U.S. patent number 3,734,087 [Application Number 05/197,824] was granted by the patent office on 1973-05-22 for external pressure circulatory assist.
This patent grant is currently assigned to Medical Innovations, Inc.. Invention is credited to John M. Colman, Nubar D. Hagopian, Harold S. Sauer.
United States Patent |
3,734,087 |
Sauer , et al. |
May 22, 1973 |
EXTERNAL PRESSURE CIRCULATORY ASSIST
Abstract
Improved external pressure circulatory assist device of the type
which utilizes an electrocardiogram signal to facilitate
synchronization of its pressure pulse with the heartbeat. The
improvements include a more efficient and clinically suitable
mechanical means to induce pressure variations in the legs of a
patient, and an automatic control means to maintain the proper
pressurization even during physiological changes in the limbs of
the patient being treated, and control means to monitor and adjust
the pressure wave to achieve the proper phasing of the pressure
wave with the cardiac cycle during treatment of the patient.
Inventors: |
Sauer; Harold S. (Carlisle,
MA), Hagopian; Nubar D. (Bedford, MA), Colman; John
M. (Lexington, MA) |
Assignee: |
Medical Innovations, Inc.
(Waltham, MA)
|
Family
ID: |
22730894 |
Appl.
No.: |
05/197,824 |
Filed: |
November 11, 1971 |
Current U.S.
Class: |
601/152 |
Current CPC
Class: |
A61H
9/0078 (20130101); A61H 31/006 (20130101); A61H
2205/10 (20130101); A61H 2201/1645 (20130101); A61H
2201/1238 (20130101); A61H 2201/5071 (20130101); A61H
2201/0103 (20130101) |
Current International
Class: |
A61H
23/04 (20060101); A61H 31/00 (20060101); A61h
007/00 () |
Field of
Search: |
;128/24,30.2,64 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trapp; Lawrence W.
Claims
What is claimed is:
1. In apparatus for applying external pressure circulatory assist
action to the legs of a patient in cyclic synchronization with the
heartbeat of said patient by pressurizing said legs, the
improvement wherein said apparatus comprises:
A. a unitary bladder adapted for wrapping about a patient's legs
and holding a quantity of liquid,
B. mechanical displacement means in contact with outside wall of
said bladder and forming means to press against said bladder, said
means forming the primary means for obtaining the aforesaid
pressure assist action, and
C. a unitary upper leg casing member and a unitary lower leg casing
member having means, said casing members adapted for attachment to
form a compartment to enclose said bladder, said casing members
having sufficient brace means between leg sections thereof to avoid
any substantial outward deflection of said leg casing members
during said pressurizing of said fluid.
2. Apparatus as defined in claim 1 wherein said brace means
comprise:
A. triangular brace means between each of leg-enclosing zones of
each of the upper and lower casing members, and
B. a plurality of fastening means connecting said brace means
together.
3. Apparatus as defined in claim 2 wherein said leg-enclosing zones
are conical in shape and adapted to dissipate stresses exerted
thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
4. Apparatus as defined in claim 3 wherein said pressurizing means
has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke length
of up to about 3.5 inches.
5. Apparatus as defined in claim 2 wherein said casing members,
bladder and displacement means are all placed within an envelope
forming means to maintain sub-atmospheric pressure therearound.
6. Apparatus as defined in claim 1 wherein said mechanical
displacement means is placed within said compartment formed by said
casing and also comprises a platen and a power linkage forming
means to impart a power stroke thereto characterized by a
substantial loss of velocity of said platen as the platen rises
against said bladder.
7. Apparatus as defined in claim 6 wherein said pressurizing means
has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke length
of up to about 3.5 inches.
8. Apparatus as defined in claim 1 wherein said casing members,
bladder and displacement means are all placed within an envelope
forming means to maintain sub-atomspheric pressure therearound.
9. Apparatus as defined in claim 8 wherein said pressurizing means
has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke length
of up to about 3.5 inches.
10. In apparatus for applying external pressure circulatory assist
action to the limbs of a patient in synchronization with the
heartbeat of said patient, and wherein said assist is achieved by
pressurizing a fluid-filled bladder surrounding said limbs, the
improvement wherein said apparatus comprises a mechanical
pressurizing member positioned generally between said limbs and in
contact with an outside wall of said bladder and forming means to
press against said bladder, said bladder adapted for reciprocal
movement in contact with said bladder, said mechanical means
comprising a power-transmitting linkage forming means to impart a
power stroke characterized by a substantial loss of velocity of
said pressurizing member as the pressure of said contact is
increased in the bladder during said stroke.
11. Apparatus as defined in claim 10 wherein said bladder and
mechanical pressurizing means are enclosed in a rigid casing,
wherein the casing is enclosed in an envelope, and wherein a
suction pump is operably connected to the interior of said envelope
forming means to maintain a sub-atmospheric pressure within said
envelope of between atmospheric pressure and about minus 100 mm of
mercury below atmospheric pressure.
12. Apparatus as defined in claim 11 wherein said pressurizing
means has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke of up to
about 3.5 inches.
13. Apparatus as defined in claim 10 wherein said pressurizing
means has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platent through a stroke of up
to about 3.5 inches.
