Note: Descriptions are shown in the official language in which they were submitted.
Bac~ground of the Invention
1. Field of the Invention
This invention pertains to blood flow rate
controllers for pump oxygenation systems and, more
particularly, to venous blood feed responsive,
oxygenation systems for use in cardiovascular surgery
and for cardiopulmonary partial support.
2. Description of the Prior Art
Generally, a cardiopulmonary bypass system
is a medical system used in cardiovascular surgery,
intensive care and
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1 surgical recovery that is coupled to a human body to revitalize
2 snd pump blood, thereby performing certain functions of the heart
3 and lungs and often partially or fully bypassing a portion of the
4 c~rculatory system. The cardiopulmonary bypass system receives
a venous blood feed (oxygen deficient blood) from the human cir-
6 culatory system, oxygenates and warms the blood and returns the
7 blood to the circulatory system at a flow rate corresponding to
8 the ~enous drainage, thus reducing the load on the lungs and
9 heart.
A cardiopulmonary bypass system in a partial support
11 capacity is used, for example, during cardiac intensive care
12 of patients who have suffered a cardiac infarction where a
13 portion of the heart muscle has died from an insufficient blood
14 supply. The dead muscle is soft and difficult to suture sinçe
it will tear easily. The muscle may heal if the patient is kept
16 quiet and heart chambers are subject to a minimum amount of
17 pressure. Failing such care, an aneurysm may result in which
18 the softened muscle swells up and stagnates pools of blood which
19 tend to clot. The tendency toward development of an aneurysm
is minimized by reducing the pumping load on the heart with the
21 partial support system. Typically the infarcted tissue scars
22 over and thereby regains its tensile integrity in several weeks
23 during which time the cardiopulmonary bypass system must operate
24 continuously. Recent developments in pump oxygenation equipment,
such as mernbrane oxygenators having limited long term blood
26 degradation effects, have made possible long term partial
27 support of this duration. In the past, technicians have monitored
28 the flow of blood in pump oxygenation systems for a relatively
29 short period of time, such as less than four hours, during heart
~0 surgery. However, the costs and availability of technicians
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1 generally preclude their usage on a long term basis, and
2 even where they are used human error can be a significant
3 problem.
4 Conflicts between safety, costs and flexibility
must be reduced to provide a satisfactory cardiopulmonary
6 bypass system. Such desirable features include responsive-
7 ness to a gravity feed rate, minimal blood degradation and
8 long term reliability. In addition, the exposure of the
9 blood to air should be minimized, while the buildup of excess
gases should be avoided or at least indicated.
11 Many specific requirements must be met in a practical
12 partial support system. For example, the cardi~pulmonary
13 bypass system experiences a load as the blood is returned to
14 the human body. The load is variable and the flow impedance
seen by the cardiopulmonary bypass system may increase if
16 for example the arteries are constricting or decrease when
17 hemorrhaging is occurring. Yet the cardiopulmonary bypass
18 system should generally maintain a constant flow rate to the
19 human body, equal to the venous drainage. In the past, the
return flow rate has been controlled in response to central
21 venous pressure or return flow pressure. See, for example,
22 Turina, et al., "An Automatic Cardiopulmonary Bypass Unit
23 for Use In Infants", The Journal of Thoracic and Cardio-
24 vascular Sur~erv 63 (February 1972), p. 263, 264. However,
venous pressure is an inaccurate measure of blood flow and
26 may vary considerably for a constant blood flow depending
27 on the physical state of the patient.
28 Blood removal from the human circulatory system by a
29 cardiopulmonary bypass system should not cause an excessive vacuum
or suction so as to collapse the veins, yet provide a substantial
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l and generally uniform blood f]ow to effectively unload the
2 patient's cardiopulmonary system. A system utilizing a negative
3 pressure in a caval cannula is described in an article by
4 Turina et al., "Servo-controlled Perfusion Unit With Membrane
Oxygenator for Extended Cardioyulmonary Bypass", Biomedical
6 En~ineerin~ (March 1963) pp. 102-107. The Turina system however,
7 i9 rather sophisticated and complex in utilizing sensors and
8 servos for a number of controls, and thus is both undul~ costly
9 and subject to greater tendency to failure.
