattern of delivery has been capable of little, if
any, adjustment. Each of them has had a basically fixed flow
pattern. It is desirable, from the patient's standpoint, to have a
large initial flow at the beginning of the inspiratory phase and to
have the flow diminish gradually towards a smaller flow at the end
of the expiratory phase. The ventilator of the present invention
provides a flow pattern which decreases from a maximum value at the
beginning of the inspiratory phase to a minimum value at the end of
the inspiratory phase. The relationship between maximum and minimum
values is maintained independently of the duration of the
inspiratory phase and independently of the flow level required to
supply the desired volume during the inspiratory phase.
The ventilator of this invention, when used in volume-cycled
operation, provides for setting a ratio between the inspiratory
time and 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 on
the basis that, for a given time to inhale, it may be desirable to
vary the time to exhale.
In its volume-cycled mode the ventilator of this invention is also
capable of a separate noninteracting adjustment of the volume and
the inspiratory time, so that either the time or the volume can be
changed without significantly 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 accommodates these
adjustments.
The device senses the patient's airway pressure, and the patient
can override the normal cycle and initiate a new inspiratory phase
in the volume-cycled mode, the effect of the resulting vacuum being
used to trigger this action. In the pressure-cycled mode, the
patient's airway pressure generally initiates the new inspiratory
phase, but there is also a timing device for initiating a new
inspiratory cycle if the patient should fail to do so after a
predetermined period. Upon initiation of a new inspiratory phase,
the ventilator feeds the breathing gas to him at a doctor-set rate
and manner. In both modes of operation, the patient's safety is
assured by a pressure-activated safety relief valve that vents
excessive airway pressure to the atmosphere; excessive vacuums are
similarly relieved from the atmosphere through a vacuum relief
valve.
In normal breathing, from time to time a person will take an
exceptionally deep breath and then exhale that deep breath. This
sigh may be useful in maintaining or inducing health conditions.
Most breathing machines make no provision for other than consistent
uniformity. The device of the present invention makes it possible
for the doctor manually to cause such a sign whenever he wishes and
to continue to induce sighs for as long an interval as he wishes,
each sigh increasing the inspiratory phase in both volume and time
by about fifty percent, while maintaining the ratio between
inspiratory time and expiratory time, therefore increasing the
duration of the expiratory time also by about 50 percent. This is
done without having to change the regular cycling, so that when the
doctor releases the sigh actuator, the normal cycle returns.
An inspiratory phase may be initiated at any time during the
expiratory phase by pushing a manual start button. The pressure and
the vacuum are indicated on a gauge.
SUMMARY OF THE INVENTION
In volume-cycled operation the invention controls the inspiratory
time, the ratio of the inspiratory time to the expiratory time, the
volume, and the sensitivity. A pneumatic cycle generator initiates
an inspiratory phase during which a flow controller delivers
breathing gas to the patient. The duration of the inspiratory phase
is set by an inspiratory time knob on the housing of the device,
and the volume of gas delivered during that time is set by a volume
knob. The inspiratory phase is followed by the expiratory phase,
and the duration of that phase is set as a factor of the
inspiratory time by a ratio-adjusting knob. At the end of the
expiratory phase, another cycle is automatically initiated.
Override functions are available, as is a manual sigh. A feature of
the operation of the volume-cycled mode is the independence from
the impedance presented by the patient in his airway resistance and
lung compliance. Since a severe obstruction in the airway might
cause the pressure built up by the volume delivered to be very
high, the invention takes care of that contingency by providing a
pressure relief valve that exhausts part of the volume into the
atmosphere if and when a given pressure limit is reached, the
pressure limit setting being adjustable. There is also a vacuum
release to open the airway connection to atmosphere if the patient
draws a vacuum greater than a preset limit.
In the pressure-cycled mode of operation there are controls for
sensitivity, pressure, and flow. In this mode of operation a
breathing cycle is initiated as the patient draws a slight vacuum.
Initiation locks the command signal in the flow controller, which
then delivers breathing gas to the patient. The inspiratory phase
is terminated when the pressure created by the patient at the
outlet of the ventilator reaches a predetermined pressure setting.
The flow of the breathing gas may be adjusted by the volume knob,
which works in conjunction with the flow controller. The volume
delivered is thus determined by the pressure setting and the flow
adjustment, which have an adequate range to cover the cases to be
treated. The expiratory phase normally lasts until a new cycle is
initiated by the patient as he draws a slight vacuum. However, if
the patient has not started a new cycle after a certain time limit,
which can be set, the invention provides for an override switch to
initiate automatically a new inspiratory phase.
This brief summary gives some indication of what the invention can
do, but other objects and advantages of the invention will appear
from the following description of a preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIGS. 1A and 1B comprise a pneumatic circuit diagram of a
ventilator embodying the principles of the present invention, with
some parts shown representationally in elevation and in section. An
inset plan view of the gear controls for the time-volume valve
assembly shows their actual positions, which cannot be shown
correctly in the sectional view.
FIG. 2 is a simplified view in elevation and in section, combined
with a functional diagram, of a cycle generator used in the circuit
of FIG. 1B.
FIG. 3 is a group of graphs showing the functioning of the two
signals sent out by the cycle generator under two different types
of conditions, normal operation and sigh operation, plotting
pressure against time.
FIG. 4 is a graph of the first order timing constant of the timing
network, plotting change of pressure against time.
FIG. 5 is a graph of the ratio of the inspiratory time to
expiratory time as a function of inspiratory time, as provided by
the cycle generator for three different ratios.
FIG. 6 is a functional diagram and simplified view in elevation and
in section of the flow controller employed in the pneumatic circuit
of FIG. 1B.
FIG. 7 is a graph showing the domain of application of the
ventilator in terms of volume delivered versus inspiratory
time.
FIG. 8 is a front view of a ventilator housing containing the
principal items shown in FIGS. 1A and 1B and providing the various
controls.
FIG. 9 is a side view of the ventilator housing of FIG. 8.
FIG. 10 is a fragmentary view in elevation and in section of the
time-valve portion of the time-volume valve, enlarged with respect
to FIG. 1B and shown more representationally.
FIG. 11 is a view in elevation and in section of the volume-valve
portion of the time-volume valve, enlarged with respect to FIG. 1B
on the same scale as FIG. 10 and at right angles thereto and shown
more representationally.
FIG. 12 is a view in elevation and in section of the main operation
switch.
FIG. 13 is a view in elevation and in section of the pressure
sensor and controller, enlarged with respect to FIG. 1A and shown
more representationally.
DESCRIPTION OF A PREFERRED EMBODIMENT
A ventilator embodying the principles of this invention is shown
functionally and, to some extent, representationally in FIGS. 1A
and 1B. Some conventional parts, such as a face mask or other means
for connection to a patient are omitted, while other conventional
parts are only indicated by words and arrows. Some normal
directions of gas flow are indicated, but it should be understood
that in some conditions there is back flow in some of these
conduits. FIGS. 2, 6 and 10-13 show enlarged sectional views,
somewhat more representational than FIGS. 1A and 1B. FIGS. 8 and 9
show accurate representational views of the exterior of a preferred
assembly.
The ventilator of these drawings is capable of both pressure-cycled
operation and volume-cycled operation, one at a time. Some parts
are used in both modes of operation, while some are used only in
one mode. It will be apparent to one skilled in the art to which
this invention relates that a volume-cycled ventilator embodying
the principles of the operation could be made omitting parts used
only in the pressure-cycled mode and omitting the parts employed
only in the changeover from one mode to the other. Similarly, a
pressure-cycled ventilator can be made using the appropriate parts
of the device that is shown for the purposes of illustration. No
separate illustration is seen to be needed to support this fact and
to support the claims drawn to a single mode of operation.
Referring to FIGS. 1A and 1B, a supply 20 sends a desired breathing
gas under pressure into a main supply conduit 21. This supply,
suitably regulated, may be either pure oxygen or a mixture of
oxygen with nitrogen and possibly some other gases. The gas may
come, for example, from a ratio-controlling device such as is shown
in U. S. Pat. No. 3,534,753, issued Oct. 20, 1970.
Regulation of the Gas Supply (FIG. 1A)
The main supply conduit 21 may conduct the breathing gas by a
branch conduit 22 (FIG. 1A) to a pressure regulator 23, which
provides a regulated supply for both the cycle generator 50, the
airway pressure sensor and controller 200, and the switch time
override 280. The regulator 23 accepts the supply pressure to the
ventilator, which may be at from 35 to 50 p.s.i. and reduces it to
a constant figure such as 30 p.s.i. A conventional regulator design
may be used, having a diaphragm 24 in a housing 25, backed up by a
bias spring 26. An inlet 27 is connected to the conduit 22 and
leads by suitable passageways into a chamber 28 closed by the
diaphragm 24 and having an outlet 30. The force applied by the
spring 26 can be adjusted, as by a screw 31. The diaphragm 24 is
thus subjected in one direction to the outlet pressure and in the
other to the force of the spring 26. The diaphragm assembly may
actuate a poppet 32 to admit the flow necessary to maintain a
balanced condition. The force of the spring 26 is preset by the
screw 31 so that the balanced condition corresponds to a desired
outlet pressure, e.g., 30 p.s.i. The regulator 23 may be quite
compact and fit easily into a small ventilator housing 380 (FIGS. 8
and 9) along with many other elements.
Main Operation Control Switch 35 (FIG. 1A)
From the outlet 30 of the pressure regulator 23 a conduit 34 leads
to a main operation control switch 35, which determines the mode of
operation, -- volume cycled or pressure cycled. The gas is led into
an inlet 36 near the periphery of a generally cylindrical but
tapered housing or body 37. The switch 35 has two positions, one
for the volume-cycled mode (as shown in solid lines) and the other
for the pressure-cycled mode (as shown in broken lines). The basic
functional part of the switch 35 may be a tapered Teflon plug 38
which rotates in the tapered body 37. In the volume-cycled mode, a
flat surface 39 machined on the surface of the plug 38 provides the
desired interconnection from the port 36 to a port 40 by the
resulting clearance from the body 37. A second flat face 41 and a
radial passageway 42 provide a connection between a port 43 in the
body 37 and an axially extending passageway 44 in the plug 38,
having two outlets 45 and 46. There are also ports 47 and 48 in the
body 37.
When the switch 35 is in its volume-cycled mode position, the
regulated supply from the conduit 34 is led by the switch 35 from
the port 36 to the port 40 and into a conduit 49 which conducts it
to a cycle generator 50, (FIG. 1B).
The Cycle Generator 50 (FIGS. 1B and 2)
The cycle generator 50 is shown, in simplified form, in FIG. 2. It
has a housing 51, preferably made up of several individual pieces,
and it has a series of diaphragms 52 and 53 in one portion and 54
and 55 in another portion. The regulated supply conduit 49 leads in
through a port 56 to a central axial passageway 57. The diaphragms
52 and 53, which are of different area, are carried on the same
diaphragm plug 58, and at one end of the plug 58 is mounted a
closure seat 60.
A chamber 61 bounded at one end by the diaphragm 52 is provided at
its other end with a wall 62 that seats a spring 63 bearing against
a shoulder 64 of the diaphragm plug 58. A chamber 65 lying between
the two diaphragms 52 and 53 is open to the atmosphere through a
port 66, and another chamber 67 is bounded at one end by the
diaphragm 53.
In the chamber 67, an adjustable spring seat 68 is provided for a
spring 69, which bears against the lower end of the plug 58. The
adjustable seat 68 is threaded to a stem 70 which leads outside the
housing 51, and on it a gear 71 is mounted. The gear 71 is meshed
with a larger gear 72 in a magnifying-gear train, for control by a
handle 73 on a shaft 74 carrying the gear 72. As will be seen
later, this handle 73 sets the ratio of the inspiratory time to the
expiratory time when the ventilator is in its volume-cycled
mode.
The chamber 61 is in communication with another chamber 75 by means
of conduits 76, 77, and 78, and the conduit 78 is also connected by
a conduit 79 to a restricted bleed 80, which bleeds off to
atmosphere at a controlled rate.
The chamber 75 in th housing 51 is closed at one end by the
diaphragm 54. A chamber 81 lies between the diaphragms 54 and 55
and a chamber 82 lies outside the diaphragm 55. Both of the
diaphragms 54 and 55 are carried on a plug 83, which also carries a
valve seat 84 adjacent a valve port 85 leading from the chamber 82.
The chamber 82 is vented to atmosphere by another port 86.
From the chamber 75 a passageway 86 leads to a side passage 88 that
is normally closed by a spring 89 biasing a valve 90 to the closed
position. When the valve 90 is open, the passage 88 is connected to
a chamber 91 having a port 92 that is connected to a conduit
93.
A port 94 from the chamber 67 is connected by conduits 95 and 96 to
a port 97 leading into the chamber 81 so that the chambers 67 and
81 are kept at the same pressure, and the conduit 95 is connected
to a conduit 98 that is connected to a conduit 99. The conduit 98
is also connected by a time valve 100, (shown basically as a needle
valve in FIG. 2 but soon to be explained in more detail with
reference to FIG. 1B) to a conduit 101, which is connected to the
conduit 93 and also to a conduit 102 that is connected to the port
43 of the operation switch 35. The conduit 101 is also connected to
the port 85, so that the ports 85 and 92 are connected
together.
Operation of the Cycle Generator 50
From a functional standpoint, the cycle generator 50 uses a supply
regulated at, for example, 30 p.s.i. to generate two signals,
designated as PC1 at the conduit 102 and PC2 at the conduit 99 and
to vary their relative values as a function of time within a given
cycle and also to repeat the cycle continuously. Each cycle has two
phases, an ON-phase corresponding to the inspiratory phase of the
ventilator and an OFF-phase corresponding to the expiratory phase
of the ventilator.
During the ON-phase (see FIG. 3, top line) the signal PC1 is at a
constant pressure, e.g., 30 p.s.i., while PC2 (next line below in
FIG. 3) increases from a minimum preset pressure, which may lie
between 1 and 6 p.s.i., to a maximum preset pressure, which may lie
between 17 and 22 p.s.i., for example. These preset pressures can
be varied as desired, each over a range of values, but, once set,
they remain constant during a given operation.
During the OFF-phase, the signal PC1 is bled to atmospheric
pressure through the port 86, and is therefore zero above
atmospheric, while the signal PC2 decreases from its preset maximum
value to its preset minimum value. The span between the minimum and
the maximum values of the signal PC2 is constant, but the levels of
the values vary within a band of approximately 5 p.s.i. This
variation establishes the ratio between the ON-time and the
OFF-time in a given cycle. Under the limit conditions just
mentioned, for example, the ratio goes from about 1:3 to about
1:1.5.
The two signals PC1 and PC2 are sent, as will be described later,
to the flow controller 140 to establish a flow of breathing gas.
The flow from the flow controller 140 is proportional to the
difference (PC1 - PC2). During the ON-phase there is flow, and this
flow starts at a maximum value at the beginning of the phase and
decreases as PC2 increases, reaching its minimum value at the end
of the ON-phase. The flow is shut off during the OFF-phase because
PC1 becomes zero, and the difference (PC1 - PC2) is therefore
negative.
Let the effective areas of the two diaphragms 52 and 53 be A1 and
A2, and the forces created by the springs 63 and 69 be F1 and F2.
The diaphragm assembly and the plug 58 assume two different
positions, in one position (open), the seat 60 is away from the
inlet 57 which is connected to the regulated pressure of gas in the
conduit 49, and in the other position (closed) the seat 60 is
against the inlet port 57 and shuts off the flow that would
otherwise come through it.
In the open position the supply pressure transmitted through the
inlet port 57 becomes PC1, which is applied to the smaller area
diaphragm 52 and is also sent via conduits 76, 78, 77, chamber 75,
passages 87, 88, chamber 91 and conduit 93 to the conduit 101, the
port 85 being closed. A flow is established from PC1 through the
needle valve 100 to build up the pressure PC2 in the conduit 98 and
against the larger area diaphragm 53.
In the closed position the inlet port 57 is closed by the seat 60.
The pressure PC1 bleeds out from the chamber 61 to atmosphere
through the conduits 76, 78 and 79 and the fixed bleed hole 80; the
port 85 is opened to bleed off the conduit 101 immediately, and the
pressure PC2 more gradually decreases as it flows in the reverse
direction back through the needle valve 100 to the conduit 101 and
thence to the port 85 and to atmosphere through the bleed port
86.
The two conditions in which the diaphragm assembly 52, 53, 58
switches from one position to the other are determined by two
balances of forces:
1. The diaphragm assembly opens the inlet port 57 when F1 = (PC2
min. .times. A2) + F2.
2. the diaphragm assembly closes the inlet port 57 when F1 + (PC1
.times. A1) = (PC2 max. .times. A2) + F2.
The two conditions of balance are unstable. In condition (1), as
soon as the inlet port 57 opens, a force (PC1 .times. A1) is added
to F1 to keep the seat 60 away from the port 57. This condition
prevails until the condition (2) is reached, and when it is
reached, the inlet port 57 closes and PC1 bleeds off to atmosphere,
so that the force opposing (PC2 .times. A2) + F2 is suddenly
decreased by the amount (PC1 .times. A1). This keeps the diagragm
assembly and its seat 60 against the inlet port 57 until the next
condition (1) is reached. Thus, the system cycles continuously
between the two conditions.
Combining the two equations (1) and (2) we can obtain
3. PC1 .times. A1 = .DELTA.PC2 .times. A2, or
.DELTA.PC2 = PC1 .times. A1/A2.
The minimum value of PC2 is determined by F1 - F2. In this instance
F1 is a fixed force, while F2 is adjustable. The maximum value of
PC2 is [PC2 min. + .DELTA.PC2].
The duration of the ON-phase is the time that it takes PC2 to go
from its minimum value to its maximum value, and the duration of
the OFF-phase is the time that it takes PC2 to go from its maximum
value to its minimum value. Although the change in PC2 is the same
in both phases, the corresponding times are not equal, due to the
fundamental characteristic of a pneumatic timing circuit. This is
shown in the curve of FIG. 4, which shows the time it takes for a
step change in pressure to be transmitted into a capacity through a
needle valve. The time it takes to reach 63.2 percent of the total
step is called the time constant of the circuit. Since this case
concerns a resistance R and a capacity C, it is known as a first
order or RC network circuit, and the time constant is a first order
time constant. The curve is plotted as percent recovery versus time
expressed in terms of the time constant.
For example, assume that .DELTA.PC2 is 16 p.s.i. and consider that
in one case PC2 goes from 1 to 17 p.s.i. and in a second case PC2
goes from 6 to 22 p.s.i.
In the first case, in the ON-phase the total step being 30 p.s.i.,
since PC1 changes suddenly from 0 to 30 p.s.i., the pressure PC2
goes from 1/30 = 3.3 percent of the step to 17/30 = 56.5 percent of
the step. In the OFF-phase, the total step being 17 p.s.i. as PC1
changes suddenly to 0, the pressure PC2 goes from 0/17 = 0 percent
of the step to 16/17 = 94 percent of the step. In terms of time,
the ON-phase is [0.82 - 0.05] = 0.77 time constant. Similarly, the
OFF-phase is 2.85 time constant. The ratio of ON to OFF is
therefore 0.77 to 2.85 or 1 to 3.7.
In the second case, in the ON-phase the total step being 30 p.s.i.
again, the pressure PC2 goes from 6/30 = 20 percent of the step to
22/30 = 73.5 percent of the step. In the OFF-phase, the total step
being 22 p.s.i., PC2 goes from 6/22 which equals 0 percent of the
step to 16/22 = 73 percent of the step. In terms of time, the
ON-phase is [1.30 - 0.25] = 1.05 time constant. Similarly, the
OFF-phase is 1.30 time constant. Hence the ratio of ON to OFF is
1.05 to 1.30 or about 1 to 1.2.
An inspiratory time knob 103 is connected to the needle valve 100,
which sets the time of the ON-phase. This will be discussed later
in connection with the time-volume valve 110. The valve 100, though
incorporated in a separate volume-time valve assembly 110 is
associated functionally with the cycle generator 50. The ratio knob
73 is connected to a mechanical drive which changes the value of
the force F2 by changing the compression of the spring 69.
Within the practical range of ratios from 1 to 1.5 to 1 to 3, the
actual inspiratory time stays within 10 percent of a given setting
(by the knob 103) as the ratio is varied (by the knob 73) within
its range. This fact is illustrated by the graph shown in FIG. 5,
which is made from data obtained with a typical unit.
The additional circuitry incorporated in the cycle generator 50 has
the purpose of assisting a rapid switchover from the ON-phase to
the OFF-phase and thus to increase the accuracy of timing. This
accuracy is especially important at fast cycling rates, where they
may be, for example, above 50 per minute. The pressure PC1 is
applied to the inlet of the timing needle valve 100 through the
check valve 90. The diaphragm assembly 54, 55, 83 works in
cooperation with the port 85 to bleed to atmosphere the pressure
PC1 upstream of the timing valve 100 at the start of the OFF-phase.
This happens in the following sequence: During the ON-phase PC1,
which is greater than PC2, keeps the seat 84 against the port 85.
At the end of the ON-phase the pressure PC1 upstream of the check
valve 90 bleeds off to atmosphere through the fixed bleed 80.
During that very short time the check valve 90 maintains PC1
upstream of the timing valve 100, thus keeping PC2 at its maximum
value. Once the pressure PC1 upstream of the check valve is lower
than the pressure PC2, the diaphragm assembly 53, 54, 83 moves the
seat 84 away from the port 85, and the pressure PC1 downstream of
the check valve 90 is rapidly bled to atmosphere through the
chamber 82 and the port 86. The OFF-phase proceeds, as PC2
decreases by flowing back through the timing valve 100 to
atmosphere via the ports 85 and 86.
The cycle generator 50 may be assembled in a stacked type of
force-balance construction. The diaphragms 52, 53, 54, and 55 may
be made from a high strength Fairprene, an elastomer coated elastic
fabric, conservatively stressed during operation. The two diaphragm
assemblies are the only moving parts. The motion is substantially
friction free, and the travel is small, about 1/32 inch to 1/16
inch. The variable compression spring 69 is actuated by the
gear-driven screw 70, the gear train 72, 71 magnifying the action
of the ratio knob 73 and providing a more precise and more stable
setting through a 270.degree. full scale rotation to cover a
selected ratio range, such as from 1:1.5 to 1:3.
The Time-Volume Assembly 110 (FIG. 1B)
A time-volume valve assembly 110 incorporates the needle valve 100
associated with the cycle generator 50 to set the inspiratory time
and a valve 120 associated with the flow controller to set the
volume. It also includes mechanical drives to actuate the two
valves 100 and 120. This assembly 110 features a unique
compensation network through which the volume valve 120 receives
two inputs, one from a volume knob 121 and the other from the
inspiratory time knob 103, the purpose being to correct the actual
opening of the volume valve 120 whenever the inspiratory time is
changed, so that the volume delivered continues to be the same as
that indicated by the volume knob 121.
The time-volume valve 110 has a housing 111. For the time valve
100, an inlet passage 104 (connected to the conduit 101 through a
check valve 109) leads into a chamber 105. The gas entering the
chamber 105 at PC1 leaves at PC2 by the conduit 98 after passing
through a port 106 in accordance with regulation by a novel stem
107, which is provided with a logarithmic shape and is backed up by
a spring 108.
The setting of the opening between the stem 107 and the port 106 is
determined by the setting of a screw 112 that moves back and forth
a forward stem 113 engaging a forward portion 114 of the main stem
107. This screw 112 is provided with a spring 115 to assure its
seating and is controlled by the rotary position of its shaft 116,
on which a gear 117 is rigidly fixed. The time-control knob 103 is
secured to a shaft 118 to which is secured a gear 119 that meshes
with the gear 117.
The valve 120 is generally similar in construction, with some
differences. It has an inlet 122 connected to the unregulated
supply conduit 21 and leading into a chamber 123 that provides a
valve seat 124. On the other side of the valve seat 124 a chamber
125 is connected to an outlet passage 126 leading into a conduit
127. A plug 130 having a logarithmic exterior surface and backed up
by a spring 128 has a stem 129 and is urged into position by a stem
131 in contact with the stem 129. The stem 131 is controlled by a
screw 132 that has a back-up spring 133 and a stem 134 supporting a
gear 135 that meshes with the gear 119. By means of the gears 119
and 135, the position of the plug 130 is controlled by the time
knob 103. However, another gear 136 threaded to the screw 132 is
meshed with a pinion gear 137 that is mounted on a shaft 138 having
the volume control handle or knob 121.
Thus, the time-valve 100 is a precision valve in which the stem 107
is shaped to provide a logarithmic calibration of the knob 103.
This characteristic is extremely desirable for precise setting of
the time because it gives an equal percentage calibration. A given
incremental rotation of the inspiratory time knob 103 represents
the same percentage of the indicated time at any point of the
scale. For example, 10 percent of a full scale increment
corresponds to 0.05 seconds at a reading of 0.5 seconds, and at a
reading of 2 seconds it corresponds to 0.2 seconds. On a linear
scale, 10 percent increment on a full scale of 0.4 to 4 seconds
means 0.36 seconds at any point of the scale or 20 percent of 2
seconds and 80 percent of 0.5 seconds. The logarithmic
characteristic is put to good use in the compensation network. The
gear train 119, 117 which drives the needle valve 107 preferably
magnifies the action of the time knob 103 and enables a precise
setting through a 270.degree. full scale rotation in the range of
0.4 to 4 seconds.
The logarithmically calibrated plug 130 for the volume valve 120
has similar advantages. Equal percentage calibration applies in the
same way to the volume setting. Hence, for example, on a full scale
of 200 to 2,000 cc, 10 percent of the full scale increment means 50
cc at 500 cc, 100 cc at 1,000 cc on a logarithmic scale or 180 cc
at 500 cc and 180 cc at 1,000 cc on a linear scale. The volume
valve 120 is driven either through the gear train 119, 135 or the
gear train 137, 136, both of them preferably magnifying the action
of the knob 103 or 121 and enabling the precise setting through a
270.degree. full scale rotation in the range of about 200 to about
2,000 cc.
It is desirable that the inlet 104 offer no resistance to the
inflow during the inspiratory phase; but for the backflow it is
advantageous to provide a resistance in addition to that set by the
stem 107 and to make that resistance effective only in the range of
the higher flows corresponding to short expiratory times. This is
accomplished by the use of the check valve 109 in the inlet 104 and
a restriction 139 in parallel with the check valve between the
inlet 104 and the conduit 101. During the inspiratory phase, the
check valve 109 opens at once and the pressure PC1 is applied
directly to the inlet 104 from the conduit 101. During the
expiratory phase, the check valve 109 is closed and the bleeding of
PC2 is governed in part by the restriction 139. The restriction is
sized to be smaller than the orifice around the stem 107 during
short inspiratory times and larger than that orifice during long
inspiratory times, so that it lengthens the expiratory phase only
during expiratory phases that follow relatively short inspiratory
times, such as 0.5 to 1.0 second. As a result, the ratio of
inspiratory time to expiratory time is maintained more evenly in
that time range as well as over the whole time range, as shown in
FIG. 5.
The Compensation Network of the Time-Volume Valve Assembly 110
A very important feature of the time-volume valve assembly 110 is
its compensation network. The volume valve 120 actually sets a
flow, and the setting for a flow can be expressed in terms of
volume for a given time over which the flow is integrated to obtain
the volume. For example, if one assumes a time of 1.5 seconds, one
can calibrate the valve for that value of time for a volume at
1,000 cc. If the time alone is changed to 0.75 seconds, the actual
volume delivered will be 500 cc, since the same flow is integrated
over half the time. In order to correct the opening of the volume
valve 120 as the time valve 100 is changed so that the flow will be
increased in the same proportion as the time is decreased, the
compensation network is necessary.
The fundamental relationship between the three parameters is
volume = flow .times. time
or using logarithmic values
log V = log f + log t.
Thus, in order to keep log V constant as log t is changed, the
change in log f must be equal and opposite to the change in log
t.
Since both the time valve 100 and the volume valve 120 are
characterized to have a logarithmic indicating scale, their
respective indications are proportional to log t and log V. FIG. 1B
shows that the volume valve 120 is actuated in two ways; the volume
knob 121 drives the gear 137 and that drives the gear 136 in which
the screw 132 of the valve 120 is threaded; as the stem 131 is
prevented from turning, the rotation of the gear 136 moves the stem
131 longitudinally. On the other hand, the gear 136 may be
stationary for a given position of the volume knob 120 but rotation
of the threaded stem 134 within the gear moves the stem 131
longitudinally, again changing the opening of the valve 130, 124.
This second mode of actuation is connected to the mechanical drive
of the time valve 100.
Thus, in an example where the volume is set at 1,000 cc and the
time at 1.5 seconds, when the time is changed to 0.75 seconds, the
stem 134 of the volume valve 120 is simultaneously rotated within
the stationary screw 132 and moves longitudinally to increase the
opening for greater flow. The increment of flow change is equal to
the increment of time change on a logarithmic basis. Since the time
is reduced to one-half of its original value, the flow is increased
to twice its original value and as a result, the volume indicated
by the knob 121 is preserved. Hence, turning the inspiratory time
knob 103 affects the time but does not affect the total volume.
The compensation is effective within the domain of practical
application of the ventilator. The limits of the domain correspond
to average flows of 12 to 90 liters per minute. Reference may be
made to the graph of FIG. 7. Limit examples would be:
at 12 liters per minute, V = 200 and t = 1 second, or V = 600 and t
= 3 seconds;
at 90 liters per minute, V = 750 and t = 0.5 second to V = 1500 and
t = 1 second.
The Flow Controller 140 (FIGS. 1B and 6)
The flow controller 140 is a very important part of this invention.
As shown in FIG. 6, it has a housing 141 with three diaphragms,
142, 143, and 144; the diaphragms 142 and 144 have areas A3 that
are equal, while the center diaphragm 143 has an area A4 that is
smaller. The three diaphragms 142, 143, and 144 are joined by a
common diaphragm plug 145. Outside the diaphragm 142 is a chamber
146. Between the diaphragms 142 and 143 is a chamber 147. Between
the diaphragms 143 and 144 is a chamber 148, and outside the
diaphragm 144 is a chamber 149. Spring pressure is exerted against
the diaphragm plug 145 by a spring 150 which is mounted on a
movable spring seating member 151, which itself bears on the end of
a threaded member 152. The threaded member 152 extends through the
housing 141 and, once adjusted, is preferably locked in place by a
lock nut 162. A blind nut 153 is then threaded on the member 152
and sealed against a gasket ring 163. For readjustment, the blind
nut 153 is first removed and the lock nut 162 backed away. The
opposite end of the diaphragm plug 145 carries a seat 154, which is
adapted to seat against or to be moved away from a valve opening
155, which is part of the outlet conduit.
Each of the chambers 146, 147, 148, 149 has an inlet. Thus, the
chamber 146 has an inlet 156 which is connected to the outlet of
the volume valve 120 by the conduit 127. The chamber 147 has an
inlet 157 connected to the pressure PC2 by the conduit 99. The
chamber 148 has an inlet 158 connected to the pressure PC1 by a
conduit 161, which is connected to the conduit 102 through the
switch 35. Finally, the chamber 149 has an inlet 159 connected to
the supply conduit 21. The pressure of the supply conduit 21 may,
for the purpose herein be designated P1 and that of the conduit 127
(which is the result of the pressure P1 passing through the volume
valve 120) may be designated P2.
The flow controller 140 receives two command signals, PC1 and PC2,
from the cycle generator 50 and the time valve 100, and it
establishes a flow of breathing gas from the valve 154, 155 to an
airway conduit 160 proportional to the difference between the two
signals, i.e., proportional to (PC1-PC2). The flow is also
proportional to the opening of the valve 120.
The principle of operation is to generate across the valve 120 a
differential pressure proportional to the difference between the
two command signals. As indicated previously, the difference (PC1 -
PC2) is positive during the inspiratory phase and then creates a
flow proportional to its value. The flow is at a maximum at the
start of the phase and decreases with time to a lower value at the
end of the phase. The pattern of flow decreases from maximum to
minimum value is essentially the same for all durations of the
phase within the range of the inspiratory time for which the setup
is designed, typically 0.4 to 4.0 seconds. Since the flow is
governed by the differential pressure, which is proportional to
(PC1 - PC2) and to the opening of the valve 120, a predetermined
flow can be set by the valve opening. This flow, integrated over
the inspiratory time, becomes the volume delivered by the
ventilator during the inspiratory phase. The point should be
emphasized that the valve 120 sets a flow. The valve setting can be
indicated as a volume setting only for one value of inspiratory
time. Remembering the time-volume valve assembly 110, it will be
seen, however, that the flow knob 121 can be used as a volume knob
independently of the inspiratory time.
During the expiratory phase the difference (PC1 - PC2) becomes
negative and in this instance operates to shut off the flow
controller 140. The functional diagram, FIG. 6, shows how the flow
controller 140 generates the differential pressure. The diaphragm
assembly is subjected to the forces supplied by four pressures on
their corresponding effective areas:
1. Supply pressure P1 upstream of the valve on the area A3.
2. pressure P2 downstream of the valve on the area A3.
3. the command pressure PC1 on the area [A3 31 A4].
4. the command pressure PC2 on the area [A3 - A4].
The combined forces position the diaphragm assembly to establish a
flow which creates the balanced condition defined by:
(P1 .times. A3) - (P2 .times. A3) = PC1 .times. [A3 - A4] - PC2
.times. [A3 - A4].
Thus ]P1 - P2] .times. A3 = [PC1 - PC2] .times. [A3 - A4].
[P1 - P2] is a differential pressure .DELTA.P across the valve;
so
.DELTA.P = [PC1 - PC2] .times. [A3 - A4]/A3 .
Thus, the differential pressure .DELTA.P is proportional to [PC1 -
PC2]. It is positive during the inspiratory phase and is 0 during
the expiratory phase when [PC1 - PC2] becomes negative, so that the
flow controller 140 is shut off.
The outlet port 155 of this valve is adjustable and is used to
equalize the effective areas of the diaphragms, and the bias spring
150 is used to adjust the balance for a no-flow condition, so that
when [PC1 - PC2]= 0 there is no flow.
THE SIGH DEVICE (FIG. 1B)
Sigh and switch override functions may be combined in one
functional package, a unit 170 having a housing 171 which is
convenient since the two functions have a common connection with
the cycle generator.
A sigh is obtained by connecting the additional capacity of a
chamber 172 to the PC2 side of the cycle generator 50, via a
conduit 173 connected to the conduit 98 and an inlet 174 in the
housing 171. When a sigh is desirable, this chamber 172 is used to
increase the inspiratory time by a fixed amount, which may be, for
example, about 50 percent of a normal time. (See FIG. 3). The
additional capacity of the chamber 172 is connected into the
circuit by pushing manually on a button 175, which opens a check
valve 176 located between the chamber 172 and the inlet 174. When
the button 175 is released, a spring 177 closes the valve 176 and a
spring 178 urges the button 175 outwardly, and the chamber 172 and
its capacity are again isolated from the cycle generator circuit.
During the expiratory phase, whether or not the button 175 is held
in, the pressure remaining in the chamber 172 bleeds through the
check valve 176 until it is equal to the minimum valve of PC2. Then
the check valve 176 prevents any increase in pressure within the
capacity until the button 175 is pushed again.
When the manual sigh is applied, the increase of the inspiratory
time by about 50 percent in turn increases the time by which the
flow is integrated, and therefore the volume is increased by about
50 percent. As previously indicated, the ratio ti/te remains
unchanged, so that the expiratory time is also increased by the
same approximate 50 percent. This is illustrated in FIG. 3, low two
graphs.
The switch override portion of the unit 170 comprises a pneumatic
switch 180 actuated by a signal that comes from the airway pressure
sensor 200, which is explained below, via a conduit 181. When a
vacuum condition in the patient's airways is sensed by the airway
pressure sensor 200, it creates a signal sufficient to move a
diaphragm 182, and a plug 183 of the override switch, carrying a
seat 184 away from a port 185, and then the PC2 pressure from the
conduit 98 is bled to atmosphere via the port 185 and a port 186,
and as a result, a new inspiratory phase is started when the PC2
pressure reaches its minimum value. The plug 183 is biased toward
its closed position by a spring 187, and the signal from the
conduit 181 is applied via a port 188 to a chamber 189 between the
diaphragm 182 and a second diaphragm 190 carried by the same plug
183 in a single diaphragm assembly.
The pressure PC1 is applied from the conduit 101 by a branch
conduit 191 and a port 192 to a chamber 193 closed by the diaphragm
190. Thus, the pressure PC1 is applied to one end of the diaphragm
assembly 182, 183, 190, and the pressure PC2 is applied at the
other end of the same diaphragm assembly, while the signal from the
conduit 181 is applied between the diaphragms 182 and 190.
During the expiratory phase, the pressure PC1 is zero; so it does
not interfere with the initiation of a new inspiratory phase by the
override switch 180. At the start of such an inspiratory phase, the
pressure PC1 immediately is applied to the chamber 193 at its
maximum value, and the diaphragm assembly 182, 183, 190 moves the
seat 184 against the port 185 and stops any bleeding of the
pressure PC2 to atmosphere, assuring that the set inspiratory time
will be preserved, since the pressure PC2 begins increasing from
its minimum value where it switches the cycle generator 50 to the
inspiratory phase and continues to increase at it normal rate.
As breathing gas is delivered to the patient's airway, the pressure
becomes positive, and the signal from the sensor 200 returns to a
low value at approximately atmospheric pressure and the override
switch closes its port 185. At the next inspiratory phase, when the
pressure PC1 returns to zero, the seat 184 remains against the port
185, since the signal from the sensor 200 is very low. The
diaphragm assembly 182, 183, 190 and its bias spring 187 are sized
to open the seat 184 away from the port 185 when the signal from
the pressure sensor 200 via the conduit 181 is greater than about
15 p.s.i. Other values may be chosen if that is desired.
The Airway Pressure Sensor and Controller
The airway pressure sensor and controller 200 senses the airway
pressure and generates the pneumatic signal that is sent to the
override switch 180 by the conduit 181 when the airway pressure is
negative and is lower than a value set by a sensitivity knob 210.
As has just been explained, this pneumatic signal is applied to the
override switch 180 to initiate an inspiratory phase when the
ventilator is set to operate in the volume-cycled mode. In the
pressure-cycled mode the operation is different, as will be seen
after the structure has been described.
The unit 200 comprises a hollow housing 201 mounted on one side of
a manifold plate 199. A large diaphragm 202 divides chambers 203
and 204 and is supported by a support member 205. A large flat
spring 206 urges the diaphragm support member 205 and the diaphragm
202 in one direction, and a coil spring 207 urges them to the
opposite direction. A partially threaded sensitivity adjusting stem
208 is threaded into a support member 209 that is secured to the
opposite side of the manifold plate 199 from the diaphragm 202 and
the end of the stem 208 bears on the flat spring 206 and adjusts
the force it exerts against the diaphragm support member 205. The
stem 208 is controlled by the sensitivity know 210. The chamber 204
has a port 211, connected by a branch conduit 165 to the airway
conduit 160, at the outlet pressure from the flow controller 140.
Thus, the airway pressure is applied to one side of the large
diaphragm 202, while the other side is at atmospheric pressure; as
the airway pressure decreases below atmospheric pressure, movement
of the large diaphragm 202 is opposed by the flat spring 206.
In communication with the chamber 203, which is kept at atmospheric
pressure by a port 212, is a smaller diaphragm 213, supported by a
member 214. The support member 214 is also secured to another
diaphragm 215, to provide a two-diaphragm assembly. Between the
diaphragms 213 and 215 is a chamber 216 having a port 217. The
other side of the diaphragm 215 is open to the atmosphere. A spring
218 biases the diaphragm assembly 213, 214, 215.
