Note: Descriptions are shown in the official language in which they were submitted.
~(1182602
Thls application is divided from applicants copending application
Serial No. 256,091 filed June 30th 1976 and directed to a breathing apparatus
and in particular to a positive pressure ventilator used for controlled or
assisted ventilation.
The present invention also lies in the field of breathing apparatus.
More specifically, it is concerned ~ith an automatic type of ar~ificial ven-
tilation or controlled respiration.
Most of the commonly used ventilators that are on the market today
have one or more of the ollowing drawbacks. First, their controls are in-
terdependent, making i~ difficult for the physician to set the device to a
desired condition. Second, the tidal volume delivered to the patient is a
function of the respiratory parameters of the patient, hence constant read-
justments o the controls are necessary as the respiratory param~ters of the
patient change. Also the prior art devices are constructed of electrical or
electro-mechanical switches, relays, etc., which are subject to malfunction
and failure; these devices are correspondingly difficult to maintain by
hospital personnel.
This invention is directed at providing a reliable, simple ventilator
that has independent control of the basic variables that may be required to be
changed and to provide a number of safeguards to the patient.
According to the present invention; there is provided a positive
pressure ventilator comprising: a. a source of breathing gas; b. a normally ~`
closed first valve means for directing the breathing gas from sai~ source to ;
the patient; c. a first bistable means for controlling said first valve means, ~ `
said first bistable means having a first set of opposed control inputs; d. a
first and a second time delay means, each independently adjustable in time
dela~; e. means responsive to said first time delay means to operate one of
said first inputs of said first bistable means to open said first valve means,
and to trip said second time deIay meansJ and to initiate the inhalation ac-
tion; f. means responsive to the operation of said second time delay means to
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~ - 1 - ..
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1(~826~2
operate a second one of said first inputs of said first bistable means to
close said first valve means and to trip said first time delay means and ini-
tiate the exhalation action; and further including g. diaphragm valve means
responsive to the patient pressure, said patient pressure being positive, and
o~ sufficient magnitude during the inhalation phase to close said diaphragm
valve means; a second bistable means having a set of opposed control inputs
back pressure switch means responsive to the closing of said diaphragm valve
.. . ..
means to apply fluid pressure to a first input of a second bistable means, a
second input to said second bistable means connected through a resistance to
the output of a digital amplifier responsive to said first bistable means,
an output of said second bistable means connected to a first input of a first
monostable means, a second input of said first monostable means connected to
said output of said digital amplifier, the pressure on said first input keep-
ing the output of said first monostable means a logical zero; and i. alarm
means responsive to a logical one on said output of said first monostable
means; when the patient is disconnected from said breathing apparatus, said
patient pressure never gets high enough to close said diaphragm valve, whereby
said back pressure switch never operates and said second input resets said
second bistable means, taking said pressure at said first input off of said
first monostable means and permitting output of said first monostable means - :
to change to a logical one and activate an alarm.
In the preferred embodiment, the ventilator is basically a time
cycled, volume preset, maximum pressure limited device. However, due to the
versatility of the basic circuit, and the independency of the basic controls,
five different control options are available:
~1) Independent control of inhalation time, exhalation time, and flow
rate to the patient.
(2) Independent control of inhalation time, exhalation time and tidal -
volume.
C3) Independent control of inhalation time to exhalation time
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~8260~ ~
ratio, frequency of cycling, and flow rate.
(4) Independent control of frequency of cycling and tidal volu~e.
(5) Independent control of maximum pressure during inhalation
at the patient~s mouth~ exhalation time~ and f]ow rate.
The basic fluidic control circuit comprises a low frequency
oscillator for timing the inhalation and exhalation phases, a digital
amplifier for amplifying thé output of the oscillator, and a two-way on-
off valve for directing the breathing gas from the source to the patient.
Along with the basic timing circuit, the control circuit of the ventilator
10 ~ includes seven other features: -
(1) A maximum pressure control which terminates the inhalation
phase and initiates the exhalation phase when the patient pressure reaches
a preset limit.
(2) A sensitivity control which initiates an i~halation phase by
terminating the exhalation phase when the patient inspiratory effort reaches
a preset limit.
(3) A positive end-exhalation pressure control which enables
it to retain a positive pressure in the patient~s lungs during the exhalation
phase~ without a significant "retard" effect.
(4) An Intermittent Mandatory Ventilation (IMV) control which
allows the patient~s breathing rate to be reduced as low as one breath per
minute.
