U.S. patent number 3,892,229 [Application Number 05/422,208] was granted by the patent office on 1975-07-01 for apparatus for augmenting venous blood flow.
Invention is credited to Harry F. Everett, Richard C. Everett, Duane F. Taylor, Norman C. Williams.
United States Patent |
3,892,229 |
Taylor , et al. |
July 1, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus for augmenting venous blood flow
Abstract
Apparatus, adapted for use in explosive as well as non-explosive
atmospheric environments, for alternately applying intermittent
compression to the legs of a patient during surgery, post-operative
recovery periods and other periods of muscular inactivity to
accelerate venous blood flow in the lower extremities and inferior
vena cava and thereby prevent blood clotting in these vessels. A
pair of double-walled pneumatic leggings adapted to extend from the
ankle to the knee of the patient are provided for fitting on each
leg. Each legging is connected by a separate conduit to a
non-electrical regulating and timing control circuit adapted to
receive compressed air, oxygen or other pressurized gas from any
available source and transmit it by means of periodic intermittent
pulses alternately to each legging. The control circuit includes a
pressure regulating valve for reducing the available inlet supply
pressure to a suitable working pressure and adjustable metering
valves for controllably varying the volumetric flow rate of gas to
each legging to thereby control the time rate of pressure build-up
of each pulse. Respective adjustable pressure relief valves are
also provided for variably controlling the maximum pressure
permitted in each legging and for relieving the pressure at the end
of each pulse. The control circuit includes a timing system for
causing the pulses to be delivered at alternate regular intervals
to the respective leggings, such timing system being adapted to
operate entirely by pneumatic actuation so as to eliminate
explosion hazard in high oxygen environments. Such timing system
comprises a two-diaphragm cycling valve for automatically
regulating the alternate charge and discharge of a pair of
accumulator tanks, each tank controlling by means of a
predetermined rate of pressure increase the timing of the pulses to
the respective leggings. The timing system is operatively
independent of legging pressure to eliminate the possibility of
cycle failure if a legging should develop a leak or become
disconnected.
Inventors: |
Taylor; Duane F. (Salem,
OR), Everett; Richard C. (Lake Oswego, OR), Everett;
Harry F. (Lake Oswego, OR), Williams; Norman C. (West
Linn, OR) |
Family
ID: |
23673850 |
Appl.
No.: |
05/422,208 |
Filed: |
December 6, 1973 |
Current U.S.
Class: |
601/152 |
Current CPC
Class: |
A61H
9/0078 (20130101); A61H 2201/5056 (20130101) |
Current International
Class: |
A61H
23/04 (20060101); A61h 001/00 () |
Field of
Search: |
;128/38-40,24R,64,DIG.10,DIG.20 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trapp; Lawrence W.
Attorney, Agent or Firm: Klarquist, Sparkman, Campbell,
Leigh, Hall & Whinston
Claims
What is claimed is:
1. An alternating leg compression control unit adapted to be
coupled with a pair of pressure leggings, said unit comprising:
a. inlet port means adapted for coupling to a source of pressurized
fluid;
b. a pair of outlet port means adapted for coupling to said
respective leggings; and
c. control means for conducting said fluid from said inlet port
means to said respective outlet port means in periodic flow
increments alternating between said respective outlet port means,
said control means including fluid-operated timing means for
starting each said flow increment in a predetermined periodic
sequence, said timing means having no electrically actuated
components.
2. The apparatus of claim 1 including a pressure regulator coupled
with said inlet port means for automatically decreasing the
pressure of said fluid received from said source to a predetermined
pressure.
3. An alternating leg compression control unit adapted to be
coupled with a pair of pressure leggings, said unit comprising:
a. inlet port means adapted for coupling to a source of pressurized
fluid;
b. a pair of outlet port means adapted for coupling to said
respective leggings;
c. control means for conducting said fluid from said inlet port
means to said respective outlet port means in periodic flow
increments alternating between said respective outlet port
means;
d. said control means including timing means for starting each said
flow increment in a predetermined periodic sequence, said timing
means comprising a pressure responsive shuttle valve coupled to a
pair of accumulator timing tanks, said valve having a first
position for feeding pressurized fluid to a first one of said
timing tanks and a second position for feeding pressurized fluid to
said second timing tank; and
e. said control means further comprising a pair of control valves,
each responsive to the pressure in one of said timing tanks, for
selectively initiating or interrupting the flow of pressurized
fluid to a respective one of said outlet port means in response to
said timing tank pressure.
