Note: Descriptions are shown in the official language in which they were submitted.
' 17~935
VOLU.'~ V~ILATOP
Technical Field
This invention relates to ventilator eauipment
for use by patients requiring mechanical ventilatory
assistance in intensive care, respiratory care, cardiac
care units, and postoperative recovery rooms.
~ackaround of the Invention
A medical ventilator is an apparatus to give
artificial respiration. A volume ventilator delivers a
given volume regardless of the pressure in the breathing
system in which a patient is connected.
Present day nechanical ventilators are typically
used in one of five manually selected modes. A first is a
control mode in which the patient is totally inactive and
patient inhalation is controlled solely by the ventilator.
Under such circumstances, exhalation is always passive
with no participation by the ventilator except to open a
conventional expiratory valve. A second mode is an
assist-control technique in which an inspiratory cycle is
triggered either by the patient's inspiratory effort, or
by:the machine, whichever occurs first. Once triggered,
the ventilator delivers a selected tidal volume. In a
purely assist mode, the inspiratory cycle is triggered
only by the patient's inspiratory effort. The machine
does not initiate the inspiration automatically. Once
the inspiratory cycle is started, the ventilator delivers
the full tidal volume. A fourth mode is known as cpon-
taneous in which the ventilator supplies only the breath-
ing gas, and the patient breathes on his or her own
without any assistance. A fifth mode is referred to as
Ir~V (Intermittent Mandatory Ventilation). For this mode,
the ventilator is set to a very low rate, such as one or
two breaths per minute. The ventilator usually delivers
! 172935
-- 2
as in the assist mode. The reason for the I~IV is to
assure at least the set amount of ventilation if the
patient should decrease breathing spontaneously or should
stop breathing altogether.
In present day clinical practice and physiology,
ventilation is thought of in terms of minute volume
ventilation as a basic parameter. A derivation of minute
volume requires a calculation of, for example, tidal
volume and respiratory rate.
The presently available and commercially used
ventilators are all mechanical devices which are incapa-
ble of performing such calculations and are not equipped
for the adjustment of the mechanical functions according
to the calculated results. As a consequence, prior art
ventilators require manual settings of the mechanical
functions such as flow, expiration time, inspiration time
and the like, rather than the familiar physiological para-
meters, such as minute volume ventilation. Resultingly,
the prior art ventilators have proven very confusing and
cumbersome for the average nurse and physician.
Disclosure of the Invention
Deficiencies of the prior art are ameliorated
by the provision of an exemplary embodiment of the inven-
tion comprising a volume ventilator having a control
module, a pneumatic drive and oxygen mixing module, gas
flow control apparatus, an automatic mode control and
continuous positive airway pressure facility, and patient
breathing apparatus. The exemplary ventilator is eauipped
for three modes of operation, namely a standby mode, a
control mode and an automatic mode. In the standby mode,
the ventilator functions to monitor a patient inhalation
and exhalation, breathing rate and other parameters. For
the standby mode, no gas/oxygen is delivered by the venti-
lator to the patient. In the control mode, the ventilator
automatically delivers to a patient a prescribed minute
~ 172935
-- 3
volume of an air/oxygen mixture at a preset respiration
rate and inspiration-to-expiration ratio. The auto~atic
mode is a new modality in which a mandatory minute volume,
or MMV, is delivered to a patient for breathing. As the
name implies, the MMV mode assures that the patient has
adequate ventilation at all times even if his or her own
respiratory drive ceases completely.
The control moAule provides for dial adjust-
ments in physiological terms of minute volume, respira-
tion rate, inspiration-to-expiration ratio, inspiratory
plateau, and oxygen concentration. Logic circuitry in
the module performs all of the calculations needed for
determining the minute volume. The logic circuitry
advantageously controls the oxygen mixing and driving
module as well as the gas flow control apparatus for
determining the duration of inspiration and expiration
cycles, the air/oxygen concentration in the system, and
the automatic mode switching operations from spontaneous
patient breathing to assisted and/or control mode breath-
ing. The control module receives oxygen from a sourceand supplies it to the driving and oxygen mixing module
in accordance with the set physiological adjustments.
The driving and oxygen mixing module comprises
two cylinders, one for mixing air with the received
oxygen and a second for driving the mixture through the
gas flow control apparatus to either the automatic mode
control and CPAP facility or the patient breathing
apparatus. The two cylinders are mounted vertically in
opposing directions and are divided from one another by
a spacing and channeling block. ~,ach of the cylinders
has an interior chamber, each of which houses a flexible
bellows. A connecting rod extends through the channeling
block and is secured at each of its ends to weighted
plates secured to the bellows. This arrangement provides
for the compression and expansion of the two bellows in
~ 172935
-- 4
unison, but in opposite directions, and fixes the interior
volume of the two bellows. Resultingly, when the interior
volume of one bellows is decreasing during a vertical
movement, the volume in the other bellows is increasing
by the same amount.
The driving cylinder receives oxygen from the
control module during an inspiration cycle and utilizes
it to move upwardly the driving bellows for forcing an
air/oxygen mixture therein to the gas flow control
apparatus. The air/oxygen mixture is placed in the
driving bellows during an expiration cycle and from the
mixing bellows via a duct in the channeling block and a
pressure check valve. The oxygen in the driving cylinder
is conveyed to the mixing cylinder via electromagnetic
exhaust valve actuated by the control module during the
expiration cycle and under the influence of the mixing
bellows moving downward under the weight of its plate
member and thereby moving the driving bellows within the
driving cylinder.
During the succeeding inspiration cycle, the
oxygen in the mixing cylinder is transferred to the
mixing bellows via an electromagnetic mixing valve
actuated under control of the control module. The dura-
tion of the valve actuation determines the oxygen mix-
ture with air concentration during the inspiration cycle.
When the valve is deactuated and closed, the remainder
of the oxygen in the mixing cylinder, if any, is expelled
to the atmosphere external to the ventilator and air is
drawn into the mixing bellows via a pressure check valve
for the remaining duration of the inspiration cycle. At
the start of the next succeeding expiration cycle, the
air/oxygen mixture is transferred from the mixing bellows
to the driving bellows via a conduit in the channeling
block and a check valve for delivery to the gas flow
control apparatus during the following inspiration cycle.
:,.''
~ 1 72935
The gas flow control apparatus switchably
conveys a received gas mixture to either the patient
~ breathing apparatus or the automatic mode control and
CPAP facilities. The switching is accomplished by means
of an electromechanical valve controllably actuated by
the control module. Another electromechanical valve
actuatable by the control module switchably drives a
patient expiratory valve in the patient breathing
apparatus.
The automatic mode control and CPAP facilities
provide a flexible bellows assembly for receiving and
storing a gas mixture and for supplying that mixture under
a constant positive airway pressure to the patient
breathing passageway via the gas flow control apparatus.
The constant pressure illustratively is developed on the
stored gas mixture by a variable pressure source exerting
a force on a bellows plate secured to an upper portion of
the bellows.
In another embodiment, the bellows is located
within a cylinder and the pressure within that cylinder
is kept at a prescribed level. That level illustratively
is supplied by a blower with a Tee and butterfly valve
which restricts the flow and creates the air pressure.
Resultingly, the bellows plate moves vertically upward
and downward in response to the stored gas mixture and in
synchronism with patient breathing.
During patient exhalation in both the control
mode and the automatic mode, the diaphragm of the patient
expiratory valve is connected to the constant positive
airway pressure in the CPAP bellows via the multiport
valve of the gas flow control apparatus. As a result,
patient exhalation is regulated to exceed only the CPAP
magnitude.
