U.S. patent number 3,817,246 [Application Number 05/313,983] was granted by the patent office on 1974-06-18 for flow responsive respiration apparatus.
This patent grant is currently assigned to Puritan-Bennett Corporation. Invention is credited to James Weigl.
United States Patent |
3,817,246 |
Weigl |
June 18, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
FLOW RESPONSIVE RESPIRATION APPARATUS
Abstract
Respiration apparatus for IPPB therapy in which the inspiratory
effort of the patient to initiate an inspiration phase is sensed by
a flow sensor which operates by directing a laminar jet of gas
across a conduit of the apparatus toward a receiver, to produce a
normal pressure in the receiver when there is no flow in the
conduit. A second receiver establishes a reference pressure, and
the change in the pressure relationship between the receivers,
resulting when the patient creates a cross-flow across the jet, is
used as a pilot signal to operate an actuator for opening a flow
control valve. Similarly, as the flow rate is reduced near the end
of the inspiration phase, the pressure relationship is restored and
the actuator closes the control valve. One embodiment uses a
laminar jet that is directed into an aligned receiver to raise the
pressure therein relative to a receiver spaced from the jet, and
referenced to actual patient delivery pressure, until a cross-flow
disturbance changes the jet to turbulent, thereby reducing the
pressure in the aligned receiver. Another embodiment uses a
turbulent jet directed between two longitudinally spaced receivers,
disposed in close proximity to one another, to establish equal
pressures therein until the jet is deflected longitudinally toward
one of the receivers and away from the other in response to a
cross-flow.
Inventors: |
Weigl; James (Santa Monica,
CA) |
Assignee: |
Puritan-Bennett Corporation
(Kansas City, MO)
|
Family
ID: |
23218030 |
Appl.
No.: |
05/313,983 |
Filed: |
December 11, 1972 |
Current U.S.
Class: |
128/204.24;
137/842 |
Current CPC
Class: |
A61M
16/00 (20130101); G01F 23/161 (20130101); A61M
2205/42 (20130101); Y10T 137/2273 (20150401); A61M
16/0866 (20140204); A61M 16/0063 (20140204); A61M
2016/003 (20130101); A61M 16/107 (20140204) |
Current International
Class: |
A61M
16/00 (20060101); G01F 23/14 (20060101); G01F
23/16 (20060101); A61m 016/00 () |
Field of
Search: |
;128/145.8,145.6,145.7,145.5,145 ;137/842 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Dunne; G. F.
Attorney, Agent or Firm: Fulwider Patton Rieber Lee &
Utecht
Claims
I claim:
1. Flow responsive respiration apparatus for administering
intermittent positive pressure breathing therapy to a patient from
a source of gas under pressure and through delivery means into
which the patient breaths to initiate an inspiration phase of a
respiration cycle, said apparatus having, in combination:
conduit means connectible between said source and said delivery
means for carrying gas intermittently therebetween;
a flow control valve in said conduit means having an inlet port
connected to said source by said conduit means, an outlet port
connected to said delivery means by said conduit means, a closure
member movable between a first position establishing communication
between said ports and a second position disconnecting said ports,
and pressure-responsive means for moving said closure member to
said first positive in response to a first pressure signal, and to
said second position in response to a second pressure signal;
a flow sensor in said conduit means adjacent said delivery means
comprising means for directing a jet of gas across said conduit
means, and a receiver spaced from said jet-directing means to be
pressurized thereby in accordance with the condition of said jet,
to a first pressure level when there is no cross-flow in said
conduit means and to a second pressure level when there is a
cross-flow resulting from breathing by the patient;
actuator means connected to said flow control valve and to said
flow sensor and operable to produce said first pressure signal when
said first pressure level exists in said receiver, and to produce
said second pressure signal when said second pressure level exists
in said receiver, thereby to open said flow control valve and
initiate the inspiration phase in response to breathing by the
patient through said flow sensor;
and means for reducing the rate of flow of gas through said
apparatus to the patient in response to increasing back pressure
therein as the lungs of the patient are inflated, and thereby to
reduce the flow rate through said flow sensor during said
inspiration phase until said first pressure level is restored, to
close said flow control valve and terminate the inspiration
phase.
2. Flow responsive respiration apparatus for administering
intermittent positive pressure breathing therapy to a patient from
a source of gas under pressure and through delivery means into
which the patient breaths to initate an inspiration phase of a
respiration cycle, said apparatus having, in combination:
conduit means connectible between said source and said delivery
means for carrying gas intermittently therebetween;
a flow control valve in said conduit means having an inlet port
connected to said source by said conduit means, an outlet port
connected to said delivery
and means for reducing the rate of flow of gas through said
apparatus to the patient in response to increasing back pressure
therein as the lungs of the patient are inflated, and thereby to
reduce the flow rate through said flow sensor during said
inspiration phase until said first pressure level is restored, to
close said flow control valve and terminate the inspiration
phase;
and wherein
said flow sensor has a first receiver aligned with said jet,
said jet-directing means maintains laminar flow in said jet at said
first receiver only until said cross-flow disturbs the jet,
and the resulting change to turbulent flow produces a marked
pressure drop in said first receiver, said sensor also having a
second receiver spaced from said first receiver to establish a
reference pressure level with respect to which said first and
second pressure levels are detectable in said actuator means.