4. The apparatus of claim 3 wherein said shuttle valve includes
means responsive to the pressure in said respective timing tanks
for interrupting the flow of fluid to a respective timing tank when
the pressure in said tank increases to a predetermined level, and
simultaneously therewith initiating a flow of fluid to said other
timing tank.
5. The apparatus of claim 4 wherein said shuttle valve comprises a
pair of flexible diaphragms joined together for movement in unison
with one another, said valve including means responsive to the
pressure in said respective timing tanks for moving said diaphragm
pair in one direction when the pressure in a respective timing tank
increases to a predetermined level and for moving said diaphragm
pair in the opposite direction when the pressure in the other said
timing tank increases to a predetermined level.
6. The apparatus of claim 3 wherein each of said control valves
includes means for initiating a flow of pressurized fluid to a
respective outlet port means whenever the pressure in a respective
timing tank decreases to a predetermined pressure level.
7. The apparatus of claim 3 including first restrictor means
interposed between said first timing tank and said shuttle valve
and second restrictor means interposed between said second timing
tank and said shuttle valve for controlling the rate of flow of
pressurized fluid into said respective timing tanks.
8. The apparatus of claim 3 including means for isolating the fluid
in said timing tanks from the fluid conducted to said outlet port
means so as to render the pressure in said timing tanks independent
of the pressure at said outlet port means.
9. The apparatus of claim 3 including pressure regulator means
coupled with said inlet port means for automatically decreasing the
pressure of said fluid received from said source to a predetermined
pressure.
10. The apparatus of claim 3 including relief valve means coupled
to said outlet port means for limiting the pressure at said outlet
port means to a predetermined maximum pressure.
11. The apparatus of claim 10 wherein said relief valve means
comprises a pair of relief valves, each coupled with a respective
one of said outlet port means and each having adjustable means for
independently varying the predetermined maximum pressure at said
respective outlet port means.
12. The apparatus of claim 10 wherein said relief valve means
comprises a pair of relief valves, each coupled with a respective
one of said outlet port means and each having means responsive to
the pressure in a respective timing tank for retaining said relief
valve in its relieving condition for a predetermined period of time
after said predetermined maximum pressure has been reached.
13. The apparatus of claim 12 wherein each said relief valve
includes means for interrupting the flow of pressurized fluid to
said respective outlet port means while said relief valve is in
said relieving condition.
14. The apparatus of claim 3 including adjustable metering valve
means interposed between said inlet port means and said outlet port
means for variably regulating the flow rate of pressurized fluid to
said outlet port means.
15. The apparatus of claim 14 wherein said metering valve means
comprises a pair of metering valves, each interposed between said
inlet port means and a respective one of said outlet port means and
each having adjustable means for independently varying the flow
rate of pressurized fluid to said respective outlet port means.
16. An alternating leg compression control unit comprising means
for delivering pressurized fluid through a pair of outlet ports to
a pair of pressure leggings in periodic flow increments alternating
between said respective outlet ports, and adjustable means for
varying the time rate of pressure increase at said outlet ports
when said leggings are coupled thereto.
17. The apparatus of claim 16 wherein a pair of said adjustable
means for varying said rate of pressure increase are provided, each
being coupled to a respective outlet port and each being separately
adjustable for varying the time rate of pressure increase at said
respective outlet ports independently of one another.
18. An alternating leg compression control unit comprising means
for delivering pressurized fluid in flow increments through a pair
of outlet ports to a pair of pressure leggings, and timing means
adapted to operate solely by fluid pressure for automatically
initiating each said flow increment in a periodic sequence.
19. An alternating leg compression control unit comprising:
means for delivering pressurized fluid through a pair of outlet
ports to a pair of pressure leggings in periodic flow increments
alternating between said respective outlet ports,
and a pair of said adjustable pressure limiting means for variably
limiting the maximum pressure at said respective outlet ports,
each of said adjustable pressure limiting means being coupled to a
respective outlet port and each being separately adjustable for
varying the maximum pressure at said respective outlet ports
independently of one another.