For the automatic mode of operation, the patient
is enabled to breathe spontaneously from the gas mixture
stored in the CPAP bellows and the automatic mode control
~ 1 72935
- 6 -
facilities automatically inform the control module whether
such patient breathing is within or without a desired
range. To do so, the automatic mode control facilities
are illustratively furnished with four individual con-
ductors on a vertical slide bar arrangement and with awiper arm which is attached to the CPAP bellows plate and
which moves vertically over the bar conductors in response
to the elevation of the CPAP bellows. A photocell and
light source arrangement is advantageously used instead
of the bellows elevation slide bar conductors such that
the bellows interrupts the light supplied by the source
thereby indicating the elevated bellows position. Such
an arrangement suitably utilizes three light sources and
photocell pickups located at opposite sides of the bellows
to detect the bellows interrupting the light paths.
The bellows elevation is indicative of the gas
mixture stored therein and of the magnitude of patient
breathing in the automatic mode. An electrical signal is
applied to the wiper and is conveyed to one of the four
bar conductors for alerting the control module of the gas
mixture in the CPAP bellows. One of the conductors iden-
tif:ies a low bellows fill due, for example, to heavy
patient breathing. When the electrical signal is applied
through the wiper to that conductor, the control module
is effective to operate the driving and oxygen mixing
module for supplying to the CPAP bellows via the gas flow
control apparatus a preprogrammed large amount of gas mix-
ture to aid the spontaneous patient breathing.
A second one of the bar conductors identifies
that a patient is spontaneously breathing in the desired
range. Accordingly, when the wiper couples the electrical
signal to that conductor, the control module functions to
maintain the preset parameters of the gas mixture minute
volume.
A third one of the bar conductors identifies
the CPAP bellows is filled due to a patient breathing less
.
' ''''
! 1 7 2 9 3 5
- 7 -
than the desired volume during the automatic mode of
operation. It significantly indicates a need for assisted
breathing and causes the ventilator automatically to re-
configure itself to supply the mandatory minute volume of
the gas mixture in synchronism with the patient breathing.
The reconfiguration is accomplished when the electrical
signal is coupled through the bellows wiper to that third
bar conductor for activating the control module for auto-
matically switching the ventilator into an operation such
that the inhalation of a patient which is initiated by
the patient is equal to the tidal volume corresponding to
the dial settings so that a prescribed mandatory minute
volume of gas mixture is inhaled by the patient. When the
CPAP bellows is in the elevation where the wiper contacts
the third conductor bar,each breath is triggered by
sensing the patient's spontaneous start of a breath. The
ventilator continues to perform this operation as long as
the patient breathing requires the mandatory minute volume
of assisted breathing. When the breathing returns to the
spontaneous range and the CPAP bellows wiper rests on the
second bar conductor, the control module is activated for
reswitching the ventilator from the triggered operation
to the spontaneous patient breathing.
The fourth one of the bar conductors identifies
when the CPAP bellows is excessively filled due to a
patient breathing much less than the desired spontaneous
range. When the electrical signal is connected through
the bellows wiper to the fourth conductor, the control
module is automatically switched from the automatic to
the control mode to supply the mandatory minute volume
for patient breathing. The ventilator thereafter remains
in the control mode until the patient respiration spon-
taneously increases to at least the level corresponding
to the dial settings.
The gas flow control apparatus is strategically
equipped with safety check valves which enable the patient
~ 1 72~3~
-- 8
to breathe freely from the atmosphere when a pressure
decrease occurs in the patient breathing passageway
through the gas flow control apparatus. These valves
perform these functions in all modes of ventilator
operations.
Flow and pressure signal transducers are located
at strategic passageways in the gas flow control apparatus
for furnishing electrical signals to the control module.
The signals are monitored by the control module and enable
it to perform the logic operations needed for ventilator
functions including the aforementioned control and auto-
matic mode switching and gas volume control actions. One
such flow transducer is located in the inlet passageway
between the gas mixture driving bellows and the gas flow
control apparatus. A second transducer is located in the
inlet passageway to the patient breathing apparatus. A
third transducer is located in the expiratory passageway
between the patient expiratory valve and the atmosphere
éxternal to the ventilator.
A pressure gauge is provided in the gas flow
control apparatus for visually displaying the pressure in
the inlet passageway to the patient breathing apparatus.
In the same passageway, a transducer continuously monitors
the airway pressure for providing electrical signal infor-
mation to the control module for effecting a patient
pressure limit not to exceed a desired set limit. Another
pressure transducer monitors the CPAP pressure providing
electrical signal information to the control module for
enabling it to regulate the CPAP pressure in the CPAP
facilities. The pressure transducer advantageously is
utilizable for regulating the CPAP pressure and the set
maximum airway pressure or pressure limit by controlling
the opening valve pressure
An applique to the ventilator is a nebulizer for
utilizing a gas flow for producing an aerosol effect in
~ t 72935
g
administering medication. The nebulizer is equipped with
automatic timing facilities which are activated by a con-
trol device on the ventilator for activating the nebulizer
for a fixed time during which the desired flow is supplied
to the patient. The control module of the ventilator is
advantageously equipped with flow logic which controls the
valve driver for reducingly adjusting the total flow
supplied to the driving and oxygen mixing module to com-
pensate for the flow introduced by the nebulizer and to
insure that the desired flow is supplied to the patient in
accordance with the control dial settings. Thus, the
minute volume supplied to the patient is the same whether
the nebulizer is on or off.
The control module illustratively is equipped
with a scaler and calculations circuit which cooperates
with the front face controls for minute volume, respira-
tory plateau, nebulizer, sigh frequency, manual cycle, and
manual sigh for producing output electrical signals for
calculated tidal volume, rate timing, binary flow, manual
breaths and inspiration gating. The scaler and calcula-
tions circuit is disabled during the ventilator standby
mode of operation and is operative during ventilator
control and automatic operating modes. Sigh scaling and
calculation functions are enabled during the ventilator
control operating mode.
The binary flow signals control valve enable
logic in the control module for activating valve drivers
circuitry illustratively to, in turn, actuate six valves
combinationally for supplying binary weighted valves of
flow to the driving and oxygen mixing module. The valve
enable logic is enabled by a tidal volume comparator
which supplies a flow gate enable signal during the
period of actual flow.
The tidal volume comparator compares the calcu-
lated tidal volume signal from the scaler and calculations
.,
} ~72935
-- 10 --
circuitry with an instantaneous tidal volume signalgenerated by an actual flow integrator. The tidal volume
comparator supplies the flow gate enable signal as long
as the calculated tidal volume signal is greater than the
- 5 instantaneous tidal volume signal. During this period,
the flow gate enable signal actuates and maintains
actuated the exhaust valve in the driving and oxygen
mixing module.
The actual flow integrator is initially reset
in response to a rate timing pulse from the scaler and
calculations circuit to initiate a breathing cycle. It
then integrates an actual flow signal received from a
summer circuit. The latter combines the binary output
flow signals from the valve enable logic with a nebuli7er
"ON" signal to produce a resultant actual flow signal.
Another tidal volume comparator in the control
module compares the instantaneous tidal volume signal
from the actual flow integrator with a compensated cal-
culated tidal volume signal from the scaler and calcula-
tions circuitry. The compensation is effected by a frontface control dial adjustment for oxygen concentration in
the range from approximately 21 to 100~ oxygen concentra-
tion. The desired concentration is achieved by having
the comparator actuate an oxygen mixing valve in the
driving and oxygen mixing module for combining desired
oxygen with air for desired time periods.
