U.S. patent number 3,808,706 [Application Number 05/327,503] was granted by the patent office on 1974-05-07 for pneumatic lung analog.
This patent grant is currently assigned to Michigan Instruments, Inc.. Invention is credited to Clare E. Barkalow, Kenneth C. Mosley.
United States Patent |
3,808,706 |
Mosley , et al. |
May 7, 1974 |
PNEUMATIC LUNG ANALOG
Abstract
A vertically oriented bellows has a fixed plate at one end and a
movable plate at the other end. As air flows into the bellows, the
movable plate pivots relative to the fixed plate and the free end
thereof is cooperative with a readout panel to indicate the volume
of the bellows. The plates are interconnected by an adjustable
spring urging the plates toward each other when the bellows are
expanded to simulate lung compliance. Selected tubes having
calibrated flow characteristics interconnect the bellows to a lung
ventilator to simulate lung resistance. Preferably, a pair of
bellows are arranged in mutual association together to simulate a
pair of lungs in order to analyze their interdependency.
Inventors: |
Mosley; Kenneth C. (Grand
Rapids, MI), Barkalow; Clare E. (Comstock Park, MI) |
Assignee: |
Michigan Instruments, Inc.
(Grand Rapids, MI)
|
Family
ID: |
23276803 |
Appl.
No.: |
05/327,503 |
Filed: |
January 29, 1973 |
Current U.S.
Class: |
73/865.9;
434/272; 73/729.1 |
Current CPC
Class: |
A61B
5/093 (20130101); G09B 23/28 (20130101) |
Current International
Class: |
A61B
5/093 (20060101); A61B 5/08 (20060101); G09B
23/28 (20060101); G09B 23/00 (20060101); G09b
023/28 () |
Field of
Search: |
;35/17 ;128/2.08
;73/410 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Skogquist; Harland S.
Attorney, Agent or Firm: Price, Heneveld, Huizenga &
Cooper
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A pneumatic lung analog comprising, in combination: a frame; a
bellows in said frame, said bellows simulating a lung, said bellows
having a stationary end plate secured to said frame and a movable
end plate secured to said frame, said movable end plate being
pivotal relative to said stationary plate; said bellows having air
inlet and air outlet means for inflating and deflating said
bellows, said movable end plate pivoting away from said stationary
end plate when the flow of air is into said bellows and moving
toward said stationary end plate when the flow of air is out of
said bellows, said air inlet means defining a passageway having a
preselected cross section flow area to simulate a preselected flow
resistance through the respiratory track; means biasing said
movable end plate toward said stationary end plate, said biasing
means acting as a resistance to the expansion of said bellows, said
biasing means simulating the respiratory compliance in a lung; and
indicating means associated with said movable end plate, said
indicating means providing a performance readout of said lung
analog in response to flow through said air inlet means.
2. The lung analog according to claim 1 wherein said means biasing
said movable end plate toward said stationary end plate is a spring
connected at one end to said movable end plate and at the other end
to said frame, said spring providing a force against said movable
end plate urging it toward said stationary end plate when said
bellows is expanded.
3. The lung analog according to claim 2 wherein the force of said
spring acting on said movable plate is adjustable by an attachment
means anchoring the ends of said spring at various locations
radially from the axis of pivot of said movable end plate so that
the tension on said spring can be varied for a given angular
movement of said movable end plate.
4. The lung analog according to claim 3 wherein said attachment
means includes a pair of spaced guide rails, one of said guide
rails being anchored on said movable end plate and extending
radially from the axis of pivot of said movable end plate, the
other of said guide rails being anchored to said frame and aligned
with said one guide rail, and clamp means movable along said guide
rails for receiving the ends of said spring, said clamp means
positioning said spring radially with respect to the pivot axis of
said movable end plate.
5. The lung analog according to claim 4 wherein said adjustment
means includes a calibrated scale along one of said guide rails to
provide a visual readout of the position of said spring relative
the pivot axis of said movable end plate.
6. The lung analog according to claim 1 wherein said analog is
further characterized by an adjustable stop anchored to said frame
and limiting the movement of said movable end plate toward said
stationary plate to assure the exact position of said movable end
plate relative said stationary end plate when said bellows is
deflated.