The rate and changes in rate of blood flow indicate
ll the physical state of the patient, and thus it would be desirable
12 to monitor the blood flow rate. The physician may find it
13 necessary to increase or decrease the return flow rate of the
14 blood. Increasing the blood flow rate in excess of the drainage
rate often requires the addition of blood to the system. It
16 would be advantageous to have a cardiopulmonary bypass system
17 which could introduce quantities of blood to the blood flow in
18 addition to the blood supplied by the patient's circulatory system.
19 The quantity of blood flowing in the circulatory
system of a neonate or young infant is extremely critical. For
21 example, hyaline membrane disease attacks the alveolar sacks of
22 infants. When this occurs, the lining of the lungs is impervious
23 to oxygen and CO2. Since the infant having this disease receives
24 insufficient oxygen, the treatment in the past has been to
increase, in concentration and pressure, the oxygen provided to
26 the infant. Although the disease is often cured by this technique,
27 other serious conditions may set in which are caused by the
28 toxic effects of oxygen such as retrolental fibroplasia, in which
29 the retina is destroyed. By using a cardiopulmonary bypass
system, the lungs are allowed to heal. The control of blood volume
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lS extremely important since the nyaline disease typically
occurs with underweiyht infants, typically less than 2500 grams
and having a total blood volume of only 150-300 cc,
Thus it would be desirable to have a cardiopulmonary
bypass system that is safe, reliable, gravity feed responsive,
and volume alterable.
Summar of the Invention
Y
In broad terms the present invention provides a
system for providing a controlled blood flow to a human
circulatory system comprising: collector means for receiving
a blood feed from a patient; means coupled to the collector
means and responsive to the volume of the blood therein for
providing an indication related thereto; oxygenation means
coupled to the collector means for revitalizing the blood;
and variable rate pump means coupled to the collector means
for providing a return flow of blood to the patient at a flow
rate responsive to the indication.
Accordingly, a cardiopulmonary bypass system for use
with a human circulatory system in accordance with this invention
comprises variable volume, air-free means for collecting a
gravity feed blood flow from a patient and transducer means
- coupled to the collector means for providing a blood volume
responsive signal related to the feed rate of the blood. After
oxygenating and warming the blood from the collector means,
pump means coupled to the collector means returns the blood to
the patient at a flow rate controlled by the signal from the
transducer means such that the blood flow returning to the
patient is substantially the same as the drainage rate from the
patient.
In a preferred embodiment of the invention, a first
collapsible bag is coupled to receive a gravity fed flow of
blood. The bag is collapsible and air evacuable so that any
blood-gas interface may be substantially eliminated, The bag
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is also flexible so as to inhibit air suction when empty and
thereby prevent an air embolism to the eirculatory system,
A standpipe extending from the bag is eoupled to a
gas pressure responsive transducer. The standpipe provides
a eonfined gas volume, the pressure within which acts on the
transducer. Blood flow rate changes into the bag manifested
by blood volume changes of the bag result in fractianal
ehanges in the confined gas volume and subse~uent pressure
ehanges that are mueh
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l amplified with respect to the fractional blood volume changes
2 of the bag. A second collapsible bag is provided that functions
3 generally in a buffer capacity and supplies revitalized blood to
4 the patient. Revitalization means generally comprising a pump,
a membrane oxygenator and a heat exchanger is coupled between
6 the first and second bags. A recirculation path communicating
7 between the second bag and the first bag provides a positive
8 recirculation of a part of the blood flow, relieving excess
9 pressure in the second bag and insuring equilibrium in the flow
rates. A main variable speed pump coupled to the second bag
11 delivers a controlled blood flow from the second bag to a human
- 12 circulatory system. To regulate pump speed, a rate setting control
13 responsive to the transducer signal drives the main pump at a
14 rate which tends to maintain the blood volume of the first bag
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at a predetermined point for a particular blood drainage rate
~ 16 such that the return blood flow rate is held at substantially the
; 17 rate of the venous blood flow. The rate setting control may
18 be manually varied by a supervising physician to directly
l9 change the rate of flow without shutting off the automatic
system.