The control module is further equipped with
nebulizer flo~ logic which is controlled by a nebulizer
switch and an inspiratory flow sensor in the gas flow
control apparatus for operating the flow valve driver to
reduce the binary weighted flow delivered to the driving
and oxyger. mixing module by a magnitude equal to that
supplied to the patient inhalation by the nebulizer.
A fill monito~ circuit is furnished in the con-
trol module for cooperating with the automatic mode
-- 1 1 --
control and CPAP module for controlling the valve enablelogic illustratively to deliver 100 liters per minute
flow to the driving and oxygen mixing module whenever the
patient breathes more than the magnitude set by the con-
trol module dials. The delivered flow reestablishesdesired fill in the automatic mode control and CPAP module
with the control module actuation of control and expira-
tory valves in the gas flow control apparatus. The valve
actuation is effected by inverter and gate logic under
control of the fill monitor. The latter is operated by
a fill sensor in the automatic mode control and CPAP
module when the patient breathes more than has been set.
The gate logic comprises AMD and OR gates for
advantageously controlling the expiratory and control
valves in the flow control apparatus for assist and con-
trol levels of patient breathing. A necessity of
operating at the latter levels is sensed by the assist
and control level sensors in the automatic mode control
and CPAP module. The gates are also ena~led by inspira-
tory logic and comparator circuitry in the controlmodule which are driven by the patient inspiratory flow
sensor in the gas flow control apparatus and a sensiti-
vity control dial of the control module.
The control module is further e~uipped with
pressure comparator circuitry for comparing patient
inhalation pressure with a prescribed pressure limit and
for activating a pressure relief valve when that limit
is exceeded.
A servo control ~rrangement in the control
module analyzes pressure in the CPAP module with a CPAP
control dial setting for controlling patient CPAP
pressure.
.
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' 17293~
- 12 -
Drawing Description
FIG. 1 is a block and schematic diagram of the
illustrative volume ventilator;
FIGS. 2 through 8 are functional schematic
diagrams depicting operational modes of the structure
in FIG. l;
FIG. 9 is a block schematic diagram of the
control module of FIG. l; and
FIG. 10 depicts waveforms for a cycle of
breathing and illustrates the inspiratory period
including a flow time with an inspiratory pause and
the su~sequent expiratory period.
Reference is made to our copending Unites States
Patent Application Serial ~o. 11,636 filed February 12,
1979, entitled "Flow Control ~quipment," which discloses
circuit configurations suitable for use in various circuit
components of this application. The disclosure of that
application is incorporated herein by reference as though
f-ully disclosed.
` 25
'"
- 13 - l~7293
Detailed Descri~tion
As shown in F~G. 1, the volume ventilator com-
priaes rive basic building blocks including a control
mcdule 1, a driving and oxygen mixing module 2, a gas flow
- 5 control apparatus 3, an automatic mode control and CPAP
(Continuous Positive Airway Pressure) structure 4, and a
patient breathing apparatus S. Control module 1 is
equipped with a plurality of controls 6 through 9 for
respectively adjusting minute volume, respiratory rate,
inspiration-to-expiration ratio, and the oxygen concentra-
tion for the system. Module 1 is furnished with addition-
al control dials and buttons, namely; 105 for sensitivity
control in assisted breathing, 106 for patient pressure
control, 107 for inspiratory plateau percentage control,
lS switch 108 for timed nebulizer operation, 109 for sigh
frequency control, button 110 for manual sigh control,-
111 button for manual cycling, 112 for CPAP dial control,
and switch 90 for mode selection.
Briefly, module 1 performs several principal
functions. A primary function is to deliver an appropri-
ate flow of the driving gas, oxygen, from a source (not
shown) via tubes 10 and 11, a check valve 12 and a tube 13
into an interior chamber 14 of a drive cylinder 15.
Another function of module 1 is that is furnishes the
logic and timed electrical signals for strategically oper-
ating the various electromechanical valves utilized in the
volume ventilator system.
The mixing module 2 comprises two cylinders 15
and 16 having a respective interior chamber 14 and 18,
each of which houses a respective flexible bellows 19, 20.
Ends 21, 22 of each such bellows are affixed to a surface
23, 24 of block 17. ~ree, or movable, ends 25, 26 of
each of the bellows 19 and 20 are secured to respective
; pla,e members 27 and 28, thus to provide respective inner
cha~ers 29, 30. To fix the interior volume of the two
bellows chambers 29, 30, a rigid rod 31 extends through a
l 1 72935
- 14 -
bore 32 in block 17 and is secured at its ends 33, 34 to
facing surfaces 35 and 36 of plate members 27 and 28.
The bore 32 has a slightly larger diameter than that of
rod 31 so that chambers 29 and 30 are effectively sealed
off from one another and so that the bellows 19 and 20
are free to move up and down within the cylinders 15 and
16. Thus, the interior volume of each of the cylinders
15 and 16 is the same. Significantly, the inner volume
of the two bellows 19 and 20 is fixed and, because of
the interconnecting rod 31, they must move in unison, but
in opposite directions. As a consequence, when the volume
of bellows 19 is decreasing during an upward travel, the
volume within bellows 20 is increasing by the same amount.
During a downward travel of bellows 19, its volume in-
creases while that of bellows 20 decreases during itsconcurrently downward travel.
The operations of module 2 are subdivided into
a driving function for both the patient breathing apparatus
5; and the automatic mode control and C~AP structure 4 and
an air/oxygen mixing function. The driving function
involves inspiration and expiration cycles controllable
by:the control module 1. The mixing function is effected
during the inspiration cycle and is performed in the
mixing cylinder 16. During this time the inner chamber 29
of bellows 19 is filled, as explained later, with a pre-
scribed mixture of air and oxygen preparatory to an inspir-
ation cycle.
Referring to FIGS. 1 and 2, an inspiration cycle
is now described. Proximate to the start of such a cycle,
the control module 1 supplies an electrical signal to com-
plete a circuit path through a winding 37 of an exhaust
electromagnetic valve 38 to a negative battery potential
for actuating and closing that valve and thereby precluding
an exhaustion of o~ygen from the interior chamber 14 of
cylinder 15. At about the same time, oxygen is applied via
the control module 1 and tube 13 in,o chamber 14 so that
.. ... . . .
~ 1 72 93 ~
the pressure in that chamber and on plate member 27
increases for causing a compression of bellows 19. As
soon as the pressure in bellows lg becomes higher than the
opening pressure of a check valve 39 therein, that valve
moves upward for closing a communicating bore 40 extend-
ing between the inner chamber 30 and chamber 29 via valve
39. The contents of bellows 19 are concurrently extended
through a channel 41 in block 17 and a tube 42 to the gas
flow control apparatus 3 for delivery to either the CPAP
bellows structure 4 or the patient breathing apparatus 5
as explained later. The inspiratory cycle consists of a
flow portion as explained above which may be followed by
a shorter period, also part of the lnspiratory cycle,
during which there is no flow. This no-flow period is
referred to as inspiratory plateau. At the termination of
the flow portion of the inspiration cycle, the check valve
12 closes to seal the interior chamber 14 of cylinder 15.
Concurrently, the control module 1 causes the deactuation
of the exhaust valve 38 by withdrawing the aforementioned
actuating signal. Resultingly, as depicted in FIGS. 1 and
3, the weights of plate members 27 and 29 urge the bel-
lows 19 and 20 downward for effecting an opening of check
- valve 39 and, in turn, allowing an air/oxygen mixture in
chamber 30 to be communicated through bore 40 for filling
chamber 29. As the bellows 19 descends, it displaces the
previously delivered oxygen from chamber 14 through the
exhaust tube 44, valve 38 and tube 43 into chamber 18 of
cylinder 16 and until the bellows reach their lower excur-
sion limit and as illustrated in FIG. 4. The delivered
oxygen remains in chamber 18 for the duration of the
inspiratory plateau period and the expiration cycle pre-
paratory to a mixing-with-air operation which occurs on
the next inspiration cycle. The expiration cycle is
defined as the period from the end of inspiratory plateau
to the start of inspiratory flow.