7. The lung analog according to claim 6 wherein said movable end
plate is parallel to said stationary end plate when said bellows is
deflated.
8. The lung analog according to claim 6 wherein said adjustable
stop is a shaft threadably anchored to said frame and extending
toward said movable end plate, said shaft having a free end
abutting said movable end plate when said bellows is deflated.
9. The lung analog according to claim 1 wherein said analog is
further characterized by a stop anchored to said frame and limiting
the movement of said movable end plate away from said stationary
plate when said bellows is inflated.
10. The lung analog according to claim 9 wherein said stop is a
wire means having a preselected length, one end of said wire means
being anchored to said frame, the other end of said wire means
being anchored to said movable end plate to limit the movement of
said movable end plate away from said stationary plate.
11. The lung analog according to claim 1 wherein the axis of said
bellows extends vertically when said bellows is deflated and said
end plates extending horizontally, said movable end plate extending
parallel to and spaced above said stationary end plate when said
bellows is deflated; and adjustment means cooperatively associated
with said movable end plate to neutralize the effect of its weight
as a force acting against said bellows when said bellows is
deflated.
12. The lung analog according to claim 11 wherein said adjustment
means is comprised of a spring anchored at one end to said movable
end plate and at the other end to said frame, said spring when
tensioned exerting a force on said movable end plate urging it away
from said stationary plate.
13. The lung analog according to claim 12 wherein said movable end
plate includes a bracket extending vertically downwardly, said one
end of said spring being attached to said bracket at a point spaced
below said movable end plate, said spring extending horizontally
beneath said movable end plate so that when said spring is
tensioned, the force of said spring acts on said movable end plate
through said spacing to create a moment urging said movable end
plate to pivot away from said stationary end plate.
14. The lung analog according to claim 13 wherein the other end of
said spring is movably anchored to said frame to permit selection
of the degree of tension on said spring by movement thereof
relative said one end.
15. The lung analog according to claim 1 wherein said indicating
means is comprised of a panel having printed indicia thereon, said
panel being positioned adjacent the free end of said movable end
plate and generally perpendicular thereto when said bellows is
deflated, said printed indicia having a locus of visual readouts
indicating the simulated compliance and volume of the bellows at
the associated free end of said movable end plate when pivoted
relative the stationary end plate.
16. The lung analog according to claim 15 wherein said panel is
curved to match the arcuate path of said free end of said movable
end plate to permit a direct readout of the position of said
movable end plate.
17. The lung analog according to claim 15 wherein said panel is
pivotally anchored to said frame and movable between a generally
upstanding position for indicating the position of said movable end
plate to a generally horizontal position for storage and
transportation.
18. The lung analog according to claim 17 wherein said indicating
means further includes means retaining said panel in either of said
selected positions to prevent unintentional movement towards the
other of said positions.
19. The lung analog according to claim 18 wherein said indicating
means further includes resilient bumper means engageable with said
panel in said generally horizontal position to avoid vibration of
said panel during storing and transportation of said lung
analog.
20. The lung analog according to claim 1 wherein said means
defining a passageway is comprised of a tube having a preselected
cross section and length thereby defining a preselected volume flow
at a preselected pressure, said tube being replaceable by similar
tubes of varying cross section in order to simulate various
respiratory resistances.
21. The lung analog according to claim 1 wherein means are provided
around the pleats of said bellows to restrain said bellows during
inflation from bulging nonuniformly.
22. The lung analog according to claim 21 wherein said latter means
are comprised of a plurality of thin wires encircling each of said
pleats snugly when said bellows is deflated.
23. The lung analog according to claim 1 wherein said end plates
extend horizontally and the axis of said bellows extends vertically
when said bellows is deflated, the axis of said bellows forming an
arc when said bellows is inflated, said lung analog being further
characterized by a retaining means mounted intermediate said end
plates for pivotal movement about the axis of pivot of said movable
end plate, said retaining means encapsulating one of the pleats of
said bellows to prevent said bellows from sagging or bulging while
said bellows is inflated.
24. The lung analog according to claim 23 wherein said retaining
means comprises an annular ring means positioned about said one of
the pleats and pivotally anchored to said frame by one or more
brackets.