(5) A manual control which allows the inhalation phase to be
initiated manually.
(6) A disconnect alarm which gives a visual and/or audible
signal when the apparatus is disconnected from the patient, or when a signific-
ant leak occurs in the brcathing circuit.
(7) A non-rebreathing valvc which allows the patient to breathe
¦ atmospheric air when the supply pressure of the source gas fails~ or anytime
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.
during the exhalation phase providing the patient's inspiratory effort i~
insufficient to initiate the il~alation phase.
In the preferred embodiment, a constant flow rate generator
is connected to the patient during the inhalation phase. If the inhalation
time eontrol and the flow rate control are fixed~ a given tidal volume will
be delivered independent of patient condition (i.e., air~ay resistance and
lung compliance), as long as the inhalation phase is not pressure limited.
The change-over from inhalation phase to exhalation phase may take place in
any one of the following cycling modes:
(a) Time Cycled. The time at whlch changeover occurs may be
eontrolled with the inhalatlon time control.
(b) Volume Cycled. If the inhalation tiMe control is preset,
the tidal volume at which changeover occurs may be controlled with the flow
rate control.
te) Pressure Cycled. Pressure cycling will occur if the
maximum pressure control is set below the maximum pressure that would
occur at the patient~s mouth during t~ne cycling.
(d) Patient Cycled. Patlent resists to the extent that pressure l;
in the mouth exceeds the setting of the maximum pressure control. In this
case, pressure cycling occurs as in part (c) above. -
During exhalation phase, a constant pressure generator is connected
to the patient. Two possibilities exist: ;
(a) Constant atmospheric pressure generator - i.e., simple
connection of patient to ambient through a non-rebreathing valve.
~b) Constant positive pressure generator, or as it lS sometimes
called Positive End Exhalation Pressure (PEEP) generator. ~his may be
~. .
appro~ ated by a device whiFII attcmpts to hold the pressure in the patient~s
mouth nearly constant regard]ess of flow ratc during exhalation, but without
.
¦ introducin~ an undesirable retard effect (idditional exhalation circuit
.
~ i
: : . . . . .
lO~ Z
resistance).
The changeover from exhalation phase to inhalation phase may
take place in one of the ollowing two modes:
(a) Time Cycled. Controlled with the exhalation time control
ut~ess overridden by a patient inspiratory effort.
(b) Patient Cycled. Changeover occurs when patient makes an
inspiratory effort ~level controlled by sensitivity setting).
The device also features an alarm to indicate disconnection or a
substantial leak between the device and the patient. This alarm is either
visible or audible or both.
The ventilator may be constructed completely of Muidic elements,
: ,
all of which are conventional, off the shelf items, so that they are of
reliable manufacture and operation, are well-known in the art and require no
further description. Implementation of the basic control circuitry is not
lintited to fluidics, but it is believed that fluidic implementation offers
- the maximum possible simplicity, reliability~ and ease of maintenance.
These and other objects of this invention and a better under-
standing of the principles and details of the invention will be evident~from
the following description taken in conjunction with the appended drawings,
in which: -
Figure 1 shows in schematic form the fluidic system of this
.
invelltion.
Figure 2 shows the relationship between PE~P output pressure Pu~
at~d the difference between breathing pressure PI and constant pressure PT.
This inyention relates to the design of a ventilator whi.ch can
.
operate on time cycle or pressure cycle or patient cycle or any combination
of the three. The device csn be used either in the control mode or in the
assi9t-control mode. ~uring the control mode of~operation, the patient
ventilation is entirely controlled by the machlne. In the assist-control ~ -
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t ,~
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2602
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mode the change from the exhalation phase to inhalation phase occurs when
the patient makes an inspiratory effort. The assist-control ~odc includes
a safety feature of initiating an inhalation phase after a preset exhalation
time if the patient fails to initiate the inhalation phase. In both
control modes~ and during operation~ a safety feature is p~ovided to limit
the maYimum press~lre in the mouth of the patient during the inhalation phase.