! ~ 7 2 9 3 5
- 16 -
Module 2 is equipped with facilities for
selectively transferring some or all of the oxygen stored
in chamber 18 to either the interior chamber 30 of
bellows 20 or the atmosphere exterior to the equipment.
The transfer occurs during the inspiration cycle when
both the check valve 39 for bellows 19 and the exhaust
valve 38 are closed as priorly explained during the
inspiration cycle.
An oxygen transfer from chamber 18 to chamber 30
occurs in response to both an upward movement of bellows 19
and 20 as priorly described and an actuation of valve 45
for a predetermined time period of the inspiration cycle.
The valve actuation is effected in response to an electri-
cal signal supplied by module 1 over conductor 46, as
hereinafter explained, to complete a path through a winding
47 of valve 45 to negative battery potential. Upon actua-
tion, valve 45 completes a channel 48 (FIG. 5) for com-
municating the oxygen from chamber 18 through tube 49,
opened check valve 50, tubes 51 and 52 and a conduit bore
53 in block 17 into chamber 30 of bellows 20. A simplified
schematic illustration of the structure for the oxygen
transfer to chamber 30 is depicted in FIG. 5. The check
valve 50 opens automatically and remains open as long as a
predetermined differential pressure exists between tubes
49 and 51. Vpon module 1 withdrawing the electrical
actuating signal from conductor 46, valve 45 is deactuated
and closes for, in turn, interrupting further transfer of
oxygen to the bellows chamber 30.
Oxyyen is expelled from chamber 18 to the atmos-
phere when valve 45 is not actuated during the inspiration
cycle. The channel for expelling the oxygen extends from
chamber 18 through tube 49, opened check valve 50~ tube 51,
and a check valve 54 to the-atmosphere. Valves 50 and 54
automatically open and remain open as long as a predeter-
mined differential pressure persists between the atmosphere
~ 1 ~293~
- 17 -
and the expelling channel. During the oxygen expelling
to the atmosphere and in response to the expansion of
bellows 20 upward during the inspiration cycle while the
mixing valve 45 is closed, air is drawn into bellows
chamber 30 via the check valve 55 and tube 52 to mix with
the oxygen contents therein. Valve 55 automatically opens
and remains open as long as a differential pressure per-
sists between the atmosphere and the bellows chamber 30.
A simplified diagram illustrating the oxygen expelling
and air intake structure is shown in FIG. 6.
~ odule 1 controls the duration of the inspiration
time during which both bellows 19 and 20 move upward. It
also controls the desired concentration of oxygen by
simply controlling the opening and closing of the mixing
valve 45 for prescribed lengths of time during the inspir-
ation cycle. Illustratively, in a case where an inspira-
tion time is two seconds, and the mixing valve 45 is open
half the time, or one-second, the gas entering bellows 20
is half oxygen and half air. Resultingly, a mixture is
produced in chamber 30 which is approximately sixty per-
cent oxygen concentration (air being twenty-one percent
oxygen).
The mixed gas in bellows chamber 30 is trans-
ferred during the succeeding expiratory cycle from chamber
30 to chamber 29 via bore 40 and check valve 39 and there-
after to the gas flow control apparatus 3 during the next
following inspiration.
Apparatus 3 performs gas flow switching, the
patient expiratory valve driving, safety, sensing, and
display control functions. The switching function in-
volves conveying a gas mixture from the input tube 42
either to the patient breathing apparatus 5 or to the
automatic mode control and CPAP facilities 4. This
switching action is effected by operations of an electro-
mechanical valve 56 under control of module 1 asexplained hereinafter. Another function is switchably
~ 172g35
- 18 -
to drive an expiratory valve 57 in the patient breathing
apparatus 5 by means of a multiport electromechanical
valve 58 actuated under control of rodule 1 as later
described. Apparatus 3 is e~uipped for safety functions.
One safety function is provided by means of a spring
loaded safety valve 59 which enables a patient to inhale
from the atmosphere in the event of machine failure to
deliver prescribed gas mixtures at predetermined pres-
sures in the gas flow conduit. Another safety function
is to limit the ?ressure in the gas flow conduit to
-the patient breathing apparatus 5 and the automatic mode
control and CPAP facilities 4 by means of variable
pressure limiting valve devices 60 and 61. Valve 61 opens
to vent the gas flow conduit to the atmosphere when the
conduit pressure exceeds a predetermined value fixed by
its adjustable spring. Valve 60 performs two functions.
One is to limit the patient pressure within the patient
breathing apparatus 5 to a maximum safety limit. The
second function is to control the pressure to a level set
v 20 by dial 106 of control module 1. Valve 60 is electrically
operated via its winding 60'. Apparatus 3 is furnished
with transducer sensors 62 and 63 which function to moni-
tor the gas flow through its input tube 42 and through a
patient inspiratory tube 64. A pressure gauge 65 is pro-
vided in apparatus 3 for visuallv displaying the pressure
in tube 64 to the patient breathing apparatus 5. A
pressure transducer 66 is included for continuously moni-
toring pressure in tube 64 and providing electrical signal
information to the control module 1 for enabling it to
regulate the maximum patient pressure in accordance with
the dial setting 106. A oressure transducer 116 is
included for continuously monitoring pressure in tube 118
and providing electrical signal information to the control
module 1 for enabling it to regulate CPAP pressure.
Before further describing the operations of the
flow control apparatus 3, it is advantageous first to ex-
plain the structural configuration of both the patient
? 1 72935
-- 19 --
breathing eauip~ent 5 and of the automatic mode control
and CPAP facilities 4. A patient is connectable to a
conventional T-piece 67 which is connected to the patient
breathing tube 64 of the flow control apparatus 3 via
corrugated hoses 68 and 69 and a gas delivery system 70.
The latter is suitably a commercially available heated
humidifier arrangement. The other end of the T-piece
advantageously is connected to a controlled expiratory
valve 57 which controls patient expiration to the atmos-
phere via an expiration transducer 71 in response to flowpressures in the expiration control tube 72.
In FIG. 1 and as functionally depicted in
FIGS. 7 and 8, the expiratory valve 57 is constructed
with an inlet 73 attached to the T-piece 67, and outlet
74 connected to transducer 71, and advantageously, a
flexible inflatable "mushroom" diaphragm 75 inflatably
connected to the expiration control tube 72. Function-
ally, diaphragm 75 is inflated when the pressure in tube
72 is e-qual to the pressure in the inlet 73. The infla-
tion occurs as hereinafter explained during inspirationand during portions of the expiration time. During
inflation, diaphragm 75 occludes the orifice of inlet 73
as shown in FIG. 7. This occurs because the total
surface area of diaphragm 75 facing the orifice of inlet
73 is larger than the surface area of the inlet lumen.
Resultingly, the inflated diaphragm 75 presses with more
force against the orifice of inlet 73 than the opposing
force produced by the pressure at inlet 73 through T-
piece 67. As a consequence, the opening pressure of the
expiratory valve 57 is controlled by the pressure applied
from the inside of diaphragm 75. When that pressure is
lower than that at inlet 73, diaphragm 75 deflates to
open the expiratory passageway from the inlet 73 to the
outlet 74 for expelling a patient expiration through
transducer 71 to the atmosphere external to the ventila-
tor. Transducer 71 senses the expired gases and provides
signals to the control module 1 for determining expiration
flow and volume.
