Pumping drive unit

A pumping unit is disclosed which alternately applies a positive and a negative pressure, both of given values, to aa drive chamber of an artificial heart. In a first and a second embodiment, air of an elevated pressure which is discharged by an air compressor is fed through a positive pressure accumulator and a positive pressure open/close valve to the drive chamber, and a negative pressure from an air decompressor is fed through a negative pressure accumulator and the negative pressure open/close valve to the drive chamber. Alternating open periods are assigned to the positive and the negative pressure open/close valve. During the open period, each valve is opened and closed in a manner corresponding to the prevailing pressure in the drive chamber so as to maintain the pressure at a constant value. In a third embodiment, a positive pressure regulator valve is interposed between the air compressor and the positive pressure accumulator, and the positive pressure open/close valve is interposed between the positive pressure accumulator and the drive chamber while a negative pressure regulator valve is interposed between the air decompressor and the negative pressure accumulator, and the negative pressure open/close valve is interposed between the negative pressure accumulator and the drive chamber. The positive and the negative pressure open/close valves are opened in an alternate fashion. The positive pressure regulator valve is operated with a given duty cycle which depends on the prevailing pressure from the positive accumulator so that such pressure is maintained at a constant value. The negative pressure regulator valve is operated with a given duty cycle which depends on the prevailing pressure of the negative accumulator so that such pressure is maintained at a given value.

FIELD OF THE INVENTION 
The invention relates to a pumping drive unit which supplies an alternation 
of a positive and a negative fluid pressure to a pumping unit which is 
effective to pump another kind of fluid in response to such alternation, 
and more particularly, to a control over the driving pressure of the drive 
unit associated with an artificial heart. 
BACKGROUND OF THE INVENTION 
By way of example, U.S. Pat. No. 4,546,760 issued to Suzuki et al discloses 
an artificial heart driving apparatus which alternately supplies an air of 
a given positive pressure and a suction of a given negative pressure. Air 
discharged from an air compressor is fed through a first positive pressure 
open/close valve to a positive pressure accumulator, the pressure of which 
is detected by a pressure sensor, with the first open/close valve being 
controlled to be turned on and off so that the accumulator maintains a 
pressure within a given range. Air of a positive pressure from the 
positive pressure accumulator is supplied to an artificial heart through a 
second positive pressure open/close valve by opening the latter during the 
systole of the artificial heart. On the other hand, a negative pressure 
from a decompressor (vacuum suction unit) is applied through a first 
negative pressure open/close valve to a negative pressure accumulator, the 
pressure of which is also detected by a pressure sensor, with the first 
open/close valve being controlled to be turned on and off, so that the 
negative pressure accumulator maintains a pressure within a given range. 
The negative pressure from the negative pressure accumulator is applied to 
the artificial heart through a second negative pressure open/close (O/C) 
valve by opening the latter during the diastole of the artificial heart. 
The positive and the negative pressure alternately applied to the 
artificial heart are substantially equal to the pressures which prevail in 
the positive and the negative pressure accumulator, respectively. In this 
manner, the first positive pressure and negative pressure valves in 
combination with the positive pressure and the negative pressure sensor 
are effective to determine the magnitude of the positive pressure and the 
negative pressure which are effective to drive the artificial heart for 
contraction and expansion, respectively, while the second positive 
pressure and negative pressure valves are effective to switch between the 
positive and the negative pressure as fed to the artificial heart. 
It will be appreciated that when either accumulator has an increased 
capacity, the magnitude of a reduction in the internal pressure of that 
accumulator when the second valve is changed from its closed to its open 
condition remains low, and a variation in the magnitude of a pressure 
supplied to the artificial heart which is caused by the opening and 
closing of the first valves also remains small. If the capacity of the 
accumulator is reduced or the provision of such accumulator is omitted, 
there occurs an overhunting of an increased magnitude when the pressure 
supplied to the artificial heart rises to a given value in response to a 
switching of the second valve from its closed to its open condition, and 
there also occurs a greater variation in the magnitude of pressure 
supplied to the artificial heart which occurs in response to the opening 
and closing of the first valve for pressure regulating purposes. In 
consideration of these aspects, the cited U.S. Patent chooses a capacity 
of the accumulator on the order of 4,000 cc, for example, so that the 
overhunting of the pressure supplied to the artificial heart in response 
to a change of the second valve from its closed to its open condition as 
well as a variation in the pressure supplied to the artificial heart in 
response to the opening/closing of the first valve be maintained small. If 
the capacity of the accumulator is reduced to the order of 300 cc or less, 
there occurs a variation in the pressure supplied to the artificial heart 
during the systole and the diastole which is excessively high. 
It will be noted that in the arrangement mentioned above, a positive 
pressure drive system requires a first and a second open/close valve and a 
negative pressure drive system also requires a first and a second negative 
pressure open/close valve, thus requiring an increased number of valve 
units. The provision of the second valves is essential in order to achieve 
the pumping operation, and it may be noted that the first valves may be 
omitted by providing accumulators of sufficient capacity and providing a 
constant torque control of the compressor and the decompressor or adding a 
constant pressure relief valve. However, there may be experienced a 
difficulty in regulating the driving pressure, in particular, in achieving 
a pressure regulation of a relatively small magnitude. 
SUMMARY OF THE INVENTION 
It is a first object of the invention to provide a pumping drive unit which 
produces a reduced variation in the pressure supplied to a pumping unit 
and which is capable of reducing the capacity of or substantially 
eliminating accumulators. 
It is a second object of the invention to provide a pumping drive unit 
which enables a pressure regulation while reducing the number of valve 
units used and reducing the capacity of accumulators. 
The both objects mentioned above are achieved by a first embodiment of the 
invention comprising pressure detecting means for detecting a fluid 
pressure which prevails in a fluid space extending from a positive 
pressure open/close valve unit and a negative pressure open/close valve 
unit, which operate to supply a positive and a negative pressure from a 
positive pressure accumulator and a negative pressure accumulator, 
respectively, to a pumping unit, to a drive chamber of the pumping unit; 
and drive pressure control means operative during a preset systole of the 
pumping unit to close the positive pressure O/C valve unit in response to 
a pressure detected by the pressure detecting means which is equal to or 
greater than a first value and to open the positive pressure O/C valve 
unit when the detected pressure is less than the first given value and 
operative during a preset diastole of the pumping unit to close the 
negative pressure O/C valve unit in response to a pressure detected by the 
pressure detecting means which is equal to or less than a second given 
value and to open the negative pressure O/C valve unit when the detected 
pressure exceeds the second given value. 
