U.S. patent number 3,866,604 [Application Number 05/401,676] was granted by the patent office on 1975-02-18 for external cardiac assistance.
This patent grant is currently assigned to Avco Everett Research Laboratory, Inc.. Invention is credited to Richard W. Curless, Armando Federico, Alfred E. Magro, Michael L. Rishton.
United States Patent |
3,866,604 |
Curless , et al. |
February 18, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
External cardiac assistance
Abstract
The flow of blood through the circulatory system of animals is
augmented by sequential application of peristaltic pumping pressure
along either or both of the legs and/or arms to develop a
counterpulse in the aorta. The counterpulse is generated by
equipment interconnected with electrocardiographic equipment and
synchronized therewith to begin the same time as the beginning of
diastole in the patient. A series of bladders arrayed lengthwise
along the limb are pressurized simultaneously or in rapid sequence
for peristaltic pumping and simultaneously deflated at the end of
diastole. Each of the bladders is surrounded by casing means which
are rendered rigid during pumping operations to provide a reaction
wall and non-rigid between operations for ease of handling and
wrapping and unwrapping the limb. The apparatus as a whole provides
low real and apparent weight for the patient to carry, high speed
of inflation and deflation, low bulk and cost of related pumping
equipment, accommodation of a variety of sizes of patients and
protection against ejection from the equipment by the pressures
generated therein and fail safe mode in case of power failure. The
apparatus may be adjusted to suit the pumping needs of different
patients with simple checkout and adjustment by the clinical or
hospital technician.
Inventors: |
Curless; Richard W. (Nabnasset,
MA), Federico; Armando (Needham, MA), Magro; Alfred
E. (Woburn, MA), Rishton; Michael L. (Reading, MA) |
Assignee: |
Avco Everett Research Laboratory,
Inc. (Everett, MA)
|
Family
ID: |
23588739 |
Appl.
No.: |
05/401,676 |
Filed: |
September 28, 1973 |
Current U.S.
Class: |
601/152 |
Current CPC
Class: |
A61H
9/0078 (20130101); A61H 31/006 (20130101); A61H
2201/1238 (20130101); A61H 2205/10 (20130101); A61H
2230/04 (20130101); A61H 2201/0103 (20130101); A61H
2201/0173 (20130101) |
Current International
Class: |
A61H
23/04 (20060101); A61H 31/00 (20060101); A61h
007/00 () |
Field of
Search: |
;128/24R,64,89R,297,299,DIG.20 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trapp; Lawrence W.
Attorney, Agent or Firm: Hogan, Esq.; Charles M. Frederick,
Esq.; Melvin E.
Claims
1. Apparatus for external cardiac assistance comprising:
means defining a plurality of non-distensible gas fillable bladders
which are wrappable aobut a human limb and unwrappable therefrom,
said means including within said bladders compression preventing
means for preventing complete local compression of opposing walls
thereof at any point therein while allowing lateral gas flow;
means for selectively inflating and deflating said bladders by
admission of gas and withdrawal of gas therefrom to selectively
pressurize the cardiovascular system at the location in the limb
wrapped by said bladders;
means defining a common casing blanket for overlying a series of
bladder wrappings along a limb and being similarly wrappable about
said limb and unwrappable therefrom along with said bladders;
and
means for selectively hardening and softening the blanket casing
comprising a filling of particulate material therein and means for
drawing and releasing a vacuum therein to provide a substantially
cylindrical reaction wall for the bladders and for softening the
blanket casing to make it
2. Apparatus in accordance with claim 1 wherein: said
compression
3. Apparatus in accordance with claim 1 wherein:
said means for bladder pressurizing and depressurzing comprise
means defining a manifold and metering valves therein associated
with a series of said bladders,
the valves being separately adjustable to establish said sequential
bladder inflation sequence and alternatively to establish a common
adjustment of volume filled during inflation without movement of
any parts during the inflation, and further comprising
means for increasing deflation flow rate comprise relation to
inflation
4. Apparatus in accordance with claim 3 wherein:
said means for increasing deflation flow rate comprise passages
through said valve means and flapper valve means threreon
positioned to draw open
5. Apparatus in accordance with claim 4 wherein:
said valves comprise a valving member moveable with respect to a
valve seat to define an annular metering clearance therein,
means for adjusting the valving member/seat clearance from outside
the manifold,