21 In accordance with another feature a reservoir is
22 included for storing blood. The blood in the reservoir may be
23 selectively admitted into the first drainage bag for increasing
24 the total blood volume of the combined circulatory and cardio-
pulmonary bypass system. A valve coupled tube may be used
26 to tap off an excess quantity of blood if the flow exceeds
27 predetermined levels.
28 Description of the Drawin~s
29 Fig. 1 is a combined block and simplified broken away
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1 schematic diagram of an example of a blood flow controller in
2 accordance with the invention.
3 Detailed ~escription
4 Referring to Fig. 1, in a preferred embodiment of cardio-
pulmonary bypass system 10 in accordance with the invention, a
6 collector means 12 is disposable below a blood withdrawal point
7 on a patient for receiving a gravity fed venous blood flow from
8 a human patient's circulatory system. A gas containment means or
9 standpipe 14 coupled into the interior of the collector means
extends vertically to a pressure responsive transducer 16 which
11 is in operative relation to the interior at the upper end of
12 the standpipe 14. The collector means 12 generally comprises a
13 first collapsible bag 18 and a venous feed tube 20 coupled at
14 an inlet of the collapsible bag 18. While the collapsible bag 18
and the venous feed tube 20 may be of various material~ they here
16 are of a surgical quality neoprene and are typically disposable
17 units. The thickness of the collapsible bag 18, which is
18 preferably transparent or translucent, is sufficient for it ~.o
19 accept a substantial volume of blood without danger of rupture
or susceptibility to puncture from contact with foreign objects.
21 The bag 18 is also, however, sufficiently pliable for its walls
22 to readily conform to the interior blood volume, thereby sub-
23 stantially eliminating an interior blood-gas interface and
24 completely collapsing when all blood is removed. An outlet tube
19 at the top of the bag 18 can be closed by a clamp 21 when all
26 air has been exhausted from the bag interior.
27 The standpipe 14 is preferably a rigid and transparent
28 or trsnslucent shaped tubular element of surgical quality. The
29 standpipe 14 having a small interior volume in comparison with
the interior volume of the first collapsible bag and having
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1 nominal blood levels therein, defines a confined gas volume 22
2 within a cylindrical chamber 23 and exerting a pressure through
3 a sterility barrier 24 within the chamber 23 on the transducer
4 16. An increase of blood flow into the first collapsible bag
18 causes a distention of the bag 18 and thereby causes the blood
6 level in the standpipe 14 to increase, reducin~ the confined gas
7 volume 22. A reduction of the confined gas volume 22 causes an
8 increase in the pressure applied through the sterility barrier 24
9 to the transducer 16. Small fractional changes in the blood flow
rate into the collapsible bag 18, manifested by small fractional
11 volume changes of blood in the collapsible bag 18 causes large
12 fractional changes in the pressure of the confined gas volume 22.
13 Thus the combination of the collection means 12, the standpipe
14 14 and the transducer 16 provide a highly sensitive means of
measuring and indicating changes in the venous flow rate.
16 While the transducer 16 provides a signal related to
17 a blood flow rate from the patient into the collapsible bag 18,
18 this signal is not necessarily related to the signal which would
19 be obtained if, for example, a patient's central venous pressure
were monitored. The applicant's invention tends to provide a
21 more accurate indication of venous flow rate since a patient's
22 blood pressure may vary with changes in blood volume in the
23 patient's circulatory system and with other parameters.
24 Revitalization or oxygenation means 28 is provided for
continuous revitalization of the blood including the oxygen
- 26 transfer to oxygen deficient blood and the warming of blood which
27 has been partially cooled since removal from the patient. The
28 oxygenation means 28 generally comprises an oxygenation pump 30
29 driven by a pump motor 32 coupled thereto. The oxygenation pump
30 is coupled to a membrane oxygenator and heat exchanger 34 in
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1 series fashion, with the oxygenation pump 30 forcing blood through
2 the membrane oxygenator and heat exchanger 34. The pump motor
3 32 for the oxygenation pump 30 may be a roller blood pump in which
4 blood is carried between a membrane and a surface defining a
cylindrical chamber by rollers rotating and bearing on the mem-
6 brane and against the surface.
7 A second collapsible bag 36 comparable to the first
8 bag 18 is air evacuable and is preferably translucent or trans-
9 parent. Flow through the oxygenation means 28 is transported to the
collapsible bag 36 via a conduit 37 to provide generally a con-
11 tinuous supply of freshly revitalized (i.e. oxygenated and warmed)
12 blood to the second collapsible bag 36. The second collapsible
13 bag 36 also helps to dampen or buffer uneven or pulsating flows
14 of blood returned to the patient by way of a main pump 38. For
positive circulation under all conditions, the main pump 38 is
16 constantly driven at a slightly slower rate than the oxygenation
17 pump 30 so that the main pump 38 does not operate without a blood
18 flow supply.
19 Although two collapsible bags 18, 36 are described,
lt should be noted that a single partitioned bag may be used in
21 accordance with this invention. The collapsible nature of the
22 bags, besides limiting blood-gas interfaces, helps prevent a
23 massive air embolism. Should blood in either bag 18 or 36,
24 for some reason, be emptied and collapse occur, air which could
enter through leaks in the cardiopulmonary bypass system 10 are
26 prevented from being pumped in~o the patient's circulatory
27 system.
28 A recirculation path is defined by a tube 39 coupling
29 blood from the second bag 36 to the first bag 18, providing
pressure relief to equalize pressure between the two bags 18,
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1 36. Excess pressure would tend to be present in the second
2 collapsible bag 36 in the absence o the recirculation path,
3 because of the faster pump rate of the oxygenation pump 30 with
4 respect to the main pump 38.
S The main pump 38 is preferably a roller blood pump
6 coupled to the second collapsible bag 36 for returning the
7 oxygenated and warmed blood to the patient's circulatory system.
8 The main pump 38 maintains a blood flow rate invariant with
9 respect to a varying impedance or load of the human circulatory
system as experienced by the pump 38, despite the fact that the
11 impedance or load provided by the patient's circulatory system
12 varies with the patient's physical state. For example, a
13 constriction in the patient's circulatory system causes an
14 increased impedance, yet blood is returned to the patient at
a rate independent of that physical state.
16 A variable speed main pump motor 40 coupled to the
17 main pump 38 drives the pump 38 at a desired controllable
18 blood flow rate in response to a signal fed from controller
19 means or a rate setting control 42. The rate setting
control 42 may simply be an amplifier circuit providing an
21 error signal tending to drive the variable speed pump motors
22 at a rate equal to the venous blood flow. A preferred embodi-
23 ment given by way of example provides a rate setting control
24 42 comprising an amplifier circuit 44, a servo motor 46, a
speed reducer 48 coupled to the servo motor, a variable
26 impedance or a potentiometer 50 mechanically coupled to the
27 speed reducer 48 and a control knob 52 on ~he potentiometer
28 shaft. Rate setting control 42 is responsive to a signal
29 from the transducer 16 to provide the variable speed pump
motor 40 with a signal from the potentiometer 50, which
31 adjusts the signal from a voltage source 51 to drive the main
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1 pump 38 at a flow rate corresponding to the blood volume in the
2 collapsible bag 18. The blood volume in the collapsible bag 18
3 is maintained at a predetermined level such that the return
4 blood flow rate is held substantially equal to the venous blood
S flow. The control knob 52 coupled to the potentiometer 50 can
6 be used to manually override the rate setting control 42 to
7 exercise supervisory control of the flow rate of the main pump 38.
8 The amplifier circuit 44 amplifies a bipolar null
9 referenced signal from the transducer 16 to provide a signal
sufficient to drive the servo motor 46. This signal is bipolar
11 in that it may represent deviations from a null in either of two
~, 12 directions corresponding to either an increase in pressure
13 exerted on the transducer 16 by the confined gas volume 22 or a
~'~ 14 decrease in pressure exerted by the confined gas volume 22. In
setting up the system the pressure within the confine~ gas
, 16 volume 22 may be equalized at ambient by a closeable outlet (not
~,~; 17 shown) in the cylinder 23, the outlet being shut when a desired
18 blood level is reached in the standpipe 14. The servo motor 46
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19 rotates in accordance with the polarity of the transducer signal
t'i 20 tending to rotate the potentiometer 50 in accordance with the
21 blood volume in the collapsible bag 18, as sensed-by the
22 transducer 16.
23 The speed reducer 48 may be a gear reduction system
24 coupled between the servo motor 46 and the potentiometer 50,
` 25 reducing the angular rotation of the potentiometer 50 with
26 respect to the angular rotation of the servo motor 46 thereby
27 providing an adjustable gain in the system. Gain is adjusted
28 to allow time for ehanges in the pump rate of the main pump 38
29 to influence blood volume changes sensed by the transducer and
further rotation of the servo motor without excessive overtravel
31 of the potentiometer 50.
32 The setting of the potentiometer 50 determines the
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1 speed of the variable speed pump motor 40 which in turn deter-
2 mines the flow rate of the main pump 38. An adjustable re-
3 sistance 54 in the motor 40 energizing circuit permits further
4 adjustment to maintain a pump rate through the oxygenation
pump 30 in excess of that through the main pump 38, such that
6 a flow is recirculated back from the second collapsible bag 36
7 to the first bag 18 and the main pump 38 does not operate
8 without a blood supply.
9 Dial indicia 53 juxtaposed adjacent the control knob
52 indicates the instantaneous rate at which the main pump 38 is
ll being driven. The knob 52 may be manually rotated by overcoming
12 the torque supplied by the servo motor 46 through the speed
13 reducer 48. A slip clutch or a friction coupling between the
14 speed reducer 48 and the potentiometer 50 is suitable for a motor
46 of greater torque, but this arrangement would not comparably
16 restore the knob 52 to the proper setting when released.
17 An outlet tube 56 whose exterior surface is hermetically
18 joined to the bag 36 can be closed by a clamp 57 to permit ex-
19 haustion of interior air in the same fashion as the first bag 18.
A reservoir 58 is provided for receiving and storing an
21 excess quantity of blood from the cardiopulmonary bypass system
22 10 and for increasing the volume ~f the blood in the cardio-
23 pulmonary bypass system 10 by releasing such blood to the second
24 bag 36 through a valve 59. A valve 60 in the conduit from the
- 25 main pump 38 may be used to tap off blood from the cardiopulmonary
26 bypass system 10. The valves 59, 60 used to add blood to the
27 reservoir 58 and to release blood to the cardiopulmonary bypass
28 system 10 may be manually actuable or may be of a type actuable
29 by an electrical signal. For example, a perfusion flow servo
system is described in the Turina et al. article in the March
31 1973 issue of Biomedical En~ineerin~, previously cited. A
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1 cardiotomy tube (not shown) may also be coupled into the reservoir
2 58 to provide a blood source to the reservoir 58. The cardio~omy
3 line is used to remove blood which collects adjacent severed
4 veins and arteries resulting from incisions during an operation.
The blood, having been suctioned off from the patient, is in
6 a frothy condition and a debubbler (not shown) is typically used
7 to reduce the frothy condition of the blood before it enters the
8 reservoir 58.
9 To review the operation of the cardiopulmonary bypass
system 10, the first collapsible bag 18 is generally di~posed at a
11 level beneath that of the patient so as to promote a gravity
12 blood feed. Initially, blood is added to the first collapsible
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13 bag 18 with the bag clamps 21, 57 released. Ambient air pres$ure
14 is established in the interior volume 22 and the transducer 16 by
opening a valve (not shown) or disconnecting the standpipe 14 from
16 the cylinder 23. Blood is added until the blood level in the
17 standpipe 14 reaches a reference or priming level 62, aft~r which
18 the standpipe 22 is then reconnected to the sterility barrier 24
19 and the transducer 16. Thus the pressure in the confined volume
22 is initially equalized with respect to ambient.
21 Air that is present in the first and second collapsible
22 bags 18, 36 is forced out, either manually or by filling the bags
23 18, 36, and the outlets 19, 56 are then closed by the clamps
24 21, 57. The blood air interfaces within the bags 18, 36 are
thus minimized.
26 Venous blood flows under gravity into the first
27 collapsible bag 18, whose volume then varies in accordance with
28 the rate of blood flow therethrough. This volume establishes
29 the blood level in the standpipe 14, and as previously described
fractional changes in the blood volume within the bag 18 cause
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1 much larger variations in the pressure exerted on the transducer
2 16. Though the transducer 16 signal is generally referenced to
3 ambient pressure, an inverted U-tube arrangement (not shown) may
4 be used to provide a negative pressure head so that the transducer
may be arbitrarily oriented where the level of the collector means
6 12 varies from the position depicted in the embodiment of Fig. 1
7 and is, for example, disposed closer to the level of the patient.
8 The transducer 16 signal is applied to the amplifier
9 circuit 44, providing an energizing signal to the servo motor 46,
which rotates at a rate determined by signal amplitude and in a
11 direction determined by polarity. Through the speed reducer 48,
12 motor rotation turns the potentiometer 50 in a corresponding
13 direction at a slower speed, also rotating the control knob 52
14 so that the blood flow rate may be read off the dial 53. As
main pump 38 speed is adjusted by the motor 40 controlled by the
16 po~entiometer 50 setting, the blood level is returned toward the
17 null position 62, slowing down or reversing the servo motor 45.
18 Note that the pump motor 40 can continue to operate at or near
19 a substantially constant speed and that the system is stablized
~; 20 by gain adjustment at the speed reducer 48 although other means
21 might also be used.
22 Blood from the firs~ collapsible bag 18 is pumped
- 23 through the revitalization or oxygenation means 28, by the
24 oxygenation pump 30, which provides sufficient pressure to drive
the blood through the membrane oxygenator and heat exchanger 34
26 and to the second collapsible bag 36. Because the oxygenation
27 pump motor 32 speed is also determined by the potentiometer 50
28 8etting, the oxygenation pump 30 pumps blood at a flow rate in
29 excess of the flow rate of the main pump 38 as determined by
the setting of the adjustable resistor 54. Excess pressure
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1 developed by the oxygenation pump 30 withln the second
2 collapsible bag 36 is relieved via the tube 39 which serves
3 as a recirculation path. Blood from the second collapsible
4 bag 36 is then pumped by the main pump 38 to the patient's
circulatory system.
6 It is important to alert a physician to the existence
7 of a low blood volume condition in a patient. This condition
8 may represent internal hemorrhaging and may require that an
9 additional quantity of blood be introduced into the total
system. A physician or assistant, alerted to such a condition
11 may now increase the circulating blood volume by opening the
12 reservoir valve 59, thereby allowing blood to flow into the
13 second collaps;ble bag 36. Also, or alternatively, the
14 physician may manually override the knob 52, thereby in-
creasing the flow rate of the main pump 38 to the human cir-
16 culatory system. It should be recognized that such an increase
17 in the return flow rate without replenishment can only be carried
18 on for a limited period of time without collapse of the bags
19 18 and 36.
Thus, a simple, accurate and sensitive cardiopulmonary
21 bypass system for receiving a variable rate gravity fed venous
22 flow from a human circulatory system, revitalizing the blood and
23 returning it to the circulatory system at a rate substantially
24 equal to the venous flow rate has been described which is
volume alterable and provides means for reducing degrading
26 blood gas interfaces.
27 While the invention has been particularly shown and
28 described and with reference to a preferred embodiment thereof,
29 it will be understood by those skilled in the art that various
changes in form anddetails may be made therein without departing
31 from the spirit and scope of the invention.
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