In the operation of the first embodiment, during the systole, the positive 
pressure O/C valve unit is opened to apply a pressure from the positive 
pressure accumulator to the pumping unit. The pressure supplied to the 
pumping unit is detected by the pressure detecting means. If the pressure 
detected by the detecting means is equal to or greater than the first 
given value (a positive pressure), the drive pressure control means closes 
the positive pressure O/C valve unit, and opens the positive pressure O/C 
valve unit if the detected pressure is less than the first given value. In 
this manner, the positive pressure O/C valve unit is opened and closed to 
feed a constant pressure or so that the positive pressure supplied to the 
pumping unit assumes the first given value. 
During the diastole, the negative pressure O/C valve unit is opened to 
apply a pressure from the negative pressure accumulator to the pumping 
unit. The pressure supplied to the pumping unit is detected by the 
pressure detecting means. If the detected pressure is equal to or less 
than the second given value (a negative pressure), (more negative) the 
drive pressure control means closes the negative pressure O/C valve unit, 
and opens it if the detected pressure exceeds the second given value. In 
this manner, the negative pressure O/C valve unit is opened and closed to 
feed a constant pressure or so that the negative pressure supplied to the 
pumping unit assumes the second given value. 
In this manner, the provision of the first positive pressure and the first 
negative pressure open/close valve which have been used in the prior art 
for pressure regulating purposes can be dispensed with. If the capacity of 
the positive and the negative pressure accumulator is reduced, a given 
pressure can be supplied to the pumping unit by maintaining the absolute 
magnitude of the pressure from these accumulators relatively high with 
respect to the driving pressure used in the pumping unit. 
The both objects mentioned above can also be accomplished by a second 
embodiment of the invention comprising a positive pressure open/close 
valve unit interposed between a source of positive pressure fluid and a 
drive chamber of a pumping unit; a negative pressure open/close valve unit 
interposed between a source of negative pressure and the drive chamber, 
pressure detecting means for detecting a fluid pressure in a fluid space 
extending from the both valve units to the drive chamber; and pressure 
regulating control means operative during a preset systole of the pumping 
unit to maintain the positive pressure O/C valve unit open as long as the 
pressure detected by the pressure detecting means remains equal to or less 
than a first given value and to operate the positive pressure O/C valve 
unit with a given duty cycle when the detected pressure exceeds the first 
given value and also operative during a preset diastole of the pumping 
unit to maintain the negative pressure O/C valve unit open as long as the 
pressure detected by the pressure detecting means is equal to or greater 
than a second given value which is less than the first given value and to 
operate the negative pressure O/C valve unit with a given duty cycle when 
the detected pressure is less than the second given value. 
In the operation of the second embodiment, during the systole, the positive 
pressure O/C valve unit is opened to apply a pressure from a positive 
pressure accumulator (or if such accumulator is not provided, from a 
source of positive pressure) to the pumping unit. The pressure supplied to 
the pumping unit is detected by the pressure detecting means. The pressure 
control means maintains the positive pressure O/C valve unit open as long 
as the detected pressure remains equal to or less than the first ates the 
positive pressure O/C valve given value and operates the positive pressure 
O/C valve unit with a given duty cycle when the detected pressure exceeds 
the first given value. Accordingly, the positive pressure O/C valve unit 
is maintained open to permit the pressure supplied to the drive chamber to 
be increased rapidly when the positive pressure O/C valve unit is opened 
while the negative pressure O/C valve unit is closed during the systole 
until the pressure of the drive chamber reaches the first given value. 
When the pressure reaches the first given value, the positive pressure O/C 
valve unit is operated with a given duty cycle, providing a moderate 
pressure rise, thus preventing an overhunting of positive pressure from 
occurring. 
During the diastole, the positive pressure O/C valve unit is closed while 
the negative pressure O/C valve unit is opened to apply a pressure from a 
negative pressure accumulator (or if such accumulator is not provided, 
from a source of negative pressure) to the pumping unit. Again, the 
pressure supplied to the pumping unit is detected by the pressure 
detecting means. The pressure regulating control means maintains the 
negative pressure O/C valve unit open as long as the detected pressure 
remains equal to or greater than the second given value, and operates the 
negative pressure O/C valve unit with a given duty cycle when the pressure 
reduces below the second given value. Accordingly, the negative pressure 
O/C valve unit is maintained open to permit the pressure supplied to the 
drive chamber to be reduced rapidly when the negative pressure O/C valve 
unit is opened while the positive pressure O/C valve unit is closed during 
the diastole when the pressure of the drive chamber is reduced to the 
second given value. When the pressure reaches the second given value, the 
negative pressure O/C valve unit is operated with a given duty cycle to 
provide a moderate pressure fall, thus preventing an overhunting of a 
negative pressure from occurring. 
Accordingly, the first positive pressure and negative pressure O/C valves 
which have been used in the prior art for pressure regulating purposes can 
be dispensed with. The positive and the negative pressure accumulators may 
be of a reduced capacity or omitted, but still a given pressure can be 
supplied to the pumping unit by maintaining the absolute magnitude of the 
pressure of the accumulators (or sources) relatively high with respect to 
the driving pressure for the pumping unit. 
The first object mentioned above can also be accomplished by a third 
embodiment of the invention comprising a positive pressure open/close 
valve unit for supplying a fluid of positive pressure to a pumping unit; a 
positive pressure regulator valve unit disposed between a source of fluid 
of positive pressure and the positive pressure O/C valve unit for opening 
or closing a fluid path therebetween to regulate a fluid pressure supplied 
to the positive pressure O/C valve unit from the source; first pressure 
detecting means for detecting a fluid pressure which prevails between the 
first pressure regulator valve unit and the positive pressure O/C valve 
unit; a negative pressure open/close valve unit for supplying a negative 
pressure to the pumping unit; a negative pressure regulator valve unit 
interposed between a source of negative pressure and the negative pressure 
O/C valve unit to open or close a fluid path therebetween to regulate a 
negative pressure supplied to the negative pressure O/C valve unit from 
the source of negative pressure; second pressure detecting means for 
detecting a fluid pressure which prevails between the negative pressure 
regulator valve unit and the negative pressure O/C valve unit; pressure 
regulating control means operative to maintain the positive pressure 
regulator valve unit open as long as the pressure detected by the first 
pressure detecting means remains equal to or less than a first given value 
and to operate the positive pressure regulator valve unit with a given 
duty cycle when the pressure exceeds the first given value and also 
operative to maintain the negative pressure regulator valve unit open as 
long as the pressure detected by the second pressure detecting means 
remains equal to or greater than a second given value which is less than 
the first given value and to operate the negative pressure regulator valve 
unit with a given duty cycle when the pressure reduces below the second 
given value; and pressure switching control means operative during a 
preset systole of the pumping unit to open the positive pressure O/C valve 
unit and to close the negative pressure O/C valve unit and also operative 
during a diastole to close the positive pressure O/C valve unit and to 
open the negative pressure O/C valve unit. 