25. A pneumatic lung analog comprising, in combination: a housing;
a pair of bellows anchored at one end to said housing, said bellows
each having a movable plate means secured to the other end, each of
said plate means being pivotally anchored to said housing so that
when said bellows are inflated, said plates pivot arcuately
relative to said housing; air inlet and outlet means for inflating
and deflating each of said bellows independently of each other;
first means associated with each of said bellows for controlling
the flow of air into said bellows at a preselected flow rate at a
preselected differential pressure to simulate lung resistance;
second means associated with each of said bellows resisting the
inflation of said bellows to simulate lung compliance; and third
means associated with each of said bellows for indicating the
differential pressure, volume and compliance of said bellows.
26. The lung analog according to claim 25 wherein said first means
is comprised of one or more flow tubes connected to said inlet
means and having an arbitrary length and cross section calibrated
for a known volume flow at given pressure differentials.
27. The lung analog according to claim 26 wherein each of said
bellows includes separate air inlet means connected to a common
source of air by individual flow tubes.
28. The lung analog according to claim 25 wherein said second means
is comprised of a spring means interconnected between said housing
and movable plate means said spring means resisting inflating of
said bellows by urging said movable plate means toward said one end
of said bellows as said bellows are inflated.
29. The lung analog according to claim 28 wherein said spring means
is adjustable along a radius extending from the axis of rotation of
said plate means to vary the effective force of said spring means
to arbitrarily vary the simulated compliance of said lung
analog.
30. The lung analog according to claim 25 wherein said third means
includes a panel positioned adjacent the free end of said plate
means, said panel including graphic indicia on its face calibrated
to indicate the volume and compliance of said bellows at each
position thereof during inflation by comparing the position of the
free end of said plate means along said graphic indicia.
31. The lung analog according to claim 30 wherein said panel is
curved in accordance with the arcuate movement of said plate
means.
32. The lung analog according to claim 30 wherein said panel
includes separate graphic indicia for each of said bellows and
plate means.
33. The lung analog according to claim 30 wherein said graphic
indicia is calibrated for different differential pressures.
34. The lung analog according to claim 30 wherein said third means
further includes pressure gauges associated with each of said
bellows to provide a differential pressure readout.
35. The lung analog according to claim 25 wherein said analog
further includes stop means limiting the pivotal movement of said
plate means in either direction.
36. The lung analog according to claim 25 wherein said bellows are
mounted side-by-side, said plate means being pivotal about a
horizontal axis.
37. The lung analog according to claim 36 wherein said analog
includes fourth means for neutralizing the gravitational weight of
said plate means and bellows.
38. The lung analog according to claim 37 wherein said fourth means
includes an adjustable spring means urging said plate means and
bellows toward an inflated position, said adjustable spring means
being preset to offset the gravitational weight of said bellows and
plate means urging said bellows and plate means toward deflation.
Description
BACKGROUND OF THE INVENTION
This invention pertains to an apparatus utilized to simulate a lung
in order to evaluate the performance parameters of artificial lung
support devices such as an artificial ventilator or respirator.
A variety of devices which act as respirators or intermittent
pressure ventilators are utilized in treating and assisting
patients unable to breath properly. Ventilators are generally
characterized as being either pressure responsive or volume
responsive. The ultimate success of treatment depends, of course,
on the ability of the ventilator to provide a controlled and
predictable flow of air to the lungs during inspiration. During
ventilation, back pressure is created essentially by ventilatory
resistance and compliance. The acceptability of an inhalation
device depends on its performance in response to changes in
respiratory resistance and compliance.
To the best of applicant's knowledge, the prior art does not teach
a pneumatic lung analog capable through adjustment of simulating a
wide range of patient pulmonary physiology ranging from pediatric
to large adult patients, with various types and states of pulmonary
disease. Such a device would be extremely useful in both evaluating
and testing respiratory equipment, and in instruction in
respiratory therapy technology. The only devices known to Applicant
which relate to lung performance are spirometers. However, the
object of these devices is to measure the actual performance of the
patient's lung. They do not lend themselves to simulate the
patient's lung in order to analyze the performance of ventilation
equipment. Thus, there is an important need in this art for a
device which simulates the performance of a lung in order to
analyze the performance of therapeutic equipment utilized to
correct lung disorders.