said passage means passing through said valving member and
said flapper valve means comprising a disk secured to a face said
valving
6. Apparatus in accordance with claim 3 and further comrpsing:
means for measuring pressurization of each bladder and temporal
relation of
7. Apparatus in accordance with claim 6 and furhter comprising:
means for synchronizing bladder inflation and deflation with a
patient's cardiovascular functioning to begin inflation essentially
at the dicrotic notch portion of the aortic pressure wave and
complete deflation just prior to initiation of isometric
contraction, and wherein:
said means for increasing deflation flow comprise passages through
said valve means and flapper valve means thereon positioned to draw
open under the influence of delfation suction,
said valves comprise a vlavingmembermoveable with valving member
moveable to a valve seat to define an annular metering clearance
therein and comprising means for adjusting the valving member/seat
clearance from outside the manifold,
said passage means pass through said valving member, and
said flapper valve means comprise a disk secured to a face said
valving
8. Apparatus in accordance with claim 1 wherein:
said means for pressurizing and depressurizing said bladders
comprise
means defining a gas pump acessing each bladder through both a pump
inlet at subatmospheric pressure and a pump outlet at
superatmospheric pressure with a pressure tank and firt valve
betwen said outlet and bladders and a vacuum tank and second valve
between said inlet and bladders and means for transferring a
specific volume from said pressure tank to said bladders during
inflation and from said bladders to said vacuum tank during
9. Apparatus in accordance with claim 8 wherein:
said means for transferring a specific volume comprise means
defining a
10. Apparatus in accordance with claim 9 wherein:
said means for pressurizing and depressurizing said bladders
further comprise a manifold and third valve means interconnecting
said bladders with said first and second valves, and further
comprising:
means for increasing the rate of bladder deflation flow through
said third
11. Apparatus in accordance with claim 10 wherein:
said means for increasing deflation flow comprise passages through
said third valve and flapper valve means positioned thereon to draw
open under the influence of deflation suction,
said third valve comprises a valving member moveable with respect
to a valve seat to define an annular metering clearance therein and
also comprises means for adjusting the valving member/seat
clearance from outside the manifold,
said passage means pass through said valving member,
said flapper valve means comprise a disk secured to face said
valving member away from said valve seat,
said blanket and bladders are in a preassembled form as a pair of
pants in chaps arrangement with an array of bladders along each
leg, and
said means for selectively hardening and softening said blanket
casing comprise a filling of particulate material therein and gas
pump means separate from said bladder pressurizing gas pump means
for drawing at least two distinct levels of vacuum in said casing,
and further comprising:
means defining a supporting table for said pants and a backrest and
pants securing means on said table,
interlock means preventing bladder pressurization until said pants
are hardened, and
means for synchronizing bladder inflation and deflation with a
patient's cardiovascular functioning to begin inflation essentially
at the dicrotic notch portion of the aortic pressure wave and
complete deflation just
12. Apparatus in accordance with claim 11 and furhter
comprising:
a plurality of said third valves accessing separate bladders and
having different gas flow rates for inflation but essentially equal
gas flow rates for deflation and a plurality of bladder pressure
monitors,
means for displaying the inflation sequence of said bladders in
response to signals from said bladder pressure monitors, and
means for individually adjusting said inflation flow rates.
Description
BACKGROUND OF THE INVENTION
The present invention relates to external cardiac assistance by
developing a diastole synchronized counterpulse in the aorta. In
accordance with the present invention, such counterpulsing is
administrable in the field, hospitals, clinics and physicians'
offices with flexible, easily and used, compact equipment.
Externally assisting blood circulation has been described in U.S.
Pat. No. 3,303,841 to Dennis, U.S. Pat. No. 3,403,673 to MacLeod,
and U.S. Pat. No. 3,654,919 to Birtwell wherein the patient's legs
are encased in an hydraulic environment and the pressure on the
patient's legs is increased through the addition of hydraulic fluid
to a nondistensible volume to generate a counterpulse in the aorta.
The hydraulic environment transmits applied pressure evenly over
all surfaces. Uniform pressure over the entire leg suface prohibits
peristaltic pumping and may also cause "bubble blowing" in the
femoral artery, thereby reducing counterpulse efficiency. "Bubble
blowing" or the bubble blowing effect occurs when a section of the
femoral artery is prematurely occluded by the application of
external pressure. As a result of this premature occlusion, blood
is trapped in the femoral artery and cannot contribute to the
required counterpulse. In addition, the apparati as described are
cumbersome to use and exert additional external pressure on the leg
surface due to the weight of the hydraulic fluid.
Pneumatic pumping suits, resembling divers' or astronauts' suits,
have also been proposed for diastolic augmentation in Cohen et al.,
"Sequenced External Pulsation in the Therapy of Cardiogenic Shock,"
paper published by the Superintendent of Documents in Artificial
Heart Program Conference Proceedings, have June 9-13, 1969,
Washington, D.C.; and U.S. Pat. Nos. 1,608,293; 2,361,242;
2,528,843; 2,533,504; 2,781,041; 3,094,116; 3,411,496; 3,548,809;
and 3,659,593. In the apparatus described in the patents, a series
of non-distensible bladders arrayed along the lengths of arms
and/or legs are sequentially filled and pressurized with air to
high pressures (10 psi or more in said U.S. Pat. No. 3,659,593),
the sequence of pressurization of bladders being controlled by a
reciprocating or rotary valve distributor. An alternate possibility
for valve sequence is shown in the massage apparatus described in
French Pat. No. 1,562,252 where a series of solenoid valves are
time sequence operated to sequentially pressurize a series of
bladders arrayed along the length of a limb.
It is an important object of the invention to provide external
cardiac assistance with low real and apparent weight for the
patient to carry.
It is a further object of the invention to provide high speed of
inflation and deflation consistent with the preceding object.
It is a further object of the invention to provide low weight
consistent with one or both of the preceding objects.
It is a further object of the invention to provide peristaltic
pumping consistent with one or more of the preceding objects.
It is a further object of the invention to provide low bulk and
cost of related pumping equipment consistent with one or more of
the preceding objects.
It is a further object of the invention to accommodate a variety of
sizes of patients and protect against ejection from the equipment
by the pressures generated therein, consistent with one or more of
the preceding objects.
It is a further object of the invention to provide a fail safe mode
in case of power failure consistent with one or more of the
preceding objects.
It is a further object of the invention to augment blood flow by
application of counterpulse over a larger portion of the
circulatory cycle compared to prior art systems consistent with one
or more of the preceding objects.
SUMMARY OF THE INVENTION
According to the present invention, diastolic augmentation is
provided by a series of non-distensible bladders which are arrayed
along the length of one or more limbs, preferably both legs of a
patient, and simultaneously or sequentially pressurized to a range
of about 2-6 psi while reacting against a surrounding hard casing
providing a reaction force therefor. The casing is selectively
hardenable or relaxable and comprises a filling of irregular
particles which will lock together to harden when a vacuum is drawn
on the casing and will separate and give the casing flexibility
when the vacuum is released. The casing as a whole has a very low
real and apparent weight and its synthetic hardenability allows
effective operation of the bladders at the relatively modest
pressurization levels indicated above.
The casing is mounted on a support, preferably a table. The
apparatus preferably comprises a pair of combination casing
blanket/bladder arrays, as described above, constituting a set of
pants mounted on a table in a chaps-like arrangement. The
blanket/bladder arrays can be spread out to allow the patient to
sit down with his legs stretched across the arrays and then the
blanket/bladder arrays can be wrapped around his legs and the
wrapped legs can be strapped to the table. A bolster is provided to
maintain the patient in a sitting position during operation of the
equipment, both for his comfort and to combat reaction forces
induced by pressurization of the pants which would otherwise tend
to force the patient out of the pants. The bladders are filled with
fully reticulated foam. This, together with their short
longitudinal lengths, minimizes the possibility of inducing bubble
blowing in the femoral arteries or other adverse effects of
entrapment of air in the bladders themselves. The bladders have
multiple gas access ports to further preclude blockage of air flow
therein. The casings are segmented to prevent the particulate
material therein from shifting along length or width dimensions of
the casings and comprise air permeable dividers therein.
After a patient is seated on the table or properly aligned with
other support, the casing is partially hardened by drawing a low
vacuum thereon to partially lock the particulated material therein
and thereby partially harden the casing. The partially hardened
casing is wrapped around the patient's limb(s) with the casing
surrounding the bladder array. A higher vacuum is then drawn on the
casing to increase its rigidity and make it suitable as a reaction
member. The casing is maintained in this condition throughout the
course of treatment which may be a session of as little as five
minutes or up to several hours or round the clock diastolic
augmentation treatment. A bladder pressurization system comprises a
recirculating loop gas handling system of an air pump with an
outlet connected to a pressure tank which is, in turn connected in
successive flow sequence to a meter tank, a manifold which accesses
the bladders via a series of throttle valves, a vacuum tank and the
pump inlet. The loop also comprises appropriate valving to
establish a subatmospheric pressure in the bladders by vacuum
pumping via the manifolds alternating cyclically with
superatmospheric pressure at the modest levels indicated above by
rapid admission of pressurization charges from the metering tank
which is itself recharged from the pressure tank (or in some
systems recharged directly from the pump) between release of its
charges to the manifold.
When the bladders are to be sequentially pressurized, the throttle
valves of the manifold are adjusted to progressively narrower
openings to define a series of pressurization rates in the sequence
of bladders. However, the deflation, additional passage area is
made available to all the metering valves so that all of the
bladders can be deflated very rapidly with less differential in
their deflation rates than in their respective inflation rates.
The admission of pressure charges from the meter tank to the
manifold is synchronized with the patient's electrocardiogram and
the bladders are pressurized over some 50-70 percent of the period
of the heartbeat. Admission of air into the manifold and inflation
of the bladders is controlled to coincide with the beginning of
diastole. The pressure in each bladder being pressurized rises
rapidly, stays steady for a fixed period and then falls abruptly
when the bladders are deflated. The system can operate with hearts
which are beating very rapidly--as much as about 160 beats per
minute, i.e., repeating its cycle almost three times per
second.
Aside from controlling sequence of pressurization for peristaltic
pumping, the valves are adjustable to provide uniform adjustment in
all bladders of the inflation rate to fit the needs of different
patients.
These and other objects, features and advantages of the invention
will be apparent from the following detailed description with
reference therein to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the diastolic augmentation apparatus
according to a preferred embodiment of the invention;
FIG. 2 is a partial cross-section view of a portion of the casing
blanket/bladder array assembly used in the FIG. 1 apparatus;
FIG. 3 is a plane view of the bladder array/casing blanket assembly
used in FIG. 1 in its unwrapped position and FIG. 3A is an exploded
isometric view of the bladder air inlet/outlet fitting;
FIG. 4 is a schematic cross-section representation of the bladder
air distribution manifold and single exemplary metering valve
therein;
FIG. 5 is a cross-section view of a portion of the metering valve
in a second position of operation compared to the first position
shown in FIG. 4 therefor;
FIG. 6 is a mechanical block diagram of the pressurizing system for
bladder inflation and deflation;
FIG. 7 is an electronic block diagram of calibrating controls for
bladder inflation;
FIG. 8 is a display of panel control buttons showing control
functions of the FIGS. 6 and 7 apparatus;
FIG. 9 is a block diagram of a bladder monitoring portion;
subdivided into multiple channels, of the FIGS. 6 and 7
apparatus;
FIGS. 10 and 11 are oscilloscope traces of proper and improper
sequence of inflation, respectively, of bladders using the FIGS.
6-7 apparatus; and
FIG. 12 is a graph sketch showing qualitatively the relation of
electrocardiogram measured systolic and diastolic flow, assumed
arterial pressure and bladder pressurization.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIG. 1 there is shown a diastolic augmentation
pressurizing apparatus in the form of a pair of pants 10 supported
on a base such as a table 12, having a back 14 to enable the
patient whose legs are wrapped in the pants to sit up. The table
carries a control electronic console 16 and air pumping apparatus
(not shown). The pants comprise, in each leg, a casing blanket 18
overwrapping a length series of bladders 20 which are wrapped
around the leg(s). Metal tube piping 22 connects the casing to the
vacuum pumping apparatus therefor through redundant connections to
guard against blockage. Pipes 24 direct air flow to and from the
respective bladders under the control of metering valves 26,
described in greater detail below and which are adjustable through
lead screw hand setting knobs 28. A transducer 24g is connected to
the downstream (when pressurizing) side of each valve 26 to measure
pressure in the bladder pair associated with the valve. Straps 30
secure the wrapped casing blanket/bladder array assembly around the
patient's legs
Referring now to FIG. 2, there is shown a cross-section view of a
portion of the casing blanket/bladder array assembly, this section
being longitudinal. The overwrapping blanket casing 18 comprises
two layers of fabric 32, both layers being air permeable. The
blanket is subdivided into sections by dividing walls 34 which are
air permeable. Each such section is filled with a particulated
material 36 which may be sand, clay pellets, plastic pellets or
metal particles or other irregular shapes, preferably
heterogeneously sized. The sectioned construction 32, 34, 36
prevents the particles' shifting or settling in a single region of
the blanket. The blanket is covered by two layers of air
impermeable material 44 and 46 which completely seal it from the
atmosphere. The bladder arrays 20 comprises air impermeable plastic
films 38 forming inner and outer and longitudinally segmenting
walls to subdivide the bladders into longitudinal compartments
which contain reticulated foam 40. A disposable liner 42 for
placing between the patient's legs and bladder array 20 complete
the assemblage to be secured by holding strap 30.
Referring now to FIG. 3, the blanket/bladder array assembly is
shown in unwrapped arrangement with portions broken away for
convenience of illustration. The blanket 18 comprises holes 22a for
mating with the pipes (22, FIG. 1) which evacuate or relieve vacuum
in the casing to establish rigidity therein. There are five pairs
of bladders 20 and each bladder has an inlet/outlet port defining
assembly 24a. In FIG. 3, the port 24a is at the bottom of the
bladder and has a fitting passing through the blanket. The viewing
of the inlet port defining assembly 24a through the top layer of
film of each bladder is artificially done for purposes of
illustration only. In practice, the inner port would be obscured by
the reticulated foam described above.
FIG. 3A shows in isometric exploded form, the inlet port defining
assembly 24a comprising a tube 24b which defines an end connection
to a tube 24 (FIG. 1, FIG. 3) passes through a hole in a layer of
the blanket casing, a collar 24c securing the inlet port against
the film to prevent leakage through the hole accommodating tube 24b
, and an overlying fitting 24d having relieved portions 24e
defining multiple ports around the circumference of the fitting 24d
so that occasional blockage of one such port will not completely
cut off access to the interior of the bladder.
Referring now to FIGS. 4 and 5, the air flow arrangement through
the manifold and to the bladders is exemplified for a single pair
of bladders. The manifold 25 has a pressure port 25a and a vacuum
port 25b and a multiplicity of metering valves 26 therein, one of
which is shown. Each such valve has a pair of ports 24f for
accessing left and right leg bladders of a bladder pair via tubes
24 (FIG. 1) and a transducer 24g for measuring pressure in the
bladder pair. A valving member 31 is adjustable by a lead screw 28
to vary the size of annular passage 33 thereby determining the rate
of inflation or deflation of the bladders controlled by the valving
member. A number of orifices 35 pass through the head of the
valving member but are normally blocked during pressurization by a
washer 37 secured to the valving member by a screw 39 and butting
up against the valve member to shut off the holes 35. During
deflation of the bladder, the washer droops away from the holes 35
as shown in FIG. 5 to clear the holes for increasing passage area
for evacuation by some 100-200 percent depending on the size of
holes 38 in relation to passage 33.
FIG. 6 shows diagrammatically the inflation/deflation gas handling
system for bladders 20 and hardening system for blanket casing 18.
The bladder system comprises a pump 50, a pressure tank 52, a
metering tank 54, the manifold 25 and a vacuum tank 56 arranged in
a closed loop with normally closed control valves 58, 59 and 62.
Relief valves 64 and 66 respectively set maximum pressure in tank
52 and minimum pressure in tank 56. The blanket casing hardening
system comprises a vacuum pump 60 connected to casing 18 via a
normally open fail safe valve 63. An additional load can be imposed
on pump 60 via a solenoid operated valve 67 and a vacuum relief 69.
A pressure switch 68 senses vacuum level in casing 18 for purposes
described below.
FIG. 7 shows the electronic control 16 (FIG. 1) in block diagram
form including an electrocardiogram input signal amplifier 72,
timing and control circuit 74, set up controls and monitoring fault
indicator circuit 76 and interval control setting circuit 78. The
circuits 76 and 78 are connected to operating solenoids or other
relay drives for valves 58, 59, 61, 62, 63, and 67 and to pressure
switch 68 as indicated.
Details of the circuits are omitted here as they will be apparent
to those skilled in the art using conventional control circuits to
achieve the control functions indicated herein.
FIG. 8 shows the start-stop controls for various stages of
processing with legends as follows:
The Cycle On and Cycle Off switches start and stop the
inflation-deflation cycle, and the Cycle Off switch also causes
pressurizing of the casing.
The standby switch permits one to halt the bladder
inflation-deflation cycle without repressurizing the casing. The
Standby switch also allows vacuum to be drawn on the casing.
The Ready light indicates that the casing is properly
depressurized.
The Lo Vac switch controls the application of partial vacuum to the
casing. H,
The Hi Vac switch controls the application of harder vacuum to the
casing.
FIG. 9 shows the calibration electronics using the transducers 24g
of the five manifold valves 26 (FIGS. 1 and 4) connected, via five
respective channels of amplifier A, level detector 24h,
differentiator 24i and attenuator 24j, to a common summing
amplifier 24k and an oscilloscope 24l. Waveforms generated in
circuits 24h 24i and 24j are indicated in FIG. 9. FIGS. 10 and 11
shows summing amplifier traces for proper and improper sequence of
inflation of five bladders from ankle to hips (when peristaltic
pumping is desired). The spikes are not pressure amplitudes per se
but rather show that the measured pressure has exceeded a
previously established baseline.
The spikes appear on the scope in the sequence in which the arrayed
pairs of bladders fill. If a pair of bladders fills out of
sequence, the ramp-like character of the display changes. For
example, if the third pair of bladders fills before the second, the
spike second from the left on the scope will be larger than the
third from the left. The operator can then adjust orifice sizes in
the metering valves to speed up the filling of the second pair of
bladders or to slow down the filling of the third. In any case,
this type of display serves to indicate the filling sequence is or
is not correct and to identify which pair(s) of bladders is (are)
out of sequence.
FIG. 12 shows qualitatively the approximate interrelation of
electrocardiogram (ECG) arterial pressure in the aorta and
bladder(s) pressure on a common time cycle base.
The arterial pressure trace P', T', Q' indicates cardiovasular
function without modification and P', T', Q" indicates the nature
of the modification to be effected by the apparatus.
The external cardiac assist apparatus is synchronized with the ECG
by detecting the R-wave, and introducing a delay such that the
pressure pulse in the external assist device, starts at the time
the valve from the left ventricle to the aorta, the aortic valve
closes. The valve closes prior to the peak of the T wave which is
at about the beginning of the diastole or at the point of the
dicrotic notch DN in the aortic pressure wave. The pressures in the
bladders rise from a level A to a level B in a time of between 50
and 100 milliseconds with the pressure in the first bladder rising
to its peak first, followed by the second, etc. as indicated by the
transistions B.sub.1, B.sub.2, B.sub.3, B.sub.4, B.sub.5. The
duration of pressure pulse in the bladder is adjustable and is set
as a percentage of the heart beat cycle. For this, the interval
between R-waves is stored and used as a time base. The deflation
transition is indicated at B.sub.1.
A unique advantage of the external counterpulsation timing system
is the capability to adjust the time at which bladder deflation
occurs as a percentage of the time between R-waves. This method
optimizes the assist interval by compensating for varying heart
rates. Setting the beginning of deflation slightly before the
R-wave precludes the possibility of residual gas pressure in the
bladders causing some resistance to the contracting ventricle;
thereby increasing the work load on the heart.
OPERATION
At the start of operation, the Power On/Off switch is activated to
an On position to energize the electronics, start pump 60 and pump
50. Activation of the Standby switch closes the normally open
manifold vent valve 61 and the normally open fail safe casing vent
valve 63. When open, these valves connect the bladders and the
casing to the atmosphere. The pressure switch 68 is in a position
or state which inhibits opening of valves 58, 59 and 62. The
bladders are wrapped about the patient's legs and hips and the
casing 18 is positioned about the bladders and around the legs and
hips. To facilitate the positioning of the casing, a partial or
small vacuum is applied to the pants. When the Lo Vac switch on the
console is pressed, valve 67 opens, pump 60 draws air from the
casing past the pressure switch 68 and valve 63 and also some air
from the atmosphere through the vacuum relief valve 69. Because air
is being drawn through the valve 69, the pressure in the casing is
reduced only enough to make it slightly rigid.
Pressure switch 68, which may be a bellows-type with an electrical
contact, still inhibits the various valve drives. Switch 68 is
adjustable to operate at various pressures and preferably is set to
operate at 15 inches of mercury or half an atmopshere. This
prevents pressure from being applied to the bladders before the
casing becomes rigid. The application of pressure to the bladders
without the casing surrounding and confining them could cause
damage. When the casing is positioned satisfactorily, the Hi Vac
switch on the console is pressed, and valve 67 is now shut to
connect pump 60 directly to the casing. The casing is then pumped
down to hard vacuum. When the presure in the pants reaches 15
inches of mercury, the pressure switch 68 changes state which now
permits the meter valve 58, pressure valve 59 and vacuum valve 62
to cycle. The Ready light on the console comes on. The vacuum pump
continues to operate.
When the patient is ready and the pants are rigid, the Cycle On
button on the console is pressed and the automatic sequence begins.
The ECG signal is processed and the timing and control unit
automatically tracks the R-wave and provides control signals to the
various drive valves. Pump 50 which operates continuously,
pressurizes tank 52 to a pressure controlled by valve 64, which is
adjustable, and pumps out the tank 56 to a pressure controlled by
the valve 66. The pressure set on the pressure relief valve and the
relationship between the volumes of the pressure tank 52 (typically
7 gallons) and tank 54 (typically 2 gallons) determine the pressure
in the tank 54 during operation assuming the pump is not
overloaded. The volumes of the tanks are fixed so that regulating
or changing the valve 64 regulates the pressure in the tank 54 and
the pressure to which the bladders are pumped. Valves 64 and 66 are
also safety valves. Valve 66 establishes a minimum pressure below
which the pressure in tank 56 will not go. Another safety feature
is that bladder inflation is initiated by the ECG so if the heart
beat beat rate changes, the bladders will not inflate out of phase
with the heart.
Prior to the beginning of the cycle, valves 58, 59 and 62 are
closed; valve 59 is opened to start the cycle. The pressure in the
tank 54 and in the bladders equalize with the pair of bladders
furthest from the heart filling first, the adjacent pair filling
next, and so on until the pair of bladders closest to the heart,
that is, those about the hips, fill or inflate. Because the
bladders fill sequentially, they exert pressure in a peristaltic
manner on the legs. That is, pressure is applied to the ankle
region first, then the calves, the knees, the thighs in turn and
finally the hips. So long as valves 58 and 62 remain closed, the
pressure remains steady and is exerted over the entire length of
the leg, assuming that there are no leaks in the bladders or other
parts of the system.
The length of time during which the pressure remains steady is
adjustable (electronically) and is established as a percentage of
the period between R-waves. To begin the deflation portion of the
cycle, valve 59 is closed and valves 58 and 62 are opened
connecting the tank 52 to the tank 54 and the bladders to the tank
56. The pressure in the bladders and the tank 56 equalize with the
pressure in the bladders becoming about atmospheric or remaining a
little above or falling a little below depending on the setting of
the valve 66. At the time the bladders are deflating, the pressure
in the tank 52 and that in the tank 54 are equalizing. After some
small delay -- some percentage of the heartbeat period -- the
bladder inflation cycle begins again.
If at any time during the cycle there is a power failure, manifold
vent valve 61 opens connecting the bladders to the atmosphere, thus
releasing any residual pressure, and pants vent valve 63 opens
connecting the casing to the atmosphere thus causing them to
soften. The patient would not be trapped in the pants or would
pressure be exerted on his legs in the event of a power
failure.
The various features and advantages of the invention are thought to
be clear from the foregoing description. Various other features and
advantages not specifically enumerated will undoubtedly occur to
those versed in the art, as likewise will many variations and
modifications of the preferred embodiment illustrated, all of which
may be achieved without departing from the spirit and scope of the
invention as defined by the following claims:
* * * * *