In the operation of the third embodiment, during the systole, the pressure 
switching control means opens the positive pressure O/C valve unit and 
closes the negative pressure O/C valve unit, whereby a positive pressure 
is supplied to the drive chamber of the pumping unit. Conversely, during 
the diastole, the pressure switching control means closes the positive 
pressure O/C valve unit and opens the negative pressure O/C valve unit, 
whereby a negative pressure is supplied to the drive chamber of the 
pumping unit. It will be noted that such operation takes place in the 
similar manner as in the prior art. Components used also remain similar as 
those used in the prior art, except for the following differences. 
When the pressure from a positive pressure accumulator (or a corresponding 
location if such accumulator is absent) remains equal to or less than the 
first given value, the pressure regulating control means maintains the 
positive pressure regulator valve unit open, and operates it with a given 
duty cycle when the pressure exceeds the first given value. Accordingly, 
when the positive pressure O/C valve unit is changed from its closed to 
its open condition to cause a rapid reduction in the pressure from the 
positive pressure accumulator, the pressure of the positive pressure 
accumulator can be rapidly returned to its normal value without 
accompanying an overshoot. When the pressure from the negative pressure 
accumulator (or a corresponding location if such accumulator is absent) 
remains equal to or greater than the second given value, the pressure 
regulating control means maintains the negative pressure regulator valve 
unit open and to operate it with a given duty cycle when the pressure 
reduces below the second given value. Accordingly, when the pressure of 
the negative accumulator rapidly increases (meaning a reduction in the 
negative pressure) as a result of switching the negative pressure O/C 
valve unit from its closed to its open condition, the negative pressure 
accumulator can be rapidly returned to its normal negative pressure, again 
without accompanying an overshoot. 
Accordingly, the positive and the negative accumulator may be of a reduced 
capacity or may be dispensed with, but a given pressure can still be 
supplied to the pumping unit by maintaining the absolute magnitude of 
pressure of these accumulators (or sources of pressure) relatively high 
with respect to the driving pressure for the pumping unit. 
Other objects and features of the invention will become apparent from the 
following description of several embodiments thereof with reference to the 
drawings.

DESCRIPTION OF PREFERRED EMBODIMENT 
First Embodiment 
FIG. 1 shows one embodiment of the invention, which is constructed as an 
artificial heart driving apparatus. A right-hand artificial heart 11R and 
a left-hand artificial heart 11L are constructed by flexible diaphragms 
which form partitions between a suction chamber which draws blood of a 
living body and a drive chamber into which a driving air is introduced. 
The suction chamber is connected to a blood drawing piping with a check 
valve interposed therebetween, which permits a fluid flow from the piping 
to the chamber, but blocks a reverse flow. The suction chamber is also 
connected to a blood discharge piping with another check valve interposed 
therebetween, which is effective to permit a flow from the chamber to the 
piping, but blocks a reverse flow. When air of an increased pressure is 
supplied to the drive chamber, the flexible diaphragm compresses the 
suction chamber, whereby a fluid within the suction chamber flows out 
through the blood discharge piping. When a negative pressure is introduced 
into the drive chamber, the flexible diaphragm allows the suction chamber 
to expand, thus drawing fluid from the blood drawing piping into the 
suction chamber. In this manner, by alternately supplying air of a 
positive pressure and a negative pressure to the drive chamber, the 
artificial heart is effective to draw fluid (blood) from the drawing 
piping and to deliver the fluid through the discharge piping. 
The drive chamber of the artificial heart 11R is connected through a tube 
12 to an output port of a positive pressure open/close valve 15 and an 
input port of a negative pressure open/close valve 20 (or an output port 
thereof for a negative pressure). A pressure sensor 23 is disposed to 
detect a pressure or driving pressure which prevails in an air path 
communicating with the drive chamber of the heart 11R. 
The positive pressure O/C valve 15 has an input port which communicates 
with a positive pressure accumulator 16, and the negative O/C pressure 
valve 20 includes an input port which communicates with a negative 
pressure accumulator 21. An air compressor 13 which is driven by a d.c. 
motor 14 supplies compressed air to the accumulator 16 while a 
decompressor (vaccum suction unit) 18 which is driven by another d.c. 
motor 19 draws air from the accumulator 21. It is to be understood that 
the discharge pressure from the air compressor 13 is higher than a range 
of positive pressures (a level c shown in FIG. 5b) required by the heart 
11R while the absolute magnitude of the suction produced by the 
decompressor 18 is lower than a range of negative pressures (a level h 
shown in FIG. 5b) required by the heart 11R. 
The valves 15 and 20 are similar to solenoid valves which are specifically 
disclosed in cited U.S. Pat. No. 4,546,760. Specifically, each valve is 
opened to pass a fluid flow when its associated electrical coil is 
energized, and is closed to interrupt a fluid flow when the coil is 
deenergized. 
The pressure sensor 23 is connected to a signal processing circuit 31, 
which comprises an A/D converter (including a combination of a comparator 
and an encoder) effective to convert an analog pressure signal from the 
sensor 23 into a corresponding digital data, an output latch, and a timing 
circuit which activates the output latch for updating purposes with a 
preselected short period and which also delivers a latch command pulse to 
a microprocessor (hereafter referred to as CPU) 34. The output latch 
normally feeds digital data to CPU 34. 
Solenoid drivers 27 and 28 are constructed in a known manner, and when a 
high level H is applied thereto from CPU 34, each of them is effective to 
energize the electrical coil of either solenoid valve 15 or 20 to open the 
respective valves. 
Motor drivers 25 and 26 each include a potentiometer which allows the 
magnitude of a drive torque to be adjusted. When a high level H is applied 
to either motor driver from CPU 34, it energizes the corresponding motor 
14 or 19 with a current of a magnitude which is determined by the position 
of the potentiometer for producing a given torque. It will be noted that 
CPU 34 is connected to a master unit 60 through an interface 33. 
It will be understood that a remedy of hearts normally requires a pair of 
artificial hearts for a single patient to assist in the operation of or 
substitute for the function of his hearts. Accordingly, a drive unit 10 
associated with a right-hand artificial heart (11R) and another drive unit 
50 associated with a left-hand artificial heart (11L) and having the same 
construction as the drive unit 10 are both connected to the master unit 
60. 