SUMMARY OF THE INVENTION
In accordance with the invention, simulation of the lung is
provided by a bellows secured at one end to a stationary plate
means and at the other end to a movable plate means. The bellows
are interconnected by a tube to the inhalation equipment for
inflation. The movable plate pivots relative to the stationary
plate as the bellows is inflated and the free end thereof in
association with printed indicia on a panel positioned adjacent
permits a visual readout of the volume and compliance
characteristics of the inhalator. Compliance is simulated by an
adjustable spring means interconnected between the end plates which
spring means urges the movable plate toward the fixed plate as the
bellows are inflated. Resistance is simulated by calibrated flow
resistant tubes interconnected between the bellows and inhalation
equipment.
In other and more narrower aspects of the invention, means are
provided to eliminate the gravitational effect of the movable plate
when the bellows are arranged vertically and stop means are
provided to limit the upper and downward movement of the movable
end plate. A pair of bellows having independent adjustments are
arranged together mutually for operation by the inhalation device
in order to simulate the interdependency of a pair of lungs.
In yet narrower aspects of the invention, a restraining means is
cooperatively associated with the bellows to assure a uniform
inflation of the bellows.
In accordance with the foregoing, a unique lung analog is provided
for studying and evaluating the performance characteristics of
inhalation equipment. The test lung is also extremely useful as a
teaching aid and is housed in a compact composite portable
structure to permit utilization of the lung in a variety of
environments.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the apparatus of my invention
illustrating one of the lung simulating bellows inflated;
FIG. 2 is a side elevation view of the apparatus illustrated in
FIG. 1;
FIG. 3 is an enlarged fragmentary side elevation view of the
apparatus of my invention;
FIG. 4 is an enlarged fragmentary front elevation view of the
apparatus illustrated in FIG. 3;
FIG. 5 is a fragmentary rear elevation view of the illustration in
FIG. 3;
FIG. 6 is a fragmentary side elevation view with the graphic panel
folded down; and
FIG. 7 is a fragmentary plan view of the restraining support for
the bellows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings in detail, FIG. 1 illustrates a
box-like support case or frame 10 comprising a pair of sides 12,
14; bottom panel 16 and top panel 18. The front end 20 of support
case 10 is open during use while the rear end 22 is closed by a
rear panel 26 which extends above top 18.
A movable plate 26 is pivotally anchored to support case 10 by a
pair of L-shaped brackets 28 and 30 secured to top 18 at the top
end 20 of case 10. The rear edge 32 of plate 26 is free so that
plate 26 pivots about a horizontal axis passing generally through
the front end 34 of plate 26. The axis of pivot is spaced above top
panel 18 so that when plate 26 is level, it is spaced above top
panel 18.
A bellows 36 (FIG. 2) is positioned intermediate plate 26 and top
panel 18 and closed thereby so that when bellows 36 is inflated,
plate 26 pivots relative to top plate or panel 18. A unique graphic
panel 40 is arranged in front of the free end 32 of plate 26 and
has printed indicia 42 printed thereon in the form of a graph which
permits a visual readout of the position of plate 26 relative top
18. As will be described in more detail hereinafter, this provides
an accurate readout of the volume and compliance of bellows 36
which in accordance with the invention is an analog of the
lung.
Inflation of bellows 36 is achieved by the introduction of air into
the bellows through a flow passageway comprised of a tube 42 having
one end positioned in a fitting 44 and the opposite end in a
Y-fitting 46. Fitting 44 is a permanent part of the support housing
and is interconnected to the bellows by a second tube (not shown)
which is connected between fitting 44 and bellows 36. A primary
supply tube 47 interconnects the Y-fitting 46 with the inhalation
device (not shown). The alternative branch of fitting 46 is
interconnected to tube 42a and fitting 44a for supplying the second
bellows (not shown) of the lung analog. Tubes 44, 44a and 47 are
calibrated tubes having defined flow characteristics. They simulate
the resistance of ventilating air flow through a pulmonary system.