3. Flow responsive respiration apparatus for administering
intermittent positive pressure breathing thereapy to a patient from
a source of gas under pressure and through delivery means into
which the patient breathes to initiate an inspiration phase of a
respiration cycle, said apparatus having, in combination:
conduit means connectible between said source and said delivery
means for carrying gas intermittently therebetween;
a flow control valve in said conduit means having an inlet port
connected to said source by said conduit means, an outlet port
connected to said delivery means by said conduit means, a closure
member movable between a first position establishing communication
between said ports and a second position disconnecting said ports,
and pressure-responsive means for moving said closure member to
said first position in response to a first pressure signal, and to
said second position in response to a second pressure signal;
a flow sensor in said conduit means adjacent said delivery means
comprising means for directing a jet of gas across said conduit
means, and a receiver spaced from said jet-directing means to be
pressurized thereby in accordance with the condition of said jet,
to a first pressure level when there is no cross-flow in said
conduit means and to a second pressure level when there is a
cross-flow resulting from breathing by the patient;
actuator means connected to said flow control valve and to said
flow sensor and operable to produce said first pressure signal when
said first pressure level exists in said receiver, and to produce
said second pressure signal when said second pressure level exists
in said receiver, thereby to open said flow control valve and
initiate the inspiration phase in response to breathing by the
patient through said flow sensor;
and means for reducing the rate of flow of gas through said
apparatus to the patient in response to increasing back pressure
therein as the lungs of the patient are inflated, and thereby to
reduce the flow rate through said flow sensor during said
inspiration phase until said first pressure level is restored, to
close said flow control valve and terminate the inspiration
phase;
and wherein said flow sensor has two receivers connected to said
actuator means and longitudinally spaced apart on opposite sides of
the path of said jet, to be equally pressurized by the jet while
there is no cross-flow through said sensor, and to be pressurized
unequally when the jet is deflected toward one of said receivers by
a cross-flow.
4. Respiration apparatus for administering intermittent positive
pressure breathing therapy to a patient from a source of gas under
pressure and through delivery means into which the patient breathes
to initiate a respiration cycle, said apparatus having, in
combination;
conduit means connectible to said source for carrying gas therefrom
intermittently to said delivery means;
a flow control valve in said conduit means operable to close the
latter in a first condition of the valve and to open the same in a
second condition;
a pressure-responsive flow regulator for reducing the flow rate
through said conduit means to said delivery means as back pressure
builds up in said conduit means during inflation of a patient's
lungs;
and a flow sensor in said conduit means for actuating said flow
control valve between the open and closed conditions in response to
breathing-in by said patient through said conduit means, said flow
sensor including means for directing a jet across said conduit
means, first and second receivers opening into said conduit means,
said first receiver being positioned across said conduit means from
said jet-directing means to be pressurized by said jet, thereby to
produce a first pressure relationship between said receivers when
there is no flow through said conduit means and a second and
different pressure relationship when there is a disturbance of said
jet by a flow through said conduit means resulting from breathing
by the patient;
and actuator means responsive to the change from said first
pressure relationship to the second and operable to produce an
amplified pressure signal and thereby to actuate said flow control
valve and initiate an inspiration phase of said apparatus in
response to said flow.
5. In a respiration apparatus for administering intermittent
positive pressure breathing therapy to a patient from a source of
gas under pressure through delivery means into which the patient
breaths to initiate a respiratory cycle, the combination of:
conduit means connectible to said source for carrying gas therefrom
to said delivery means;
a flow control valve for opening and closing said conduit
means;
flow sensing means including means for directing a jet of gas
across said conduit means, and receiver means positioned across
said conduit means to receive gas from said jet-directing means and
produce a pressure signal having one value when there is no flow
transversely of said jet resulting from breathing of the patient
through said conduit means;
and actuator means responsive to changes in said signal, for
producing an amplified pressure signal to open and close said
valve.
6. In a respiration apparatus for administering intermittent
positive pressure breathing therapy to a patient, and including a
source of gas under pressure, delivery means for administering the
gas to the patient, conduit means connecting said source to the
patient to carry the gas to the delivery means, and a selectively
operable flow control valve for opening and closing said conduit
means between said source and said delivery means, the combination
of:
means for directing a jet of gas under pressure across a portion of
said conduit means through which the patient breathes in drawing a
breath through said delivery means;
receiver means positioned across said portion of said conduit to be
pressurized by said jet to a first level when said jet is
undisturbed, and to a second level when said jet is disturbed by
cross-flow in said portion of said conduit means resulting from
breathing by the patient;
and actuator means responsive to the change in the pressure in said
receiver means from said first level to said second level for
producing an amplified pressure signal to open said control
valve.
7. A respiration apparatus as defined in claim 6, in which said
receiver means include a first receiver positioned across said
portion of said conduit means in alignment with said jet, and in
which said jet-directing means produces a jet which remains laminar
at said first receiver as long as the jet is undisturbed, and
changes to turbulent at said first receiver when disturbed by a
cross-flow.
8. A respiration apparatus as defined in claim 7 further including
a second receiver in said conduit means spaced from said first
receiver to establish a reference pressure with respect to which
said first and second levels are detectable in said means for
opening said control valve.
9. A respiration apparatus as defined in claim 7 further including
a disturbance amplifier in said portion of said conduit means,
having an edge alongside the path of said jet, adjacent said first
receiver.
10. A respiration apparatus as defined in claim 9 further including
a plurality of flow-straightening vanes in said portion of said
conduit means for directing the cross-flow perpendicular to said
jet.
11. A respiration apparatus as defined in claim 6 in which said
portion of said conduit is a first restricted conduit communicating
with said delivery means, and further including a second, larger
conduit also communicating with said delivery means around said
first conduit, and having check means therein for directing said
cross-flow through said first conduit and passing the flow of gas
from said source to said delivery means.
12. A respiration apparatus as defined in claim 6 in which said
receiver means comprise two receivers spaced apart on opposite
sides of the path of said jet to be pressurized equally thereby
when there is no cross-flow in said portion of said conduit means,
one of said receivers being positioned to be pressurized to a
higher level as said jet is deflected by said cross-flow.
13. A respiration apparatus as defined in claim 12 in which said
portion of said conduit means is a tube adjacent said delivery
means through which the patient breathes and through which all of
the gas is supplied to the patient.
Description
BACKGROUND OF THE INVENTION
This invention relates to respiration apparatus, and more
particularly to apparatus for administering intermittent positive
pressure breathing (IPPB) therapy to a patient.
In such therapy, air, oxygen or oxygen-enriched air under pressure
is supplied to a patient cyclically through delivery means such as
a face mask or the like. Each inspiration phase is initiated in
response to a slight inspiratory effort by the patient, and begins
with a peak flow rate which inflates the patient's lungs, the flow
rate then being reduced to a relatively low level at which all flow
is terminated. Following the inspiration phase, the lungs are
vented to atmosphere during an expiration phase, which terminates
when the next inspiratory effort by the patient initiates the next
cycle.
Examples of prior IPPB apparatus are shown in U.S. Pat. No.
3,362,404 and No. 3,368,555, illustrating two different approaches
to the manner in which inspiration may be initiated and terminated.
In U.S. Pat. No. 3,362,404, the patient draws air through the
delivery means to create a pressure drop in the diaphragm chamber
of a triggering valve, and this pressure drop is used to open a
flow responsive valve which initiates the inspiration phase and
eventually terminates inspiration in response to a selected low
terminal flow level. In U.S. Pat. No. 3,368,555, a similar
inspiratory effort by the patient is applied as a biasing signal to
a control fluid amplifier of the monostable, lock-on type to switch
a fluid flow therein from a preferred channel to another channel,
thereby switching the flow through a main fluid amplifier of the
bistable, lock-on type to initiate an inspiration cycle. The flow
in the control amplifier switches back to the preferred channel
automatically when the biasing signal is removed, and this switches
the main amplifier to terminate inspiration at a selected low
terminal flow rate.
Both of these approaches are effective to initiate inspiration in
response to slight inspiratory efforts, but both utilize the actual
reduction of pressure caused by the patient's inspiratory effort as
the source of an actuating pressure signal, with the result that
there is a perceptible resistance to inspiratory effort at the
beginning of inspiration until the machine overcomes its internal
delays and begins to flow gas through the delivery means. A primary
object and advantage of the present invention is the reduction of
this resistance to an almost imperceptible level, to increase the
comfort of the patient during IPPB therapy, in a novel manner that
does not detract in any way from other performance characteristics
of the apparatus.
SUMMARY OF THE INVENTION
The present invention resides in a respiration apparatus of the
foregoing general character in which the inspiratory phase of each
respiration cycle is initiated by a flow-sensing device that does
not require the patient to create a pressure drop any greater than
that required to produce a slight flow of air within the conduits
of the apparatus. In other words, the sensing device of the present
invention is capable of initiating the inspiration phase in
response to an inspiratory effort by the patient that is virtually
the same as the normal effort during involuntary breathing, and is
effective to initiate the inspiration phase with an open air
circuit through the apparatus, preferably through a filter for
mixing air with the primary flow of gas from the source.
This is accomplished by incorporating a fluidic flow sensor in one
of the conduits of the apparatus, including means on one side of
one of the conduits for directing a jet of gas under pressure
across the conduit and receiver means in the path of the jet
reference pressure relationship between two receivers of the
receiver means, in the absence of any flow in the conduit. When a
very low threshold flow is created in the conduit by the
inspiratory effort of the patient, for example, a flow as low as 2
to 4 liters per minute, or even less, this cross-flow disturbs the
air jet, changes the reference pressure relationship between the
receivers, and produces a pressure signal that is used to initiate
the inspiration phase of the apparatus. A pressure-actuated control
valve responds to the signals of the flow sensor to initiate the
supply of respiration gas, and a conventional regulator controls
the flow rate to the patient.
As long as there is flow through the flow sensor, the changed
pressure relationship is maintained to maintain the apparatus in
the inspiration phase. As flow rate is reduced during inflation of
the patient's lungs, however, the cross-flow through the jet is
reduced to a low rate which falls below the threshold level for the
flow sensor, the reference pressure signal is restored to the
reference relationship, and the inspiratory phase is terminated by
the control valve.
In one form of flow sensor disclosed, a turbulent jet is directed
between two receivers disposed in close proximity to each other, to
establish equal pressures therein until the jet is deflected
longitudinally by a cross-flow, and all flow passes through the
sensor, which may have a relatively high flow area capable of
handling the peak flow rate of the apparatus. In another, more
sensitive form, a normally laminar jet is directed into an aligned
receiver, and a reference receiver is spaced from the jet to
establish a reference pressure, the jet being converted to
turbulent by a cross-flow, thereby dropping the pressure in the
aligned receiver sharply. The flow area in this form is restricted,
and a by-pass is provided around the sensor, for carrying peak flow
rates to the patient.
Other aspects and advantages of the invention will become apparent
from the following detailed description, taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of one embodiment of a respiration
apparatus constructed in accordance with the present invention;
FIG. 2 is a similar schematic view of an alternative embodiment of
the invention;
FIG. 3 is an enlarged longitudinal cross-sectional view of a flow
sensor incorporated in the apparatus of FIG. 2;
FIG. 4 is an enlarged cross-sectional view of a flow sensor
incorporated in the apparatus of FIG. 1, the view being taken in a
plane indicated by line 4--4 of FIG. 5;
FIG.5 is a cross-sectional view taken along line 5--5 of FIG. 4;
and
FIG. 6 is an enlarged cross-sectional view of a pilot-operated flow
control valve suitable for use in both embodiments of the
invention.
DETAILED DESCRIPTION
As shown in the drawings for purposes of illustration, and with
particular reference to FIG. 1, the invention is embodied in an
IPPB respiration apparatus 10 for delivering an intermittent flow
of air under pressure to a patient from a compressor 11, through
the various conduits and control components of the apparatus and
delivery means 12 such as a face mask adapted to be worn over the
patient's mouth and nose. The compressor draws outside air in
through a filter 13 and a silencer 14, and pumps the air through a
second filter 15 into a main flow conduit 17 in which the pressure
is controlled by a regulator 18.
From this conduit 17, the air is passed intermittently through a
selectively operable control valve 19 and through a conduit 20 to a
conventional pressure-responsive relief valve 21 for reducing the
flow rate to the patient as back pressure in the system indicates
that the patient's lungs are approaching full inflation. The outlet
22 of this relief valve is connected through two conduits 23 and 24
to the delivery means 12. The entrance into the relief valve 21 is
shown as a jet 25 for directing the gas into a venturi section 27,
thus creating a pressure drop for drawing outside air through a
filter 28 and entraining this air with the primary air flow from
the valve 21.
Thus, the opening and closing of the control valve 19 initiates and
terminates the inspiration phases of successive respiratory cycles
of the apparatus 10, and the relief valve 21 controls the flow rate
during each such phase. The relief valve initially passes a
relatively high peak flow, and then reduces this flow to a
relatively low terminal flow rate before the valve 19 is closed to
terminate inspiration. A gauge 29 preferably is provided to
indicate system pressure.
After termination of inspiration, the patient is permitted to
exhale naturally through the delivery means 12 and an exhalation
valve 30 in the conduit 24 adjacent the delivery means, this valve
comprising an exhalation port 31 which is closed during inspiration
by a pressure-actuated closure 32, herein an inflatable "mushroom"
or "balloon" closure connected through a conduit 33 and a pressure
divider formed by two restrictors 34, to the conduit 35 that is
pressurized during inspiration. When air is being supplied to the
patient, the closure is inflated and the exhalation valve is
closed. During exhalation, the pressure in the closure is relieved,
and the valve opens to allow exhaled gas to escape.
If medication is to be administered to the patient as an incident
to the IPPB therapy, a conventional nebulizer 36 may be included
with the delivery means and supplied with nebulizing air under
pressure through the conduit 35, a one-way check valve 37, and a
needle valve 38. Nebulizing air also may be supplied during the
expiration phase by means of a conduit 39 connected to the conduit
17 ahead of the control valve 19 and having a flow restrictor 40
therein, this conduit being connected to the conduit 35 between the
check valve 37 and the needle valve 38.
In accordance with the present invention, the inspiration phases
are initiated and terminated by a fluidic flow sensor 42 in which a
jet 43 is directed across one of the conduits of the apparatus,
herein the conduit 23, toward receiver means which establish a
reference pressure relationship and maintain that relationship as
long as there is no disturbance in the conduit. When a disturbance
occurs, as a result of inspiration by the patient through the
delivery means 12 and the conduits of the apparatus, the pressure
relationship departs from the reference, and this change is used to
open the control valve 19 and initiate an inspiration phase of the
apparatus. Similarly, when the flow rate is reduced to the low
terminal flow rate, the pressure relationship is restored to the
reference level, and this change is used to close the control valve
and terminate the inspiration phase of the apparatus.
More specifically, as shown schematically in FIG. 1 and in detail
in FIGS. 4 and 5, the flow sensor 42 comprises a jet tube 44
opening into one side of the conduit 23 and shaped and positioned
to direct a controlled laminar jet of gas (herein air from a
conduit 45 connected through a restrictor 47 to the conduit 17)
across the conduit 23 and across the path of air drawn through the
conduit when the patient begins to breathe through the respiration
apparatus.
Directly across the conduit and aligned with the jet tube 44 to
receive the air jet 43 is a first receiver tube 48, the pressure in
which is a function of the laminarity (as opposed to turbulence) of
the air jet. Such a jet remains laminar for a considerably distance
downstream from the orifice of the jet tube, and then breaks up
into turbulence. The receiver tube is positioned closer to the jet
orifice than the distance to the point of turbulence, and thus
normally receives a laminar flow.
Spaced along the conduit from the first receiver tube 44 is a
second receiver tube 49, or reference tube, in which the pressure
is essentially unaffected by the jet flow. Thus, a predetermined
pressure differential normally exists between the two receiver
tubes 48 and 49, the difference being the pressure increase in the
tube 48 produced by the jet 43, as long as it remains laminar in
character at the entrance to the tube.
When a patient begins to breathe through the apparatus, the
external influence on the pressures at the two receiver tubes 48
and 49 is the same, but the disturbance of the air jet by the
cross-flow of air in the conduit substantially reduces the distance
to the point of turbulence. The receiver tube 48 is farther from
the jet orifice than the reduced distance to the point of
turbulence, and thus receives turbulent, rather than laminar, flow.
The result is a marked decrease in the pressure in the receiver
tube 48, relative to original pressure. This decrease serves as a
pilot pressure signal to actuate the control valve 19 and initiate
the inspiration phase, herein through a pressure-operated actuator
50.
Similarly, as the flow to the patient is reduced by the relief
valve 21 near the end of the inspiration phase and the rate of flow
through the conduit 23 declines, the disturbance of the air jet 43
is terminated, and the flow again becomes laminar at the entrance
to the receiver tube 48. When this occurs, the pressure in the tube
increases markedly, and this increase serves as a pilot-pressure
signal which acts through the actuator 50 to close the valve
19.
Shown in FIGS. 4 and 5 is a specific embodiment of a suitable flow
sensor 42, in a form which may be injection molded as a small and
inexpensive part, in two pieces, with the jet tube 44, the receiver
tubes 48 and 49, and the conduit 23. Basically, the sensor
comprises two flat plates 51 and 52 fitted together as shown in
FIG. 5 and having adjacent recessed sides defining the tubes and
the conduit.
The patient end of the conduit 23 is a port 53 in the plate 52, and
the inlet end is a similar port 54 in the same plate. The air jet
tube 44 is formed by an elongated channel in the plate 52, which
channel may be rectangular in transverse cross-sectional shape for
convenience of manufacture. The two receiver tubes 48 and 49 may be
similar channels, permissibly of shorter length. When the upper
plate 51 is clamped over the lower plate, the recesses, which may
be in one or both plates, define the various ports.
It should be evident that it is very important for the jet tube 44
to be smooth-walled, to avoid premature transition to turbulent
flow. Suitable connectors 55 are formed on the plate 52 with
passages 57 to carry the jet flow into the jet channel 44 and for
connection of signal lines to the receiver channels 48 and 49.
It will be seen in FIG. 4 that a plurality of elongated parallel
fins 58, 59 and 60 are formed in the left-hand portion of the
conduit 23, perpendicular to the path of the jet 43 across the
conduit. These fins serve as flow straighteners, and also reduce
the cross-sectional flow area of the conduit, to concentrate the
cross-flow on the air jet. The flow area in the opposite end
portion is greater by an amount equal to that occupied by the fins,
and also is increased by widening of the conduit 23, the resulting
restriction being indicated schematically at 61 in FIG. 1.
In addition, it will be seen in FIG. 4 that the upper fin 60,
farthest from the orifice of the jet tube 44, has a downstream end
62 which is closely adjacent the normal path of the jet 43 when the
flow is laminar. This fin is intended to intercept and amplify the
eddy currents along the edge of the jet that are created by
cross-flow, and thus to promote crisp switching of the sensor.
The sensitivity of the flow sensor 42 may be adjusted to different
threshold flow rates by moving the disturbing cross-flow either
closer to or farther from the jet orifice along the axis of jet
flow. Accordingly, the inspiration phase can be initiated and
terminated at different flow rates through the conduit 23. For
example, for high sensitivity, at a threshold flow rate on the
order of 1 to 2 liters per minute, the cross-flow is directed at
the jet at a location relatively close to the supply jet orifice.
For a lower degree of sensitivity, at a threshold rate of 2 to 4
liters per minute, the cross-flow is directed at the jet at a
location farther away from the jet orifice and closer to the
receiver orifice.
While high sensitivity is desirable for ease in initiation of
inspiration, lower sensitivity can be desirable for termination at
a somewhat higher terminal flow rate. Thus, a comprise may be made
between these two considerations, or a by-pass may be provided so
that only a portion of the flow is passed through the flow sensor
42.
The illustrative pressure-operated actuator 50, shown in FIG. 1,
includes two inflatable members 63 and 64, which may be of the
"mushroom" type comprising freely flexible, hollow plastic bodies.
These members are disposed on opposite sides of a lever 65 to urge
the lever back and forth relative to an orifice 67 through which
air under pressure from a conduit 68 escapes when the lever is
spaced from the orifice. The member 63 on the left-hand side is
connected by a conduit 69 to the receiver tube 48, and thus will be
inflated when there is no flow through the conduit 23, to urge the
lever 65 toward the orifice 67 into a blocking position. The member
64 on the right-hand side of the lever is connected by a conduit 70
to the receiver tube 49, to be subjected to the lower patient
delivery pressure, and tending to swing the lever to an open
position. A light spring 71 is positioned to exert an opening force
on the lever, and to cooperate with the member 64 in developing an
opening force moment that is less than the closing moment when jet
flow is undisturbed, but greater than the closing moment when the
jet flow is disturbed.
A manual control 72 is shown in FIG. 1 for shifting the lever 65
into and out of its blocking position, independently of the forces
exerted by the members 63 and 64. This is simply a yoke 73 that is
pivotally mounted on a pin 74 above the free end of the lever, with
the legs of the yoke straddling the lever and a knob 75 projecting
upwardly therefrom and normally held in the centered position
shown, by two springs 77. The knob can be shifted in either
direction to cause the yoke to pick up the lever and shift it into
a selected position.
Air under pressure is continuously supplied to the signal conduit
68 through the control valve 19 to escape through the orifice 67
when it is unblocked by the lever 65, and to build up an actuating
back-pressure signal in the conduit when the orifice is blocked.
This back-pressure signal from the normally blocked orifice holds
the control valve in a closed condition, indicated by the
dotted-line arrow 78 in FIG. 1, and permits the valve to open when
the orifice is unblocked, as indicated by the arrow 79.
Various control valves are available to serve this function, one
suitable valve construction being shown in detail in FIG. 6. This
valve has a body 80 formed with two internal diaphragm chambers 81
and 82 with diaphragms 83 and 84 therein, the upper diaphragm 83
serving normally to close a passage 85 through a partition 87
between the chambers, and the diaphragm 84 serving normally to
close a passage 88 extending out through the lower end of the body
and connected to the conduit 20 leading to the relief valve 21.
The conduit 17 from the compressor 11 is connected to a port 89 on
one side of the body, and delivers compressed air through this port
to a cross-passage 90 in the body, feeding the air into the lower
chamber 82 beneath the diaphragm 84, through a passage 91, and also
through restrictors 92 and 93 into two vertical passages 94 and 95.
The upper ends of these passages have venting restrictors 97 and 98
therein, which cooperate with the restrictors 92 and 93 in
maintaining selected reduced pressures in the vertical passages 94
and 95. For example, when 10 psi air is supplied to the
cross-passage 90, the restrictors 93 and 98 may be equal in size to
maintain 5 psi in the passage 95, while the vent restrictor 97 is
sufficiently larger than the restrictor 92 to maintain about
one-third of 1 psi in the passage 94.
It will be seen in FIG. 6 that a conduit 99 leads from the passage
94 to the upper diaphragm chamber 81, above the diaphragm 83, to
hold this diaphragm down to close the upper central passage 85 when
the signal conduit 68 is blocked at the orifice 67. At the same
time, 5 psi pressure from the vertical passage 95 is applied to the
lower diaphragm chamber 82, above the diaphragm 84, through a
passage 100. The resulting force, plus a light spring 101 above the
diaphragm, holds the latter down to close the lower passage 88.
This is the closed, or "off," condition of the valve 19 in which no
flow is delivered from the "in" port 89 to the "out" passage
88.
When the orifice 67 is unblocked by the lever 65 in response to
disturbance of the air jet 43 by the patient's breathing through
the conduit 23, pressure above the upper diaphragm 83 is relieved,
and the higher pressure from the chamber 82 below, acting through
the central passage 85, lifts the diaphragm and is vented through a
conduit 102. This relieves the pressure above the lower diaphragm
84, so that the lifting force of the pressure beneath it overcomes
the spring 101 to raise the diaphragm and open the "out" passage
88, connecting this passage to the supply conduit 17 through the
lower chamber 82, beneath the diaphragm 84, and through the
cross-passage 90 and the "in" port 89.
Accordingly, air flows through the valve 19 to the relief valve 21,
and thus to the patient, as long as the orifice 67 is unblocked by
the lever 65. When the lever is returned to the blocking position,
pressure is restored above the upper diaphragm 83, closing the
central passage 85 and thereby restoring the pressure above the
lower diaphragm 84 to close the "out" passage 88. This shuts off
the flow out of the valve 19.
It has been stated that the pressure relief valve 21 may be of
conventional construction, the valve illustrated being of the type
sold by Bennett Respiration Products, Santa Monica, Calif., as the
No. 1694 A Relief Valve. As will appear subsequently, the same
function may be accomplished by a Bennett Respiration Products No.
0666 Diluter Regulator, which is preferred when the source supplies
oxygen rather than air.
In general, the relief valve 21 defines a chamber 103 into which
the primary flow of air is injected through a venturi device where
room air is entrained past the outside-air filter 28, one side of
this chamber being formed by a diaphragm 104 adjustably loaded by a
spring 105 and adjusting screw 107 for setting the pressure control
range. When ambient pressure exists in the chamber 103, a closure
108 carried by the diaphragm covers a "dump" port 109 opening out
of the chamber, thus preventing escape of air except through the
normal outlet 22 leading to the conduits 23 and 24.
As back pressure builds up in the chamber 103 as a result of
inflation of the patient's lungs, the diaphragm 104 is raised away
from the "dump" port 109, lifting the closure 108 to allow air to
escape from the chamber. The action of the relief valve is
progressive, and eventually results in dumping of almost all of the
supply flow, and delivery of only a low terminal flow to the
patient.
The entrance 110 of conduit 24 is closed during initiation and
termination of the inspiration phase, by a flexible leaf-type check
valve 111 which is closed initially to pass all of the flow from
the patient's breathing to the sensor 42, and opens in response to
delivery of the peak flow of air through the relief valve 21, thus
increasing the flow capacity far beyond the practical flow through
the restriction 61 in the flow sensor 42. This leaf valve closes
again as the flow rate is reduced by the relief valve 21, for
example, when the rate drops within the range of 10 to 20 liters
per minute, and thereby routes all of the flow through the sensor
as the inspiration phase nears completion.
Design criteria for the flow sensor 42 can be worked out in
accordance with known principles in the art, examples of existing
reference literature being the book "Fluidics--Components and
Circuits," by Foster and Parker, published by Wiley-Interscience,
and specifically pages 301-308 thereof. Other reference works are
Siwoff, "Improve-of the Static and Dynamic Behaviour of the
Turbulence Amplifier (etc.)," Third Cranfield Fluidics Conference
(1968), Paper -2; Verhelst, "On the Design, Characteristics and
Production of Turbulence Amplifiers," Second Cranfield Fluidics
Conference (1967), Paper F2; Siwoff, "A Method for Dimensioning the
Turbulence Amplifier," Fourth Cranfield Fluidics Conference (1970),
Paper A5; and "The Turbulence Amplifier in Control Systems" by R.
N. Auger of Fluid Logic Control Systems, New York, N.Y.
A flow sensor 42 specifically designed for the system shown in FIG.
1, and constructed in the manner shown in FIGS. 4 and 5, uses a jet
tube 44 about 1 inch in length and about 0.018 of an inch square,
with the receiver tube 48 spaced 0.31 of an inch from the jet
orifice. The effective flow area of the wider end portion of the
conduit 23 is about 0.5 of a square inch, and the effective flow
area of the restricted end portion is about 0.02 of a square
inch.
With this sensor, a jet flow rate of about 0.3 of a liter per
minute, at a pressure of 0.5 of one psi, can be used, and a
pressure drop on the order of 0.05 of one centimeter H.sub.2 O at
the port 53 creates enough flow through the conduit to trigger the
sensor. In contrast, prior turbulence amplifiers have required a
relatively large triggering pressure drop on the order of 1
centimeter H.sub.2 O, utilizing substantially smaller passages.
It bears emphasis that the flow sensor 42 is a highly sensitive
type which is simple and inexpensive, easy to maintain, and stable
in operation, and can operate with a low-pressure jet of low flow
rate, sensitive to low cross-flow disturbances. This sensor can be
characterized as a switching type, in which the pressure drop in
the receiver tube 48 is sharp, when the normal laminar flow at the
entrance to the receiver is changed to a turbulent flow. Because
its effective flow area is small, however, high peak flow rates are
by-passed around the sensor through the conduit 24.
Shown in FIG. 2 is an alternative form of the respiration apparatus
112 with a flow sensor 113 of the fluid jet deflection type (FIGS.
2 and 3). In this case, all of the patient flow during the
inspiration phase passes through the sensor, eliminating the need
for a by-pass conduit such as the conduit 24 of FIG. 1. This type
of sensor may be somewhat less sensitive and stable, however, than
the type shown in FIGS. 1, 4 and 5, but is effective to control
inspiration in substantially the same manner, while having the
advantageous capability noted above.
In this case, the sensor 113 has a tubular body 114, and a jet tube
115 opens into the body on one side thereof to direct a jet 117 of
air across the conduit 118 defined by the body. This jet may
travel, for example, about 0.5 inches and is directed toward a
receiver formed by two tubes 119 and 120 (e.g., about 0.020 inches
in internal diameter) spaced a short distance apart (e.g., about
0.040 of an inch) on opposite sides of the jet's path, preferably
equidistant therefrom so that the jet creates equal pressures into
the two receiver tubes.
A relatively high-pressure jet is used, for example, at 10 psi,
delivering about 3 liters per minute, and the reference pressure
relationship established comprises equal pressures in the two
receiver (e.g. about 60 centimeters H.sub.2 O) rather than
different pressures as in the first embodiment.
As the patient breaths air through the delivery means 121 and the
sensor 113, the flow of air deflects the jet 117 toward the
receiver 119, increasing the pressure linearly in this receiver,
relative to the pressure in the receiver 120, as the flow rate in
conduit 118 increases. The pressure change is applied to an
actuator 122, through signal conduits 123 and 124, to operate a
control valve 125 that may be the same as the valve 19 in FIGS. 1
and 6.
In this case, the actuator 122 is responsive to a preselected
pressure differential, including an increase in the pressure at the
receiver tube 119 produced by a given degree of deflection of the
jet 117 toward the delivery means 121. The change in the pressure
differential is proportional to the deflection of the jet and
therefore the cross-flow, and the actuator 122 can be set to
operate the valve 125 at a selected level. For background
information regarding a fluid jet deflection device of this general
type, reference is made to a report of J. W. Tanney, "An Anemometer
for Very Low Velocities," File M49--7--82, February, 1967, Low
Speed Aerodynamics Section, National Aeronautical Establishment,
National Research Council of Canada.
As before, the actuator 122 has two inflatable actuating members
127 and 128 that are pressurized through the conduits 123 and 124,
a lever 129 between these members, an orifice 130 positioned to be
blocked and unblocked by the lever, and a spring 131 for assisting
the member 128 in urging the lever toward the blocking position. An
adjusting screw 132 is provided to vary the spring force, thereby
to set the actuator for operation at a selected output pressure
level of the signal produced by the sensor 113.
When the orifice 130 is blocked, a back-pressure signal is applied
through a conduit 133 to the control valve 125 to maintain it in
the closed condition, as described in connection with FIG. 6,
thereby preventing any flow of primary gas through the main flow
conduits of the system. In this embodiment, a main flow conduit 134
connects a pressure-regulated source 135 to the valve 125, which is
connected through another main conduit 137 to a flow-rate
regulating valve 138, from which gas flows to the sensor 113 and
the patient through a conduit 139, the conduit 118 of the sensor
being a section of this conduit. A conduit 136 connects the source
to the jet tube 115.
In this instance, the source 135 supplies oxygen, which may be
diluted in the regulating valve 138. For this purpose, the valve
138 is a diluter/regulator of the type sold by Bennett Respiration
Products as No. 0666, previously mentioned.
When the patient starts to withdraw air from the apparatus 112, the
flow control valve 125 is opened in response to the increased
pressure in the receiver tube 119, resulting in the unblocking of
the orifice 130. Then oxygen flows through the valve from the
conduit 134 to the conduit 137, and thus to the diluter/regulator.
Initially, the flow enters a control chamber 140, from which it
flows through a conduit 141 through a venturi device 142 where
outside air is drawn in through a filter 143. Then the mixture is
delivered through a conduit 144 to a pressure chamber 145 in the
diluter/regulator, and passes out through the conduit 139 leading
to the sensor 113 and the delivery means 121.
In the pressure chamber 145, the back pressure in the system is
sensed by a diaphragm 147 that is backed by a spring 148 adjusted
by a screw 149 to set the pressure range of the device. As the back
pressure increases during the inspiration phase, the diaphragm
bulges upwardly, and acts through a linkage 150 to shift a
flow-restricting plunger 151 towards an orifice 152 forming the
inlet to the control chamber 140. The plunger is moved
progressively closer to the orifice, thereby progressively reducing
the flow rate as the back pressure increases.
As the flow drops to a selected low flow rate, the jet 117 of the
sensor 113 returns toward its normal position between the two
receivers 119 and 120, and the pressure differential declines to
the threshold level, whereupon the lever 129 is returned to its
blocking position to close the valve 125 and terminate inspiration.
The expiration phase then occurs in the same manner as in the
apparatus of FIG. 1, the exhalation valve being formed by a port
154 adjacent the delivery means 121, and an inflatable closure 155
pressurized during inspiration through a conduit 157 that
communicates with the main flow conduit 137 through a restrictor
158. A restricted bleed passage 159 relieves pressure in the
closure 155 when the inspiration flow in the conduit 137 is
terminated, so the patient can exhale through the port 154.
From the foregoing, it will be evident that the present invention
provides an improved respiration apparatus that is truly flow
responsive, being operable in response to a flow on the order of 1
to 4 liters per minute that can be drawn through an open system of
conduits, without need for a positively operated check valve for
isolating the patient from the air supply openings in the relief
valve 21 or the diluter/regulator 138. The result in an apparatus
that can be much more comfortable in use, since the resistance of
the apparatus to the initial breath is almost imperceptible, and
the opening of the control valve 19, 125 supplies gas for pressure
breathing as a smooth continuation of the patient's first slight
effort.
Sensitivity is high, particularly in the apparatus 10, and is
easily varied, and low pressure, low quantity jet flows can be
used, again particularly the form 10, in which the flow sensor can
be made as relatively inexpensive, easy-to-clean, molded plastic
part.
It also will be evident that, while two specific embodiments have
been illustrated and described, various modifications and changes
may be made without departing from the spirit and scope of the
invention.
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