Referring now to the drawing, the principal part of the ventilator
is indicated generally by numeral 10. This is the time control portion of
the apparatus which controls the operation of a breathing gas valve 4~ indicat-
ed generally by numeral 11 ~Yhich provides breathing gas through a control
needle valve RS to the patient. There is a maximum pressure control
indicated generally by the numeral 12 which serves to initiate the exhalation
portion of the cycle in the event that the gas pressure at the patient's
mouth exceeds a preset level. There is an assist-control indicated generally
by ~the numeral 14 which monitors the pressure at the patient~s mouth and ;
starts the inhalation portion of the cycle whenever the patient generates a
pressure lower than the difference between the output pressure ~P~) of a
positive pressure of end exhalation pressure ~PEEP~ clrcuit and a preset
reference pressure ~PR). There is a PEEP control indicated by the numeral
53 which holds a preset positive pressure in the patientls lungs at the end
of exhalation. There is a manual control indicated by the numeral 60 which
allows the initiation of the inhalation phase at any time during thè
exhalation phase. There is a disconnect alarm indicated generally by the
numeral 16 which operates an alarm whenever~the breathing apparatus~is
disconnccted from the patient, or there is a substantial leak in the patient
circuit.
sourcc of breathing gas indicated by the designation T2 goes
~ by way of pressure regulator 38 through a pilot operated valve 40, a constant
j ~low control valve or adjustable resistance R5 and a non-rebreathing valve 55
_ 5 _
~08266)Z
.
to the patient. For a given setting of the flow control R5, the flow
rate delivered to the patient during the inhalation ph~se is constant, and
is independent of the patient's conditions. The pressure in the mouth of
the patient~ that is~ at 70, the junction of the non-rebreathing valve 55
and the patient, is the pressure signal I. There are four auxiliary
controls which are responsive to ~his pressure signal I.
The source Tl of control fluid, through pressure regulators 36
~Id 58 serves to operate the fluidic circuits. This source can be any
suitable gas, or mixture of gases. The pressure regulator 58 controls the
supply pressure S to all fluidic elements e~cept TDRl and TDR2, which are
controlled by the pressure regulator 36. TDRl has a time delay control
which is comprised of a variable flow resistance element R1. Similarly,
TDR2 has an independent time delay control comprlsing variable flow resistance
R2. There is an E input to TDRl and an F input to TDR2. These inputs are
derived from a ~irst flip flop FFl 32. The E and F outputs of the FFl go to
the TDRl and TDR2 and also go as inputs to a digital amplifier 34, an output
of which~ G~ goes to the main control valve 11. When there is pressure on G
the valve 40 opens and breathing gas flows from T2 through the flow control
valve R5, and non-rebreathing valve 55 to the patient. TDRl has an A output
and TDR2 has a B output. These two outputs A and B go to flip flop FFl
indicated by nuDIer~il 32 and are the primary inputs. They operate the FFl
in the cycle set by the time delays provided by the TDRl and TDR2 circuits.
Consider that there is an operation of the TDRl (initiation of
alation phase) and output A has a loglcal one momentarily~ which~means
that it has pressure. This pressure pulse at input ~ on the FFl causes the
output F to assume a logical one, the output F to assume a logica] ~ero, and
the TDRl to be reset. The logical one output o~ F going to the TDR2
initiates a time delay set by the control R2 which corresponds ~o the
i~lalation tiDle. The pressure on the OUtpllt F goes also to the input of the
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~L~8:Z6a)2
digital amplifier 34 and causes the G output to have a logical one, and to
apply pressure to the valve 40, causing it to open. This is the start of
the inhalatioll phase. ~fter the time delay set by R2 the pressure at
the B output of TDR2 changes from a logical zero to a logical one momentarily.
This pressure pulse applied to FFl causes it to switch so .that output E is
a logical one, output F is logical zero, and TDR2 is reset. The logical one
output on E going to TDRl initiates the time delay set by Rl which
corresponds to the exhalation time. The logical one E output of FFl also
causes the digital amplifier 34 to switch the G output from a logical one to
10 ~ a logical zero, which permits the valve 40 to close, thus initiating the
start of the e~alation phase. The cycle continues to repeat itself. The
actual on and off time of the two time delay relays 28~ 30 can be set
independently of all factors.
The time delays provided by the TDRl and TDR2 circuits can be
controlled by two other methods.` In the first method, the resistances Rl
and R2 are set at some predetermined values which set a particular ratio of
inhalation time to e~lalation time, (I/E) ratio, and the frequency of cycling
is thel~ varied by varying the supply pressures to the two time delay relays
by means of the pressure regulator 36. In the second method, the inhalation
and e~lalation times are controlled by pla~ing variable resistors in the two
lines leading to the E and F inputs. In this method the supply pressure to
the time delay relays is kept constantg and for fi~ed values of resistors Rl
and R2, the time delays are varied using the variable resistors~connected to
the inputs E and F. Thus the system can operate on an inhalation/exhalation
ratio and frequency (first method), or it can be operated on a time of
inhalation and a time of exhalation (second method). Wlth both of these
- methods thc patient can be adequatcly ventilated under diffcrent conditions.