These tubes can be replaced by tubes of varying resistance and are
preferably in the form of plastic endotracheal tubes which are
plugged into the systems between fittings 44, 44a and 46. For this
purpose, the end of each plug-in tube 44 or 44a is fitted with a
standard 15 mm fitting (not shown) which plugs into either
Y-fitting 46 or fittings 44, 44a. To inflate both lungs
simultaneously Y-fitting 46 is provided with three female openings
accepting the endotracheal tube fittings. If inflation of only one
bellows is desired, the alternative branch of Y-fitting 46 is
plugged or a calibrated tube can be connected directly between a
bellows and the respirator.
The resistor tubes are calibrated in centimeters of water per liter
per second at a differential pressure of 20.0 centimeters of water.
Since the flow of gas through a tube is not linearly related to
differential pressure (it is approximately proportional to the
square root of the differential pressure), the resistance cannot be
treated as a constant as differential pressure changes. Flow versus
differential pressure curves are included for the standard resistor
supplied with the lung analog. Other types of resistors can be
devised yielding approximate linearity over limited ranges, and
could be substituted for resistors described.
Referring to FIGS. 1 and 2, the simulation of compliance is
provided by a spring 50 connected at one end to plate 26 and at its
opposite end to case 10 so that as plate 26 is pivoted upwardly by
the inflation of bellows 26, an increasing spring force urges the
plate back toward its normal horizontal position. The spring is
adjustable along the length of plate 26 so that its effective
spring force is movable radially with respect to the axis of
rotation of plate 26. Preferably, a first guide rail 52 is located
along one edge of plate 26 and a second guide rail 54 extends along
the lower margin of sidewall 12. An upper slide 46 is movable along
guide rail 52 while a lower slide 58 is movable along guide rail
54. Each slide includes a means for attaching the ends of spring 50
thereto in addition to a clamp mechanism for securing each slide at
a preselected point along the guide rails. Preferably the clamp
mechanism is provided by a thumbscrew 60 threadable through the
sidewall of each slide and engageable with the guide rail to lock
the slide to the guide rail when the thumbscrew is tightened.
The overall operation of the lung analog can now be readily
appreciated. For a given respirator input through tube 42 (FIG. 1)
the inflation of bellows 46 will be proportionate to the selected
resistance provided by the selection of a calibrated endotracheal
tube 42 mounted intermediate the bellows and input tube 47 as well
as the preselected compliance selected by the spring force of
spring 50 and its location radially from the axis of pivot of plate
26 which rotates upwardly as bellows 46 is expanded. The volume of
the bellows is visually read by the alignment of free edge 32 of
plate 26 with the graphic printed indicia on panel 40 and the
particular pressure can easily be momitored by a pressure gauge 62
in communication with bellows 26 through tube 64. Referring back to
FIG. 1, the pressure in bellows 26 or bellows 26a (not shown) is
read directly by pressure gauges 62 and 62a. It is envisioned that
the gauges could be mounted directly in panels 26, 26a in the
openings 27 shown in FIG. 1. It will be appreciated that only
one-half of the analog has been described. The other half is
identical thereto and similar elements are identified by the same
reference numerals with the suffix a added.
Turning now to the preferred structural details of the embodiment
illustrated, as well as additional features provided by the analog,
FIG. 4 illustrates in more detail the configuration of plate 26 and
its mounting relative to top panel 18. Plate 26 has an overall
rectangular configuration with a downwardly projecting flange
portion 66 extending from beneath its front end 34. Flange 66 does
not extend quite as far as side 12 of support case 10 so that a
threaded pin 68 can be mounted through L bracket 28. The interior
end of flange 66 is similarly secured to bracket 30 which has an
overall inverted T-shaped configuration since bracket 30 also
anchors the second movable plate 26a. A pin 70 extends through the
stem portion of bracket 30 to pivot both interior ends of flange 66
and 66a.
The plates 26 and 26a are shown in their horizontal position in
FIG. 4 and it will be readily appreciated that upon expansion of
the bellows as described hereinbefore, the plates will pivot up and
away from top plate 18 about the axis of pins 68 and 70. The
spacing provided between plates 26, 26a and top 18 of support case
10 is primarily provided to contain the bellows intermediate the
movable plates 26, 26a and stationary top plate 18.