~ 1 72935
- 20 -
The automatic mode control and CPAP facilities 4
comprise a flexible bellows 76 attached at a lower end 77
to a supporting block 78. The latter is constructed with
a bore 79 affixed to a tube 80 coupled to a control valve
(CPAP fill valve) 56. Bellows 76 receives a gas mixture
from bellows 19 upon an opening of valve 56, as explained
later, and resultingly moves upward for storing prescribed
volumes of the received gas within its internal chamber 81.
An upper end 82 of bellows 76 is secured to an enclosing
plate 83 against which is applied an adjustable force from
a source 84. The latter suitably comprises a constant
torque motor, pneumatic cylinder and piston, a simple
weight or bellows 76 may be enclosed in a housing. Source
84, under control of motor 113, blower 114 and a servo
Y 15 valve 115 and transducer 116, produces a positive CPAP
pressure upon the gas mixture stored within the bellows
chamber 81. Motor 113 operates the blower 114 to supply
air flow from inlet 166 via conduit 117, servo valve 115,
conduit 119 to the atmosphere. Valve 115, under control
of module 1, as later explained, closes or opens until the
pressure in conduit 118, as sensed by transducer 116 is
equal to the setting of dial 112 of module 1. Changes in
the setting of dial 112 cause valve 115 to adjust to
maintain the CPAP pressure. Any changes of the motor
speed, air density, atmospheric attitude and the like,
are all accounted for by the servo control to maintain the
dialed-in CPAP pressure.
An electrical ground potential is applied to
plate 83 for extension to a wiper arm 85 affixed thereto.
Wiper 85 is arranged slidably to move across four fixed
and independent vertically aligned conductors 86, 87, 88
and 89 in response to the vertical movement of bellows 76.
One of the conductors 86-89~receives the ground potential
from wiper 85 upon the elevation of bellows 76 and so as
to signal the control module 1 of the volume of gas within
~ t 7293~
- 21 -
bellows chamber 81. The sround potential on wiper 85 is
extended to conductors 86, 87, 88 and 89, respectivcly,
to specify the following: (1) fill bellows 76 due to
patient breathing more than set minute volume, (2) bellows
76 adequately filled for spontaneous patient breathing,
(3) bellows 76 filled by greater amount due to patient
breathing less than the set minute volu~e and breathing
assistance required by patient, and (4) bellows 76 filled
excessively due to very little patient breathir.g and
switching to controlled patient breathing required.
The ventilator of FIG. 1 is designed to operate
in three modes; namely, a standby mode-, a control mcde and
ar. automatic mGde. Preparatory to operating in one of
these three modes, the controls 6-9 and 107 of module 1
are set to establish the vital parameters of prescribed
minute volume (6), respiration rate (7), inspiratory
plateau (107), inspiration-to-expiration ratio (8), and
oxygen concentration (9). Resultingly, oxygen is delivered
through modules 1 and 2 to the inlet tube 42 of the gas
flow control apparatus 3 as priorly explained and at the
prescribed air/oxygen mixture, minute volume, respiration
rate, inspiratory plateau, and inspiration-to-expiration
ratio established by the setting of controls 6-9 and 107.
In the standby mode, a selector switch 90 of the
control module 1 is moved to its standby position for dis-
abling the control module circuitry from effecting a
delivery of any gas to the driving and oxygen module 2
while the patient monitoring operations continue to func-
tion as hereinafter described.
For the contrcl mode of the ventilator operation,
a selector switch 90 of module 1 is moved to a position
which opens the actuating circuit for the magnetic valve
56 and thereby causes its closing. As a result, all of
the gas delivered from bellows 19 to tube 42 during the
inspiration cycle of the driving module 2, as priorly
described, is directed to the patient via a passageway
! 172935
- - 22 -
including transducer 62, check valve 91, tube 92, check
valve 93, tube 94, transducer 63, tube 6a, hose 68,
humidifier 70, hose 69 and T-piece 67. Check valves 91
and 93 automatically open when the pressure of the
delivered gas mixture exceeds that within the described
passageway leading to the patient. At the same time, the
control module 1 actuates the magnetic valve 58 via its
energizing winding 97 for connecting the e~piratory valve
57 via tube 72 to tube 92 of the described passageway to
the patient. As a consequence, pressure within the mush-
room diaphragm 75 is the same as in the patient passageway
and thereby inflates diaphragm 75 for closing the lumen
of inlet 73 so that all of the gas supplied by bellows 19
and the described passageway is delivered to the patient.
During the expiratory cycle of the driving
module 2 operation, the control mcdule 1 actuates valve 58
via its second energizing wir.dir.g 98 for switching the
expiratory valve diaphragm 75 from tube 92 into connection
wit~. the CPAP bellows 76 via tubes 72 and 80. Accordingly,
the opening pressure of the expiratory valve 57 decreases
to the CPAP pressure maintained in bellows 76. Thus,
diaphragm 75 deflates for opening valve 57 and the patient
exhales through transducer 71 to the atmos~her~ until the
pressure at inlet 73 becomes proximately equal to the CPAP
pressure of bellows 76.
If, during operation in the control mode, t~e
vo'ume of gas in bellows 76 drops sufficiently for any
reason, wiper 85 slides onto the bellows fill conductor 86
for signalirg the control and driving modules 1 and 2 to
actuate and open valve 56 so that a predetermined larger
volume of gas is delivered to bellows 76 via tuke E0 for
maintaining the prescribed CPAP function with wiper 85 on
the spontaneous breathing conductor 87.
The automatic mode of the ver.tilator operation
i5 established by operating the selector switch 90 of
control module 1 to a second position for thereby effecting
.. . .. . . .. . ~ .. . . , . . .. . , ... . ~ . ~ ..
l 1 7293~
- 23 -
an operation of valves 56 and 58 of FIG. 1. Valve 56operates over a path extending from negative battery
potential through the valve energizing winding 95 and
- conductor 96 to an electrical signal (not shown) sup-
plied by module 1. Upon operating, valve 56 provides a
conduit for extending the prescribed minute volume of gas
mixture from the interior chamber 29 of bellows 19 to the
interior chamber 81 of bellows 76 via a path from cham-
ber 29 through opening 41, tube 42, transducer 62, check
valve 91, tube 92, valve 56, tube 80 and bore 79.
The last-mentioned operation of valve 58 is
effected over a path from negative battery potential
through a second one of the valve energizing windings 98
and conductor 99 to an electrical signal (not shown) sup-
plied by module 1. In operating, valve 58 is effectiveto couple the interior chamber 81 of bellows 76 to the
inflatable diaphragm 75 of the expiratory valve 57 over a
path including tube 72, vaive 58, tube 80 and bore 79.
Resultingly, diaphragm 75 is inflated due to equal pres-
sures in tube 72 and the inlet 73 of valve 57. Thus, theairway pressure and the opening pressure of the expiratory
valve 57 are the same as the pressure in chamber 81 of the
CPAP bellows 76.
Thereafter, a patient connected to the T-piece 67
can breathe freely from the CPAP bellows 76 via tube 80,
check valves 167 and 93, tube 94, transducer 63, tubes 64
and 68, humidifier 70, tube 69 and T-piece 67, advantage-
ously at any time rather than under control of the control
module 1 and driving and mixing apparatus 2. Bellows 76
functions essentially as a reservoir for the gas mixture
breathed by the patient. It is replenished in bellows 76
by the driving apparatus 2 continuously delivering the set
minute volume of gas mixture at the respiration rate and
inspiration-to-expiration ratio set by controls 6-9 of
module 1. During patient exhalation, the expiratory
valve 57 is opened for enabling the patient to exhale
through transducer 71 to the atmosphere. The valve opens
~ 72935
- 24 -
as a result of the pressure at its inlet being greater than
that in tube 72. The pressure differential across check
valve 93 during ~atient exhalation also causes it to
close which insures that all of the exhalation is through
exhalation valve 57 and transducer 71 to the atmosphere.