It will be noted that the master unit 60 essentially comprises a computer 
system including a display unit 61 including a character display, 
indicator lamps and buzzers, an operating board 62, an interface 63, CPU 
64, ROM 65, RAM 66 and a system controller 67. CPU 64 is connected with a 
cardiograph and other medical instruments which detect or monitor the 
status of various organs of a patient in which the artificial hearts 11R 
and 11L are incorporated, through the interface 63. Based on drive 
pressures (R-positive pressure, L-positive pressure, R-negative pressure 
and L-negative pressure) fed from the operating board 62, R-ratio (the 
ratio of the systol to the diastole of the right-hand artificial heart), 
L-ratio (the ratio of the systole to the diastole of the left-hand 
artificial heart) and the heart rate (the number of heartbeats per minute, 
required when the cardiograph is not connected) or a cardiographic pulse 
from the cardiograph, CPU 64 of the master unit 60 calculates the timing 
to initiate the systole and the diastole (or to end the diastole or the 
systole, respectively) for the right-hand and the left-hand artificial 
hearts 11R and 11L, respectively. A pulse (IN1 interrupt pulse) 
representing the timing to initiate the systole and a pulse (IN2 interrupt 
pulse) representing the timing to initiate the diastole are developed for 
each of R and L hearts, and are delivered to the drive units 10 and 50 
associated therewith. R-positive pressure (a first given value for R) and 
R-negative pressure (a second given value for R) are transmitted to the 
drive unit 10 while L-positive pressure (a first given value for L) and 
L-negative pressure (a second given value for L) are transmitted to the 
drive unit 50. Such transmission takes place upon entry from the operating 
board 62. 
FIG. 2a shows a control operation by CPU 34 of the drive unit 10 associated 
with the right-hand artificial heart 11R. FIGS. 2b and 2c show interrupt 
operations responsive to the timing pulses, namely, IN1 and IN2 interrupt 
pulses for R. 
Initially referring to FIG. 2a, when the power is turned on at step 1 (in 
the subsequent description, it is to be noted that a step number is 
indicated by a number appearing in parentheses), CPU 34 presets the 
signals at its input and output ports to their standby or off condition 
(16, 20, 14, 18), clears internal timers, counters, registers and flags, 
and inhibit IN1 and IN2 interrupts (2). CPU 34 then demands CPU 64 to 
supply data (3). 
The data transfer between CPU 34 and CPU 64 takes place in the form of a 
frame comprising start bits, data bits, end bits and error check bits, and 
when demanding data at step 3, CPU 34 places "ready" in the "data" term of 
this frame. When CPU 64 receives one frame from CPU 34, it places any data 
which is then to be transmitted to CPU 34 into the "data" term of one 
frame for transmission to CPU 34. When it has no data to be transmitted 
(meaning that the current status is to be continued), CPU 64 places "ACK" 
(acknowledge) into the "data" term of the frame which is to be 
transmitted. 
Upon issuing data demand to CPU 64 (3), CPU 34 sets up a timer T.sub.0 
(program timer) and waits for its timeout (5). If it receives a 
transmission from CPU 64 before the time-out, the program proceeds to step 
6. When there is no transmission, it transmits another frame to CPU 64. 
Subsequent operation of CPU 34 and CPU 64 will be described in a manner 
corresponding to a key operation of an operator on the operating board 62. 
I. When an operator enters R-positive pressure on the operating board 62, 
CPU 64 transmits it to CPU 34, which in response proceeds through steps 4, 
6, 7, 8 and 11 where it stores it in a positive pressure register (an 
internal register of CPU 34). L-positive pressure is also set up in the 
drive unit 50 in a similar manner. 
II. When an operator enters R-negative pressure on the operating board 62, 
CPU 64 transmits it to CPU 34 which in response proceeds through steps 4, 
6, 7, 8, 9 and 12 where it stores it in a negative pressure register (an 
internal register of CPU 34). L-negative pressure is set up in the drive 
unit 50 in a similar manner. 
III. When a cardiograph is not connected to the arrangement of the 
invention, CPU 64 calculates the period of one heartbeat Th, the period of 
R-systole Trc and the period of L-systole Tlc on the basis of R-ratio, 
L-ratio and the heart rate which are entered through the operating board 
62. A pulse having the period Th (representing IN1 interrupt pulse for R) 
is developed by a timer controlled operation and is delivered to IN1 
interrupt port of CPU 34. Another pulse (IN2 interrupt pulse for R) is 
developed with a time delay of Trc from the IN1 interrupt pulse for R, and 
is delivered to IN2 interrupt port of CPU 34. On the basis of phase 
displacement data representing a phase displacement of L relative to R 
which is input from the operating board 62, CPU 64 calculates a phase 
displacement Tpd of L relative to R,a nd the pulse 9IN1 interrupt pulse 
for L) is displaced so as to be phase displaced by Tpd with respect to IN1 
interrupt pulse for R, and is delivered to the drive unit 50. Another 
pulse (IN2 interrupt pulse for L) which is delayed by Tlc with respect to 
IN1 interrupt pulse for L is developed and delivered to the drive unit 50. 
The process of generating these pulses extends from a point in time 
immediately preceding a "start" command until immediately after such 
command, which is applied to the drive units 10 and 50. When there is an 
updated input from the operating board 42 during such process, the 
described calculations are performed again to update the timing to 
generate these pulses. 
Where a cardiograph is employed, CPU 64 develops IN1 interrupt pulse for R 
as a cardiographic wave (pulse) occurring with the period of the heartbeat 
delayed by a time delay which is inputted from the operatingt board 62. 
Other pulses are developed in the manner mentioned above as referenced to 
the IN1 interrupt pulse. 
IV. When "start" is entered on the operating board 62 and CPU 64 responds 
thereto by transmitting "start" command to CPU 34, the latter proceeds 
through steps 4, 6, 7 and 13, enabling IN1 and IN2 interrupts (13), 
delivering a command signal which causes the energization of the 
compressor motor 14 to the motor driver 25, by establishing a 
corresponding level at its associated port (14) and waiting for the time 
duration T.sub.1 to pass during which a transient high current due to the 
starting of the motor prevails (15) before delivering a command signal 
which causes an energization of the decompressor motor 19 to the motor 
driver 26 (16). The program then proceeds to a demand for data (3). CPU 64 
similarly supplies "start" command to the drive unit 50, whereupon a 
microprocessor (not shown) of the drive unit 50 operates in the similar 
manner as CPU 34 described above. 
Since the interrupt operation is enabled at step 13, in response to IN1 
interrupt pulse for R delivered to the interrupt port IN1 of CPU 34 and to 
IN2 interrupt pulse for R delivered to the interrupt port IN2 of CPU 34, 
both from CPU 64, CPU 34 executes an IN1 interrupt subroutine (37) shown 
in FIG. 2b in response to IN1 interrupt pulse or executes an IN2 interrupt 
subroutine (40) shown in FIG. 2c in response to IN2 interrupt pulse for R. 
These subroutines are executed until step 31 where IN1 and IN2 interrupts 
are inhibited. 
In response to IN1 interrupt pulse for R, CPU 34 proceeds to the IN1 
interrupt subroutine (34) shown in FIG. 2b where it clears a negative 
pressure flag (data indicating the systole) (38) and sets a positive 
pressure flag (data representing the diastole) (39). The program then 
returns to the main routine shown in FIG. 2a at a point which immediately 
precedes the interrupt subroutine (37). 
In response to IN2 interrupt pulse for R, CPU 34 enters the IN1 interrupt 
subroutine (40) shown in FIG. 2c where it clears a positive pressure flag 
(41) and sets a negative pressure flag (42). The program then returns to 
the main routine at a point which immediately precedes the interrupt 
subroutine (40). 
CPU 64 delivers IN1 interrupt pulse for L and IN2 interrupt pulse for L to 
the drive unit 50 also, the microprocessor of which executes an interrupt 
operation in a similar manner as mentioned above in connection with CPU 34 
(see FIGS. 2b and 2c). CPU of the drive unit 50 operates in the same 
manner as CPU 34, and the drive unit 50 is arranged and operates in the 
similar manner as the drive unit 10, and therefore will not be described. 
Thus, the ensuing description covers only the drive unit 10. 
V. Returning to FIG. 2a, when the compressor 14 and the decompressor 19 are 
energized in response to the "start" command as mentioned previously, CPU 
34 executes data demand (3), receives one frame of data from CPU 64 (4) 
and then proceeds to step 6 where it is examined if there is any 
additional parameter data. Unless updated input, representing a change in 
the operating parameters, is input from the operating board 62, the data 
in the frame represents "ACK" and includes no fresh data. Accordingly the 
program proceeds to step 18 where CPU 64 reads an output or pressure data 
from the signal processing circuit 31. The circuit 31 includes an internal 
output latch which is updated with a given short period, by applying a 
latch pulse to the output latch. This latch pulse is applied to CPU 34. 
Output data from the circuit 31 exhibits a degraded reliability during a 
pulse interval, which may be at H level, for example, of the latch pulse, 
and hence when CPU 34 proceeds to the step 18 of reading pressure data 
during such pulse interval (H), it waits for this pulse interval to pass 
or until the latch pulse is removed or assumes an L level, whereupon CPU 
64 reads output data from the circuit 31. After passing through the step 
18, CPU 34 executes a "pressure control" comprising steps 19 to 26, after 
which the program returns to the data demand step 3. 
Unless fresh input is supplied from the operating board 62, CPU 64 does not 
transmit parameter data while transmitting only "ACK" in response to the 
data demand at step 3. Accordingly, CPU 34 loops around the steps 3, 4, 6, 
18, 19 to 26 and 3, thus in effect repeating a reading of pressure data at 
step 18 and the "pressure control" comprising steps 19 to 26 with a fixed 
period. 
VI. During the "pressure control" comprising steps 19 to 26, it is 
initially examined if either the positive or the negative flag is set (19, 
23). If neither flag is set, this means that the "start" command has not 
been issued, and hence the program returns to the step 3. The "pressure 
control" is not executed in effect. 
However, when the positive pressure flag is set, as by the IN1 interrupt 
subroutine (37) shown in FIG. 2b, this signifies that it is now in the 
systole, thus midway from the occurrence of IN1 interrupt pulse to the 
occurrence of IN2 interrupt pulse. At this time, the solenoid valve 20 is 
turned off to close its associated valve (20a), and pressure data or 
detected pressure which is obtained at the step 18 of reading the pressure 
data is compared against the content of the positive pressure register (a 
first given value: corresponding to an R-positive pressure which has 
previously been input from the operating board 62 and supplied through CPU 
64) (20b). If the detected pressure is equal to or greater than the first 
given value, the solenoid valve 15 is turned off to close the valve. If 
the detected pressure is less than the first given value, the solenoid 
valve 15 is turned on to open the valve in order to compensate for a 
reduced pressure. 
When the negative pressure flag is set, at the IN2 interrupt subroutine 
(40) of FIG. 2c, this signifies that it is now in the diastole, namely, 
midway from the occurrence of IN2 interrupt pulse to the occurrence of IN1 
interrupt pulse. At this time, the solenoid valve 15 is turned off (24a), 
and pressure data or detected pressure which is obtained at the step 18 of 
reading the pressure data is compared against the content of the negative 
pressure register (a second given value: corresponding to R-negative 
pressure which has previously been input from the operating board 62 and 
fed through CPU 64) (24b). If the detected pressure is equal to or less 
than the second given value, the negative pressure has an excessively high 
absolute magnitude, and accordingly, the solenoid valve 20 is turned off. 
If the detected pressure exceeds the second given value, meaning a small 
absolute magnitude of the negative pressure, the solenoid valve 20 is 
turned on. 
As a result of the pressure control mentioned above, the solenoid valve 20 
remains closed while the solenoid valve 15 is opened and closed to achieve 
a pressure detected by the sensor 23 which is equal to the first given 
value during the systole when the positive pressure flag is set. On the 
other hand, during the diastole when the negative pressure flag is set, 
the solenoid valve 15 remains closed while the solenoid valve 20 is opened 
and closed to achieve a pressure detected by the sensor 23 which is equal 
to the second given value. In this manner, by providing a single solenoid 
valve 15 or 20 in each of the positive and the negative pressure system, 
an alternate switching between the positive and the negative pressure is 
achieved together with a constant positive and negative pressure control. 
VII. When there is an input from the operating board 62 during the 
execution of the pressure control or while the artificial heart 11R is 
being driven, the operation takes place in a similar manner as described 
above under paragraphs I and II. Specifically, CPU 64 transmits data to 
CPU 34, which updates the content of the registers by the received data. 
CPU 64 re-calculates the timing, thus modifying the interrupt pulses so as 
to be based upon the re-calculated data. Accordingly, the pressure control 
mentioned above under paragraph VI changes to one which is based upon the 
data and pulses thus modified. 