The patient is connccted to the machine via a brcath mg hose 71 ~ ~ -
and a non-breathing valve 55. During inhalationg the signal G from flip
~ 7 -
flop FFl 32 causcs the OR/NOR gate 57 to switch, malcing the output signal
Gl to be a logical one. The signal Gl applies pressure at the input V of pilot-
operated valve 55~ causing it to close. The patient then receives the
breathing gas through valves 40 and R5. During exhalation, the signal Gl -;
will be 3ero, valve 40 closes, valve 55 opens, and the patient can exhale
through the valve 55. The pressure at the end of exhalation may be
either atmospheric or higher depending on the setting of the PEEP control
which is discussed later.
There is a maximum pressure control indicated generally by the
numeral 12. This comprises a Schmitt trigger 44 labeled STl which has t~o
inputs, an I input and a Q input. There is a D output. The pressure signal
I from the patient at junction 70 goes as input to the STl via line 72. The
Q input is a pressure set by a variable resistance R4. The Schmitt trig~er
44 is controlled by the opposition of the gas pressure at the I and Q
inputs. The Q input is set at a desired value above the normal I lnput.
When the pressure at-the I input exceeds this preselected value~ it causes
:. .
the STl 44 to switch the D output to a logical one. This applies pressure
at the D input to the FFl 32. This D input is a second input, in parallel
with the B input~ and causes the FFl to be switched to provide a logical one
at the E output which causes the exhalation phase to begin.
It must be noted that the maximum pressure control may be used
to intentionally pressure cycle the ventilator. With proper sett mg of the
~lalation tine, flow rate control~ and the maximum pressure control, the
i~lalation phase l;ay be terminated when the patient pressure reaches a desired
value. The e~lalation phase may be either timed by the TDRl circuit or
controlled by the patient.
There is a second feature which is used when the instrument is i`~
called upon to assist the patient in breathing. When the patient through
inspiratory effort causes the prcssure at I to be rcduced sufficiently, the
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1~2602
inhalation phase will be initiated. The Schmitt trigger ST2 indicated
generally by the n~leral 14, senscs this reduccd pressure and provides a
correction. The ST2 has an I input, an R input, and a Z input. The Z
input is a pressure signal equal to the PEEP setting. The R input is a
positivc pressure controlled by a needle valve R3. The pressure signal at R
normally `over balances the differential pressure between the inputs at I
and Z, and the output C is then a logical 7ero. When the input signal at I
reduces~ the differential pressure between inputs at I and Z will overcome
the pressure at input R, and the C output of ST2 becomes a logical one and
applies pressure to the C input of the flip flop FFl 32~ causing it to
switch, initiating the inhalation phase. In other words, a reduction of
pressure on the I input in line ~2 causes the valve 40 to open, which in
turn directs breathing gas to the patient. It should be noted that the
sensitivity control lS independent of the PEEP setting becausè the switching
of the Schmitt trigger ST2 depends only on the differential pressure
between I and Z and not their absolute values.
To operate the ventilator as an assistor-controller, the
exhalation time is set significantly longer than desired by the patient and
the sensitivity is set sufficiently low so that the patient can initiate the
inhalation phase. If for some reason the patlent does not initiate the
inhalation phase, auton~atic initiation will occur at the end of the time
set by the exhalation time control. This is an inherent safety feature
built into the circuit to prevent loss of cycllng when patlent is not able
to initiate inhalation. ~ ~ ~
The positive end exhalation pressure (PE~P) control is indicated
generally by the n~ncral 53. It consists of a proportional ~nplifier 54
; labeled PA which has two inputs, I and T. There is an output U connected to
port Y of valve 55 through a restrictor R8. A refcrence bias pressure is
introduced at T through a variable resistor or needlc va]ve R6. Figure 2
.
~Z6~2
shows the plot of the pressure at U versus the differential pressure betweon
I and T. The operation of the PEEP control is explained using the following
example.
Assume that the bias pressure PT at T is set such that point 1 in .
Figure 2 represents the output pressure at port U(pu) of the proportional
amplifier 54 at the end of exh;alation. During inhalation, the valve 40 is
open and valve 55 is closed, and breathing gas is delivered to the patient.
The patient pressure PI will increase during inhalation and hence the
pressure PU ~nll increase during inhalation and hence the pressure PU will
increase (say it reaches Point 2 at the end of inhalation)O At the end of
inhalation, the signal from the port G of the digital amplifier will become
a logical zero, and the force due to the spring and the patien~ pressure
acting on one side of valve 55 will overcome the force due to the pressure
acting on port Y, thus opening the valve. So~the patient will exhaleO
The exhalation will continue until the patient pressure decreases to a
level at which the force acting on port V is sufficient to close the valve
55. Since the spring force is very small~ the force due to PV is mainly
balallced by the force due to the patient pressure. Hence different baclc
pressures (PE~P) C.~l be achieved by different settings of Py through the
resistor R6.
The ventilator circuit shown in Figure 1 can also operate in the
~termittent mandatory ventilation (IMV) mode. In this mode thè resistance
R2 of TDR2 is set to obtain a desired inhalation time for the mandatory
.:
breath. The resistance Rl of TDR1 lS then adJusted to a particular exhalation
time ~hich ~ill yield a desired rate for IMV. The tidal vol~me for the
mandatory breath may be obtained using the flow rate control R5. The
operation of the timc control portion of tho apparatus has been explainod
` earlier.
The output signal G of the digital amplifier 3~ is off for
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~3~ Z 6C)z
duration of the e.xhalation time set by resistor R1. During this time, the ~-
valve 40 is closed and the signal at input V of valve 55 is off. The spring
force acting on valve 55 will open the valve thus connecting the patient
to atmosphere. Hence the patient can breathe atmospheric air spontaneously
through valve 55 between spontaneous breaths.
` There is a safety feature of this device which is indicated
generally by the numeral 16. This is a warning signal (visual or audible)
to indicate when the gas line 71 from the ventilator to the patient has been
disconnected or has developed a substantial leak, i.e. the patient is not
receiving gas in accordance with the control settings.
The sensor for this condition is a diaphragm valve 18 which has
the pressure PI on one side. So long as the patient is connected to the
device the pressure PI will build up during the irhalation phase and the
valve 18 will be closed. However, if the patient becomes discomlected, the
pressure PI will not reach the normal level during the inhalation phase,
and the valve 18 will remain open.
-~hen the valve 18 is closed, a back pressure is built up in line
48 connected to the back pressure switch (BPS) 20. The line 48 is connected
to the supply port S of BPS 20 through a fixed resistor 50. When the valve
18 is open, there is no back pressure built up in line 48. However, when the
valve 18 closes a pressure will build up in the line 48 and at the input
O of the BPS 20. This will cause the L output to switch to a logical one.
This is communicated to the L input of the FF2 (flip flop) 22. The other
I illpUt side of the FF2 22 is connected to the G output of thè digital
amplifier 34 through a resistor R7.
During the inhalation phase, the output G of D~ 34 is a logical
one. This prcssure signal, applied at input port G of NOR 24 and at input
port P of FF2 22, causes thcse two elemcnts to switch making output X of NOR
24 and output W of FF2 22 equal to logical one. If the connection between
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the patient and the ventilator ls normal, patient pressure PI buil~s up
during the i~lalation phase and closes valve 18. The clos;ng of valve 18
causes a pressure signal to be applied at input port 0 of BPS 20 making
the output L a logical one. The output L of BPS 20 is applied at input port
L of FF2 22. The pressure PL at input port L is larger in magnitude than
thc pressure Pp at input port P (because of the resistance R7). This
causes FF2 22 to switch malcing outp~lt W logical zero and output K logic.al
one. The output K of FF2 22 is applied at input K of NOR 24. This input
alonO with thc input at G keeps NOR 24 switched making output X a logical
one and output Y a logical ~ero (i.e., no alarm).
During the exhalation phase~ the output G of DA 34 is a logical
zero. Hence~ there is no pressure signal applied at elther port G of
NOR 24 or port P of FF2 22. As the patient exhales the pressure PI decreases~ - ;
and thus opens valve 18. This causes BPS 20 to switch making output L a
logical ~ero and output J a logical one. Hence~ during echalation the
pressure signal at input L of FF2 22 is zero. However, the output K of ,~
FF2 22 continues to be a logical one since no reset signal is applied at
input port P. The output at port K keeps the NOR 24 in the switched state
making output X a logical one and output Y a logical zero (i.e., no alarm).
,
If there is either a disconnectlon between the patient and the
vcntilator or if there is a substantial leak in the patient circuit, the
patient pressurc PI does not reach the normal value during the inhalation
phase~ and valve 18 remains open. Hence~ no pressure s1gnal lS applled at
input port O of BPS 20 during inhalation phase and the output L remains a
. .
logical zero. The FF2 22 continues in the reset condition with output W a
logical one and output K a loglcal zero. The pressure at input G sl~itches
NOR 24 malcing output X a logical one and output Y a logical zero. However~
during the exhalation phase, *he pressure signals at ~oth the inputs G and K
of NOR 24 are zero and hence the output X will be n ]oglcal zcro and
- 12 -
output Y will be a logical one indicating the discolmection. Th~ alarm is
intermitt~nt, off during the inhalation phase and on during thc e~chalation
phase.
There is a provision for manually triggering the inspiration
cycle. This is done by pressing the push button PB, indieated by numeral
60~ whieh will apply an input pressure at A to the FF1 32. This results in
output F being equal to a logical one, which initiates the inhalation phase.
The inhalation phase is timed by the TDR2 circuit as explained earlier.
Normal cycling will occur if PB 60 is not activated.
There is also a safety feature built into the unit in the event
of failure of thc source pressure Tl. In such a case~ the pressure signal
at the input V of valve 55 will be ~ero and the spring force will cause the
vAlve to open. The patient can breathe the atmospheric air through the
valve 55.
,:
The invention has been described in ~erms of generalized circuit
elements~ sueh as flip flops, Schmitt triggers, NOR gates, ete., all of
whicll may be ealled fluidic devices. These are standardized devices for use
in fluidie systems. A large number of manufacturers now supply these deviees
whieh are available from stock, and can be descrlbed by a eatalog number.
The detailed description ean be provided by the manufacturer and need not be
dcscribed in detail here.
~camples of these deviees are as follows~
1. Breathing gas eontrol valve part II. Catalog #192621~ Fluidie
Produets Dept., Corning~Glass l~orks~ CorningjNew York 14830.
.
2. Time~delay Relay, parts 28 and 30. Catalog ~19:L465, Corning,
New York. ~ ~
,,-- ~
3. OR/NOR Gato, parts 24 and 57. Catalog th91445~ Corning, Ncw Yorlc.
4. Flip Flop, parts 22 and 32.~ Catalog ~191446, Cornlng, New Yorlc.
5. Digital Amplifier~ part 34. Catalog #191452, Corning~ New York.
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10~260~
S. Schmitt Trigger, parts 44 and 46. Catalog #1914~8, Corning,
New York.
7. Back Pressure Switch~ part 20. Catalog ~191479~ Corning,
New Yorlc.
8. Proportional Amplifier, part 54. Catalog #191711, Corning~
New Yorlc.
9. Push Button, part 60. Catalog #192496, Corning, New York.
10. Visual Indicator~ part 26. Catalog ~191817~ Corning~ N~ Yor~
11. Pressure Regulators, parts 36, 38 and 58. Catalog #1914
Corning, New York.
The non-rebreathing valve 55 has been mentioned at a number of ;
places in the preceding description. This is a standard piece of app~ratus
:: :
which is available off the shelf, and is well-knolYn to a man skilled in the
art, and need not be illustrated. A brief description will suffice.
The conventional non-rebreathing valve consists of a passage,
one end connected to the ventilator at point 70, the other end connected to
a tube to the patient. There is a side opening in the passage oonnected to~
the atmosphere. This side opening lS covered by a poppet valve which i5
controlled by a diaphragm and opposed by a spring. When the pressure PI ;
on the diaphragm is high enough to overcome the fo-rce of the spring the
poppet valve is closed.
During the inhalation phase~ the diaphragm is inflated~ forcing
,
.. ..
the poppet closed against the spring force. The gas from the ventilator
passes through the`passage to the patient. During exhalatlon~the diap~ra~m
is deflated~ and the spring pushes the poppet opcn~ and the patient ca~
.
breathe out to the atmosphere. ~
.i
The valve is so designed that whcn the poppet is off thc seat
.
thF r`esistance to thc flow of gas through the valve is minimal. ~Icn.c~. ~hen
thc diaphraom is not inflated, thc patient can breathe spontaneously throu~h
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~26~2
the valve.
I~lile the invention has been described with a certain degree of
particularity, it is manifcst that many changes may be made in details of
construction and the arrangement of components. It is understood that the
invention is not to be limited to the specific embodiment set forth herein
by way of e~emplifying the invention, but the invention is to be limited
only by the scope of the attached claim or claims, including the full range
of equivalency to which each element or step thereof is entitled.
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