Several conditions may occur during patient
breathing. For example, the patient may breathe more or
less than the minute volume set by control 6. If the
patient breathes more, the level of bellows 76 drops as
priorly explained, and wiper 85 extends ground to con-
ductor 86 and over a lead 101 of cable 100 for signaling
the control module 1 to supply a preprogram larger volume
of gas mixture through apparatus 2 and 3 to bellows 76 so
that it operates in the spontaneous breathing range with
wiper 85 on conductor 87. When wiper 85 rests on that
conductor, ground is supplied over lead 102 of cable 100
for signaling the control module to supply the gas mixture
needed for patient breathing.
- Automatic breathing assistance is given to the
patient when bellows 76 excessively fills and resultingly
signals that the patient is breathing less than the pre-
scribed minute volume. When bellows 76 fills to the
extent that wiper 85 slides into contact with conductor 88,
the control module 1 is signaled over lead 103 of cable 100
to that effect and, if the control module concurrently
senses a flow signal through transducer 63, module 1
deactuates and closes valve 56 by withdrawing the ener-
gizing signal from the conductor 96. Concurrently,
module 1 deenergizes winding 98 and energizes winding 97
of valve 58 as priorly explained for connecting the
expiratory valve diaphragm 75 via tube 72 to tube 92. This
switchover operation causes the remaining portion of the
tidal volume to be delivered from the driving bellows 19
directly to the patient. Consequently, the patient trig-
gered the inspiration by breathing less and the ventilatorincreases the depth of the breath in synchronism with the
. .
~ 1 7293~
- 25 -
patient breathing. Switchback to the automatic mode of
the ventilator operation is effected when the bellows
fill decreases to the point where wiper 85 rests again on
- conductor 87 and a ground signal is applied thereover to
conductor 102 for causing module 1 to reenergize valves 56
and 58 to again establish the automatic mode of operation,
as already explained.
If the patient breathes very little or not at
all, bellows 76 fills to a level which causes the venti-
lator to switch automatically to its control mode ofoperation. This action occurs when bellows 76 fills to
the point where wiper 85 slides over contact 88 to con-
tact 89. As wiper 85 slides over contact 88, it effects
the automatic switchover to assisted breathing, as already
described. When wiper 85 slides onto conductor 89, it
effects the automatic switchover to control breathing.
When wiper 85 slides onto conductor 89, it extends the
ground signal over lead 104 of cable 100 to the control
module l for signaling it to switch the ventilator into
its control mode of operation with subsequent patient
breathing directly from the driving bellows chamber 29.
: Turning now to FIG. 9, the circuitry of control
module 1 for controlling its flow control valves as well
as the strategic flow valves in the driving and oxygen
mixing module 2, gas flow control apparatus 3 and the
automatic mode control and CPAP module 4 is now described.
Module 1 is equipped with a scaler and calculations cir-
cuit 120 which receives dial-in, switch and pushbutton
electrical data on input conductors 121 through 128 for
scaling and conversion into calculated output voltages
and other electrical signals on conductors 129 through 133
for the flow control and timing operations. A tabulation
of the dial, switch and pushbutton devices, together with
illustrative range or setting information and the conduc-
tor on which the functional data is received is asfollows:
! 172935
- 26 -
R~NGE OR FUNCTIONALINPUT
DEVICE SETTING CO~DUCTOR
Minute volume dial 6 2 to 30 liters/minute 121
- Respiratory rate 6 to 40 breaths/minute 122
dial 7
Inspiration-to- 1:1 to 1:4 123
expiration dial 8
Inspiration plateau 0 to 40% of inspiratory 124
dial 107 time, during which time
there is no flow and no
patient exhalation.
Nebulizer switch 108 Controls a connection 125
of a nebulizer to the
patient inhalation line
for a timed period.
Sigh frequency OFF, 32, 64 and manual 126
rotary switch 109 positions operatively
corresponding to every
32 or 64 breaths auto-
matically or manually
under control of push-
button 110 and conduc-
tor 127. Sigh has the
effect of increasing the
25 -' tidal volume of a par-
ticular breath by 50%
with a maximum 2-liter
tidal volume.
Manual cycle Manual initiation of a 128
30 pushbutton 111 start of a respiratory
cycle.
A tabulation of the calculated outputs from
circuit 120 together with a brief description of the
; output signals and the conductors on which they are
supplied is as follows:
OUTPUT
CALCULATED OUTPUT DESCRIPTION CONDUCTOR
Tidal volume voltage A voltage corresponding129
to the tidal volume and
proportional in magni-
tude to minute volume/
rate. Voltage limited
to the value correspon-
ding to 2 liters.
! 17293S
- 27 -
OUTPUT
CALCULATED OUTPUT DESCRIPTION COND~CTOR
Rate timing pulse A short pulse (approxi- 130
mately 10 milliseconds
nominal) which is used
to initiate a breathing
cycle. The interval be-
tween successive pulses
is related to the rate
dial setting by interval
in seconds equal to 60/
rate.
Binary flow signal Multidigit binary number 131
voltages corresponding
to the actual flow re-
quired during the flow
portion of the inspira-
tory cycle. This flow
signal is proportional
to
~lV(l + I)
1 - % plateau
when the nebulizer is
! ~. "OFF" and proportional
- to
MV(l + R)
I nebulizer
1 - % plateau flow
when the nebulizer is
"ON". Illustratively,
the nebulizer flow is
approximately 10 liters/
minute. The binary num-
ber is in 2 lite-s/minute
steps and has a value
which is limited to 100
liters/minute. The signal
is on 6 lines represented
by conductor 131 and corres-
pGnds to 2, 4, 8, 16, 32
and 64 liters per minute.
~ 1 7293~
- 28 -
OUTPUT
CALCULATED OUTPUT DESCRIPTION CONDUCTOR
Inspiratory gate A voltage whose duration 132
signal is equal in seconds to
60/Rate (1 + Expiration/
Inspiration) which is the
total inspiratory period
including any inspiratory
plateau.
Turning now to FIG. 10, it illustrates a some-
what idealized waveform of a cycle of breathing for
illustrating the inspiratory pause portion of the inspira-
tory time in relation to the actual flow portion of
inspiration. Thus, inspiration time is divided into two
parts, namely flow time and inspiratory pause. During
flow time actual rlow takes place and during the pause,
there is no flow. During the total inspiratory time,
the exhalation valve 57 of FIG. 1 is closed. This action
serves to keep the patient's lung expanded for the inspira-
tory pauQe.
, The inspiratory pause is expressed as a percen-
tage of the total inspiratory time I. Using the
parameters F = flow, MV = minute volume, and E = expira-
tory time and t = inspiratory pause, the following
relationship is derived:
MV(l + I)
F =
(1 ~ I)
With no inspiratory pause, t = 0 and the relationship
reduces to
F = MV(l + I)
The range of I as utilizable in the ventilator is 0 to 40%
and is controlled by the inspiratory plateau dial 107 of
FIG. 1. For a given setting of MV and I:E ratio by
controls 6 and 8 of FIG. 1, the flow F is increased with
the increasing percentage of inspiratory plateau as the
1 172935
- 29 -
actual flow is "ON" for a shorter portion of the inspira-
tory time. The inspiratory plateau control 107 is
illustratively a potentiometer which forms part of a
voltage divider (not shown) circuitwise incorporated into
the scaler and calculations circuit 120 of FIG. 9.