20. An alternating leg compression control unit comprising:
means for delivering pressurized fluid through a pair of outlet
ports to a pair of pressure leggings in periodic flow increment
pulses alternating between said respective outlet ports,
and a pair of said adjustable means for varying the duration of
each of said pulses,
each of said adjustable pressure limiting means being coupled to a
respective outlet port and each being separately adjustable for
varying pulse duration at one of said outlet ports independently of
pulse duration at the other said outlet port.
Description
BACKGROUND OF THE INVENTION
This invention relates to improvements in apparatus for
intermittently compressing a patient's leg muscles during surgery
or any other periods of muscular inactivity or paralysis in order
to accelerate venous blood flow and thereby prevent blood clot
formation in the lower extremeties and pelvis. More specifically
the apparatus is of the type wherein individual pneumatic leggings
are provided for fitting around the patient's lower leg wherein a
pneumatic control circuit is provided for automatically regulating
the timing, rate of pressurization and maximum pressure of periodic
pneumatic pulses delivered alternately to each legging.
Persons undergoing surgery and extended post-operative recovery or
prolonged bed rest and inactivity for any reason have in the past
been particularly susceptible to a condition known as "deep vein
thrombosis" which is a clotting of venous blood in the lower
extremities and pelvis. The clotting occurs because of the absence
of sufficient muscular activity in the lower legs required to pump
the venous blood, and can be life-threatening if a blood clot
migrates to the heart and interferes with pulmonary blood
circulation. Statistics indicate that deep vein thrombosis occurs
to some degree either during or shortly after surgical procedures
in approximately 30% of all surgical patients.
Because of the high incidence and potential severity of the
condition, several means of thrombosis prevention have been devised
in the past. Most notable among these is the provision of pneumatic
leggings or boots adapted to fit around the calf and foot of a
patient's legs, such leggings being connected to pump apparatus
which sends alternate intermittent pulses to each of the leggings
to periodically compress and release the calf muscles and thereby
accelerate blood flow. No appreciable venous backflow results from
such intermittent compression because a series of one-way valves in
the venous system permits the blood to move only in an upward
direction. Although such apparatus has proven to be effective in
the prevention of deep vein thrombosis, it has also suffered from
several disadvantages. One serious deficiency has been the reliance
if such apparatus on electrical power for pneumatic pumping and
timing cycle control, causing a serious fire or explosion hazard
when such electrical components are utilized in a surgical or
post-operative environment where highly inflammable substances such
as anesthesias and oxygen abound. Another disadvantage of prior
apparatus is that they provide insufficient adjustability of the
pressurization process, such as regulation for each leg of the rate
of pressure build-up, the duration of the duty cycle and the
maximum pneumatic pressure applied. Consequently the prior
apparatus are not sufficiently versatile to be used on a patient
whose legs, for example, may be especially tender or sore requiring
lower pressure levels, nor is such apparatus adapted to permit the
gradual increasing of pressure levels so that the patient may,
without experiencing pain, gradually adapt himself to a higher
pressure level. Because of the lack of adjustability such prior
apparatus are also not adaptable for the treatment of certain
conditions where a lower pressure range than that normally desired
for the treatment of deep vein thrombosis would be advantageous,
such as in the treatment of "venous insufficiency related stasis
ulcer". Finally, pneumatic leggings used in the past have been
constructed so as to compress most or all of the foot as well as
the muscles of the lower leg, a feature which not only provides no
particular advantage but tends to limit circulation in the foot and
thus may be harmful.
Accordingly there presently exists a need for an improved
alternating leg compression system which operates entirely without
electricity, thereby eliminating all fire or explosion hazard, and
is independently adjustable for each leg with respect to
compression levels and the rate of pressure application so that it
is adaptable for use with patients having widely varying leg
conditions.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to an alternating leg compression
apparatus of the general type described featuring a novel control
circuit for automatically and alternately providing intermittent
compression pulses to a pair of pneumatic leggings, such control
circuit being adapted to connect to any pressurized gas supply
normally available in hospital settings and operating entirely by
means of pneumatic power without electrical input or circuitry of
any kind. Precise cycling of the alternate pneumatic pulses
delivered to the respective leggings is provided by a timing system
comprising a unique shuttle valve which automatically controls the
alternate pneumatic charge and discharge of a pair of accumulator
timing tanks, each controlling the period of the pulses to a
respective legging in response to the time required to charge each
tank to a predetermined pressure. The timing tanks are coupled to
respective diaphragm-controlled valves which regulate the input of
pneumatic flow increments to the leggings and also isolate the
timing system from the presssure levels in the leggings to insure
against misapplication of pressure if one of the leggings should
inadvertently become disconnected or develop a leak.