Below the large diaphragm 202 as seen in FIGS. 1A and 14, is a
detector 220. This includes a smaller diaphragm 221 that closes the
chamber 204 and defines one end of another chamber 222 which is
kept at atmospheric pressure by a port 223. The member 205 also
carries a seat 224 in the chamber 222. Many of these ports may be
located in the manifold plate 199 in an opening 225 therein. Below
the plate 199 is a detector housing 226 in which is a diaphragm 227
that closes the other end of the chamber 222. On the opposite side
of the diaphragm 227 is a chamber 228 in the housing 226 that is
supplied with gas from the conduit 34 through an inlet 234 and a
fixed restriction 229.
The diaphragm 227 is carried by a plug 230 having an extended
tubular member 231 and a passage 232 extends through the tubular
member 231, the plug 230 and the diaphragm 227 connecting the
chamber 228 to the chamber 222, so that, normally, the incoming
pressure from the conduit 34 through the restricted orifice 229
flows through the passage 232 and is vented to atmosphere by the
port 223. However, when the airway pressure decreases below
atmospheric pressure, the reduced pressure in the conduits 160 and
165 acts in the chamber 204 and acts to move the large diaphragm
202 and with it the seat 224 toward the end of the tubular member
231 first throttling the passage 232 and then closing it, so that
the pressure in the chamber 228 rises. A spring 233 acts on the
sensor diaphragm assembly 227, 230, 231 to provide a positive
feedback "snap" action described later.
The detector 220 incorporates a relay 235 which functions as a
power amplifier that provides the actual pressure to the conduit
181. While its output pressure is approximately equal to that of
the pneumatic signal furnished by the detector proper, the flow
handling capacity of the relay 235 is greatly increased over that
of the detector proper. The combination of the detector 220 and the
relay 235 gives a fast response; on the one hand, the detector 220
has a fast reaction since its internal volume is very small; on the
other hand the relay 235 has a high flow handling capacity to
supply the functional assemblies connected to its output.
The relay 235 may be in the detector housing 226 and includes a
pair of diaphragms 236 and 237. The upper diaphragm 236 closes a
chamber 238, which is connected by a conduit 239 to the chamber
228. The chamber 238 is therefore at the same pressure as the
chamber 228, so that that side of the diaphragm 236 is acted on by
that pressure, which may here be termed the signal pressure. A
chamber 240 between the diaphragms 236 and 237 is open to the
atmosphere by a port 241. A chamber 242 below the diaphragm 237 has
an outlet 253 connected to the conduit 181. Both of the diaphragms
236 and 237 are mounted on the same support member 243, which has
an axial conduit 245 leading to a radial conduit 244 in the chamber
240. The chamber 242 has a lower portion 246 having an inlet 247
connected to the conduit 34 and a poppet valve 248 biased by a
spring 249 and acting on a seat 250. An extension 251 of the poppet
valve 248 can engage the axial passageway 245 and close it. The
diaphragm assembly 236, 237, 243 actuates the poppet 248 so that a
regulated pressure equal to the command signal is created in the
upper part of the chamber 242. Any difference between the pressure
in the chamber 242 and that in the chamber 238 moves the poppet 248
to restore a balance. If the regulated pressure in the chamber 242
is lower than the command signal in the chamber 238, the poppet 248
is opened to let in more pressure from the portion 246 and conduit
34. If the regulated pressure in the chamber 242 is higher than the
command signal in the chamber 238, the poppet 248 is closed, and
the excess in the chamber 242 is bled to atmosphere through the
passages 245 and 244, the chamber 240 and the port 241. The spring
249 is retained by a threaded cap 252, which also seals the chamber
246 with the aid of a washer 254.
It will be apparent from this that the sensitivity knob 210,
causing the screw 208 to act on the flat spring 206 determines the
vacuum at which the large diaphragm 202 and its seat member 224 are
able to close off the passage 232, thereby controlling the
sensitivity of the device to vacuum conditions in the patient's
airway. This signal then produces the flow into the conduit 181
from the relay 235.
The housing 201 also may contain a manually adjustable pressure
regulator having a stem 256 with a handle 257 acting through a
spring 258 on a diaphragm 260 that bounds a chamber 261. The
diaphragm 260 carries a support 262 having a stem 263 that can
engage a stem 264 on a poppet 265 to move the poppet 265 away from
a seat 266, to which the poppet 265 is normally urged by a spring
267. An inlet port 268 is connected by a conduit 270 to the port 47
in the operation control switch 235. An outlet port 271 is
connected to a conduit 272, which leads to a fixed bleed 273 to
atmosphere and to a conduit 274. The conduit 274 leads to the port
217.
The fixed bleed 273 downstream of the pressure regulator 255
establishes a desirable minimum flow for good response. The bleed
273 is also used in conjunction with the time override valve 280 in
determining the initial level of pressure setting when the time
override valve 280 is actuated.
When the ventilator is in the pressure-cycled mode, the pneumatic
signal generated at and around the detector diaphragm 227 and
transmitted to the relay 235 is sent by the conduit 181 and port 48
through the operation switch 35 to different conduits to perform
two different functions. It is applied (1) to the flow controller
140 through the port 46 and the conduit 161 to act as PC1 to
produce a flow of breathing gas in the airway conduit 160, (2) at
the same time via the port 47, conduit 270, pressure regulator 255,
and conduits 272 and 274 to the port 217 and chamber 216 to act on
the small diaphragm assembly 213, 214, 215, and (3) at the same
time via the port 45 to a pressure switch 320, an exhalation switch
300, and a time override valve 280.
This small diaphragm assembly 213, 214, 215 actuated by (2) above
then locks the pressure sensor 200 by positive feedback action on
the diaphragm 202 in a position to maintain the pneumatic signal in
the conduits 181 and 161 at its maximum value, which is
approximately or nominally 30 p.s.i.,--i.e., PC1. However, the full
pressure of the pneumatic signal from the conduit 181 is not
applied to the small diaphragm assembly 213, 214, 215 for it is
reduced by the network which includes the adjustable pressure
regulator 255 and the fixed bleed 273 downstream from the pressure
regulator 255. The reduced downstream pressure in the conduit 274
creates the force acting on the small diaphragm assembly 213, 214,
215 which is applied to the large diaphragm 202. As the breathing
gas is delivered by the flow controller 140, the pressure in the
airway conduit 160 increases. When the force on the large diaphragm
202 that is created by the pressure in the conduits 160 and 165
becomes equal to that applied by the reduced pneumatic signal at
the port 217, the large diaphragm assembly 202, 205 moves away from
the end of the sensor tube 231, and the pneumatic signal in the
conduit 181 is bled to its minimum value, i.e., atmospheric
pressure. At the same time the pressure acting on the small
diaphragm assembly 213, 214, 215 is also bled to atmosphere by the
conduit 274 and the bleed 273. Thus, the pneumatic signal in the
conduits 181, 161 is kept at its minimum value, and the flow
controller 140 is shut off during the expiratory phase.
As noted earlier the adjustable flat spring 206 opposes the motion
of the diaphragm 202 towards the sensor tube 231, and a vacuum is
required to bring the diaphragm assembly 202, 205 against the
sensor tube 231, the amount of vacuum required being adjustable by
the sensitivity stem 208. Preferably, the range of adjustment is 0
to 6 centimeters of water.