Utilization of the foregoing in the control
module 1 is, by a derivation of two flows, as follows:
fl = MV(l + I) and
MV(l + I)
f2 t
(1 ~ I)
The first flow fl defines the "I" time by an integration
of an electrical value of fl until the calculated tidal
volume TV = RMte is reached. The second flow f2 defines
the actual output flow from the valves 12. Flow f2 is
greater than fl causes the tidal volume to be reached
before the inspiratory time I and is the actual inspira-
tory portion of I.
The three different modes of the ventilator
operation are selected hy the mode selection switch 90
depicted by a block in FIG. 9. In the standby mode,
switch 90 supplies a signal for disabling the operation
of the scaler and calculations circuit 120 and the fill
monitor circuit 134. Resultingly, output 131 of
circuit 120 controls the valve logic 135 and valve
driver 136 for deactuating the flow valves 137 through
142 and thereby blocking the flow of gas via tube 11,
check valve 12 and tube 13 to the driving and oxygen mixing
module 2. The remainder of the ventilator operations for
patient monitoring such as inhalation, exhalation,
breathing rate and the like are functional as hereinafter
described for the automatic and control modes of operation.
In the automatic mode and with the CPAP wiper 85
in contact with bar conductor 87 of FIG. 1, the operation
~ 172935
- 30 -
is as follows: Starting at the beginning of an inspira-
tion cycle, the scaler and calculations circuit 120 sup-
plies a rate timing pulse over conductor 130 for resetting
the actual flow integrator 144 and, in turn, its output
to zero. Comparator 145 compares the calculated tidal
volume signal received from circuit 120 over conductor
129 with the output of integrator 144. Initially, the
integrator output is less than the calculated tidal vol-
ume and, resultingly, comparator 145 generates a flow gate
voltage at its output for controlling the exhaust valve 38
of module 2, valve enable logic 135, and fill monitor 134
of FIG. 9.
The flow gate voltage actuates and closes the
, exhaust valve 38 and thereby precludes an exhaustion of
i' 15 oxygen from chamber 14 of module 2, as priorly explained.
. Concurrently, the flow gate voltage enables the
logic circuitry 135 to pass the binary number signals
from circuit 120 to activate the valve driver 136 and, in
turn, to actuate prescribed ones of the flow valves 137-
142 which supply oxygen to module 2 of FIG. 1 via tube 11,
check valve 12 and tube 13.
The digital signals from the logic circuitry 135
are summed with a nebulizer signal from a nebulizer
switch 108 in a summing circuit 146. The resultant sum
output signal which is proportional to the actual flow is
directed to the input of integrator 144. Flow from
module 1 to module 2 via tube 11, check valve 12 and tube
13 continues until the output of integrator 144 is equal
to the calculated tidal volume, at which time the flow
gate signal is withdrawn by comparator 145. As a result,
logic circuitry 135 is disabled and, in turn,deactivates
the valve driver 136 to close the actuated ones of the
valves 137-142. This action represents the end of the
flow. At about the same time, valve 38 of FIG. 1 deactu-
ates in response to the removed flow gate signal. Nofurther flow from module 1 to module 2 occurs until after
the integrator 144 is reset to zero by the rate timing
signal pulse for initiating another cycle.
} 172g35
- 31 -
The aforementioned nebulizer switch 108 is effec-
tive to produce a reduced flow signal from scaler and cal-
culations circuit 120 to the valve enable logic 135 and
driver 136 whenever the nebulizer is "ON." The magnitude
of the reduction is essentially equal to the magnitude of .
the flow introduced by the nebulizer into the patient
inhalation path via the patient breathing apparatus 5 of
FIG. 1. Driving gas for the nebulizer is supplied from
valve 143 which is controlled by nebulizer flow logic 165.
In order for valve 143 to be actuated, two conditions
exist: (1) nebulizer control switch must be closed ("ON")
and (2) flow must be present at inspiratory flow
sensor 63.
At the aforementioned beginning of the
inspiration cycle, the control module 1 is effective to
actuate the oxygen mixing valve 45 of module 2 (FIGS. 1
and 9) for enabling a transfer of a prescribed concentra-
tion of oxygen from chamber 18 to chamber 30, and selec-
t:ively, from chamber 18 to the atmosphere, as priorly
described. In FIG. 9, valve 45 is actuated in response
to an output signal from a tidal volume comparator 147,
which signal is generated just following the resetting of
the flow integrator 144 of FIG. 9 by the rate timing
pulse on conductor 130 at the beginning of the inspira-
tion cycle, as already explained. Comparator 147 com-
pares the flow integrated output of integrator 144 with
a compensated value of the calculated tidal volume signal
on conductor 129. The compensation is effected by the
oxygen concentration dial circuitry 9 which suitably
comprises a variable voltage divider serially between
conductor 129 and one of the compare inputs 148 of com-
parator 147. The dial 9 is settable between 21 and 100%
oxygen as hereinbefore described, which setting actually
sets a voltage on input 148 that is a proportion of the
calculated tidal volume on conductor 129. If the
latter voltage is equal to the tidal
~ 1~2935
- 32 -
volume voltage on conductor 129, dial 9 is set to 100%
for 100~ oxygen. If voltage on input 148 is equal to
zero, dial 9 is set to 21% for air concentration in
chamber 30.
As long as the tidal volume voltage output of
the flow integrator 144 is less than the voltage on input
148, the output of comparator 147 actuates and maintains
actuated the valve 45. At the point where the voltages
are equal, the comparator 147 output changes state for
effecting a deactuation of valve 45 and causing oxygen
from chamber 18 to be expelled to the atmosphere via check
valve 50 and 54 of module 2, FIG. 1, as priorly explained.
Concurrently, air is drawn into bellows chamber 30 of
module 2 via check valve 55 of FIG. 1, as already des-
cribed, and for the duration of the flow gating signalfrom the output of comparator 145. The latter signal
occurs as priorly described until the prescribed tidal
volume has been supplied.
- The foregoing describes ventilator operations
when the patient is breathing the same amount as the
minute volume set by dial control 6 and effectively, the
gas in chamber 81 of E~IG. 1 is essentially constant, and
wiper 85 is in contact with bar conductor 87. The fol-
lowing description explains ventilator operations for
situations where the patient breathes more and less than
the minute volume set by dial control 6.
When the patient breathes more than the set
minute volume, the wiper 85 of FIG. 1 contacts the low
fill level sensor conductor 86 as bellows 76 descends
due to the emptying of chamber 81, as priorly described.
As a consequence, ground potential is applied over
conductor 101 for operating the ~ill monitor circuit 134
of FIG. 9 to produce an output fill signal on conductor
149 immediately upon the removal of the flow gating signal
of comparator 145 which theretofor had maintained the fill
33l 7~9~5
monitor 134 reset. The fill signal on eonductor 149 is
effective to:
(1) activate the scaler and calculations
eircuitry 120 of FIG. 9 for setting the
calculated tidal volume signal on con-
ductor 129 to 2 liters and to initiate
a new breathing cycle,
(2) operate the valve enable logic circuitry
135 of FIG. 9 for producing 100 liter/
minute binary signals (64, 32 and 4 liter
binary signals) to the valve driver 136,
thus to override the binary flow signals
supplied by eircuitry 120 and to produce
a 100 liter per minute flow from module 1
to module 2, and
(3) aetuates the eontrol valves 56 and 58 of
FIG. 9 via inverter 150 and the AND gate
151 so that the flow in FIG. 1 from
ehamber 29 is only direeted to ehamber 81,
as priorly deseribed. This fill action
serves to cause bellows 76 to return
: rapidly to a filled state. This fill
eyele prevents the bellows 76 from
beeoming empty whieh, ln turn, would
eause the patient to reeeive inhalation
via bypass valve 59 of FIG. 1. If the
patient breathed through valve 59, the
oxygen pereentage would be that of air,
and any CPAP pressure from souree 84 of
FIG. 1 would not be available to the
patient,and the patient would be inhaling
at atmospherie pressure.