VIII. When an operator enters a "stop" command on the operating board 62, 
CPU 64 transmits it to CPU 34. Upon receiving the "stop" command, CPU 34 
proceeds through steps 4, 6, 7, 8, 9, 10 and 27, ceasing to drive the 
decompressor (27), waiting for the transient stop period T.sub.2 to pass 
(28), ceasing to drive the compressor 14 (29), waiting for the transient 
stop period T.sub.3 to pass (30), and inhibiting IN1 and IN2 interrupt 
operations (31). The artificial heart 11 ceases to operate since IN1 and 
IN2 interrupt subroutines (FIGS. 2b and 2c) are no longer executed to 
update the flags. CPU 34 then turns the solenoid valve 15 on (32), waits 
for a transient period T.sub.4 associated with the energization of the 
coil to pass (33), and then turns the solenoid valve 20 on (34). As a 
result of turning the both solenoid valves 15 and 20 on, the compressed 
air from the positive pressure accumulator 16 flows into the negative 
pressure accumulator 21, whereby the pressure within the both accumulators 
16 and 21 approach the atmospheric pressure. CPU 34 then clears both the 
positive and the negative pressure flag (35), and waits for a time period 
T.sub.5 to pass which is sufficient to neutralize the pressures of both 
accumulators (36) before proceeding to the data demand step 3. 
As mentioned, during the systole, the solenoid valve 15 is closed when the 
detected pressure is greater than the first given value (R-positive 
pressure) and is opened when the detected pressure is less than the first 
given value, thereby applying a pressure which is substantially equal to 
the first given value to the artificial heart 11. During the diastole, the 
solenoid valve 20 is closed when the absolute magnitude of the detected 
pressure is greater than the absolute magnitude of the second given value 
(R-negative pressure) and is opened when the detected pressure is less, 
thus applying a pressure which is substantially equal to the second given 
value to the artificial heart 11R. In this manner, the pressure of the 
accumulator 16 is chosen higher than the first given value while the 
absolute magnitude of the pressure of the negative pressure accumulator is 
chosen to be higher than the absolute magnitude of the second given value. 
It will be seen that the capacity of these accumulators may be reduced by 
an amount corresponding to the chosen higher pressures. Where the solenoid 
valves 15 and 20 exhibit rapid response, it is preferred to choose as high 
a pressure as possible of the accumulator in order to reduce the size of 
the accumulator. In such event, if it is required to provide a smooth 
rising or falling edge of the positive or negative pressure, a function 
generator such as an integrating circuit, ROM or RAM which provides a 
desired rising response may be used and activated in response to IN1 and 
IN2 interrupt pulses, and the solenoid valves 15 and 20 may be turned on 
and off as a result of a comparison of an output from the function 
generator against the pressure detected by the sensor 23. 
It will be seen that according to the first embodiment of the invention, 
both a positive and a negative pressure system may include a single 
solenoid valve to produce a fluid of a given pressure during a specified 
interval, thus dispensing with pressure regulator valves required in the 
prior art practice and thus reducing the number of valves used. The 
capacity of the accumulators may also be reduced. In the prior art 
practice, a pressure sensor has been required for each pressure regulator 
valve, and hence two sensors must be provided. However, according to the 
invention, the number of pressure sensors required can be minimized to 
one. 
Second Embodiment 
Referring to FIG. 4, the signal processing circuit 31 applies an analog 
signal representing a pressure detected by the sensor 23 to a pair of 
digitized pressure regulating circuits 37p and 37n. When a high level H is 
applied to solenoid drivers 27, 28 from the circuits 37p and 37n, 
respectively, the drivers energize the electrical coils associated with 
the solenoid valves 15 and 20, respectively, which are provided for 
opening to operate to supply or interrupt the positive and the negative 
pressure, respectively. When a low level L is applied to the drivers, the 
latter deenergizes the electrical coils to close the valves. 
CPU 34 of the drive unit 10 responds to an R-positive pressure (a target 
value of R-positive pressure) from the master unit 60, by latching it in a 
latch 36p. Similarly, responsive to an R-negative pressure, a target value 
of R-negative pressure, CPU 34 latches it in a latch 36n. 
CPU 34 of the drive unit 45 delivers a command signal having an H level 
which commands the valve 15 to open (thus representing a systole signal) 
to the digitized pressure regulating circuit 37p through an output port p 
of the interface 33 during a time from the reception of IN1 interrupt 
pulse to the reception of IN2 interrupt pulse from the master unit 60. It 
also delivers a command signal having an H level which commands the valve 
20 to open (thus representing a diastole signal) to the digitized pressure 
regulating circuit 37n through an output port n of the interface 33 during 
the time interval from the reception of IN2 interrupt pulse to the 
reception of IN1 interrupt pulse from the master unit 60. 
In addition to the command signal to open the valve 15 (systole signal), 
the digitized pressure regulating circuit 37p receives R-positive pressure 
data from a latch 36p, a pulse a having a duty cycle of 75% from a pulse 
oscillator 38 and a pulse b having a duty cycle of 25% from an inverter 
39, which represents an inversion of the pulse a. In addition to the 
command signal to open the valve 20 (diastole signal), the digitized 
pressure regulating circuit 37p receives R-negative pressure data from a 
latch 36n, the pulse a from the pulse oscillator 38 and the pulse b from 
the inverter 39. 
The arrangement of each of the pressure regulating circuit 37p and 37a are 
illustrated in FIG. 5a. Initially considering the circuit 37p, R-positive 
pressure (a target value Prp of positive pressure) fed from the latch 36p 
is converted into an analog signal c having a level corresponding to 1.05 
times Prp (see FIG. 5b) by a D/A converter 40p to be applied to an 
inverting input of a comparator 41p. The analog voltage c is divided into 
signals d=1.0 Prp and e=0.90 Prp (first given value) by means of a 
variable resistor 47p, which are applied to inverting inputs of 
comparators 42p and 43p. An analog signal representing the pressure 
detected by the sensor 23 is applied to non-inverting inputs of 
comparators 41p to 43p. 
When the pressure detected by the sensor 23 is equal to or less than e=0.90 
Prp (region 4 shown in FIG. 5b) when CPU 34 is delivering the command 
signal to open the valve 15 (or systole signal: shown by "33-p" in FIG. 
5b), all of the comparators 41p to 43p deliver outputs of a high level H, 
whereby only one, A3, of AND gates A1 to A3 provides an output of a high 
level H, which is applied through OR gates R1 and R2 to AND gates A4 and 
A5. The gates A4 and A5 feed the signals a and b to 0R gate R3, which then 
provides a logical sum of the signals a and b, or an open (on) signal, 
having a high level continuously, to the solenoid driver 27. Accordingly, 
the solenoid valve 15 remains open continuously, rapidly increasing the 
pressure applied to the artificial heart 11R. 
When the pressure detected by the sensor 23 exceeds the first given value 
e=0.90 Prp (region 3 shown in FIG. 5b), the comparators 42p and 41p 
provide outputs of a high level while the comparator 43p provides an 
output of a low level, whereby only gate A2 provides an output of a high 
level H, thus enabling only the gate A4 to feed only the signal a to the 
solenoid driver 27. As mentioned previously, the signal a represents a 
pulse having a duty cycle of 75% and a frequency of 200 Hz which is 
developed by the pulse oscillator 38. Accordingly, the solenoid valve 15 
is opened and closed in an oscillating manner at such frequency and with 
such duty cycle. This reduces the rate of supplying the positive pressure, 
whereby the positive pressure which is applied to the artificial heart 11R 
rises more gently. 
When the pressure detected by the sensor 23 becomes equal to or exceeds the 
target value d=1.00 Prp (region 2 shown in FIG. 5b), only the comparator 
41p provides an output of a high level H while the comparators 42p and 43p 
provide outputs of a low level L. Thus only the gate A1 provides an output 
of a high level H, disabling the gate A4 and enabling the gate A5. 
Consequently, the signal b having a frequency of 200 Hz and a duty cycle 
of 25% is delivered to the solenoid driver 27, causing the solenoid valve 
15 to be opened and closed in an oscillating manner at such frequency and 
with such duty cycle. This represents an insufficient rate of supplying 
the positive pressure, whereby the positive pressure applied to the 
artificial heart 11R decreases gently. Consequently, the pressure detected 
enters the region 3, whereby the rate of supplying the positive pressure 
rises gently. In this manner, a control continues which alternates between 
the regions 3 and 2. 
If the detected pressure becomes equal to or greater than c=1.05 Prp 
(region 1 shown in FIG. 5b), all of the gates A1 to A3 provide outputs of 
a low level L, disabling the both gates A4 and A5, whereby the valve 15 
remains closed, returning the pressure to the region 2 rapidly. 
The digitized pressure regulating circuit 37n is constructed in the similar 
manner as the circuit 37p mentioned above. When the pressure detected is 
equal to or greater than the second given value f=1.05 Prn (region 4 shown 
in FIG. 5b) when CPU 34 is delivering the command signal to open the valve 
20 (diastole signal: shown at "33-n" in FIG. 5b), it maintains the 
solenoid valve 20 open in order to reduce the pressure rapidly. When the 
detected pressure is less than f=1.05 Prn and is equal to or greater than 
R-negative pressure (the target value of negative pressure) g=1.00 Prn 
(region 5 shown in FIG. 5b), it applies the signal a to the solenoid 
driver 18 in order to reduce the pressure gently. When the detected 
pressure reduces below g=1.00 Prn, it applies the signal b to the solenoid 
driver 28 in order to raise the pressure gently. If the detected pressure 
becomes equal to or less than h=0.95 Prn, it applies a signal L to the 
solenoid driver 28 which commands the valve 20 to be closed in order to 
raise the pressure rapidly. 
The upper half of the table shown in FIG. 5c indicates valve energizing 
signals applied by the circuit 37p to the solenoid driver 27 in a manner 
corresponding to the pressure detected by the sensor 23 (regions 1 to 4 
shown in FIG. 5b) when the command signal to open the valve 15 is 
delivered to the circuit 37p. When such command signal is not applied or 
when the output p of the interface 33 assumes a low level L, the gates A5 
and A6 in the circuit 37p are both disabled, whereby a low level L 
commanding the valve to be closed is applied to the solenoid driver 27. 
The lower half of the table shown in FIG. 5c indicates valve energizing 
signals applied by the circuit 37n to the driver 28 in a manner 
corresponding to the pressure detected by the sensor 23 (regions 4, to 7. 
shown in FIG. 5b) when the command signal to open the valve 20 is 
delivered to the circuit 37n. 
When such command signal is not applied or when the output n of the 
interface 33 assumes a low level L, the gates A5 and A6 in the circuit 37n 
are both disabled, whereby a low level L commanding the valve to be closed 
is applied to the solenoid driver 28. 
As mentioned previously, in response to IN1 interrupt pulse and IN2 
interrupt pulse from the master unit 60, CPU 34 alternately develops the 
command signals to open the valves 15 and 20 and apply them to the 
digitized pressure regulating circuits 37p and 37n, respectively. In 
response to R-positive pressure data (d=Prp) from the master unit 60, CPU 
34 latches it in the latch 36p. In response to R-negative pressure date 
(g=Prn) received from the master unit 60, CPU 34 latches it in the latch 
36n. 
FIG. 6 is a flowchart illustrating a control operation by CPU 34 of the 
drive unit 10 which drives the right-hand artificial heart 11R. It is to 
be understood that the interrupt operation performed by CPU 34 in response 
to timing pulses (IN1 and IN2 interrupt pulses for R) from the master unit 
60 remains the same as that illustrated in FIGS. 2b and 2c. 
Referring to FIG. 6, when the power is turned on (1), CPU 34 presets 
signals at its input and output ports to their standby condition or off 
condition (15, 20, 14 and 19), clears internal timers, counters, registers 
and flags, and inhibit IN1 and IN2 interrupts (2). CPU 34 then demands 
data from CPU (not shown) of the master unit 60 (3). 
A data transfer between CPU 34 and CPU of the master unit 60 takes place in 
terms of a frame comprising start bits, data, end bits and error check 
bits. During the data demand at the step 3, CPU 34 places data 
representing "ready" in the "data" term item of the frame. Upon receiving 
one frame from CPU 34, CPU of the master unit 60 places any data which is 
then to be transmitted to CPU 34 into the "data" item of one frame for 
transmission to CPU 34. When it has no data to be transmitted, meaning 
that a current status is to be maintained, CPU of the unit 60 places "ACK" 
(acknowledge) in the "data" item of the frame for transmission. 
Upon demanding data from CPU of the unit 60 (3), CPU 34 presets a timer 
T.sub.0 (program timer) and waits for its time-out (5). If it receives a 
transmission from CPU of the unit 60 before the time-out, the program 
proceeds to step 6. When there is no transmission, it transmits another 
frame to CPU of the unit 60. 
The operation of CPU 34 and CPU of the unit 60 will now be described in a 
manner corresponding to a key operation on an operating board (not shown) 
of the unit 60 by an operator. 