The control circuit is adapted for connection to virtually any
source of pressurized air, oxygen or other gas normally available
in a hospital by virtue of a pressure regulator at its inlet port
which automatically reduces the supply pressure to a level suitable
for use in the system. Msximum pressure in each legging may be
adjusted by means of a pair of manually adjustable relief valves
which automatically relieve the pressure in a respective
independently varied by means of a pair of manually adjustable
metering valves which regulate the volumetric flow rate of gas into
the respective leggings. Improved double-walled pneumatic leggings
are provided for fitting on the lower portion of a patient's legs
between the ankle and knee, such leggings being constructed so as
not to include the patient's foot within the pressure application
zone.
It is therefore a primary objective of the present invention to
provide an improved apparatus for augmenting venous blood flow in
the leg as a means of preventing blood clot formation in the lower
extremities and pelvis, particularly under surgical and
post-operative recovery conditions.
It is a primary feature of the present invention that such leg
compression apparatus is adapted to utilize virtually any
pressurized gas supply normally available in hospitals and requires
no electrical power or electrical actuation of any kind to achieve
the alternating periodic pulses and pressure adjustments desired,
so as to eliminate any possibility of fire or explosion in
inflammable environments.
It is a further feature of the present invention that highly
variable adjustments of the maximum pressure exerted on each leg,
the rate of pressure rise of each pneumatic pulse and the duration
of each pulse be provided so as to adapt the apparatus to varying
patient conditions and requirements.
It is a still further feature of the present invention that the
pneumatic leggings utilized be constructed so as to compress the
patient's leg muscles without simultaneously exerting pressure on
the foot, so as to prevent interference with foot circulation and
compression-abrasion and blister formation of the heels and between
the toes.
The foregoing and other objectives, features and advantages of the
present invention will be more readily understood upon
consideration of the following detailed description of the
invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing application of the alternating
leg pressure unit to a patient's legs.
FIG. 2 is an enlarged detail view of a pneumatic legging utilized
in the present invention.
FIG. 3 is a sectional view of a pneumatic legging taken along line
3--3 of FIG. 2.
FIG. 4 is a schematic diagram of the control circuit for delivering
alternating periodic pulses to the respective leggings, with the
structure of certain valves shown in section
FIG. 5 is a front view of the operator console of the control
circuit. FIG. 6 is a graph illustrating the alternating periodic
pulses generated by the control circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The alternating leg compression apparatus of the present invention
comprises a compression control unit, designated generally as 10 in
FIG. 1, adapted to be coupled by means of a pair of conduits 12 and
14 to respective pneumatic leggings 16 and 18. As best seen in
FIGS. 2 and 3 each legging comprises a sleeve adapted to fit around
a person's lower leg, such sleeve being constructed of vinyl or
other flexible, fluid impervious material and having an outer wall
20 and an inner wall 22 defining a fluid compression chamber 24
adapted to extend from the knee to a position no lower than the
ankle. The chamber 24 is divided into two sections by a seam 26
which extend through most but not all of the length of the chamber,
thereby providing for a coupling portion 28 at one or both ends of
the chamber by which both chamber sections communicate with one
another. Each legging has a fluid input coupling 30 and 32
respectively adapted for coupling by means of conduits 12 and 14
with the respective fluid outlet ports 34, 36 of the control unit
10.
The leggings receive alternating periodic flow increments or
"pulses" of pressurized fluid from the outlet ports 34, 36 in a
manner to be described more fully hereafter, each such pulse
constituting a gradual pressure rise during which the chamber 24 of
each legging is filled so as to compress the enclosed leg muscle
followed by a relatively abrupt relief of such pressure permitting
the chamber 24 to collapse and thereby release compression on the
muscle. A tie string 38 is provided at the lower end of each
legging for snugly securing the sleeve to the leg. This feature
prevents any downward slippage of the chamber 24 below the ankle
regardless of whether the chamber is in a pressurized or collapsed
condition and thereby insures against the application of pressure
to that patient's foot which might impede circulation.
The control unit 10 which delivers the alternating periodic flow
pulses to the respective leggings is of a unique construction
adapted particularly for use under inflammable or explosive
atmospheric conditions, having no electrically actuated components
of any kind and providing a high degree of adjustability with
respect to the maximum pressure and duration of pulses exerted on
each leg. Referring specifically to FIG. 4, the circuit of the
control unit 10 essentially comprises an inlet port 40 adapted for
coupling to any suitable source of pressurized fluid normally
available in hospitals, for example pressurized air or oxygen,
respective outlet ports 34, 36 adapted for coupling with the
pressure leggings 16, 18 and an exclusively fluid-operated control
circuit interposed between the inlet port and outlet ports. The
control circuit comprises a pressure regulating vlave 42 for
automatically decreasing the pressure of the fluid received from
the available source to a predetermined pressure suitable for use
in the leg compression system. Source pressure, indicated by a
pressure gauge 44, may range anywhere from approximately 8 to 100
psi and is preferably reduced by the pressure regulator 42 to
approximately 5 psi, depending on the setting of adjustable
regulator spring 43. Fluid at reduced pressure flows through lines
46 and 48 to the respective leggings 16, 18 in alternating periodic
flow increments or pulses determined by the automatic actuation of
a pair of control valves 56, 58 interposed in the respective
lines.
The alternating cyclic actuation of the control valves 56, 58 is
controlled by an automatic fluid operated timing system comprising
a pressure responsive shuttle valve designated generally as 50
coupled to a pair of accumulator timing tanks 52, 54. The shuttle
valve has a first position for feeding pressurized fluid to timing
tank 54 and a second position for feeding fluid to timing tank 52.
The positions are exclusive of one another so that only one timing
tank is being filled at any given time. When one timing tank has
filled to a predetermined pressure, such pressure acts
automatically to shift the shuttle valve to a position to begin
filling the opposite timing tank, and in so doing triggers its own
exhaust. The exhaust of a timing tank causes the respective control
valve 56 or 58 to which the particular tank is connected to
initiate a pulse to a legging. Since the shuttle valve 50 causes
the respective timing tanks to fill during alternate intervals, the
pulses in the respective leggings 16, 18 are therefore initiated
alternately. Having briefly summarized the function of the timing
system, the structure and operation will now be explained in
detail.
The shuttle valve 50 receives pressurized fluid from the pressure
regulator 42 through line 60 into its inlet chamber 62. The fluid
pressure is applied upwardly and downwardly against a pair of
flexible diaphragms 64, 66 which are joined togther by a connecting
member 68 so as to move upwardly and downwardly in unison. Because
the diaphragm pair is unstable unless in a fully "up " or fully
"down" position, the pair will instantly assume one of the two
positions (for example the down position indicated in FIG. 4) upon
exposure to inlet pressure and be held there due to the difference
in exposed area of the two diaphragms to the inlet pressure. In the
down position, inlet fluid from line 60 goes through inlet chamber
62, timing restrictor 72 and timing tank feed line 70 to an
accumulator timing tank 54. Simultaneously flow is blocked by
diaphragm 64 to the timing tank feed line 74 which communicates
with tank 52 (no appreciable flow occurs through pilot line 76 due
to the extremely small restriction imposed by restrictor 78). As
the pressure in timing tank 54 begins to rise, diaphragm 77 of
control valve 58 is pushed down, blocking fluid flow in line 46
while diaphragm 79 of valve 80 is also pushed down against spring
81 to insure that chamber 82 of valve 88 is exhausted, thereby
permitting spring 86 to open valve 88 downwardly. The opening of
valve 88 ultimately will permit fluid flow through line 90 into
legging 16 when control valve 58 subsequently opens. During the
period of pressure build-up in tank 54, no fluid flow or pulse is
initiated or maintained at outlet port 36 or im legging 16.
When the pressure in tank 54 rises to approximately 60% of the
pressure in inlet chamber 62, the pressure imposed through lines 91
and 92 on the underside perimeter areas of the diaphragms 64, 66
causes both diaphragms to lift slightly, allowing fluid at tank
pressure also to enter chamber 94 beneath diaphragm 66. This adds
to the effective pressure area tending to push the diaphragms
upward, and instantly causes the diaphragm pair to snap into its
upward position. The shift in diaphragm position blocks any further
supply of fluid through line 70 to timing tank 54, there being no
appreciable flow of fluid to tank 54 through line 91 due to the
severe restriction imposed by restrictor 96. Simultaneously with
the upward movement of the diaphragm pair, a flow of pressurized
fluid through restrictor 98 and timing tank feed line 74 is
initiated so as to begin the rise of pressure in the opposite
timing tank 52. As the pressure in tank 52 begins to build up, it
acts through pilot line 100 to shift diaphragm 102 upwardly thereby
opening the exhaust valve 104 of timing tank 54. This immediately
exhausts the pressure in tank 54, resulting in the simultaneous
opening of control valve 58 and the closing of valve 80. The
opening of valve 58 initiates the beginning of a flow increment or
pressure pulse through line 46, valve 58, line 90, valve 88, outlet
port 36 and conduit 12 to legging 16. At this time no pulse is
being transmitted to the other legging because pressure is rising
in tank 52 and control valve 56 is therefore closed.
The initiation of fluid flow to legging 16 causes a gradual
pressure build-up in the compression chamber of the legging, the
time rate of pressure build-up being determined by the volumetric
flow of the fluid which is controlled by a manually adjustable flow
metering valve 106 interposed in line 46. Flow to legging 16
continues until the pressure in the legging, as sensed in chamber
82, of valve 88, rises to the point where the upward force on
diaphragm 107 overcomes the downward force exerted by spring 86 and
thereby raises valve 88 to a closed position. In the act of
closing, valve 88 raises a flexible rubber disc poppet 108 against
the force of spring 110, thereby permitting the pressurized fluid
in the legging 16 to exhaust through chamber 112 and exhaust port
114 and relieve compression on the leg. Accordingly valve 88 acts
as a relief valve which terminates each pulse as soon as the
pressure in the legging 16 reaches a maximum predetermined pressure
determined by the force exerted by spring 86. Such spring force is
manually adjustable by means of screw adjustment 116, so as to vary
the maximum pressure setting.
It should be noted that relief valve 88 is bi-stable in the sense
that, once the maximum predetermined relief pressure in legging 16
has been reached, thereby forcing valve 88 upward, the valve is
retained in its upward "relieving" condition by the fact that
chamber 82 remains pressurized until the pressure is subsequently
relieved by the opening of valve 80. Valve 80 does not open however
until the pressure in timing tank 54 once more begins to rise,
which occurs only after the passage of a predetermined time period
when the pressure in the opposite timing tank 52 has risen
sufficiently to shift the diaphragm pair 64, 66 once more into a
downward position.
During the period that the flow increment pulse was being delivered
to legging 16, pressure in timing tank 52 was gradually rising due
to the upward position of the diaphragm pair 64, 66, while timing
tank 54 was open to atmosphere through exhaust valve 104. The rate
of pressure rise in tank 52 is precisely the same as the rate of
pressure rise in tank 54 by virtue of the fact that the tanks are
the same size and timing restrictors 98 and 72 respectively are
identical, causing identical volumetric fluid flow rates to the
tanks during their respective charging periods. Since the tanks 52
and 54 and their associated valveing are duplicates of one another,
the pressure rise in tank 52 has the same effect on valves 56, 118
and 120 as did the pressure rise in tank 54 on corresponding valves
58, 80 and 88. After the pressure in tank 52 has risen to the same
level previously required to cause the upward shifting of the
diaphragm pair 64, 66, the pressure imposed upon the upward
perimeter areas of the diaphragms through lines 76 and 122 causes a
downward snapping of the diaphragms, thereby terminating flow to
tank 52 and initiating flow to tank 54. As soon as the pressure in
tank 54 rises to the same level previously required to open exhaust
valve 104, such pressure acting through line 124 on diaphragm 126
opens the opposite exhaust valve 128, thereby exhausting tank 52
through line 122. This in turn opens control valve 56, initiating a
pressure pulse in legging 18 at a rate of pressure rise determined
by adjustable flow metering valve 130. The pressure rise continues
in legging 18 until the maximum predetermined pressure, as
determined by adjustment 132, is reached and the pressure in
legging 18 is thereby relieved. While the pulse is being delivered
to legging 18, pressure in timing tank 54 is once more building up
toward the point where it will shift the diaphragm pair upwardly,
resulting in the exhaust of tank 54 and the initiation of a new
pulse to legging 16, and so on repeatably until the control unit 10
is disconnected from the pressure source.
Accordingly it will be recognized that the two sides of the control
circuit which feed outlet ports 34 and 36 and leggings 18 and 16
respectively are identical in operation with respect to the
initiation of pulses, the initiating cycle for each side of the
circuit occurring during alternate intervals because of their
mutual coupling through the shuttle valve 50. The resultant pulse
pattern produced by the control circuit is illustrated in FIG. 6.
The initiation of each pulse is triggered by the exhaust of a
respective timing tank. Since the exhaust of one timing tank is
substantially concurrent with the beginning of pressure rise in the
opposite timing tank, the interval between initiation of a pulse in
legging 16 and the initiation of the next succeeding pulse in
legging 18 is the time necessary to charge one tank to a pressure
sufficient to initiate the exhaust of the tank through the shifting
of shuttle valve 50. The period between the initiation of
successive pulses in the same legging is twice this charge time.
Available data indicates that practical and optimum venous blood
flow is attained at compressive increases of approximately 8 mm. of
mercury per second, reaching a maximum pressure of about 60 mm. of
mercury. No appreciable dwell time at maximum pressure is needed,
but a substantial decompressive pause is desirable for venous
filling before recompression. Accordingly, in the preferred
embodiment, the timing system has been designed so as to provide
for an interval of 60 seconds between the initiation of successive
pulses in the same legging. This means that the charge time for
each timing tank will be at least 30 seconds and, as a practical
matter, probably a few seconds more to account for some time lag
between the initiation of flow to one tank and the exhaust of the
other occasioned by the time necessary to open the respective tank
exhaust valves 104 and 128. The tank charge times, and the
resultant intervals between pulse initiations, can be precisely
determined by proper selection and matching of restrictors 72 and
98, and can be varied by changing such restrictors.
Although the control circuit operates symmetrically with respect to
the timing of pulse initiations, the maximum pressure, rate of
pressure rise and duration of the pulses delivered to the
respective leggings need not be identical and in fact are
separately adjustable so as to provide sufficient versatility to
accommodate patients having varying leg conditions. The maximum
pressure of the pulses in each legging is separately controllable
by the aforesaid adjustments 116 and 132 respectively which control
the spring forces on relief valves 88 and 120. These adjustments
should preferably provide maximum pressure variation within a range
of at least 20 mm. to 80 mm. of mercury. The adjustment controls
are provided on the face of the control unit 10 as shown in FIG. 5,
the unit being provided with separate pressure gauges 134 and 136
coupled with the respective outlet ports 34 and 36 to indicate the
precise pressure levels in the respective leggings as an aid to
adjustment. With the foregoing separate pressure adjustments it is
possible to have a large discrepancy between the maximum pressures
of the pulses in the respective leggings to accommodate a patient
who, for example, may be suffering soreness in one leg but not the
other.
The duration of the compressive pulses may also be adjustably
varied separately in each legging, independently of both pulse
interval and maximum pressure setting. This is accomplished by the
individual adjustment of variable metering valves 106 and 130 so as
to provide particular predetermined time rates of pressure increase
in the respective leggings, thereby variably controlling the point
in time when each pulse reaches the predetermined maximum relief
pressure and thereby terminates itself.
It is significant that the adjustment of maximum pressure and
duration of the individual pulses in no way affects the time
interval between initiation of the respective pulses. This is due
to the unique isolation of the timing system from the remainder of
the control circuit by the diaphragms of valves 56, 58, 80 and 118.
These diaphragms separate the fluid in the timing tanks 52 and 54
from the fluid delivered to the respective outlet ports 34, 36 and
thereby render the pressure in the timing tanks independent of
outlet port pressure. Thus not only is the timing system isolated
from any effect of the aforesaid adjustments but also from any
effect of pressure leaks or accidental disconnection of the
leggings, thereby eliminating any chance of timing cycle failure
and resultant injury to the patient.
It will thus be appreciated that the improved alternating leg
compression system of the present invention operates entirely
without electricity, thereby eliminating all fire or explosion
hazards, while providing a high degree of adjustability with
respect to pressure and compression duration.
The terms and expressions which have been employed in the foregoing
abstract and specification are used therein as terms of description
and not of limitation, and there is no intention, in the use of
such terms and expressions of excluding equivalents of the features
shown and described or portions thereof, it being recognized that
the scope of the invention is defined and limited only by the
claims which follow.
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