A positive feedback feature is incorporated in the detector 220 by
having the exhaust nozzle 232 mounted on the detector's diaphragm
227. As the large diaphragm assembly 202, 205 approaches the tube
231, the pneumatic signal in the conduit 181 starts to increase,
and as it reaches about half of its maximum value, it overcomes the
force of the spring 233 and creates a snap action that holds the
nozzle 231, 232 firmly against tthe seat 224, thereby locking the
pneumatic signal in the conduit 181 at its maximum value acting
through the relay 235. This snap action also moves the seat 224 and
the large diaphragm assembly 202, 205 upwardly, the length of the
snap-action stroke being limited, in order to prevent excessive
movement, by engagement of the plug 230 with a shoulder 275, the
distance of movement of the plug 230 being carefully calculated to
afford the desired limit. Thus the nozzle 231 and the seat 224 are
locked together at this time. Conversely, the pneumatic signal in
the conduit 181 starts to decrease from its maximum value when the
airway pressure in the conduit 160 is sufficient to move the large
diaphragm assembly 202, 205 away from the nozzle end 231. When the
signal goes below about one-half of its maximum value, the
diaphragm 227 is moved by the spring 233, and the nozzle tube 231
is suddenly moved further away from the seat 224, and the pneumatic
signal in the conduit 181 then drops to its minimum value, again by
snap action.
As noted above, the large diaphragm assembly 202, 205 is also
subjected to the force applied to it by the small diaphragm
assembly 213, 214, 215 in a direction that opposes the action of
the airway pressure on the large diaphragm 202. This gives a
reference force acting in a direction that reinforces the locking
action described in the preceding paragraph and provides the force
that eventually will have to be undone or overcome by the airway
pressure in order to release the lock. There is snap action in both
directions. The reduced pneumatic signal from the conduit 274
creates its force on the effective area of the small diaphragm
assembly 213, 214, 215, the effective area being the difference
between the areas of two diaphragms 213, and 215, and that is the
force exerted on the large diaphragm assembly 202, 205. When the
reduced signal from the conduit 274 is at its minimum value, the
small diaphragm assembly 213, 214, 215 is kept away from the large
diaphragm assembly 202, 205 by the light bias spring 218. The
reduced signal operating level may be adjustable from approximately
3 to 7 p.s.i., which corresponds to an airway pressure of about 0
to 40 centimeters of water on the large diaphragm. The knob 257
actuating the pressure regulator 255 enables the doctor to set the
pressure for this pressure-cycled operation.
Thus, the patient normally initiates a new inspiratory phase, and
the pressure-cycled mode, by breathing in and lowering the pressure
in the conduits 160 and 165 and in the chamber 204. When the seat
224 closely approaches the nozzle 232, they are forced against each
other and moved upwardly by the snap action discussed and the
downward movement of the small diaphragm assembly follows. The
inspiratory phase, thus started, causes the pressure in the
conduits 160 and 165 to increase until the seat 224 is moved away
from the nozzle, again by snap action. The expiratory phase, thus
started, continues until the next inspiratory phase is
initiated.
Time-Override Valve 280 (FIG. 1B)
A time override valve 280 is also provided in this invention
principally for use in the pressure-cycled mode. It is set to
receive two inputs, one being the continuous regulated supply from
the conduit 34, via a branch conduit 281, the other being the
intermittent pressure from the operation switch 35 and the conduits
282 and 283, this being the same pressure PC1 as that sent by the
conduit 161 to the flow controller 140 at 30 p.s.i. during the
inspiratory phase only of the volume-cycled or pressure-cycled
modes; this pressure is zero during the expiratory phase. The
intermittent pressure from the conduit 283 is supplied through a
check valve 284 to a chamber 285 on one side of a diaphragm 286,
while the supply pressure from the conduit 281 is applied through a
port 287 to a chamber 288 on the other side of the diaphragm 286.
The diaphragm 286 may be mounted on a plug 290. A bias spring 291
exerts a force in a direction to move the diaphragm 286 and its
seat 292 against an outlet port 293.
When the two inputs are both at about 30 p.s.i., the seat 292 on
the diaphragm plug 290 is forced against a seat on an outlet port
293 by the spring 291. When the intermittent pressure drops to 0
during the expiratory phase, a 30 p.s.i. pressure is trapped by the
check valve 284 in the chamber 285, and bears against the diaphragm
286. A needle bleed valve 294 bleeds the chamber 285 to atmosphere
through a port 295, and when the pressure decreases to
approximately 15 p.s.i., the force of the supply pressure on the
diaphragm 286 is sufficient to overcome the bias spring 291 and
move the seat 292 away from the port 293. The 30 p.s.i. pressure is
then applied through the port 293 via a conduit 296 to the chamber
216 of the small diaphragm assembly 213, 214, 215. This in turn
acts on the sensor 200 and starts a new inspiratory phase.
The bleed valve 294 is preferably adjusted so that it takes
approximately ten seconds from the end of the inspiratory phase to
the start of a new one. Of course, under normal conditions an
inspiratory phase would have been started sooner, either (in the
volume-cycled mode) by the cycle generator or (in the
pressure-cycled mode) by the patient, but this is a safety feature
to insure that the phase does not run any longer than the time
which is set by this time override valve 280.
As noted earlier, the fixed bleed 273, to which the time override
valve 280 is connected by the conduits 296 and 274, is used in
determining the initial level of pressure setting when the time
override valve 280 is actuated.
The Exhalation Switch 200
An exhalation switch 300 is provided to receive a command signal
from the outlet 45 of the operational switch 35 via the conduits
282 and 301 and 302, this being the same signal as that which is
sent to the flow controller 140 by the conduit 161. In the
exhalation switch 300 two diaphragms 303 and 304 are joined by a
plug 305, and the signal moves the diaphragm assembly 303, 304, 305
to close a seat 306 against a port 307 or to open it, so that a
conduit 308 leading to the port 307 is vented to atmosphere via a
port 309. The conduit 308 is connected to the airway pressure
conduit 160 through a restriction 310 and is connected through a
conduit 311 to a fitting 312 for a low-pressure exhalation valve.
During the inspiratory phase the command signal in the conduits
282, 301, and 302 is at 30 p.s.i.; it then overcomes a bias spring
313 to move the seat 306 against the port 307 and to seal the
control line 308 for the exhalation valve fitting 312. During the
expiratory phase, the command signal in the conduits 282, 301, and
302 is at atmospheric pressure, and the bias spring 313 moves the
diaphragm assembly 303, 304, 305 and the seat 306 away from the
port 307 and opens the control line 308 of the exhalation valve
fitting 312 to atmosphere. Since the command signal is the outlet
of the operation switch 35, the exhalation switch 300 is actuated
in both modes of operation, volume cycled and pressure cycled; in
the volume-cycled mode a signal from the cycle generator
synchronizes the exhalation valve with the flow controller to
assure that the exhalation valve will be open during the expiratory
phase and closed during the inspiratory phase; in the
pressure-cycled mode the synchronizing signal is derived from the
detector.
This exhalation switch 300 may be used with a low pressure bladder
type of exhalation valve, such as a Bennett valve, for which
control pressure is taken from the airway pressure 160 through the
restriction 310.
The Pressure Switch 320
A pressure switch 320 is also provided to supply a small nebulizer
(not shown but connected to a fitting 321) and a humidifier (also
not shown but connected to the fitting 322) with gas, preferably
taken downstream from the volume valve 120 and coming from the
conduit 127 via a conduit 323 and to do this only during the
inspiratory phase. Taking the gas from the conduit 127 means that
the portion of the total volume delivered to the patient by the
ventilator through the nebulizer fitting 321 and the humidifier
fitting 322 is included in the volume set by the knob 121 of the
volume valve 120.
The pressure switch 320 receives a command signal from the outlet
45 of the operational switch 35, via the conduits 282, 301, and
324, this being the same signal as that sent to the flow controller
140 via the conduit 161. This signal is applied to one side of a
two-diaphragm assembly comprising diaphragms 325 and 326 and a
support 327. The signal from the conduit 324 is applied to a
chamber 328 on one side of the diaphragm 325, and the gas supply
from the conduit 323 is applied to a chamber 329 on the opposite
side of the diaphragm 326, via a chamber 330 that is opened and
closed by a poppet 331 and seat 332. The general assembly is like
that of the relay 235 and the action is basically similar, though
there are some differences.
A chamber 333 between the diaphragms 325 and 326 is vented to the
atmosphere through a port 334, and the chamber 329 is vented to the
chamber 333 by an axial passage 335 and a radial passage 336 in the
support member 327 when an extension 337 of the poppet 331 opens
the passage 335. A bias spring 338 acts on the poppet 331.
The diaphragm assembly 325, 326, 327 actuates the poppet 331, so
that a regulated pressure equal to the command signal from the
conduit 324 is created in the chamber 329. Any difference in
pressure between the chambers 328 and 329 acts on the diaphragm
assembly 325, 326, 327 and it, in turn, moves the poppet 331 to
restore a balance. If the regulated pressure of the signal in the
chamber 329 is lower than the command signal in the chamber 328,
the poppet 331 is opened to enable flow from the chamber 330 into
the chamber 329, whence it flows by an outlet 340 and a conduit 341
to the nebulizer fitting 321 and the humidifier fitting 322. If the
pressure in the chamber 329 is higher than the command signal in
the chamber 328, the poppet 331 is closed and the excess pressure
in the chamber 329 is bled to atmosphere through the passages 335
and 336, the chamber 333, and the port 334.
The pressure in the conduit 341 transmitted to the nebulizer
fitting 321 and humidified fitting 322 is about 30 p.s.i. during
the inspiratory phase and is zero during the expiratory phase.
A feature of the pressure switch 320 is that it bleeds the
connection to the nebulizer very rapidly after the end of the
inspiratory phase. This is important in preserving a precise ratio
of the inspiratory time to the expiratory time, especially when the
signal is also used to actuate a Bird type of exhalation valve as
can be done. This type of valve (not shown, but connected to a
fitting 342), is operated at high pressure, and when that type of
exhalation valve is used, the signal to the conduit 341 is used
also for actuating the exhalation valve, through the fitting 342.
Only one type of exhalation valve is used at a time; so valves 343
and 344 may be provided to shut off the one not in use.
Since the command signal in the conduits 282, 301, and 324 comes
from the outlet 45 of the operations switch 35, the pressure switch
320 is active during the inspiratory phase in both modes of
operation, volume cycled and pressure cycled.
The Manual Start 345
In both modes of operation, the physician may desire or require a
manual device for initiating a new inspiratory phase whenever he so
desires. A manual start 345, shown in FIG. 1A, may therefore be
placed in parallel with the switch time override 280, as by a
conduit 346 connected to the conduit 272. The conduit 346 leads
from an outlet 347 from the manual start 345 to the chamber 216 of
the small diaphragm assembly 213, 214, 215. The outlet 347 is
connected by a passage 348 to a chamber 349. The passage 348 is
normally blocked by a valve seat 365 having an O-ring seal 366. The
seat 365 is held in its closed position by a biasing spring 367 but
can be manually opened by pushing on a stem 368. The chamber 349 is
connected by a conduit 369 to the conduit 34 from the regulator 23.
Thus, whenever the stem 368 is pushed, the regulated pressure in
the conduit 34 is applied, with some reduction by the bleed 273, to
the chamber 216 and an inspiratory phase is initiated. Once so
initiated, the phase continues, though the stem 368 is released,
until the delivered pressure reaches the value set by the pressure
setting knob 257.
Relief of Pressure and Vacuum
As mentioned earlier, if the pressure in the airways gets too high,
it must be vented, and for this purpose a relief valve 350 is
connected to the airway conduit 160. The pressure in the conduit
160 is applied to one side of an O-ring sealed valve member 351 and
develops a force which is opposed by the force of a spring 352. The
force of the spring 352 can be adjusted by a handle 353 and screw
354, having a return spring 355. When the force from the pressure
in the airway conduit 160 becomes greater than that of the spring
352, the valve member 351 is moved and a portion of the flow
controller output is exhausted to atmosphere through a valve
opening 356.
The pressure at which the relief flow starts may be adjusted by
adjusting the compression of the spring 352, which is preferably
kept within a range of 20 to 80 centimeters of water. The pressure
setting incorporates a locking feature to prevent that setting from
being disturbed. This comprises the collar 357 threaded on to the
handle 353 and bearing when locked on the support member 358. The
pressure limit is a critical factor for the safety of the patient,
for if it is too low, it will limit the flow delivered to the
patient and if it is too high, it may permit an excessive pressure
to build up in the airway. Hence, it is important that the pressure
setting, once determined, be maintained.
As stated earlier, for similar reasons it is important to have a
vacuum release, and so a vacuum release valve 360 is connected to
the airway conduit 160. The airway pressure is applied to an
O-ring-sealed valve member 361. When the pressure is positive, the
valve 361 is pushed against its seat 362, and when the pressure is
negative, there is a force in the direction that tends to move the
valve 361 away from its seat 362 and to enable outside air from the
atmosphere to flow into the airway conduit 160, so that the patient
will at least get air at atmospheric pressure. In order to open the
valve 361, the negative pressure has to overcome the force of a
bias spring 363, which is set so that the valve will open with a
desired pressure, such as 6 to 8 centimeters of water of
vacuum.
Other Connections to the Airway Conduit 160
Also connected to the airway conduit is an outlet group, which may
include three outlet connections: (1) a large-diameter, 22 mm. for
example, outlet valve 370, (2) the small-diameter outlet fitting
312 for control of an exhalation valve such as the Bennet type, (3)
the other small diameter outlet fitting 321 supplied by the output
of the pressure switch 320 and connected to a small nebulizer, and
(4) the fitting 342 for the Bird type of exhalation valve.
The small diameter connection 312 for control of the Bennett type
of exhalation valve is supplied through the restriction 310, which
may, for example be 1/32 inch diameter. Downstream of the
restriction 310 the line is also connected to the exhalation switch
300. When the switch 300 is closed, airway pressure builds up in
the control line 308 during the inspiratory phase. When the switch
300 is open, the control line 308 is bled off to atmosphere, and
the exhalation valve opens under the action of the airway pressure
during the expiratory phase.
The large diameter fitting 370 for the outlet hose incorporates the
one-way valve or check valve 371 to prevent back flow of various
liquids from the patient during the expiratory phase. This may be
accomplished by a thin diaphragm 372 which seals against a
perforated body of a fitting on reverse flow but offers little
resistance to flow from the ventilator to the airway.
The pressure in the line to the airway may be indicated by a gauge
375. For example, the gauge may have a diaphragm type pressure
sensor driving a pointer in front of a circular dial 376.
Preferably, the dial 376 displays two color-coded zones, a positive
pressure zone 377 from 0 to 70 centimeters of water designated as
"delivered pressure" and a negative pressure zone 378 from 0 to 20
centimeters of water designated as "inspiratory effort."
FIGS. 8 and 9 show a commercial embodiment of the ventilator having
a housing 380 inside which is the circuit of FIGS. 1A and 1B except
for the main supply and the outlet fittings. All the regulatory
knobs appear here.
THE OPERATION SWITCH 35 IN USE
A summary of what the operation switch 35 does may be helpful. As
noted before, the switch 35 has two positions and controls by its
change from one position to another all that is needed to change
from the volume-cycled mode to the pressure-cycled mode and vice
versa.
In the volume-cycled mode, the port 36 is connected to the port 40,
so that the conduit 34 from the regulator 23 is connected to the
conduit 49 that leads to the inlet 56 of the cycle generator 50.
Also, the port 43 is connected to the outlet 46 through the axial
passage 44, so that the conduit 102 for PC1 pressure is connected
to the conduit 161 that leads to the port 158 of the flow
controller 140. The outlet 45 is, of course, also thereby connected
to the port 43 through the axial passage 44, so that the pressure
PC1 from the conduit 102 is also applied via the conduits 282, 283,
301, 302 and 324 to the time-override valve 280, the exhalation
switch 300, and the pressure switch 320.
In the pressure-cycled mode, the port 36 is cut off from the port
40, and the port 43 is cut off from the outlets 45 and 46. In this
mode the pneumatic signal from the pressure sensor 200 is connected
by the conduit 181 to the port 48 and from there (1) by the outlet
46 to the conduit 161 leading to the flow controller 140 and (2) by
the outlet 45 to the time-override valve 280, the exhalation switch
300, and the pressure switch 320. Also, the port 48 is connected to
the port 47, so that the conduit 181 is also connected by the
conduit 270 to the pressure regulator 255 and from there to the
conduit 274, the fixed bleed 273, and the chamber 216.
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.
* * * * *