U.S. patent number 3,572,979 [Application Number 04/809,681] was granted by the patent office on 1971-03-30 for pumps.
Invention is credited to Paul Greville Morton.
United States Patent |
3,572,979 |
Morton |
March 30, 1971 |
PUMPS
Abstract
In a blood pump a fluid pressure circuit is provided which is
operative to feed a variable frequency pulsating flow of water to
one side of a flexible diaphragm. The other side of the flexible
diaphragm is connected into a patient's bloodstream and thus
flexure of the diaphragm results in a pulsatile flow of blood on
said other side of the diaphragm. The specification describes a
number of devices for alternately applying suction and pressure to
the water in said fluid pressure circuit and thereby to the
diaphragm as well as describing one practical form of pumping head
including such a diaphragm.
Inventors: |
Morton; Paul Greville
(Stafford, EN) |
Family
ID: |
10033283 |
Appl.
No.: |
04/809,681 |
Filed: |
March 24, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Mar 22, 1968 [GB] |
|
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14005/68 |
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Current U.S.
Class: |
623/3.21;
417/427; 604/151; 128/DIG.3; 600/16; 417/390 |
Current CPC
Class: |
F04B
43/113 (20130101); A61M 60/40 (20210101); Y10S
128/03 (20130101); A61M 60/894 (20210101); A61M
60/268 (20210101); A61M 60/892 (20210101) |
Current International
Class: |
A61M
1/10 (20060101); F04B 43/00 (20060101); F04B
43/113 (20060101); F04b 009/08 (); F04b 017/00 ();
F04b 035/00 () |
Field of
Search: |
;103/152,45
;417/390,(Inquired) ;128/1 (Rand/ Heart-Lung/ Digest)/ |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Freeh; William L.
Assistant Examiner: Vrablik; John J.
Claims
I claim:
1. An artificial heart pump for connection into a vascular system
including:
a diaphragm pump having first and second chambers separated by a
flexible diaphragm, the first chamber having a first valve through
which it can receive blood from the vascular system and a second
valve through which it can deliver blood to the vascular system,
the second chamber being connected to hydraulic fluid operated
control means which causes a pulsating flow of blood through the
first said chamber;
the hydraulic fluid operated control means including:
a reservoir of hydraulic fluid,
a first pump for pumping fluid from the reservoir into the second
chamber of the diaphragm pump to cause blood to flow from the first
chamber through the said second valve and into the vascular system,
and
a second pump for pumping fluid from the second chamber of the
diaphragm pump into the reservoir to cause blood from the vascular
system to flow into the first chamber of the diaphragm pump through
the said first valve
a spool valve submerged in the hydraulic fluid and comprising a
valve body having first, second and third ports therein and a
two-land spool slidably mounted within the valve body;
means connecting the first port to the outlet from the first
pump;
means connecting the second port to the inlet to the second
pump;
means connecting the third port to the second chamber of the
diaphragm pump; and
means for reciprocating the two-land spool within the valve body so
as to connect the second chamber of the diaphragm pump
alternatively with the outlet of the first pump and the inlet of
the second pump.
2. An artificial heart pump according to claim 1 in which the spool
valve is disposed within the reservoir of hydraulic fluid.
3. An artificial heart pump according to claim 1 including means
for adjusting the position of the valve body relative to the
two-land spool to vary the times during which the second chamber of
the diaphragm pump is connected with the outlet of the first pump
and the inlet of the second pump.
4. An artificial heart pump according to claim 2 including means
for adjusting the position of the valve body relative to the
two-land spool to vary the times during which the second chamber of
the diaphragm pump is connected with the outlet of the first pump
and the inlet of the second pump.
5. An artificial heart pump according to claim 1 in which the
diaphragm pump comprises:
an outer rigid tubular member having a port in the wall of the
member adjacent one end thereof;
a flexible tubular member disposed within the outer tubular member
and spaced therefrom;
an end fitting at each end of the tubular members for sealing each
end of the inner tubular member to the adjacent end of the outer
tubular member so that the space within the inner tubular member
defines said first chamber and the space between the two tubular
members defines the second chamber;
the said first valve being accommodated in that end fitting which
is adjacent the port in the wall of the outer tubular member;
the said second valve being accommodated in the other end fitting;
and
the means connecting the third port of the spool valve to the
second chamber of the diaphragm pump including means communicating
with the port in the outer tubular member.
Description
This invention relates to pumps for use in cardiac surgery.
The roller-type pump used in present-day cardiac surgery has the
disadvantage that the outflow of blood from the pump is essentially
of a nonpulsating nature thus being different from the natural
outflow of blood from a heart, and furthermore the very localized
squeezing action applied by the rollers through a flexible
diaphragm to the blood itself during operation of such a
roller-type pump results in damage to the constituents of the
blood.
According to this invention, a pump for use in cardiac surgery
includes a housing separated into two areas by a flexible
diaphragm, one of the areas being adapted for connection into a
patient's bloodstream for taking over the function of the patient's
heart, and the other area forming part of a control fluid circuit
which is operable to apply a pulsating control fluid pressure to
said other area whereby to cause a pulsating flow of blood from
said one area.
Preferably, two lines are provided from said one area for
connection into the patient's bloodstream, each line being provided
with a nonreturn valve and the valves being arranged so that one
valve permits flow into said one area and the other valve permits
flow from said one area.
The housing and the flexible diaphragm may be in the form of tubes,
in which case the diaphragm tube is mounted coaxially within the
housing tube and is sealed to the latter at its ends, the bore of
said tube constituting said one area and an annular space between
said tubes constituting said other area, and said nonreturn valves
are carried by end fittings for the housing tube.
It will be appreciated that the frequency of pulse of said
pulsating control fluid pressure may be varied so as to vary the
frequency of the pulsating flow of blood.
In a preferred form of this invention the control fluid in the
control fluid circuit is an incompressible fluid.
The control fluid circuit may include first conduit means providing
communication between said other area and a pressure source of said
control fluid, second conduit means providing communication between
said other area and a suction source of said control fluid, valve
means for controlling communication between said other area and
said pressure source on the one hand and said suction source on the
other hand, and actuating means adapted to actuate said valve means
such that the control fluid pressure and the suction pressure are
applied separately to said other area whereby to apply said
pulsating control fluid pressure.
The valve means may comprise a spool valve unit and, where the
control fluid is an incompressible liquid (for example water), the
spool valve unit may be mounted within a reservoir of the control
liquid so as to be completely submerged within the liquid.
The present invention conveniently enables a blood pump to be
produced for use in cardiac surgery which is sterile, easily
cleaned, rugged, easily operated and cheap, and which can provide a
pulsating outflow of blood without subjecting the blood to a
localized squeezing action, and furthermore, which may be adjusted
to provide a pulsating blood flow of a desired frequency so as to
simulate the output of a heart.
Embodiments of this invention will now be described, by way of
example, with reference to the accompanying drawings, of which:
FIG. 1 is a schematic diagram illustrating the principle of
operation of a blood pump in accordance with this invention,
FIG. 2 illustrates a practical embodiment of a valve and valve
actuating mechanism for a blood pump according to this
invention,
FIG. 3 is a diagram illustrating the relative positions and the
profiles of the cams employed in the embodiment of FIG. 2,
FIG. 4 is a second practical embodiment of a valve and valve
actuating mechanism for a blood pump according to this
invention,
FIG. 5 is a modification of the embodiment of FIG. 4,
FIG. 6 is a third practical embodiment of a valve and valve
actuating mechanism for a blood pump according to this
invention,
FIG. 7 illustrates a practical embodiment of a pumping head for use
in a blood pump in accordance with this invention,
FIG. 8 is a schematic circuit diagram of electrical means for
operating the actuating device according to another preferred
embodiment of the invention, and
FIG. 9 shows a circuit waveform of the pressure signal applied to
the pipe 18 of FIG. 5.
Referring to FIG. 1, a blood pump includes a pumping head 10 which
comprises a housing 11 divided internally into two areas 12 and 13
by a flexible diaphragm 14.
The area 12 on one side of the diaphragm 14 is provided with two
nonreturn valves 15 and 16 arranged so that one permits flow into
the area 12 and the other permits flow out from the area 12. The
pumping head 10 is adapted to be connected into the patient's blood
system by way of the nonreturn valves 15 and 16, the area 12
providing a bypass around the patient's heart.
The area 13 on the other side of the diaphragm 14 forms part of a
control fluid circuit. The control fluid circuit is a closed
circuit, that is a circuit in which no fluid losses have to be made
up. The preferred fluid is water. The area 13 is connected to a
device 17 by a pipe 18. The control fluid circuit also includes two
centrifugal pumps 19 and 20, a reservoir 21 and pipes 22 to 26
respectively connecting the output of the pump 19 to the device 17,
the input of the pump 19 to the reservoir 21, the output of the
pump 20 to the reservoir 21, the input of the pump 20 to the device
17, and the reservoir 21 to the device 17. The surface of the water
contained within the reservoir is open to atmosphere.
The device 17 includes valve means for connecting the pipe 22 to
the pipe 18 or the pipe 26 so that the output of the pump 19 is
placed in conduit communication with either the area 13 or the
reservoir 21. The device 17 also includes valve means for
connecting the pipe 25 to the pipe 18 or to the pipe 26 so that the
input of the pump 20 is placed in conduit communication with either
the area 13 or the reservoir 21.
In operation of the blood pump, the pumps 19 and 20 are driven
continuously so that water is circulated around the closed control
fluid circuit. The water pressure in the area 13 governs the
position of the diaphragm 14 and movement of the diaphragm causes
blood to be drawn into or expelled from the area 12 through the
appropriate valve 15 or 16. It will be seen that when the output of
the pump 19 is first connected to the area 13 through the actuating
device 17, the diaphragm 14 is deflected suddenly so that blood is
suddenly expelled from the area 12. It will also be seen that when
the conduit communication between the output of the pump 19 and the
area 13 is blocked by the diversion of the water through the device
17 to the reservoir 21, and when the input of the pump 20 is
connected to the area 13 through the device 17, suction pressure is
applied by the pump 20 to the diaphragm 14 drawing the diaphragm
towards the device 17 and sucking blood into the area 12. It will
be understood that by suitably controlling the interconnection
between the pipes 22, 25 and 26 on the one side of the device 17
and pipe 18 on the other side of the device 17 the pressure in the
area 13 acting on the flexible diaphragm can be varied in a
pulsating manner so that the outflow of blood from the area 12 is
correspondingly pulsatile. Furthermore, it will be understood that
the frequency of pulse can be varied to suit requirements.
It will be appreciated that various refinements and modifications
to the system illustrated in FIG. 1 may be employed without
departing from the basic principle of operation. For example, it is
not essential to have a closed control water circuit; where the
water supply pressure is suitable the pipe 22 may be connected to a
domestic water tap, thus dispensing with the pump 19. Furthermore,
it is not essential to connect the pipe 25 to the pipe 26 when it
is not required to apply the suction pressure to the area 13; the
pipe 25 may simply be blocked by any convenient means. Moreover, it
is not essential to employ a centrifugal pump 20; any other
suitable means for providing the required suction pressure may be
employed, for example a standard venturi device.
Experiments have been carried out and these show that, in a blood
pump in accordance with this invention, the pump 19 should
preferably be capable of supplying water at a rate of flow
sufficiently great to eject the full stroke volume (that is up to
30 ccs. in the case of a dog and up to 100 ccs. in the case of a
man) from the area 12 in less than 0.1 seconds. This needs a water
pump capable of delivering, in the case of a dog, greater than 4
gallons per minute, and for a man, greater than 131/2 gallons per
minute. The suction device 20 should preferably be capable of
applying a vacuum of more than 20 feet of water at flow rates of
about 1 gallon per minute and 4 gallons per minute for dog and man
respectively.
Referring to the embodiment illustrated in FIGS. 2 and 3, there is
illustrated a practical form of the device 17 of FIG. 1. Where
appropriate the reference numerals of FIG. 1 have been applied to
the corresponding parts. The centrifugal pump 20 is replaced by a
water jet pump 30 which operates on the venturi principle. The
inlet of the pump 30 is connected to the reservoir (not shown)
through a pipe 31, and the pipe 25 is connected to an intermediate
port 32 of the pump 30.
The three pipes 22, 25 and 26 are passed through a valve mechanism
of the actuating device 17. In this arrangement the pipe 26 is a
branch from the pipe 22, the connection being upstream of the valve
mechanism.
The valve mechanism includes three pairs of opposed anvils, the
upper anvil 33 of each pair being carried by a fixed bar 34 and the
lower anvil 35 of each pair being carried by the end of a
corresponding one of three levers 36 which are pivotally mounted at
their other ends on a rod 37. The actuating means for the valve
mechanism comprises a cam shaft 38 which extends below the three
lower anvils 35 and carries three cams 39, 40, 41, which each
cooperate with a corresponding one of the levers 36. The cams 39
and 41 are similarly profiled and similarly positioned relative to
the cam shaft 38 so that they impart similar movements to their
respective cooperating levers 36 whereby they control flow through
the pipes 25 and 26 respectively. The cam 40 controls flow through
the pipe 22. The relative positions and profiles of the cams 39, 40
and 41 can be seen from FIG. 3.
In operation of a blood pump incorporating the arrangement
described above, the cam shaft 38 is rotated about its axis. Thus
it will be seen that when the cams 39 and 41 hold their
corresponding lower anvil member in their uppermost positions,
these anvil members 35 cooperate with their corresponding upper
anvil members 33 to close the pipes 25 and 26 which are made of
rubber or any other suitable flexible material, leaving the pipe 22
fully open and supplying water under pressure to the area 13. As
the cam shaft 38 rotates, the lower anvil members 35 operated by
the cams 39 and 41 fall, opening the corresponding pipes 25 and 26,
and thus diverting some of the water under pressure from the pipe
22 to the pipe 26 and also applying suction pressure to the area 13
through the pipe 25 so as to initially gradually reduce the
pressure in the area 13 until rotation of the cam shaft 38 closes
the pipe 22 by way of the cam 40. When pipe 22 is closed no water
under pressure is supplied to the area 13 and full suction pressure
is applied. Further rotation of the cam shaft 38 opens the pipe 22
and then closes the pipes 25 and 26, and it will be seen that as
the cam shaft 38 rotates, a pulsating control water pressure is
applied to the diaphragm 14.
It will be understood that the variation of pressure applied to the
diaphragm 14 during one rotation of the cam shaft 38 can be varied
by suitable selection of cam profiles and cam positions. Moreover,
the frequency of pulse of the pulsating control pressure applied
and thus of the pulsating flow of blood induced by the blood pump
can be altered by varying the speed of rotation of the cam shaft
38. A tap (not shown) may be provided in pipe 22 whereby the flow
of water flowing through the pipe 22 may be altered so as to
correspondingly alter the amount of blood which is caused to flow
by the blood pump.
Referring to FIG. 4, there is illustrated a second practical form
of the device 17 of FIG. 1. Where appropriate the reference
numerals of FIG. 1 have been applied to the corresponding parts.
The device 17 in this embodiment comprises a spool valve unit which
is immersed within the water contained within the reservoir 21.
Consequently the pipe 26 connecting the actuating device 17 to the
reservoir 21 is not required. The spool valve unit has a balanced
two-land spool 42. The spool 42 is mounted for reciprocatory
movement within a valve body 43. The pipes 18, 22 and 25 are
connected to the valve body in such a way that the spool 42
connects either the pipe 22 or the pipe 25 to the pipe 18 and
blocks the other. A bearing housing 44 is mounted on the valve body
43 so as to support a crank 45 for rotation. The radially outer end
of the crank 45 is pivotally connected to one end of a connecting
rod 46, the other end of the connecting rod being pivotally
connected to an extension member 47 carried by the valve spool
42.
In operation of a blood pump incorporating the actuating device
described above, the crank 45 is rotated continuously so that the
valve spool 42 is reciprocated within the valve body 43 through the
connecting rod 46 and the extension member 47. Reciprocation of the
valve spool 42 connects the pipe 22 or the pipe 25 to the pipe 18
alternately, thus applying pressure or suction to the flexible
diaphragm 14 alternately, as in the arrangement described
hereinbefore with reference to FIGS. 2 and 3. The length of the
connecting rod 46 may be adjusted so that the valve spool 42 dwells
longer in either the pressure applying or suction positions as
required. As in the previous embodiment, the frequency of the
pulsating pressure applied to the diaphragm 14, and thus the
frequency of the pulsating flow of blood expelled from the pump,
may be altered by varying the speed of rotation of the crank 45,
and the flow of the water flowing through pipe 22 may be altered so
as to alter the amount of blood which is caused to flow by the
blood pump.
Location of the spool valve unit below the level of water in the
reservoir 21 permits said valve to be made with liberal tolerances,
since water leakage and air entrainment due to a poorly fitting
spool are no problem.
Referring to FIG. 5, this shows a modified form of the arrangement
of FIG. 4 and like parts have been given the same reference
numerals. In this modified arrangement, the spool valve 48 is
carried by a screw device 67 which is arranged with the
longitudinal axis of its threaded part 68 vertical and with the
threaded part engaged in two longitudinally aligned tapped blocks
69, 70 carried one at each end of the valve body 43. The screw
device 67 is mounted in a fixed structure 71 outside the reservoir
21 in such a way that it is prevented from moving along its
longitudinal axis but may be rotated about that axis. The valve
body 43 is orientated in such a way that the longitudinal axis of
the spool 42 is vertical and is suitably held against lateral
movement so that rotation of the threaded part 68 of the screw
device 67 causes vertical movement of the valve body 43.
In this modified arrangement, the extension member 47 described
with reference to FIG. 4 for connecting the spool 42 to the
connecting rod 46, is replaced by a spring coupling 72 which is
flexible in bending but is fairly stiff in tension. The bearing
housing 44 of FIG. 4 is also dispensed with, the crank 45 being in
the form of an eccentric and being supported by a shaft 73 by which
it is rotatably driven.
The operation of this modified arrangement is the same as for the
arrangement of FIG. 4, except that the adjustment, whereby the
spool 42 dwells longer in the pressure-applying or suction position
as required, is effected by rotation of the screw device 67 so that
the valve body 43 is raised or lowered relative to the spool
42.
Referring to FIG. 6, there is illustrated a third practical form of
the device 17 of FIG. 1 employing a spool valve in a manner similar
to the embodiments of FIGS. 4 and 5. Where appropriate, the
reference numerals of FIGS. 1, 4 and 5 have been applied to the
corresponding parts.
In this arrangement a three-land spool valve 48A is mounted below
the level of water in the reservoir 21 with the longitudinal axis
of its valve spool 42A vertical. The bottom port of the spool valve
48A opens directly into the reservoir 21; the other three ports are
connected to the pipes 18, 22 and 25 in a similar manner to the
spool valve 48 of FIG. 5, so that the spool valve 48A controls the
flow of water through the pipe 18 in much the same way. A
three-land spool valve 49 is also mounted below the water level
within the reservoir 21 with the longitudinal axis of its spool 50
vertical. The spaces below the lower land of each spool valve 48A
and 49 are connected together by a pipe 51 which is also connected
to the space below a piston 52 in a cylindrical 53. The cylinder 53
is also mounted below the water level within the reservoir 21 with
its longitudinal axis vertical. The piston rod 54 of the piston 52
and the valve spools 42A and 50 all extend vertically and are
loaded respectively with weights 55 to 57.
The spool valve 49 has four ports 58 to 61 respectively which are
spaced apart from each other vertically, the lowermost port being
the port 58. The port 58 opens directly into the reservoir 21, the
port 59 is connected to the pressure pipe 22 through a branch pipe
62, the port 60 is connected to the pipe 51 through a branch pipe
63, the port 60 is connected to the pipe 51 through a branch pipe
63, and the port 61 is connected to the suction pipe 25 through a
branch pipe 64. The three lands of the spool 50 are arranged so
that the port 60 communicates with either the port 61 or the port
59, and thus with either suction or pressure, through the space
between the upper and middle lands of the spool, and so that the
port 58 always communicates with the space between the middle and
lower lands of the spool 50 and is never connected to either of the
ports 59 or 61. The cylinder 53 carries an adjustable stop 74 which
is abutted by the topside of the piston 52 at the top of the
piston's stroke.
In operation of a blood pump incorporating the actuating device
described above, the spool valve 48A controls the supply of fluid
pressure to the pumping head 10 through the pipe 18 in much the
same way as has been described above with reference to FIGS. 4 and
5. The difference between the embodiment of FIGS. 4 and 5 and the
present embodiment lies in the actuation of the valve spool
42A.
Starting from the normal rest position in which the valve spools
42A and 50 and the piston 52 are at the bottom of their respective
strokes and in which the ports communicating with the respective
pressure-applying pipes 22 and 62 are open, when water under
pressure is supplied through the pipes 22 and 62, it is applied to
the flexible diaphragm 14 of the pumping head 10 through the spool
valve 48A and the pipe 18 and to the area under the piston 52
through the pipes 63 and 51. The piston 52 moves vertically upwards
against the action of the weight 55, until it abuts stop 74,
whereupon there is a buildup of water pressure beneath the lower
lands of the spools 42A and 50 forcing the spools to move
vertically upwards against the action of the respective weights 56
and 57. The inertia of this upward movement carries the spools 42A
and 50 through the point at which they close the respective ports
communicating with the respective pressure-applying passages 22 and
62 to the position in which they open the ports which are in
communication with the respective suction-applying passages 25 and
64. It will now be appreciated that suction pressure is applied to
the flexible diaphragm 14 and to the area below the piston 52 so
that the piston 52 descends under the influence of its weight
55.
Once the piston 52 reaches the bottom of the cylinder 53 the
suction pressure acts upon the underside of the lower lands of the
valve spools 42A and 50 causing them to descend under the influence
of their respective weights 56 and 57. This downward movement
carries the spools 42A and 50 through the point at which they close
the respective ports communicating with the respective
suction-applying passages 25 and 64 to the position in which they
open the ports which are in communication with the respective
pressure-applying passages 22 and 62. It will be understood that
once this cycle of motion of the valve spools and the piston has
been initiated, it will continue as long as water pressure and
suction pressure are applied through the respective pipes 22 and
62, and 25 and 64.
The magnitude of the weight 56 may be adjusted so that the valve
spool 42A dwells longer in either the pressure-applying or
suction-applying positions as required. The frequency of the
pulsating flow of water supplied to the diaphragm 14 through the
pipe 18 may be altered by adjusting throttle valves 75 provided in
the pipes 51, 62 and 64, or by adjusting the position of the stop
74, or by altering the magnitude of the weights 55 to 57, and the
volume of water flowing into the pipe 18 may be altered by
adjusting throttle valves 76 provided in the pipes 22 and 25.
Springs may be employed in place of the weights 55 to 57. Such
springs would preferably be compression springs acting on the
topside of the spools 42A and 50 and of the piston 52. However,
should the weight of the spools 42, 50, and the piston 52 be
sufficient to ensure movement of the spools through the midposition
(that is the position shown in FIG. 6 where the lands block both
the pressure and the suction ports) then external loading means
such as the weights 55 to 57 or the compression springs referred to
above may be disposed with.
It will be appreciated that both the spool valves 48A and 49 may be
replaced by two land spool valves 48 of FIG. 5. However, in this
embodiment it would be necessary for the valve spool of such a
two-land spool to be very good sliding fit in the valve body in
order to minimize the likelihood of water under pressure from the
pipes 22 or 62 leaking past the lower land into the pipe 51. Use of
three-land spools as in the arrangement of FIG. 6 avoids this
problem.
Referring to FIG. 7, there is illustrated a suitable form of
pumping head 10 which may be employed in a blood pump in accordance
with this invention. The pumping head 10 is generally tubular in
form with the nonreturn valves 15 and 16 being located at each end
of the head 10. Extending between the two valves 15 and 16 and
surrounding the appropriate inlet or outlet of the respective valve
15, 16, is a thin tube of flexible material, such as suitable
rubber or polythene, which acts as the flexible diaphragm 14
separating the areas 12 and 13. Coaxially surrounding the tubular
diaphragm 14 is a thick tube 65 of a transparent plastics material,
although it is to be understood that any other suitable material
may be employed. The tube 65 is clamped at each end to the
respective valve body of the corresponding valve 15, 16, by screwed
end fittings 66. The tubular diaphragm 14 has enlarged shaped end
portions 67 which fit into correspondingly shaped annular grooves
68 in the respective valve bodies; the shaped end portions 67 are
clamped between the tube 65 and said respective valve bodies by the
end fittings 66. The pipe 18 extends radially through the wall of
the tube 65 and opens into the area 13 at a position adjacent the
inlet valve 15 via an annular water feed groove 18A formed in the
tube wall 65, which groove prevents the diaphragm 14 from blocking
the pipe opening in operation.
In operation of the pumping head 10 illustrated in FIG. 7, it will
be seen that when water under pressure is supplied through the pipe
18 it forces its way around the tubular flexible diaphragm 14
inside the thick tube 65 and presses the tubular flexible diaphragm
14 radially inwards, thus reducing the volume of the area 12
between the two valves 15, 16 and within the tubular flexible
diaphragm 14 so as to force blood out of that area 12 through the
nonreturn outlet valve 16. Furthermore, it will be understood that
when the pressure of the water supplied through the pipe 18 is
subsequently reduced and replaced by suction pressure, the flexible
diaphragm 14 is sucked radially outwards until it contacts the
inner surface of the tube 65, thereby increasing the volume of the
area 12 and drawing blood into that area 12 through the nonreturn
valve 15.
It will be appreciated that the pipe 18 opens into the space 13
adjacent the valve 15 to ensure that a maximum amount of blood may
be fed, if required, through the valve 16 during the pressure
applying stroke.
All the arrangements described so far have employed an essentially
mechanical means for operating the device 17. It is also possible
to use electrical means for this purpose, and a suitable circuit is
illustrated in FIG. 8. A high-gain amplifier 100, a positive
feedback resistor 101, a negative feedback network 102 and a
capacitor 103 together form a multivibrator which produces an
output signal of the form shown in FIG. 9. This signal is applied
to the coil 109A of a reed relay, whose contact 109B in turn drives
the coil 110A of another relay. The contact 110B of the latter
relay energizes one or other of two solenoids 111 and 112 according
as the coil 110A is energized or not. The solenoids 110 and 112 are
connected to opposite ends of a spool valve 113 which may be
similar to the spool valve 48 of FIG. 5. Thus the pressure signal
applied to the pipe 18 will vary substantially, as the waveform of
FIG. 9.
The circuit includes a pair of linked switches 104A and 104B. With
these switches in the positions shown, the multivibrator is
free-running; by moving the switches to their other positions, the
multivibrator can be synchronized with a patient's own heartbeat by
means of signals fed in on line 114 from a cardiograph.
The operation of the circuit is as follows. Assume that the
switches 104A and 104B are in the free-running positions as shown,
and that the output of the amplifier 100 is slightly positive. This
positive output is fed back through the resistor 101 to the
positive input to the amplifier, driving its output more positive,
so that it immediately saturates with its output at the maximum
positive level. This positive output is also applied through the
network 102 to the negative input of the amplifier 100; however,
the capacitor 103 is also connected to this negative input, so that
the voltage at this negative input can only rise gradually as the
capacitor charges through the network 102. Eventually however the
voltage at the negative input of amplifier 100 will exceed the
voltage at the positive input from resistor 101, and the output of
the amplifier will therefore go negative. Resistor 101 will now act
to hold the output at its maximum negative level, and this negative
level will be fed back through the network 102 to charge the
capacitor 103 in the opposite direction. Eventually, the signal at
the negative input of amplifier 100 will again overpower the signal
from the resistor 101 at the positive input, and the output will go
positive one more. The circuit will continue to switch between
positive and negative outputs in this manner indefinitely.
The network 102 consists of two separate paths. When the output of
amplifier 100 is positive, diode 105 is forward-biassed and current
can flow through the variable resistor 106, diode 107 being cut
off; when the output of amplifier 100 is negative, current can flow
through diode 107 and variable resistor 108, diode 105 being cut
off. By adjusting the resistors 106 and 108 the durations of the
positive and negative outputs from the amplifier 100, i.e. of the
times t1 and t2 respectively (FIG. 9), can be individually
adjusted.
In order to operate the circuit in the synchronized mode, the
switches 104A and 104B are moved to their other positions. The
signals on line 114 are amplified by an amplifier 115 and coupled
over a coupling network 116. Also a variable resistor 117 is
connected in series with resistor 106, thus increasing the period
t1. This decreases the natural frequency of the multivibrator, so
that the synchronizing signal can increase its frequency again to
the required value.
The power supply to the relay coil 110A and to the solenoids 111
and 112 may be the AC mains.
* * * * *