14. In apparatus for applying external pressure circulatory assist
action to the limbs of a patient in cyclic synchronization with a
heartbeat of said patient, and wherein said assist is achieved by
means for pressurizing a fluid-filled bladder surrounding said
limbs, the improvement wherein pump means is provided for adding to
or subtracting fluid from said bladder, said pump means being
responsive to the pressure within said bladder, through a
bladder-pressure sensing means and a control circuit, and wherein
said pump is responsive to said sensing means to receive an
independent command signal therefrom on each heartbeat cycle of
said patient.
15. Apparatus as defined in claim 14 wherein said pump means has an
operating period of about 0.5 seconds.
16. Apparatus as defined in claim 14 comprising a reciprocating
mechanical member forming displacement means to engage said bladder
and pressurize the fluid therein.
17. Apparatus as defined in claim 16 wherein said pressure-sensing
means is an indirect sensing means comprising a
displacement-sensing monitor adapted to sense the position of said
mechanical pressure-transmitting device, to transmit a signal
indicative of said position, and consequently indicative of said
pressure in said bladder.
18. Apparatus for applying external pressure assist action to the
limbs of a patient in cyclic synchronization with the heartbeat of
said patient, wherein said assist is achieved with means for
transmitting pressure to said limbs through a fluid-filled bladder
surrounding said limbs, the improvement wherein the apparatus
includes a visual cycle-phasing monitor comprising:
A. a multi-channel display device adapted to display
1. an EKG trace, and
2. a trace derived from an arterial pressure sensor,
B. means for visually displaying of the relative time duration of a
pressure command signal on said traces, and
C. manual means to adjust the relative timing and duration of said
pressure command signal, while simultaneously achieving a visual
adjustment of said signal to bring it into the desired relationship
to said EKG trace, or arterial trace.
19. Apparatus for applying external pressure assist action to the
limbs of a patient in cyclic synchronization with the heartbeat of
said patient, wherein said assist is achieved with means for
transmitting pressure through a hydraulic cylinder to said limbs
through a fluid-filled bladder surrounding said limbs, the
improvement wherein the apparatus includes
A. an ideal pressure waveform generator means,
B. actual leg pressure waveform sensing means,
C. means for continually comparing said ideal and actual waveforms,
and
D. variable valve means, responsive to a signal from said comparing
means, to modify fluid flow to said hydraulic cylinder and thereby
more nearly achieve said ideal-pressure waveform.
20. Apparatus as defined in claim 19 comprising:
A. a multi-channel oscilloscope adapted to display
1. an EKG trace, and
2. a trace derived from an arterial pressure sensor,
B. means for visually displaying of the relative time duration of a
pressure command signal on said traces, and
C. manual means to adjust the relative timing and duration of said
pressure command signal, while simultaneously achieving a visual
adjustment of said signal to bring it into the desired relationship
to said EKG trace.
21. Apparatus as defined in claim 20 wherein pump means is provided
for adding to or subtracting fluid from said bladder, said pump
means being responsive to the pressure within said bladder, through
a bladder-pressure sensing means and a control circuit, and wherein
said pump is responsive to said sensing means to receive an
independent command signal therefrom on each heartbeat cycle of
said patient.
22. Apparatus as defined in claim 1 wherein said pressurizing means
has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke length
of up to about 3.5 inches.
23. In apparatus as defined in claim 1 for applying external
pressure circulatory assist action to the limbs of a patient in
cyclic synchronization with a heartbeat of said patient, and
wherein said assist is achieved by means for pressurizing a
fluid-filled bladder surrounding said limbs, the improvement
wherein pump means is provided for adding to or subtracting the
fluid from said bladder, said pump means being responsive to the
pressure within said bladder, through a bladder-pressure sensing
means and a control circuit, and wherein said pump is responsive to
said sensing means to receive an independent command signal
therefrom on each heartbeat cycle of said patient.
24. Apparatus as defined in claim 23 wherein said pump means has an
operating period of about 0.5 seconds.
25. Apparatus as defined in claim 24 wherein said leg-enclosing
zones are conical in shape and adapted to dissipate stresses
exerted thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
26. In apparatus as defined in claim 23 for applying external
pressure circulatory assist action to the limbs of a patient in
cyclic synchronization with a heartbeat of said patient, and
wherein said assist is achieved by means for pressurizing a
fluid-filled bladder surrounding said limbs, the improvement
wherein pump means is provided for adding to or subtracting fluid
from said bladder, said pump means being responsive to the pressure
within said bladder, through a bladder-pressure sensing means and a
control circuit, and wherein said pump is responsive to said
sensing means to receive an independent command signal therefrom on
each heartbeat cycle of said patient.
27. Apparatus as defined in claim 26 wherein said pump means has an
operating period of about 0.5 seconds.
28. Apparatus as defined in claim 27 wherein said leg-enclosing
zones are conical in shape and adapted to dissipate stresses
exerted thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
29. Apparatus as defined in claim 26 comprising a reciprocating
mechanical member forming displacement means to engage said bladder
and pressurize the fluid therein.
30. Apparatus as defined in claim 29 wherein said pressure-sensing
means is an indirect sensing means comprising a
displacement-sensing monitor adapted to sense the position of said
mechanical pressure-transmitting device, to transmit a signal
indicative of said position, and consequently indicative of said
pressure in said bladder.
31. Apparatus as defined in claim 1 for applying external pressure
assist action to the limbs of a patient in cyclic synchronization
with the heartbeat of said patient, wherein said assist is achieved
with means for transmitting pressure to said limbs through a
fluid-filled bladder surrounding said limbs, the improvement
wherein the apparatus includes a visual cycle-phasing monitor
comprising:
A. a multi-channel display device adapted to display
1. an EKG trace, and
2. a trace derived from an arterial pressure sensor,
B. means for visually displaying of the relative time duration of a
pressure command signal on said traces, and
C. manual means to adjust the relative timing and duration of said
pressure command signal, while simultaneously achieving a visual
adjustment of said signal to bring it into the desired relationship
to said EKG trace, or arterial trace.
32. Apparatus as defined in claim 31 wherein said leg-enclosing
zones are conical in shape and adapted to dissipate stresses
exerted thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
33. Apparatus as defined in claim 31 wherein said pressurizing
means has a displacement capacity of at least 100 cubic inches and
comprises means for actuating said platen through a stroke of up to
about 3.5 inches.
34. Apparatus as defined in claim 16 for applying external pressure
assist action to the limbs of a patient in cyclic synchronization
with the heartbeat of said patient, wherein said assist is achieved
with means for transmitting pressure to said limbs through a
fluid-filled bladder surrounding said limbs, the improvement
wherein the apparatus includes a visual cycle-phasing monitor
comprising:
A. a multi-channel display device adapted to display
1. an EKG trace, and
2. a trace derived from an arterial pressure sensor,
B. means for visually displaying of the relative time duration,
and
C. manual means to adjust the relative timing and duration of said
pressure command signal, while simultaneously achieving a visual
adjustment of said signal to bring it into the desired relationship
to said EKG trace, or arterial trace.
35. Apparatus as defined in claim 33 wherein said leg-enclosing
zones are conical in shape and adapted to dissipate stresses
exerted thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
36. Apparatus as defined in claim 34 wherein said pressure-sensing
means is an indirect sensing means comprising a
displacement-sensing monitor adapted to sense the position of said
mechanical pressure-transmitting device, to transmit a signal
indicative of said position, and consequently indicative of said
pressure in said bladder.
37. Apparatus as defined in claim 23 wherein said leg-enclosing
zones are conical in shape and adapted to dissipate stresses
exerted thereon as hoop stresses, thereby resisting any substantial
deflection or deformation of said zones.
38. Apparatus as defined in claim 1 for applying external pressure
assist action to the limbs of a patient in cyclic synchronization
with the heartbeat of said patient, wherein said assist is achieved
with means for transmitting pressure through an hydraulic cylinder
to said limbs through a fluid-filled bladder surrounding said
limbs, the improvement wherein the apparatus includes
A. an ideal pressure waveform generator means,
B. actual leg pressure waveform sensing means,
C. means for continually comparing said ideal and actual waveforms,
and
D. variable valve means, responsive to a signal from said comparing
means, to modify fluid flow to said sydraulic cylinder and thereby
more nearly achieve said ideal-pressure waveform.
39. Apparatus as defined in claim 38 comprising:
A. a multi-channel oscilloscope adapted to display
1. an EKG trace, and
2. a trace derived from an arterial pressure sensor,
B. means for visually displaying of the relative time duration of a
pressure command signal on said traces, and
C. manual means to adjust the relative timing and duration of said
pressure command signal, while simultaneously achieving a visual
adjustment of said signal to bring it into the desired relationship
to said EKG trace.
40. Apparatus as defined in claim 39 wherein pump means is provided
for adding to or subtracting fluid from said bladder, said pump
means being responsive to the pressure within said bladder, through
a bladder-pressure sensing means and a control circuit, and wherein
said pump is responsive to said sensing means to receive an
independent command signal therefrom on each heartbeat cycle of
said patient.
41. Apparatus as defined in claim 40 wherein said pump means has an
operating period of about 0.5 seconds.
42. Apparatus as defined in claim 38 wherein said pump means has an
operating period of about 0.5 seconds.
43. Apparatus as defined in claim 39 wherein said pump means has an
operating period of about 0.5 seconds.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel apparatus for assisting blood
flow through the circulatory system by synchronizing the pulsing of
an external-assist means with the heartbeat. The invention also
relates to a novel control processes achieved by use of the
apparauts.
2. Background of the Invention
Methods for atraumatically assisting blood circulation of patients
have been described in the art. In U.S. Pat. No. 3,303,841 to
Dennis, a process is described whereby an external compressing of
the lower part of the body expresses a volume of blood larger than
the volume of blood pumped in a single stroke of the heart. The
blood so expressed is forced back into the aorta and greater
arterial vessels and thereby allows a reduction in ventricular
workload while maintaining a satisfactory perfusion of blood during
ventricular diastole. This general type of preocess has been
elaborated upon in an article entitled "Synchronous Assisted
Circulation" by Birtwell et al., appearing in The Canadian Medical
Association Journal (Vol. 95, pages 652-664) on Sept. 24, 1966. In
general, synchronous external pressure assist processes are
distinguishable and advantageous over pre-existing
counter-pulsation processes because the latter kind of precedure
involves the cannulation of a major artery, use of an
extra-corporeal blood handling device, the use of stringently
sterile techniques and the necessity of administering
anti-coagulants to the patient. Moreover, the blood trauma or
hemolysis produced by extra-corporeal pumping devices limits
premissible duration of the assist procedure and compromises the
condition of the patient. Finally, these trauma-requiring
procedures are not only time consuming, they can present a very
significant hazard to many patients, and they increase the risk
factor in treating all patients.
Specific apparatus usable in a synchronous assist process is also
disclosed in U.S. Pat. No. 3,403,673 to MacLeod. In general, that
apparatus consists of a leg-encasing arrangement with means for
cycling the pressure on the legs within the casing. The invention
described in U.S. Pat. No. 3,403,673 has a number of problems
associated with its use. For example, the constrictive-type seals
thereof are believed to interfere with optimum blood circulation.
Moreover, the inertia of the pressurizing system which includes
elastic-type expansible linings is believed to interfere with
obtaining optimum pressure-time profile on the legs. The apparatus
suggested in such prior art has a number of drawbacks in that it is
cumbersome to use; i.e., the patient is inserted into and removed
from the device with excessive effort; and it is excessively
difficult to achieve the proper pressure-pulsation profile and
impossible to achieve what the inventors believe is the more
advantageous mode of operation, i.e., at an ambient pressure at or
below atmospheric pressure.
In U.S. Ser. No. 92,606, filed by William C. Birtwell on Nov. 25,
1970 and now U.S. Pat. No. 3,654,919 and commonly owned with the
instant application, an improved external assist apparatus was
described wherein the effective pressure on circulatory passages of
the legs could be cycled to values at or below ambient pressure.
This apparatus is a major advance in the art and has been
extensively used as a vehicle for evaluating the therapeutic
potential of externally assisted circulation. Some results of this
work are reported in a paper entitled "The Hemodynamic Evaluation
of External Counterpulsation in Man" by T. J. Ryan et al., and
presented at the American Heart Association Scientific Sessions
held in Atlantic City, N.J., duing Nov. 1970.
At the present time the external counterpulsation method, e.g., as
generally described in the Birtwell application, is the only
controlled method of assist which requires no surgical intervention
or sterile procedures, no use of anticoagulants or anesthesia, and
produces no significant trauma. These factors are most important
because they usually allow a much earlier use of the apparatus on a
patient in, say, a state of circulatory shock than could be
justified if another type of assist apparatus had to be used.
The selective application of positive and negative pressures to the
portion of the vascular bed in the legs serves to control directly
the volume of blood within that portion of the vascular bed and,
hence, the pressures within the arterial system, particularly the
pressures of the aorta. It is these controlled changes in aortic
pressure that lead directly to a reduction in cardiac work, to
increased perfusion of the systemic circulation, and to
preferential perfusion of the myocardium.
During the past year, a considerable amount of research work has
been carried out which confirms the important contributions which
this approach can make in cardiac therapy. This success has
stimulated further inventive effort which has resulted in
improvements in the device which increase its physiological
effectiveness, the versatility in the clinical environment, and its
aesthetic appeal to the medical user.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide an improved
external pressure circulatory assist device which is readily and
safely applied and authorized by hospital employees of ordinary
skill and limited experience with such a device.
Another object of the invention is to allow such a person of
ordinary skill to easily achieve a precise phasing of a system with
the patient's heartbeat.
A further object of the invention is to provide apparatus which is
sufficiently quiet to permit its convenient use within a hospital
environment.
A further object is to provide apparatus which can operate with a
minimum AC power supply requirement.
It is also an object to provide apparatus that is readily adaptable
to patients having a relatively large range of leg sizes.
Still another object is to provide automatic control of the
pressure waveform applied to a particular patient's legs in a
circulatory assist process despite a large range of patient leg
sizes, geometries, and firmness.
Another object is to provide apparatus which is light in weight and
capable of being simply and rapidly applied to a patient.
Other objects of the invention will be obvious to those skilled in
the art on reading the instant application.
The above objects have been achieved by constructing an external
pressure circulatory assist system comprising one or more of the
following advances in the art:
A. a water-Fill System
The Water-Fill System is used to fill a leg-enclosing bladder with
the correct volume of water for the particular patient. By correct
volume is meant the particular volume that is suitable for the
particular size and geometry of an individual patient's legs. It
has been found also that because of patient movement into or out of
the machine, a patient's legs can change their effective size
during treatment. Thus the water-fill system if utilized not only
to properly fill and automatically empty water from the leg
encasing bladder; it is also used to add or remove water during
treatment, thereby to maintain an efficient hydraulic pressure
coupling between a mechanical pressure-inducing means to be
described below and the patient's legs.
Water-Fill System and Pressure-Maintenance System
During the filling operation, a pressure sensor which is positioned
between the shell which encloses the bladder and the bladder itself
senses the pressure in the bladder. When the fill-pressure reaches
a predetermined magnitude, usually about 20 millimeters mercury,
the filling action is terminated by shutting off the fill pump.
This filling operation is normally carried out with the platen in
its upward position; i.e., in a bladder-compressing position.
Once the operation of the apparatus is initiated, a displacement
sensor which is coordinated with the moving platen determines the
position of the platen at the top-most position of each upward
stroke. If this position is improper, water is pumped into or out
of the bladder until the platen again reaches its proper range.
B. the Mechanical Pressurizing Means
In order to achieve adequate counterpulsation, it is necessary that
the leg-enclosing bladder be capable of exerting a positive
pressure on the legs during cardiac diastole and removing the
pressure or producing a negative pressure on the leg (say, to minus
50 mm of mercury) during cardiac systole. The positive pressure
applied is normally between about 150 to 250 millimeters of
mercury.
It has been found most advantageous to achieve this pressure
differential by applying a moving platen to a fairly large surface
of the leg bladder containing the liquid. This platen is mounted
beneath the leg bladder to provide a reciprocal vertical motion
which controls the magnitude of the positive pressure. The pressure
within the bladder increases as the platent rises against it and
decreases to a minimum, usually about 20 millimeters of Hg, (or
lower if negative pressures are used) as the platen falls to its
lower level. If the negative pressure capability of the invention
is to be used, the platen, bladder and the patient's body are
enclosed from the waist down in a bag which is partially evacuated,
say to a negative pressure of 70 millimeters of mercury below
atmospheric pressure. The bag, although conveniently of flexible
material, is held away from the legs by the rest of the apparatus
so that a low pressure zone is maintained in which negative
pressure can be realized. The bag or suction envelope is suitably
sealed at the waist by means of a snug fit of its waistband with
the body of the patient. The apparatus as described above has a
normal operating cycle ranging within from about minus 50
millimeters of mercury to plus 250 millimeters of mercury. In
operation, the pressure will be cycled with the lower pressure of
the cycle corresponding with the systolic phase of the heart's
action and the higher pressure corresponding with the diastolic
phase.
The bladder which is advantageously a single-chambered blanket, is
placed around the patient's legs and a rigid casing is used to
enclose both the legs and the mechanical pressure-transmitting
platent. The bladder is then filled with water until the entire
region around the legs and above the platen contains water and so
that the bladder is in contact with substantially the entire
surface of the legs is fully expanded at the ankle and waist ends.
From this point on, the vertical reciprocating action of the platen
will provide the desired positive/negative-pressure cycling.
C. pressurization Waveform Control
To achieve counterpulsation, the pressure on the patient's legs
should fluctuate according to a desired waveform. The apparatus of
the invention advantageously comprises a feature whereby the
pressure at the legs is monitored, and made the source of a
feedback signal which is directly compared to a signal which is
representative of the desired waveform for the particular patient.
The difference between the signal derived from the actual waveform
and the signal representative of the desired waveform is called the
"error signal." This error signal is amplified and used to control
an electrically operated servo-valve which controls the flow of
hydraulic fluid to a hydraulic cyclinder which drives the
vertically-reciprocating platen. This flow is continuously adjusted
in proportion to the error signal causing the pressure waveform at
the transducer to be a suitable facsimile of the desired
waveform.
The monitoring of the pressure at the legs is conveniently done by
a water bladder, approximately 4 by 4 by 1/2 inches in dimensions,
which bladder is placed between the bladder-enclosing shell and the
bladder itself. Water in this sensor bladder is connected through a
short tube to a pressure transducer which provides the required
electrical signal of the actual pressure waveform. A particular
advantage of this waveform control system is that it ensures the
important characteristics of the desired waveform (e.g., duration,
rise, and fall time) as applied to the patient's legs are not
distorted. This is accomplished in spite of variations in hydraulic
coupling between the platen and the legs resulting from such things
as differences in leg geometry, size, and firmness from patient to
patient, and any dynamic stretching of the bladder or distortions
in the leg casing during operation.
Phasing the Pressure Cycle with the Cardiac Cycle
It can be shown that a deleterious, physiological effect may be
suffered if the heart is taxed by an improper timing of the start
of the external assist pressure wave with respect to the cycle of
the heartbeat itself. Moreover, though this phenomenon may be
readily understood by an operator, it is desirable to avoid chance
of operator error and to simplify the operation of the device by
providing a simple, accurate, automatic phasing means.
The inventors have provided a suitable visually monitored phasing
control system whereby an arterial waveform is displayed on a
multi-channel oscilloscope or other suitable display device the
conjunction with an ECG waveform. The arterial pressure waveform is
measured at any convenient place on the body. Normally, the wrist
will provide the most convenient placement of the arterial wave
pressure sensing device. The ECG signal will, as is normal, but
obtained by placement of sensors directly on the torso proximate
the heart.
For this application, it is important to note that it takes about
80 milliseconds (ms) for a pressure wave, introduced in the femoral
arteries with the apparatus of the invention, to reach the root of
the aorta. The subsequent transmission from the root of the aorta
to the wrist, where the arterial waveform is typically obtained,
takes another 90 ms. It is important that the artificially induced
positive pressure waves be produced in the legs sufficiently before
diastole (80 ms) and that the pressure wave reaches the root of the
aorta at the beginning of diastole.
The start of the augmented diastolic waveform, as seen at the
wrist, which results from use of the applicants' apparatus,
therefore will take place a total of 170 ms after the pressure if
applied to the legs of the patient. Thus it is desirable to have
the induced pressure wave initiated by a command signal timed to
start 170 ms before the arterial wave, as seen at the wrist
indicates the beginning of diastole and 80 ms before the ECG signal
indicates the beginning of diastole. The beginning of diastole is
indicated in the arterial wave by the so-called dicrotic notch in
good approximation by the end of the so-called "T-wave" which is
known to be positive indication of the relaxation of the left
ventricle and the end of systole.
In the subject phasing system, the leg pressurization signal is
used to intensify the ECG and arterial trace on the oscilloscope
after this pressurization signal has been delayed for 80 and 170 ms
respectively. The duration of intensification is the duration of
each positive pressurization cycle of the leg. With this system, an
operator can adjust the delay time until the intensified signal on
the ECG or arterial wave form is located at the beginning of
diastole. At that point leg pressurization can be triggered in
correct synchronization with the cardiac cycle.
D. leg Encasing Unit
A novel leg-encasing unit is employed which, by virtue of its light
weight and geometry, provides an efficient casing within which to
apply pressurization to the legs, yet is convenient and rapid to
apply to a patient.
E. platen Driving Mechanism
A novel mechanical linkage arrangement is provided for coupling the
platen to the driving hydraulic cylinder whereby a suitable
pressure-displacement characteristic is obtained at the platen for
pressurizing the bladder while at the same time minimizing the
input power requirements of the apparatus.
In this application and accompanying drawings there is shown and
described a preferred embodiment of the invention and suggested
various alternatives and modifications thereof, but it is to be
understood that these are not intended to be exhaustive and that
other changes and modifications can be made within the scope of the
invention. These suggestions are selected and included for purposes
of illustration in order that others skilled in the art will more
fully understand the invention and the principles thereof and will
be able to modify it and embody it in a variety of forms, each as
may be best suited in the condition of a particular case.
In the drawings:
FIG. 1 is a schematic cross sectional view of that apparatus of the
invention into which the legs of the patient fit.
FIG. 2 is a plan view of the leg-enclosing apparatus broken away to
show the position of a reciprocating platen.
FIG. 3 is a chart indicating the relative timing of physiological
events relative to the description of the invention.
FIG. 4a and 4b, taken together, form a schematic diagram of a
unique control system for use in external pressure circulatory
assist apparatus.
FIG. 5 is a perspective view of a platen assembly used to transmit
pressure to a leg-surrounding bladder.
FIG. 6 is a perspective view of the rigid casing into which the
patient's leg and bladders are placed and the means for quick
connection of the casing.
With reference to FIGS. 1 and 2, it is seen that legs 20 are placed
within blanket-like bladder 22 which is filled with a
non-compressible liquid, e.g., water 23. Bladder 22 completely
encloses legs 20 and is adapted for a snug fit within a rigid
casing 24 formed of an upper shell 26 and a lower shell 28. Just
beneath bladder 22 and also within casing 24 is a platen 30 mounted
for reciprocal vertical motion imparted by a mechanical linkage 32.
This linkage is driven by a hydraulic cylinder as better seen in
FIG. 5. A pressure-sensitive transducer 34 is placed in hydraulic
communication with the bladder for use in monitoring the pressure
therein; the particular function of this transducer will be
described below.
FIG. 2 illustrates how an envelope 36 encloses the casing 24. The
envelope 26 and casing 24 are broken away to illustrate the
relative position of platen 30. It will be noted that the envelope
extends beyond casing 24 and is adapted to form a snug fit with
waist 38 of a patient 40. A suction pump 39 will normally be used
to maintain the normal environment within envelope 36 at a
sub-atmospheric pressure.
There are certain cycle-phasing problems solved by the use of the
more advantageous embodiment of the invention. If a patient is to
be treated by pressure applied to his legs by pressure on bladder
22, it will typically take about 80 milliseconds (ms) for such
pressure to reach the heart and be synchronized with the heart's
beating as monitored by an ECG signal device placed on the
patient's chest. It will take another 90 ms for the pressure effect
initiated at the legs to reach the radial artery as monitored by a
sensing device placed thereon. FIG. 3 graphically (but still
somewhat schematically) shows the time phenomena related to
operation of the apparatus.
In one trace, there is shown an ECG curve 402 related in real time
to a typical cardiac period of 840 ms. In this trace, the beginning
of diastole is typically signified by the start of the drop of the
curve at 403. This drop at 403 should follow by about 80 ms, the
rise 405 in leg pressure curve 404. This is to allow the
pressure-wave induced by the apparatus of the invention to arrive
at the heart at the beginning of diastole after completion of a
trip taking 80 seconds.
The curve 407 is of radial arterial pressure as measured at the
wrist. The beginning of diastole in pressure curve 407 is signified
by the so-called dicrotic notch 409 which takes place about 90 ms
after the ECG reports the beginning of diastole. For convenience,
the apparatus is normally triggered by sensing the prominent QRS
peak 415 of the EKG.
Now referring to FIGS. 4a and 4b, an advantageous method of
utilizing the above-described phenomena in phasing and control of
the apparatus is set forth schematically and can be described as
follows:
A transducer-type pressure sensor 34 including a sensing bladder 35
is utilized to sense hydraulic pressure in bladder. If the pressure
so sensed is less than 20 millimeters of mercury (mm of Hg), then a
pressure-level amplifier 46 will provide an output to the
"and-type" gate 48. If during this low-pressure signal situation,
the operator closes a water fill switch 50, he will cause the "and
gate" 48 to transmit a signal which will activate a fill pump 52
through pump control circuit 54 and simultaneously cause a
multi-position, solenoid valve 56 to shift to its fill position,
i.e., the position allowing water to flow from conduit 58 to
conduit 60. Thereupon water will flow into the bladder 22 until a
pressure of 20 mm Hg is sensed by pressure sensor 34. The signal
from amplifier 46 will then drop consequently closing "and-gate"
48. Thereupon, fill pump 52 is deactivated and solenoid valve 56 is
shifted to its off position.
Water is emptied from bladder 22 by using an analagous system
whereby pressure is sensed by sensor 62. In a typical mode of
operation, if the temperature sensed is above a minus 15 mm Hg
value, a signal is sent to "and-gate" 64. If "empty switch" 66 is
closed, the gate 64 will allow a signal command to actuate pump
control 68 and "empty pump" 69 and cause solenoid valve 56 to shift
to its empty position, i.e., the position allowing water to flow
from conduit 60 to conduit 70 and thence back to water reservoir 72
through 74. The pump 69 will empty until a pressure of less than
the illustrative minus 15 mm Hg is sensed. At that time the
"and-gate" 64 will no longer sense the required signal from sensor
62, and the pump 69 will be turned off and valve 56 will return to
its off position.
It is noted that the above-described filling and emptying
operations are generally used at the beginning and ending of use
and not as continuous control means. Nevertheless it is emphasized
that the ability to fill the bladder to a particular pre-determined
pressure by automatic means rather than judgement means is highly
advantageous.
During operation of the apparatus, the pressure within bladder 34
is maintained at its desired level by adding or removing water from
the bladder system as follows:
A displacement sensing type transducer 76 is mounted on
hydraulically-actuated rod 78. Transducer 76 is adapted to provide
an electrical signal output proportional to the linear advance of
rod 78 at any given moment.
A normalized value of the position of cylinder 78 is provided by
feeding the signal from transducer 76 into a displacement level
sensor 80. Thence the normalized signal is provided to a level
comparator 82.
A second imput to comparator 82 is derived as follows: An ECG
signal from a patient being treated is fed into a trigger generator
84. The trigger generator is so selected that it recognizes and
responds to the so-called QRS complex rise of the ECG signal. (This
rise is identified by numeral 415 in FIG. 4). Thus when the QRS
rise periodically occurs with each heart beat, an output is
triggered which is fed to a manually controlled delay 86. The
purpose of delay 86 is to convert the original signal from first
trigger generator 84 to a second time-delayed signal corresponding
in real time with the beginning of cardiac diastole. This second
signal enters a duration signal generator 88. Generator 88 is so
selected that the signal therefrom continues for the length of time
that leg pressurization (as caused by pressure in bladder 34)
desired. This signal from generator 88 is fed to level comparator
82 through a level stroke signal generator 89.
The signal from generator 88 is also fed to a waveform generator 90
which produces a wave whose amplitude and frequency is analogous to
that desired for the leg pressurization sequence. A typical such
wave will be trapezoidal-like in shape with a rise of 60 ms, a
plateau of 250 ms, and a fall of 60 ms. This wave from generator 90
is fed to a wave form comparator 92 wherein it is continually
compared to a signal derived from the actual bladder pressure wave
as experienced by sensor 34. The output of comparator 92 is a
so-called "error signal," i.e., a signal which is indicative of the
quality and strength of the difference between the desired wave
signal from generator 90 and the actual wave signal from sensor
34.
The error signal is used to control servo-valve 94 through a
servo-amplifier 93 and thereby controls the supply of fluid to, and
consequently the movement of, hydraulic cylinder 78.
As has been described above, level comparator 82 receives two
signals: one, a periodic signal from a duration signal generator
88, via strobe signal generator 89 and the other from displacement
level sensor 80. Displacement level sensor 80 compares these two
signals, one indicative of the actual position of hydraulic
cylinder 78 at a given time. It is the periodic, or "strobe" signal
from duration signal generator 88, as modified by a level strobe
signal generator 89, which determine when this comparison is to be
made. The comparison is most usefully made at the time platen 30 is
in the upper-most portion of its stroke and pressing firmly against
bladder 22.
If level comparator 82 senses that the platen 30 is too high,
output signal is provided to a "one shot" (monostable
multivibrator) 96. This "one shot" 96 will then turn on fill pump
52 and also position solenoid valve 56 for a 0.5-second fill
period. The 0.5-second fill periods will continue during each
cardiac period (i.e., each heartbeat) until the water volume in
bladder 22 is sufficient so that the platen 30 is within an
acceptable displacement range at the top of its stroke.
If, on the other hand, the level comparator 82 receives a signal
that the platen 30 is too low in its stroke, the empty pump is
turned on for one half second in each cardiac cycle by activation
of the "one shot" device 98 and the empty pump 69. Water is then
pumped out of the bladder until the platen achieves a desired rise
during its stroke.
The general operation of the system is described above. The manner
in which the operation is phased into correct synchronization with
the heartbeat is described below:
A signal from an arterial pressure-sensing device 99 is fed into a
dual trace oscilloscope 100 along with a signal from ECG device
102. The duration of an intensification of these signals is the
duration of a pressure command signal as received from duration
signal generator 88 and appears as intensifications of ECG trace
104 and arterial trace 106. Delay devices 108 and 110, of 90
milliseconds and 80 milliseconds respectively, cause the pressure
command signal to appear on both waveforms in approximately correct
time relationship referenced to the actual ECG and arterial
pressure. Delay 86 is used to bring the intensification signal into
register with diastolic period as viewed on either the ECG or
arterial traces, thereby simultaneously phasing the pressurization
wave to the cardiac cycle.
The operator of the apparatus can also have variable control means
for changing the characteristics of the duration signal generator
88 to provide the intensified signal duration which is required for
a particular patient. On the oscilloscope 101, this duration will
show up as intensifications 103 of the oscilloscope traces.
It is to be noted in reference to waveform generator 90 that a
typical generated wave will normally have a total positive pressure
period of from about 250 to about 300 milliseconds. The rise and
fall in pressure will take about 60 ms each and rise will start
about 80 ms before diastole. In general, it is desirable to select
period-determining device which can maintain positive-pressure
periods of from about 150 ms to about 500 ms.
Referring generally to FIG. 5, a mechanical assembly 112 comprises
a base 122 on which a hydraulic cylinder 123 is mounted. Attached
to cylinder 123 is a reciprocating, operating rod 124 connected,
through a mechanical actuating means 114, to platen 116. Platen 116
has a rigid truncated-triangle like planar surface 117 for
engagement with the bladder. The cylinder moves through a short
stroke sufficient to import about a 2-inch vertical travel to
platen 16.
FIGS. 5 and 6 show the hydraulically-actuated platen assembly
112.
It is important to note in connection with this platen assembly
that one of the problems encountered in design of hospital
installations is to assure they can be used with a reasonably
available power source. This problem is particularly critical in
design of the apparatus of the invention with its suction
requirement, its hydraulic-pressurizing feature and its control
circuitry. Thus platen assembly 112 is constructed to minimize the
power requirement by utilizing a lifting means 114 whereby the
product of the vertical travel of platen 116 and the resistance it
meets during travel is maintained at a relatively constant value.
This is to say that in the lower portion of the stroke where the
reaction pressure of the bladder against the platen is relatively
low, the mechanical linkage between the hydraulic cylinder and the
platen is so designed to provide a greater displacement in
trade-off for pressure. At the upper portion of the stroke, where
bladder reaction pressure increases displacement of the platen is
reduced to obtain a pressure advantage. In this manner, the stroke
requirement of the hydraulic cylinder and, consequently the power
losses from pressure drops in the servo-valve, are held to a
minimum value. Since power used in the hydraulic system is
proportional to stroke this feature and minimize input power
requirements.
This effect is achieved by use of pivotally mounted support levers
118 and pivotally mounted lift levers 120. Because of the relative
length and angles of levers 118 and 120, as operating rod 124 moves
to the right, platen 116 drops at an accelerating velocity to its
lower position. As rod 124 moves back to the left, the platen is
raised until the angle between lever 118 and 120 is about
56.degree.. As the platen rises, it decelerates but also meets more
resistance from the bladder.
As has been illustrated schematically in FIG. 2, a rigid housing or
casing 24 is used to enclose the bladder and its mechanical
pressurizing means. This casing should be as light as is possible
without compromising the rigidity thereof.
As is seen in FIGS. 6 through 11, leg casing 24 comprises a unitary
upper shell 131 and a unitary lower shell 132. The shells are
advantageously formed of plastic material and are internally
reinforced with a rigid, low-density, organic-resin foam such as a
polyurethane foam 134.
A particularly advantageous aspect of the casing 24 is the quick
connect and disconnect means. Bolt connectors 136, mounted
generally between the leg rest are formed of bolts which are
normally captive within upper shell 131. The bolts are provided
with large heads which facilitate their quick connection by
screwing into lower shells 132.
Latch connectors mounted in inserts along the outer periphery of
lower and outer shells comprise a pin 140 which is so positioned on
connector member 142 that when connector member 144 is moved
downwardly, it will not contact pin 140 but, once lowered a lateral
movement of the upper shell wil cause the pin to lock into aperture
146 of member 144. Once this latching is achieved, bolts 136 may be
tightened and the operation may proceed.
Another important aspect of the invention is that whereby
applicants have been able to combine a relatively simple
construction, having only a single fluid bladder and an upper and
lower casing member, and yet achieve a device suitable for
excellent pressure control. This result was accomplished by
providing a unitary upper leg casing member 131 and a unitary lower
leg casing member 132, each of which comprise two truncated
semi-conical leg-receiving compartments 135. These compartments are
connected by a thinner zone (see FIG. 1), which allows a single
blanket-shaped bladder to be wrapped about the patient's legs. To
avoid any substantial deflection by the bladder, say deflection of
over about one-sixteenth of an inch at the pressure mid-point, it
was found necessary to place triangular brace means between the
leg-enclosing compartments and casing member and connect them
together. This arrangement allows even light plastic materials of
construction, such as fiberglass reinforced polyester to be used in
constructing the device. The leg-enclosing zones themselves tend to
resist substantial deflection or deformation because of the
resistance of hoop stresses which is a result of their conical
shape.
In FIG. 6, connectors 136 connect an upper traingular brace means
150 to a lower brace means 152. The upper brace means is formed out
of a resin-type honeycomb material 154.
Necessary connections, both electrical and hydraulic are made
through the envelope 36 and casing 34 as are required.
In the illustrated embodiment of the invention, the platen has a
surface area of about 100 square inches and a stroke of about 2
inches. This apparatus provides a displacement capacity of about
200 cubic inches and this has been found to be entirely adequate
not only to meet the displacement requirements resulting from the
compressability of a patient's legs, but also when combined with
pressure-wave monitoring and control system as disclosed above, to
enable the use of materials of construction which have some limited
distensibility.
In general, the platen and its actuating device should be selected
to have a displacement capacity of at least about 100 cubic inches.
The vertical stroke of the platen is advantageously maintained at
less than about 3.5 inches to avoid design and control problems
associated with excessive velocity and the mechanical and hydraulic
inertice associated therewith.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described and all statements of the scope of the invention
which might be said to fall therebetween.
* * * * *