When the fill eyele is eompleted, the wiper 85
of F~G. 1 has moved from bar eonductor 86 to 87 and, in
turn, controls the fill monitor 134 for withdrawing the
fill signal from eonduetor 149. At the eompletion of
' 172935
- 34 -
this priorly described fill cycle, the aforementioned
operations for patient breathing while wiper 85 rests
on bar conductor 87 are resumed.
~ When a patient breathes less than the minute
- 5 volume set by dial control 6, patient assist breathing
is prescribed, and the ventilator takes such action in
response to wiper 85 contacting assist level sensor con-
ductor 88 of FIG. 1 as a result of continuous gas de-
livery to chamber 81 exceeding the patient inhalation.
Essentially, chamber 81 receives more gas than the
patient inhales and bellows 76 rises. The signal from
sensor 88 is directed to AND gate 152 and when the
patient next initiates a breath, this effort is detected
by flow sensor 63 of FIGS. 1 and 9. The output of sen-
sor 63 is extended over conductor 153 to the inspiratorylogic and comparator 154 which integrates the sensed flow
and compares the resulting volume output signal voltage
to a preset voltage. (Typically corresponding to 100 to
2-00 cc. of volume.) When the preset volume is reached
and the flow through sensor 63 is greater than a thresh-
old voltage derived from the sensitivity dial 105, the
output of comparator 154 in conjunction with the signal
from sensor 88 causes output of AND gate 152 to be dir-
ected over conductor 155 through OR gate 156 to AND gate
151. The latter gate is fully enabled in response to an
inspiratory gate enable signal on conductor 132, the
absence of a fill signal on conductor 149, and the afore-
mentioned output of OR gate 156 causing valves 57 and 58
to close during the inspiratory cycle. Closure of valve
56 serves to direct the tidal volume from chamber 29
directly to the patient via tube 42, transducer 62, valve
91, tube 92, check valve 93, sensor 63, tube 64 and the
humidifier 70. Closure of valve 58 causes the pressure
in mushroom chamber 75 of valve 57 to assume the same
pressure existing at inlet 73 of valve 57, causing inlet
73 to be occluded. Resultinglyj the aforementioned tidal
volume from chamber 29 is delivered directly to the
patient.
~ 17293~
- 35 -
If the patient does not initiate a breath for the
foregoing "assist" breathing, wiper 85 with control level
sensor conductor 89 thereby supplies a signal to conduc-
tors 104 and 157 for extension through OR gate 156 to AND
gate 151. Upon enablement, gate 151 causes valves 56 and
58 to close for directing the flow directly from chamber
2g to the patient as described in the immediately preced-
ing paragraph. The signal on conductor 104 is extended
through OR gate 158 for enabling the sigh function (50%
increase in tidal volume). This action occurs at the
inspiratory period immediately following the wiper 85
contact with conductor 89 independent of the patient's
effort to initiate a breath. The action is that of com-
pletely controlled ventilation rather than assisted
ventilation. If the patient starts to breathe more than
the dial settings on module 1, the bellows 76 will fall,
and the ventilator operations will return to those pre-
viously described.
Turning now to the control mode of the ventila-
tor operation, the selector switch 90 of FIG. 9 is moved
to its control position for effecting patient breathing
in-a controlled manner. The mode selector switch extends
a signal over conductor 159 to OR gate 156 for overriding
the effects of all the inputs to that gate as previously
discussed. In order to maintain CPAP operation, bellows
76 of FIG. 1 must not be empty and the "fill" cycle, as
already explained, functions in a manner as previously
described. A signal on conductor lS9 also is extended via
gate 158 to enable the sigh function.
When the ventilator is in the control mode, the
sigh function (50% increase in tidal volume) operates in
accordance with dial control 109. In the standby, or
automatic mode of the ventilator, the sigh function is in-
operative because the flow is directed to the CPAP bellows
from which the patient is normally initiating breaths.
The sigh function is also interlocked with the signal from
~ ~7~293S
sensor 89 via OR gate 158 so that if the patient lapses
into a controlled breathing as sensed by sensor 89, the
sigh is enabled. The manual sigh button 110 initiates a
sigh cycle as described whenever the sigh function is
enabled and button 110 is actuated.
~ nytime the manual cycle button 111 is depressed,
a controlled breath is delivered to the patient under con-
trol of circuit 120, OR gate 156 and AND gate 151 as well
as valves 56 and 58, as previously described.
FIG. 9 shows a CPAP servo control circuit 160
which receives two voltage inputs, the first of which is
derived from the pressure transducer 116 of FIG. 1 and
the second from the circuitry including the CPAP electri-
cal control dial 112. The latter illustratively is set-
table in the range from 0 to 20 centimeters H2O. If the
CPAP dial 112 voltage is different than the voltage from
pressure transducer 116, circuit 160 causes servo valve
115 to alter the restriction of the flow for causing the
pressure directed to source 84 to change so that the
transducer 116 voltage is equal to the dial 112 setting
voltage.
FIG. 9 shows a patient pressure limit control
system comprising relief valve 60, comparator 168, pres-
sure limit dial circuit 106 and a patient pressure
transducer 66. If the pressure transducer voltage exceeds
the voltage corresponding to the setting of dial 106,
comparator 168 actuates relief valve 60 which causes a
reduction of pressure in tube 94 (FIG. 1) by venting the
gas in that tube to the atmosphere.
The design of this ventilator is such that all
of the input and output parameters of the scaler and cal-
culations circuit 120 of FIG. 9 are available for compil-
ing a record of the settings and derived parameters by
means of a suitable recorder (not shown). The flow
sensors 63 and 71 of FIG. 1 are monitorable for deter-
mining and recording the flow to and from the patient.
-36 -
. ~,
l 172935
These flows are integratable and processed for displaying
volumes. A comparison of the volumes to and from the
patient allow for a detection of any leak in the patient
connection and the actuation of an alarm. A list of the
available monitored signals from the ventilator include:
set minute volume, set rate, set inspiration-to-expiration
ratio, set inspiratory plateau, nebulizer signal on-off,
sigh setting; Mode: standby, auto or control, set ~
oxygen, CPAP setting, calculated tidal volume, calculated
flow, actual flow (binary signals) from circuit 120 of
FIG. 9, sigh activation, CPAP pressure via transducer 116,
patient pressure via transducer 66, actual flow, total
inspiratory period, signals to indicate a fill, assist
and control cycle.
The front panel of the ventilator is suitably
equipped with devices for furnishing visual indications
of mode and operation status of the ventilator and for
certain alarm functions. These include: standby, assist
or control modes of operation, spontaneous breathing, CPAP
on-off, airway pressure meter, sigh indicator for when
sigh is taking place, oxygen enriched (when oxygen is
greater than 21~), nebulizer on, patient breath trigger
of ventilator, patient pressure alarm to indicate when
patient tried to exceed the setting of dial 106 of FIG. 1
(transducer 66 signal utilizable for comparison with dial
106 setting), dial setting exceeds specifications alarm
when settings call for greater than 2 liters per minute,
temperature readout of airway to patient, fill empty
humidifier, power failure, and ventilator inoperative.
,:
