U.S. patent number 3,903,881 [Application Number 05/460,621] was granted by the patent office on 1975-09-09 for respirator system and method.
This patent grant is currently assigned to Bourns, Inc.. Invention is credited to James Weigl.
United States Patent |
3,903,881 |
Weigl |
September 9, 1975 |
Respirator system and method
Abstract
A respirator system and method in which a constant pressure
plenum communicates through a gas bleeder with the patient gas
supply system. The bleeder is adjustable so that a gas flow can be
established from the plenum to the gas conduits at a level
sufficient to compensate for leaks from the patient's mouth and
trachea, but less than that required by the patient during
voluntary inhalation. The pressure inside the conduit system, and
hence in the patient's lungs, is thereby maintained at a level at
least as great as a minimum desired amount. A discrimination
between patient attempts at breathing and leaks from the conduit
system is achieved by sensing the gas flow rate towards the
patient, and actuating a breath assist function only in response to
that flow rate equaling or exceeding the expected inhalation rate,
without reference to the absolute pressure within the conduit
system.
Inventors: |
Weigl; James (Rialto, CA) |
Assignee: |
Bourns, Inc. (Riverside,
CA)
|
Family
ID: |
23829430 |
Appl.
No.: |
05/460,621 |
Filed: |
April 12, 1974 |
Current U.S.
Class: |
128/204.25;
128/205.13; 128/204.26 |
Current CPC
Class: |
A61M
16/022 (20170801); A61M 16/206 (20140204); A61M
16/208 (20130101); A61M 16/107 (20140204); A61M
2016/0039 (20130101); A61M 2016/0021 (20130101); A61M
2016/0042 (20130101); A61M 16/209 (20140204) |
Current International
Class: |
A61M
16/00 (20060101); A61M 16/20 (20060101); A61M
016/00 () |
Field of
Search: |
;128/145.6,142.2-142.4,145.7,145.8,145.5,146.4,146.5,188,DIG.17,203,184 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Recla; Henry J.
Attorney, Agent or Firm: Becker; William G. Koppel; Richard
S.
Claims
What is desired to be secured by Letters Patent of the United
States is:
1. A respirator system for assisting a patient's breathing during
alternate inhalation and expiration phases, said system including
gas conduit means having an inlet port, an outlet port, and a
patient supply tap intermediate said inlet and outlet ports,
recyclable means for charging gas into said inlet port during
inhalation phases for delivery to a patient, a control means for
actuating said charging means, first valve means adapted to block
an outward flow of gas through said inlet port during expiration
phases, and second valve means adapted to block an inward flow of
gas through said outlet port during inhalation phases, wherein the
improvement comprises the provision of:
a pressure plenum,
means for positively maintaining said plenum at a predetermined
pressure level,
bleeder means adapted to conduct gas from said plenum into said gas
conduit means, and
a gas flow sensing means adapted to sense a flow of gas through
said conduit means towards the patient during expiration phases and
to produce a control signal in response to said flow exceeding a
predetermined threshold flow rate,
said control means being connected to said sensing means for
actuation by said control signal, and said bleeder means providing
a gas flow path of sufficient conductance to enable a substantially
unrestricted inflow of gas into said conduit means from said plenum
at a maximum rate approximately equal to said threshold flow rate,
whereby gas leaks from the patient supply tap at leak rates not
exceeding the said threshold flow rate are replenished by a
compensating gas flow into the conduit means from the pressure
plenum without producing a control signal for actuating the gas
charging means, and the pressure in said conduit means is
maintained at a level substantially at least equal to said
predetermined plenum level despite said gas leaks.
2. The respirator system of claim 1, wherein said bleeder means
provides a gas flow path from said plenum to the outlet port of
said conduit means, and said gas flow sensing means comprises a
pressure differential sensor means operably connected to sense
pressure differences between said plenum and said outlet port, said
bleeder means including flow restriction means adapted to produce a
predetermined pressure differential across said bleeder means when
the gas flow rate therethrough to said outlet port equals said
threshold flow rate, said pressure differential sensor means being
adapted to produce a control signal in response to the sensed
pressure differential exceeding said predetermined amount.
3. The respirator system of claim 2, said flow restriction means
including adjustment means for adjusting the maximum gas flow rate
through said bleeder means within a range corresponding to the
expected range of voluntary inhalation flow rates produced by a
patient.
4. The respirator system of claim 1, wherein said gas flow sensing
means is interposed in line with said patient supply tap.
5. A respirator system for assisting a patient's breathing during
alternate inhalation and expiration phases, said system including
gas conduit means having an inlet port, an outlet port, and a
patient supply tap intermediate said inlet and outlet ports,
recyclable means for charging gas into said inlet port during
inhalation phases for delivery to a patient, a control means for
actuating said charging means, first valve means adapted to block
an outward flow of gas through said inlet port during expiration
phases, and second valve means adapted to block an inward flow of
gas through said outlet port during inhalation phases, wherein the
improvement comprises the provision of:
first and second pressure plenums, means for positively maintaining
the pressure in said first plenum at a predetermined level,
adjustable bleeder means adapted to conduct gas from said first
plenum to said second plenum to provide a pressure therein, said
second plenum communicating with said conduit means during the
expiration phases of said respirator so as to maintain said conduit
means at a pressure substantially equal to the pressure of the
second plenum during such expiration phases, and a pressure
differential sensor means operably connected to sense pressure
differences between said first and second plenums and to produce a
control signal for actuation of the control means in response to
the sensed pressure differential exceeding a predetermined
amount.
6. The respirator system of claim 5, wherein said second plenum
communicates with said conduit means through the outlet port
thereof, said bleeder means providing a gas flow path from said
first plenum to said second plenum and thereby to said conduit
means during expiration phases when said second valve means is
open, and further including vent means communicating with said
first plenum to vent expired air from the system.
7. The respirator system of claim 6, and further including a
passageway between said first and second plenums, said passageway
including a check valve enabling a unidirectional gas flow from the
second plenum to the first plenum in response to a pressure
differential therebetween of appropriate polarity.
8. A respirator system for assisting a patient's breathing during
alternate inhalation and expiration phases, said system including
gas conduit means having an inlet port, an outlet port, and a
patient supply tap intermediate said inlet and outlet ports,
recyclable means for charging gas into said inlet port during
inhalation phases for delivery to a patient, a control means for
actuating said charging means, first valve means adapted to block
an outward flow of gas through said inlet port during expiration
phases, and second valve means adapted to block an inward flow of
gas through said outlet port during inhalation phases, wherein the
improvement comprises the provision of:
means responsive to a predetermined flow rate of gas through said
conduit means to said patient supply tap during an expiration phase
for producing a control signal to actuate said control means,
and
pressure maintenance apparatus for said conduit means, said
apparatus comprising a first plenum maintained at a predetermined
pressure level, a second plenum in gas flow communication with said
conduit means through said outlet port, check valve means enabling
a unidirectional gas flow from the second plenum to the first
plenum, and a bleeder conduit connected in parallel with said check
valve means between said first and second plenums, said second
plenum having a pressure during expiration phases determined by the
pressure in said conduit means, said bleeder conduit including a
gas flow restriction valve capable of being set to restrict the
flow of gas between said plenums to a level no greater than the
expected voluntary inhalation flow rate produced by a patient.
9. A respirator system for assisting a patient's breathing during
alternate inhalation and expiration phases, said system including
gas conduit means having an inlet port, an outlet port, and a
patient supply tap intermediate said inlet and outlet ports,
recyclable means for charging gas into said inlet port during
inhalation phases for delivery to a patient, a control means for
actuating said charging means, first valve means adapted to block
an outward flow of gas through said inlet port during expiration
phases, and second valve means adapted to block an inward flow of
gas through said outlet port during inhalation phases, wherein the
improvement comprises the provision of:
a first chamber, a second chamber surrounding said conduit means
outlet port and communicating therethrough with said conduit means
when said second valve means is open, a check valve means enabling
a unidirectional gas flow from the second to the first chamber, a
bleeder conduit connected in parallel with said check valve means
between said first and second chambers, said bleeder conduit
including an adjustable gas flow restriction valve for controlling
the gas flow rate therethrough, vent means communicating with said
first chamber for venting expired air from the system, a venturi in
gas flow communication with said first chamber, and jet means
adapted to direct a substantially constant velocity gas jet through
said venturi to said first chamber, thereby maintaining the
pressure in said first chamber at a substantially constant
level.
10. The respirator system of claim 9, and further including a
pressure differential sensor means operably connected to sense
pressure differences between said first and second plenums and to
produce a control signal for actuation of the control means in
response to the sensed pressure differential exceeding a
predetermined amount.
11. The respirator system of claim 9, and further including a third
chamber interposed between said jet means and said venturi, said
third chamber including longitudinally opposed walls having ports
therein enabling the gas jet to pass through the chamber, and at
least one outlet orifice in a transverse wall of said third chamber
providing a vent for expired gas transmitted through said check
valve means.
12. The respirator of claim 9, wherein said second valve means
comprises the combination of a diaphragm and means for releasably
closing said diaphragm over said conduit means outlet port, said
diaphragm forming a wall of said second chamber.
13. A method of operating a respirator system of the type which
includes gas conduit means having an inlet port, an outlet port,
and a patient supply tap intermediate said inlet and outlet ports,
recyclable means for charging gas inwardly into said inlet port
during inhalation phases for delivery to a patient, a control means
for actuating said charging means, first valve means adapted to
block an outflow of gas through said inlet port during expiration
phases, and second valve means adapted to block an inward flow of
gas through said outlet port during inhalation phases, said method
comprising:
sensing the flow rate of gas toward a patient through said conduit
means during expiratory phases when the inlet port is blocked by
said first valve means,
supplying gas to said conduit means during expiratory phases to
compensate for gas leaks from the patient supply tap,
limiting the compensating gas flow to a rate no greater than the
patient's expected voluntary inhalation flow rate, and
actuating the control means to operate the charging means when the
sensed gas flow rate exceeds a predetermined threshold level which
is no greater than the patient's expected voluntary inhalation flow
rate.
14. The method of claim 13, and further including the step of
maintaining a plenum at a substantially constant pressure, wherein
said compensating gas flow is supplied from said plenum to said
conduit means through the outlet port thereof, and the gas flow
rate to the patient is sensed by sensing the gas flow rate from the
plenum to the conduit means.
15. The method of claim 14, wherein said compensating gas flow is
limited by restricting the gas flow from the plenum to the conduit
means, and the rate of said restricted gas flow is sensed by
sensing the pressure differential between said plenum and conduit
means.
Description
BACKGROUND OF THE INVENTION
This invention relates to medical respirator systems, and more
particularly to positive pressure respirator systems having a
breath assist mode in which delivery of gas to the patient is
initiated when the patient attempts to inhale.
Respirator systems are known in which a breath assist function is
actuated to deliver a certain volume of gas to the patient when he
or she indicates an attempt to breathe by inhaling gas from the gas
supply conduit system. A common method of identifying a patient
request for breath assistance involves a measurement of the gas
pressure within the conduits; the patient's suction reduces the
pressure to a level below a predetermined threshold, triggering the
breath assistance apparatus into operation. A controlled volume of
air is then forced through the supply system to the patient's
lungs, following which the patient exhales and then attempts to
breathe again, retriggering the breath assistance apparatus. An
override control is generally included with the respirator to
actuate breath assistance should the patient fail to voluntarily
inhale within a certain time limit.
While presently available systems can function adequately in a
loss-less environment, a dangerous situation can develop if there
are gas leaks from the supply conduit. Such leaks often develop at
the end of the flexible tube inserted into the patient's trachea,
since the trachea does not provide a perfect seal for the tube, and
gas can escape out through the patient's mouth rather than being
delivered to the lungs. In this event, there is a continuous loss
of gas from the supply conduit that can lead to an accumulating
drop in pressure therein during expiration phases of the respirator
cycle. Should the pressure drop to a level below the preset
threshold, a false triggering signal is delivered to the breath
assistance apparatus, which accordingly delivers an additional
quantity of gas before the patient is ready to receive it. Such
premature breath assistance has resulted in an unstable runaway
condition in which the breath assistance apparatus cycles at
several times the normal breathing rate, causing a buildup of
pressure within the patient's lungs above a safe amount. The
patient does not have sufficient time to relieve the excess
pressure by exhaling, and if the condition is not quickly observed
and corrected may suffer serious lung damage or worse.
A related problem with known respirator systems relates to the
maintenance of a minimum pressure level in the lungs of patients
who suffer from diseases which cause a shrinking of the alveolar
sacs. In such conditions, it is important to maintain the lung
pressure at a level at least sufficient to keep the sacs expanded.
Some of this pressure can be lost, however, if there are leaks in
the gas conduit system, such as the abovedescribed tracheal tube
leak. Even if a runaway breath assistance condition is avoided, the
pressure loss may be large enough to allow the sacs to shrink to an
unacceptable size.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel and
improved respirator system and operating method for delivering
quantities of gas in response to patient need.
Another object is the provision of a novel and improved respirator
system with the ability to discriminate between gas leaks and a
patient request for breath assistance, and to operate a breath
assistance function only in response to patient need.
A further object of the invention is the provision of a novel and
improved respirator system having means to maintain the pressure in
the gas supply conduit system at a level at least as high as a
predetermined minimum pressure, regardless of gas leaks from the
supply system.
Another object is the provision of a novel and improved respirator
system having a high degree of sensitivity in the detection of a
patient request for breath assistance, with the detection mechanism
being independent of the absolute pressure within the supplied
conduit system.
Still another object is the provision of a novel and improved
method of operating a respirator system in such a way as to achieve
the above-stated objects.
In the accomplishment of these and other objects, a respirator
system is provided that includes gas conduit means having an inlet
port, an outlet port, and a patient supply tap intermediate to the
inlet and outlet ports for conducting gas to the patient. The inlet
port receives gas from a recyclable gas charging means during
inhalation phases of the patient's breathing. Any outward flow of
gas from the conduit system through the inlet port is blocked
during expiration phases by a first valve means, while a second
valve means blocks any inward flow of gas through the outlet port
during inhalation phases. A pressure plenum with associated means
for positively maintaining the pressure therein at a predetermined
level provides a gas source to compensate for leaks, the gas
flowing through a bleeder means into the conduit means when the
pressure in the conduit means falls below the said predetermined
level. A gas flow sensing means senses the flow of gas towards the
patient during the expiration phase and produces a signal that
actuates a control for the charging means when the gas flow exceeds
a predetermined threshold flow rate, due to the onset of
inspiration by the patient. The bleeder means provides a
substantially unrestricted gas flow path from the plenum into the
conduit means for flow rates up to a maximum which is approximately
equal to the said threshold flow rate. Gas leaks from the patient
supply tap which do not exceed the said threshold flow rate are
thereby replenished by a compensating gas flow into the conduit
means from the plenum, without actuating the charging means, while
the pressure in the conduit means is maintained at a level which is
substantially at least equal to the predetermined plenum level
despite such gas leaks.
The operating method contemplated by the present invention
comprises sensing the gas flow rate towards the patient through the
conduit means when the inlet port is blocked by the first valve
means, supplying gas to the conduit means during expiratory phases
to compensate for gas leaks from the patient supply tap, limiting
such compensating flow to a rate no greater than the patient's
expected voluntary inhalation flow rate, and actuating the charging
means control to operate the charging means when the sensed gas
flow rate exceeds a predetermined threshold level which is no
greater than the patient's expected voluntary inhalation flow
rate.
In a particular embodiment of the invention, the outlet port or
expiratory end of the conduit means is engaged to maintain the
conduit pressure at or above the desired minimum level by
connecting the bleeder means between the plenum and the said outlet
port. In this embodiment, the gas flow sensor comprises a pressure
differential sensor which is operably connected to sense pressure
differences between the plenum and the outlet port. The bleeder
means includes an adjustable flow restriction means adapted to
produce a predetermined pressure differential across the bleeder
when the gas flow rate therethrough equals the threshold flow rate
for actuating the charging means. As the bleeder means provides the
only gas inlet into the conduit during expiration phases, the said
pressure differential may be equated to a voluntary inhalation by
the patient. The bleeder means enables an equilization of pressure
between the plenum and the conduit means for normally encountered
leaks that do not exceed the threshold flow rate, thereby
preventing an accumulation of gas loss from the conduit means and a
resulting false triggering of the charging means.
More detailed aspects of this embodiment include the provision of a
second plenum that communicates with the conduit means during
expiration phases through the outlet port thereof, substantially
equalizing the conduit means pressure with the second plenum
pressure. A check valve separates the two plenums and permits a
unidirectional gas flow from the second to the first for the
removal of expired air from the system. The plenums are
respectively enclosed within first and second chambers, with a jet
means provided to direct a substantially constant velocity gas jet
through a venturi and into the first chamber for maintaining the
pressure in said chamber at a substantially constant level. A third
chamber is interposed between the jet means and the venturi, and
includes at least one outlet orifice for venting gas expired by the
patient.
In another embodiment of the invention, a sensing means is
interposed in line with the patient supply tap to directly sense
the gas flow towards the patient during expiration phases. In this
embodiment, the pressure within the conduit means may be maintained
at or above the desired minimum level by means of a simple pressure
regulator communicating with the conduit means at any convenient
location.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and features of the present invention will be
apparent to those skilled in the art from the ensuing detailed
description thereof, taken with the accompanying drawings, in
which:
FIG. 1 is a partially schematic diagram of a respirator system
constructed in accordance with the invention;
FIG. 2 is an illustrative graphical representation of a typical gas
flow cycle encountered in a tube inserted into a patient's trachea
and supplied with gas by a respirator system which incorporates the
present invention, illustrating the effect of a gas leak at the end
of the tube;
FIG. 3 is an illustrative graphical representation of the gas
pressure inside the conduit system during cyclical operation of a
respirator, with the pressure pattern characteristic of the present
invention shown in solid lines and that of an unstable condition
encountered in the prior art in dashed lines;
FIG. 4 is a sectional view in frontal elevation of the pressure
control and sensing apparatus provided in one embodiment of the
invention;
FIG. 5 is a sectional view in right-side elevation of the upper
portion of the apparatus shown in FIG. 4; and
FIG. 6 is a schematic diagram of another embodiment of the
invention.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
Referring to FIG. 1, there is shown an embodiment of the invention
in which an air or air-oxygen mixture is delivered to a conduit
system by a conventional charging apparatus which includes a gas
mix box 10 in which gas is mixed to the desired composition, a
piston 12 slidably lodged in a cylinder 14, and a manifold 16 from
which gas is supplied to the delivery system. The piston 12 sucks
in air from the manifold 16 through a connecting pipe 18 during
backstrokes, producing a pressure drop in the manifold 16 that
draws in air from mix box 10 through a check valve 20. An
adjustable pressure relief valve 22 is located in the manifold 16
to assure that the gas delivered to the patient does not exceed the
pressure setting of the relief valve. The piston 12 moves forward
in response to an actuating signal from a breath assist control
switch 24, delivering a volume of gas from the manifold 16 to the
patient supply system. The gas volume may be either a preset amount
or determined dynamically by measuring the patient's lung pressure
and stopping piston movement when that pressure reaches a desired
level.
The conduit means for guiding the flow of gas to and from a patient
includes a plastic tubing network, generally indicated by numeral
26, in a T configuration. One branch 28 of the T functions as an
inlet or inhalation tube, the end of which is open and fitted over
an orifice in manifold 16 to form an inlet port 30 for the tube
network. The other branch 32 serves as a gas outlet or expiration
tube and has an open end comprising a gas outlet port 34. A spur
tube 36, which may be equated to the stem of the T, is tapped into
the tube network at a location intermediate the inlet and outlet
ports 30 and 34, and provides a conduit for both inhaled and
expired gas. An additional plastic tube 38, which may be referred
to as the tracheal tube, is tightly fitted over tube 36 and passed
down the trachea of the patient 40 to conduct air to and from the
patient's lungs. Associated with the inlet branch 28 is a pressure
gauge 42 and a filter or humidifying device 44 to treat the
supplied gas before delivery to the patient. The tracheal tube 38
is generally introduced through the mouth, but under certain
circumstances it may be directed through a nasal passage, or
surgically inserted directly into the trachea.
Gas blocking devices are provided at either branch end of the tube
network 26 to insure that gas will flow through the inlet branch
only in a direction from the manifold 16 to the patient, and
through the outlet branch 32 only from the patient to the outlet
port 34 (expect for certain triggering and leakage flows discussed
below). The flow blocking mechanism or inlet branch 28 comprises a
check valve 46 set in the inlet port 30, while the blocking
mechanism for outlet branch 32 comprises the combination of a
diaphragm 48 and a reciprocal piston 50 aligned to alternately flex
the diaphragm 48 to a position blocking outlet port 34 and to
release the diaphragm to a non-blocking position.
There will frequently be a small clearance between the tracheal
tube 38 shown in FIG. 1 and the patient's trachea, resulting in a
certain loss of gas from the patient-respirator complex that
escapes up through the trachea around the tracheal tube 38 and out
the patient's mouth, such gas losses being indicated in the figure
by arrows 52. To compensate for these gas losses without subjecting
the patient to the risks inherent in prior respirator systems, a
structure is provided at the outlet port 34 that includes first and
second chambers 54 and 56, mutually partitioned by a check valve 58
that enables a unidirectional gas flow from the chamber 56 to
chamber 54. The second-mentioned chamber 56 completely surrounds
the outlet port 34 so that all gas entering or leaving the said
port must also pass through chamber 56, fixing the pressure in
outlet branch 32 whenever the outlet port 34 is unblocked.
Diaphragm 48 forms one wall of the chamber 56, the other chamber
walls conveniently being formed from a plastic mold.
The pressure inside chamber 54 is maintained at a constant level by
means of a gas jet source 60 that delivers a steady jet stream
through openings in the longitudinally opposed walls of a third
chamber 62 to a venturi 64 that opens into the first chamber 54.
The gas jet source 60 is adjustable within a range enabling the
pressure inside chamber 54 to be set at between zero and 15
centimeters H.sub.2 O gauge (70 centimeters H.sub.2 O equaling
approximately 1 pound per square inch). The third chamber 62 is
provided with four orifices in its transverse walls, two of which
are shown in the drawings and identified by reference numerals 66
and 68, through which gas exhaled by the patient may be expelled
from the respirator system.
A bleeder conduit or line 70 is connected between chambers 54 and
56, with an adjustable needle valve 72 forming a restriction in the
bleeder line to limit the gas flow rate from chamber 54 to chamber
56 (gas flows in the opposite direction, from chamber 56 to chamber
54, are transmitted through check valve 58, which forms a parallel
bypass to the bleeder line 70 in this flow direction). The needle
valve 72 may be adjusted from a full-open position, at which the
gas flow through the bleeder line 70 is substantially unrestricted,
to a completely closed position.
A transducer 74, shown in FIG. 1, senses the pressures in chambers
54 and 56 through connecting tubes 76 and 78, respectively, and
compares the two sensed pressure. When the pressure in chamber 54
exceeds that in chamber 56 by a predetermined threshold amount for
which the transducer 74 is set, control signals are transmitted
from the transducer to the breath assist control 24 for actuation
of the breath assist mechanism, and to the piston 50 causing that
piston to move against the diaphragm 48 and block the outlet port
34. The pickup level of transducer 74 for triggering the breath
assist mechanism is adjustable within a range of, for example, 0.05
centimeter H.sub.2 O to 1.0 centimeter H.sub.2 O. The needle valve
72 and transducer 74 are set at levels determined by the expected
voluntary inhalation flow rate produced by the patient 40 such that
gas flows through bleeder line 70 from chamber 54 to chamber 56 are
substantially unrestricted by needle valve 72 for flow rates that
do not exceed the expected inhalation flow rate. For such flow
rates, the pressure inside chambers 54 and 56 are substantially
identical, and transducer 74 will not produce a control signal.
Should a back flow be established through outlet branch 32 towards
the patient that exceeds the expected inhalation flow rate, needle
valve 72 restricts the flow rate of gas through bleeder line 70 to
a level less than that which is necessary to equalize the pressure
between chambers 54 and 56, thereby producing a pressure
differential between the two chambers that causes transducer 74 to
produce a control signal.
Cyclical gas flows to and from the patient and the gas pressure
within the conduit network are illustrated respectively in FIGS. 2
and 3. Referring first to FIG. 2, the cyclical respirator operation
is assumed to be initiated when piston 12 is actuated by breath
assist control 24 to move forward into cylinder 14, producing an
in-flow of gas to the patient as indicated by line 80. When the
patient has inspired a sufficient quantity of gas, the respirator
system switches to an exhalation mode in which gas is expired from
the patient's lungs, through tube 36, and out the outlet port 34,
as indicated by line 82. When the patient has expelled a full
quantity of gas, the respirator system pauses until the patient
inhales gas from the tube network in an attempt to draw breath, the
initial inhalation attempt being indicated by the in-flow surge 84.
With a proper adjustment of the needle valve 72 and transducer 74,
this surge will exceed the trigger threshold 86 at which the
transducer 74 is set, producing a signal to actuate the breath
assist mechanism and initiate another gas charge 88 into the
respirator tube network, thereby starting another breath cycle. It
should be noted that a substantial amount of gas leakage, as
indicated by line 90, may be tolerated from the tube network
without triggering the transducer 74 to actuate the breath assist
mechanism, so long as the leakage is not so gross as to exceed the
trigger threshold level 86.
The gas pressure pattern in the respirator tubes is illustrated in
FIG. 3 against the same time scale as that of FIG. 2. The pressure
increases along line 92 as gas is charged into the tube in response
to a trigger signal, reaching a peak at the end of the charging
period and then gradually declining along line 94 to a level not
less than the minimum required to adequately expand the alveolar
sacs. The pressure pattern produced by the present invention is
shown in solid lines. During the interval 96 following full breath
expiration but preceeding the beginning of the next inhalation, the
pressure in the tubes remains steady and does not drop below the
minimum desired level, despite the continuous leakage from the
tracheal tube during this period, because a replenishing flow of
gas is supplied to the tubes through bleeder line 70 and chamber
56. A slight dip in pressure 98 occurs when the patient attempts to
inhale, this dip resulting from the patient's intake rate exceeding
the rate at which replenishing gas can be supplied through bleeder
line 70. Although slight, the pressure dip 98 is sufficient to
actuate the highly sensitive transducer 74 to produce a control
signal, recycling the breath assist mechanism. It can be seen from
the drawing that the tube pressure is maintained at a substantially
constant value during the interval 96, and successful breathing is
achieved. By contrast, an unstable condition that may occur with
prior art respirator systems is indicated in dashed lines. Such
prior art systems that do not employ compensating gas supply
mechanisms will gradually undergo an accumulating pressure loss
during an expiration phase due to the gas leak. As the breath
assist mechanism for these systems is commonly responsive to the
pressure within the tubes, rather than to the gas flow rate
measured by the present invention, a point may be reached at which
the pressure drop is sufficient to actuate the breath assist
mechanism, and a new charge of gas is supplied to the system before
the patient is ready to receive it. This occurrence is indicated at
point 100 in FIG. 3. It may lead to an unstable condition in which
the the patient does not have sufficient time to exhale before the
next charge of gas. The pressure inside the lungs which is
generally somewhat less than the tube pressure but follows a
similar rise and fall pattern, can thereby build up to the point at
which a pneumothorax occurs.
Referring now to FIGS. 4 and 5 for further details of the apparatus
at the expiratory end of the tube network, chamber 56 is formed
from a plastic block with a cylindrical tube 102 extending through
one wall to form a mounting jack for outlet tube 32 on the exterior
of the chamber, the other end of tube 102 forming outlet orifice 34
adjacent to flexible membrane 48. The chamber 54 comprises an inner
chamber 104 downstream of winged check valve 58 that communicates
with a surrounding annular gas reservoir 106 through a port 108.
The bleeder line 70 of FIG. 1 comprises a passageway 110 through
the chamber block, shown in FIG. 5, a portion of which passageway
is shaped to form a seat 112 for manually adjustable needle valve
72, which is shown in a closed position. Highly sensitive
adjustments may be made to the flow restriction produced by needle
valve 72 by rotating the valve handle 114 to lift or lower the
valve stem 116. A similar needle valve 118 is provided in the gas
jet mechanism to enable a precise control of the jet, indicated by
arrow 120, before entering the venturi 64. Gas is introduced into
the jet mechanism through a nozzle 122 at a pressure of
approximately 50 psig, passes through a filter 124 and restriction
orifice 126 to a smaller chamber 128 at a pressure in the order of
10-20 psig, and then proceeds through valve 118 for deflection
upward to the chamber 62, venturi 64, and chamber 54. The valve 118
is adjustable within a range which results in a gas pressure in
chamber 54 of between zero and 15 centimeters H.sub.2 O gauge, as
mentioned previously.
A solenoid 130 is arranged about a rearward extension 132 of the
piston 50 to move the piston alternately into and away from the
diaphragm 48, blocking and opening outlet port 34. The solenoid is
connected by leads 134 for control by the transducer 74.
In operation, the tracheal tube 38 is inserted into the patient's
trachea and the respirator turned on with the needle valve 72 fully
open. At this point, the flow of gas through bleeder line 70 from
chamber 54 to chamber 56 will generally be substantially
unrestricted, even for flow rates as large as that produced by the
patient inhaling, and the breath assist apparatus will not respond
to the patient's breathing. The needle valve 72 is then gradually
closed until the restriction presented to the flow of gas through
the bleeder line 70 during patient inhalation attempts is
sufficient to produce a pressure drop that exceeds the threshold
level of transducer 74, thus triggering the breath assist apparatus
into action. This point may be detected by observing when the
pressure inside the conduit network, as indicated by pressure gauge
42, first begins to follow the patient's rhythmic breathing rate
and exhibits a cyclical pattern such as that shown in FIG. 3 With
the needle valve 72 at this setting, the flow path through bleeder
70 is sufficiently open to enable a replenishing gas flow from
chamber 54 to chamber 56 and thence into the conduit network 26 to
compensate for all except unusually large gas leaks from that
network, without triggering the breath assist apparatus. At the
same time, patient attempts to inhale will produce a pressure drop
that does trigger the breath assist.
A full cycle of the respirator operation, beginning at a time just
after the transducer 74 has sensed an attempt to breath, will now
be described. At the beginning of the cycle to the solenoid, an
energizing signal is transmitted from the transducer 74 over leads
134 to the solenoid 130, producing a magnetic field that urges
piston 50 against diaphragm 48 to close the outlet port 34. The
transducer 74 also transmits a control signal to the breath assist
control switch 24, which actuates piston 12 to move into cylinder
14, thereby forcing gas out of manifold 16, past check valve 46,
and into the conduit network through inlet port 30. With the outlet
port 34 closed, a volume of gas equal to that charged into the
conduit system is forced out through tap 36 and the tracheal tube
38. Most of this gas will be supplied to the patient's lungs, but
some may be lost by leakage at the end of the tracheal tube 38.
At the end of the inhalation phase, the piston 12 is retracted,
drawing a new supply of gas into the manifold 16 from mix chamber
10, and the patient begins to exhale. At about the same time, the
energizing signal is removed from solenoid 130 and the piston 50 is
spring urged back from diaphragm 48, opening outlet port 34. Check
valve 46 blocks any outflow of gas through inlet valve 30, so that
all of the patient's expired gas flows through outlet port 34 into
chamber 56, through check valve 58 and chamber 54, and out through
vents 66, 68 and the vents not shown in the drawings. After active
expiration ends, there is a pause before the next breath and
renewed operation of the breath assist apparatus, during which time
gas leaks may continue to drain gas from the conduit network.
During this period, the chamber 54 is maintained as a substantially
constant pressure plenum by the gas jet mechanism 60 acting through
venturi 64. The gas leaks are made up by a compensating,
substantially unrestricted gas flow through the bleeder line 70
from chamber 54 to chamber 56, thus maintaining the latter chamber
also as a substantially constant pressure plenum. Since chamber 56
communicates openly with the conduit network through outlet port
34, the pressure in that network may be kept at or above a minimum
desired lung pressure so long as the pressure in chamber 54 is
maintained.
When the patient attempts to draw breath, a sudden inflow of gas to
the tap 36 is created which, due to the restriction of needle valve
72, cannot be fully met by a compensating flow through bleeder line
70. As a result, the pressure within the conduit network drops
momentarily, creating a pressure differential between the plenums
of chambers 54 and 56 that exceeds the threshold of transducer 74,
which instrument thereupon produces appropriate signals to start
another respirator cycle.
The above-described embodiment is highly sensitive to gas flows,
and is therefore particularly useful for patients such as infants
who process a relatively small amount of gas with each breath.
Another embodiment of the invention shown in FIG. 6 that is
intended to be used with adults. This embodiment employs a
simplified apparatus to achieve a somewhat lesser degree of
sensitivity that nonetheless is sensitive enough for older
patients. Several elements of this embodiment are carried over from
the embodiment of FIG. 1, and the same numerals have been used to
indicate elements common to both.
Gas is cyclically charged into the conduit network, as in the
previous embodiment, by breath assist apparatus which includes a
piston 12 slidably lodged in cylinder 14, a gas mix chamber 10, and
a manifold 16 which is connected by pipes or tubes to the last two
elements. Check valve 46 prevents any reverse gas flow out of the
conduit inlet port 30, while an expandable balloon or bladder 136
is positioned adjacent to outlet port 34 to block that port during
inhalation by expanding under the influence of air pumped in
through a balloon stem 138.
Instead of sensing a patient's attempt to breathe by measuring
pressure differentials at the expiration end of the conduit
network, a gas flow sensing mechanism 140 is interposed directly in
line with the patient tap 36. Gas flow sensor 140 may be of any
convenient type, for example an ultrasonic device such as the
sensor described in U.S. Pat. NO. 3,680,375 to Joy et al., so long
as it is able to detect gas flows caused by a patient's attempt to
inhale. A pressure regulator 142 is tapped into the inlet conduit
branch 28 through a bleeder arrangement such as check valve 144
that permits gas to flow only into the conduit, the pressure
regulator 142 comprising essentially a constant pressure plenum
which is maintained at the minimum desired expiratory pressure.
Gas flow sensor 140 is connected in a control circuit with the
breath assist control 24 through a switch 146, and also to the
balloon 136, switch 146 being closed during expiration but open
during inhalation to prevent the breath assist apparatus from being
triggered. In operation, gas is charged into the conduit network to
the patient for the patient to inhale, with balloon 136 expanded to
block outlet port 30. After the patient has received a full breath,
balloon 136 is permitted to go flacid and the patient expires
through outlet branch 32 and outlet port 34. Should the pressure in
the conduit network begin to fall below the level necessary to keep
the alveolar sacs expanded, for instance because of gas leakage
from tracheal tube 38, a gas flow commences from the pressure
regulator 142 into the conduit system that holds the pressure
therein at an acceptable level. When the patient again attempts to
inhale, the large inrush of gas exceeds the setting of flow sensor
140, which thereupon initiates a control signal to trigger the
breath assist control 24 and the input mechanism for balloon 136,
beginning a new breath cycle.
It is obvious that many modifications may be made to the subject
invention which come within its true scope and spirit. Thus, the
scope of the subject invention is considered to be limited only by
the appended claims.
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