The accuracy of the device of my invention is greatly increased by
neutralizing the gravitational weight of movable plates 26, 26a.
Referring to FIGS. 1-4, a spring compensating mechanism 70 is
provided which elimates the gravitational effect of plate 26 as a
factor in the inflation of bellows 36. A bracket 72 (FIGS. 1 and 4)
is attached to flange 66 and extends vertically beneath flange 66
with an aperture 74 provided toward its free end for receipt of one
end of coil spring 76. Flange portion 72 as shown in FIG. 4 is
comprised of a rectangular piece of stock metal anchored to flange
66 by a pair of threaded fasteners 78.
Referring to FIG. 1, a second L-shaped bracket 80 is anchored to
top plate 18 of support case 10 and has an upwardly extending leg
portion 82 which is aligned with the opening 74 when movable plate
26 is in the horizontal position. A pin 84 is inserted through
opening 82 and has an eye hook 86 at one end for receipt of the
opposite end of spring 76 and a threaded end engageable by a
fastener 88. Pin 84 slides freely through opening 82 so that the
tension in coil spring 76 can be adjusted by the relative position
of pin 84. This is accomplished by rotating fastener element 88 in
a clockwise or counter-clockwise direction to move pin 84 toward or
away from the front end of plate 26. The concept of spring
mechanism 70 is to manipulate the device with movable plate 26 in a
horizontal orientation so that the weight of the plate against
bellows 36 is eliminated.
It will be appreciated that as a spring force is exerted on flange
portion 72 (FIG. 3) a moment about the axis of rotation of plate 26
through pin 68 is created urging plate 26 toward clockwise rotation
relative to top plate 18 of support case 10. The tension in spring
76 can be adjusted so that the plate is in a state of unstable
equilibrium in that it remains in the horizontal position with the
urgency for clockwise rotation being counteracted by its
gravitational weight.
Referring to FIGS. 1-3, and especially FIG. 2, a pin 90 is anchored
to top panel 18 near the rear end 22 of support case 10 to provide
a stop for plate 26 as it pivots counter-clockwise into a
horizontal position. The function of pin 90 is to assure proper
positioning of plate 26 when bellows 36 are deflated. The height of
pin 90 can be adjusted by threading a screw 92 concentrically
through the free end of pin 90. An additional stop 94 in the form
of a chain 96 prevents accidental over-expansion of bellows 36.
Since the bellows are highly accurate elements, they are quite
expansive and stop 94 prevents unintentional injury. The chain 96
is anchored at one end to plate 18 and at the other end to the
underside of plate 26. The upper maximum position of plate 26 is
shown in FIG. 2 with chain 96 being taut.
Referring now to FIG. 4, upper guide rail 52 mounted along the
outer edge of movable plate 26 is comprised of an elongated rail
having an L-shape configuration. One leg 100 is affixed to the
upper marginal surface of plate 26, and the other leg 102 projects
perpendicular to the upper surface of plate 26 to form the rail.
The lower guide rail 54 has a generally inverted U-shape
configuration. One of the legs 104 is attached to the side 12 of
case support 10 while the other leg 106 projects downwardly
opposite the direction of leg 102 of the upper guide rail forming
the sliding rail portion of the lower unit. The slides 56 and 58
which interconnect spring 50 between case support 10 and movable
plate 26 are identical to each other although they are oriented in
the opposite direction. Each slide has a generally hook-shaped
cross section forming a track engaging groove 108. The web portion
110 of each slide is biased by spring 50 into engagement with the
upper end of each arm 102 and 106 of the guide tracks for sliding
engagement therealong. The groove 108 acts to capture each slide
into operative engagement with guide rails 52 and 54. A thumbscrew
60 is threadable through the sidewall of each side for abutting
engagement against arms 102 and 106 respectively of the slides to
clamp each slide at a selected position along the rail. The free
end 112 of each slide includes an opening 114 for receipt of the
ends of spring 50.
As noted earlier, the effect of spring 50 and its positioning along
the guide rails 52 and 54 simulates lung compliance in that it
offers a resistance to the inflation of bellows 26 which resistance
increases as the bellows is expanded. A scale 116 (FIG. 1) is
conveniently located adjacent the upper guide rail 52 to provide a
quick and simple readout of the compliance setting. Through the
calibration of spring 50, compliance can be selected over a range
from 0.01 to 0.2 liters per centimeter of water for each bellows.
The 0.01 setting shown in FIG. 2 with the spring set nearest the
axis of rotation of plate 26.
Total pulmonary compliance is obtained by summing the two
individual bellows compliance settings. The individual volumes may
be read directly from chart 42 or panel 40 as will be described
hereinafter. In setting compliance, the bellows should be opened to
atmosphere or totally deflated, whereupon the top and bottom slides
56 and 58 are released from clamping engagement with the guide
rails by loosening thumbscrew 60. The preferred way to set the
compliance is to set the top slide 56 to the value desired by
aligning it with the setting indicated on scale 116. This slide
should then be locked by tightening thumbscrew 60. Next, the bottom
slide 58 is positioned in its "natural" position of vertical
alignment below top slide 56. This slide is then tightened and the
lung analog is ready for operation. It has been found through use
that only the top clamp location is critical for purposes of
accuracy. The bottom may be mislocated appreciably without
significant adverse effect.
Referring now to FIG. 2, as movable plate 26 is pivoted by the
expansion of bellows 26, the rear or free edge 32 along with the
entire plate rotates arcuately about the axis of pins 68 and 69.
The volume of ventilation achieved in the bellows for the
particular compliance and resistance settings is visually
ascertained by the graphic indicia printed on the unique panel 40
illustrated in FIG. 1. The panel is curved to match the arcuate
path of free edge 32 to provide a direct correlative readout of the
volume of bellows 36. Due to several factors which effect the
volume of bellows 36 as it expands, the graphic readout illustrated
by charts 42 and 42a are calibrated for different compliance
settings. The vertical lines on the chart indicate the particular
compliance setting since the actual volume of a lung simulated by
the device varies depending on the compliance in a nonlinear
fashion. One reason for this variance is the compressibility of gas
depending on the compliance pressure and the slight bulging of the
bellows during inflation. Thus, the volume scale must be calibrated
for each setting of compliance. The result of these calibrations
are curves represented generally by the horizontal lines on the
charts. This method of calibrating the volume scale eliminates the
slight error introduced by the variable spring force of spring 50
and variations in bellows volumes due to variable pressures.
Turning to FIGS. 2, 5 and 6, panel 40 is pivotally mounted to back
panel 22 of support case 10 in such a way that it is biased into
either a generally vertical position illustrated in FIGS. 1-3 or a
generally horizontal position illustrated in FIG. 6. One of the
advantages of the lung analog of the invention is its compactness
and portability permitting free transportation of the unit to
various areas of use. As noted earlier, the back panel 24 extends
above top panel 18. Preferably, it extends a distance above top
panel 18 to compensate for the vertical height of bellows 36 and
movable plates 26 and 26a when the bellows are deflated. Panel 40
when in the horizontal position fits over the top of movable plates
26 and 26a. Although not shown, when the lung analog is transported
and not used, a cover fits over and snaps onto the top of the case
while a front panel snaps onto the open front end 20 of the support
case. Preferably, the front panel (not shown) which snaps over the
open front end 20 of the support case 10 includes a carrying handle
so that the unit can be carried similar to a suitcase.
Referring briefly to FIG. 3, bottom 16 and rear panel 24 include a
plurality of rubber bumpers 118 to permit supporting the unit on
its bottom or end.
Referring now in detail to FIGS. 3, 5 and 6 the upper margin 120
(FIG. 5) of end panel 24 is generally recessed vertically with
respect to the upper corners 122 so that panel 40 can be pivotally
mounted with respect to the corners 122 and hence fit slightly
within the recessed area adjacent upper margin 120. A square rod
124 extending the entire length of panel 40 is attached thereto
along its lower margin at the rear surface. A pin 126 is anchored
in each end thereof and extends axially from bar 124 for receipt in
a groove 128 (FIG. 5) formed in the rear surface of corners 122.
Pins 126 are retained in grooves 128 by a pair of resilient spring
elements 130 (only one of which is shown) biased against bar
124.
Spring element 130 is spaced from panel 124 by a spacer block 132
(FIG. 3) and extends essentially vertically for engagement with the
rearwardmost surface 138 of bar 124. The urgency of spring element
130 against bar 134 is in a generally horizontal inward direction
as described previously. When graphic panel 40 is manually flipped
up into a vertical position as illustrated in FIGS. 3 and 5, the
corner 140 of bar 124 cams spring element 130 rearwardly thereby
increasing the effective force spring element 130. As the rearward
surface 138 becomes aligned with the upper portion 136 of spring
130, the spring acts as a biased keeper assisting the upper
movement of graphic panel 40 so that it snaps into the vertical
position shown in FIG. 5. The force of spring element 130 in effect
becomes a keeper element retaining panel 40 in its vertical
position.
The same functional operation toward the horizontal orientation is
shown in FIG. 6. Corner 140 cams the spring outwardly to increase
its effective force rate and as soon as it passes the midpoint of
rotation approximately 45.degree. from either the vertical or
horizontal, the spring urges panel 40 into its downwardly
horizontal position as a result of its tendency to seek alignment
with the lower surface 142 of bar 124. Thus, the effect of spring
element 130 is to urge panel 40 into either the horizontal or
vertical orientation thereby preventing unintentional movement of
the panel out of either selected position. Preferably, a rubber
bumper 144 is positioned on the outer free end of the top surface
of movable plate 26 so that when panel 40 is rotated into a
horizontal "storage" position as shown in FIG. 7, the upper margin
146 is not permitted to come into contact with the top surface of
plate 26. This avoids unnecessary scuffing of plate 26 and in
addition, the urgency against the rubber bumper avoids unnecessary
rattling or other noise problems as the device is carried about
through normal usage. It will be appreciated, that while pin 126 is
urged within groove 128 by spring element 130, the entire panel 40
can be quickly and easily removed from support case 10 by pushing
outwardly until pin 126 clears groove 128.
Referring now in detail to FIGS. 1 and 2, a unique arrangement is
provided to minimize the tendency of bellows 36 from bulging
unevenly as they are inflated. Although the inflation of bellows 36
is generally vertical, it does move arcuately as it follows the
pivotal movement of plate 26. As a result, there is a tendency of
the bellows to sag in certain directions and bulge in other
directions since the axis of deflection through the center of the
bellows is not a straight line.
Two separate potential problems exist in expanding a bellows such
as bellows 36. First, the pleated sections 150 (FIGS. 2 and 3)
which are intermediate each accordion section 152 will sometimes
bulge causing uneven inflation characteristics. To counteract this
a very fine piano wire 154 is wrapped snugly around each pleat 150
when the bellows are deflated. This acts as a restrainer against
bulging when the bellows are inflated assuring a uniform expansion
of each accordion section 152. A second problem, caused especially
by the arcuate expansion of bellows 36 is the tendency for sagging
especially on the inside or short radius. Also, the lower accordion
sections do not expand as uniformly as the upper accordion
sections. To counteract this effect, a bracket 160 (FIGS. 2 and 7)
is used to confine or guide the bellows to their proper position.
Bracket 160 preferably consists of a sheet metal plate 162 having a
punched hole 164 just larger than the pleat of the bellows. Bracket
160 is hinged at its inner end 166 by a pair of arms 167, 167a for
rotation about the axis of pins 68 and 70 so that it is free to
move up and down with the bellows. However, it defines the position
of the bellows in that it prevents for example, the midsection
during inflation from sagging inwardly at the point of its smallest
radius. Likewise, it prevents outward sagging or bulging.
Preferably, the plate is confined about the bellows at its
midsection to provide assistance throughout the operational
position of bellows 36.
The many advantages and features of my invention provide a unique
instructional tool as well as a very precise lung analog with which
to test and compare existing lung supportive devices. Applicant is
unaware of any prior existing devices.
Although but one embodiment has been shown and described in detail,
it will be obvious to those having ordinary skill in this art that
the details of construction of this particular embodiment may be
modified in a great many ways without departing from the unique
concepts presented. It is therefore intended that the invention is
limited only by the scope of the appended claims rather than by
particular details of construction shown, except as specifically
stated in the claims.
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