I. When an operator enters R-positive pressure on the operating board, CPU 
of the unit 60 transmits it to CPU 34, which then proceeds through steps 
4, 6, 7, 8 and 11, latching it in a latch 36p at step 11. This takes place 
by switching a data selector 35 to the output of the latch 36p and 
delivering R-positive pressure data and a latch command pulse to the data 
selector 35. L-positive pressure is similarly preset in the drive unit 50. 
II. When an operator enters R-negative pressure on the operating board, CPU 
of the unit 60 transmits it to CPU 34, which upon receiving it, proceeds 
through steps 4, 6, 7, 8, 9 and 12, latching R-negative pressure in the 
latch 36n at step 12. This takes place by switching the data selector 35 
to the output of the latch 36n and delivering R-negative pressure and 
latch command pulse to the data selector 35. L-negative pressure is 
similarly preset in the drive unit 50. 
III. When no cardiograph is used, CPU of the unit 60 calculates the period 
Th of heartbeat, R systole period Trc and L systole period Tlc on the 
basis of R ratio, L ratio and the heart rate (the number of heartbeats per 
minute) which are inputted from the operating board. It develops a pulse 
(IN1 interrupt pulse for R) with a period Th by a timer control, and 
applies it to IN1 interrupt port of CPU 34. It also develops another pulse 
(IN2 interrupt pulse for R) which is delayed by Trc from the IN1 interrupt 
pulse and applies it to IN2 interrupt port of CPU 34. CPU of the master 
unit 60 also calculates a phase displacement Tpd of L relative to R on the 
basis of phase displacement data which is input from the operating board, 
and develops a pulse (IN1 interrupt pulse for L) having a phase 
displacement of Tpd relative to IN1 interrupt pulse for R, and applies it 
to the drive unit 50. It also develops another pulse (IN2 interrupt pulse 
for L) which is delayed by Tlc with respect to IN1 interrupt pulse for L, 
and also applies it to the drive unit 50. The generation of these pulses 
extends from a point immediately before the occurrence of a "start" 
command until immediately after a "stop" command. If there is updated 
input from the operating board during the generation of these pulses, the 
described operation is performed again to update the timing of developing 
the pulses. 
Where a cardiograph is used, CPU of the master unit 60 develops IN1 
interrupt pulse for R as having a time delay, which is input from the 
operating board, with respect to a cardiographic wave (pulse) which occurs 
with the period of the heartbeat. Other pulses are developed as referenced 
to this IN1 interrupt pulse. 
IV. When a "start" command is entered on the operating board and CPU of the 
master unit 60 responds thereto by transmitting a "start" command to CPU 
34, the latter proceeds through steps 4, 6, 7 and 13, enabling IN1 and IN2 
interrupts (13), delivering a signal which commands the energization of 
the compressor motor 14 to the motor driver 25 or delivering such signal 
to an output port thereof (14), waits for a time duration T.sub.1, during 
which a transient high current occurs due to the starting of the motor, to 
pass (15) and then delivers a signal which commands the energization of 
the decompressor motor 19 to the motor driver 26 after the time duration 
T.sub.1 has passed (16). The program then proceeds to the data demand step 
3. CPU of the master unit 60 also provides a "start" command to the drive 
unit 50, the microprocessor (not shown) of which operates in the same 
manner as CPU 34. 
Since the interrupt operation is enabled at step 13, when CPU of the master 
unit 60 applies IN1 interrupt pulse for R to an input port IN1 of CPU 34 
and applies IN2 interrupt pulse for R to interrupt port IN2 of CPU 34, the 
latter responds thereto by executing IN1 interrupt subroutine (37) shown 
in FIG. 2b or executing IN2 interrupt operation (40) shown in FIG. 2c. 
This takes place until IN1 and IN2 interrupt operations are inhibited 
(31). 
In response to IN1 interrupt pulse for R, CPU 34 enters IN1 interrupt 
subroutine (37) shown in FIG. 2b where it clears the negative pressure 
flag (data indicating the diastole) (38) and sets the positive pressure 
flag (data indicating the systole) (39). The program then returns to the 
main routine (FIG. 6) at a point which immediately precedes the interrupt 
subroutine (37). 
In response to IN2 interrupt pulse for R, CPU 34 enters IN1 interrupt 
subroutine (40) shown in FIG. 2c where it clears the positive pressure 
flag (41) and sets the negative pressure flag. The program then returns to 
the main routine at a point immediately preceding the interrupt subroutine 
(40). 
CPU of the master unit 60 delivers IN1 and IN2 interrupt pulses for L to 
the drive unit 50, CPU of which executes the interrupt operation in the 
similar manner as CPU 34 (see FIGS. 2b and 2c). CPU of the drive unit 50 
operates in the similar manner as CPU 34. Since the drive unit 50 is 
constructed and operates in the same manner as the drive unit 10, the 
ensuing description only covers the drive unit 10. 
V. Returning to FIG. 6, when the compressor motor 14 and the decompressor 
motor 19 are energized in response to the "start" command, CPU 34 executes 
the data demand (3), receives one frame of data from CPU of the master 
unit 60 (4), and since there is no additional data or parameter data in 
the transmitted frame unless updated input or a change in the operating 
parameters is input from the operating board (6), executes a "switching 
control" comprising the steps 19 to 25, after which the program returns to 
the data demand step 3. 
Unless a fresh input is entered from the operating board, CPU of the master 
unit 60 does not transmit parameter data (it only transmits "ACK" in 
response to the data demand (3)). Accordingly, CPU 34 loops around the 
steps 3, 4, 6, 19 to 25 and 3, thus repeating the "switching control" 
comprising the steps 19 to 25 with a substantially constant period. 
VI. During the "switching control" comprising the steps 19 to 25, it is 
initially examined if the positive or the negative flag is set (19, 23). 
If neither flag is set, this means that the "start" command has not been 
issued yet, and accordingly the program returns to the step 3 without 
substantial execution of the "switching control". 
If the positive pressure flag is set as by the IN1 interrupt subroutine 
(37) shown in FIG. 2b, this signifies that it is now in the systole or a 
time interval during which the valve 15 is commanded to be opened, namely, 
from the occurrence of IN1 interrupt pulse to the occurrence of IN2 
interrupt pulse. In this instance, a command signal which requires the 
solenoid valve 20 to be turned off is applied to the output port n of the 
interface 33 (20), and a command signal to open the solenoid valve 15 is 
applied to the output port p of the interface 33. 
When the negative pressure flag is set as by the IN2 interrupt subroutine 
(40) shown in FIG. 2c, this signifies that it is now in the diastole or 
time interval during which the valve 20 is to be opened, namely, from the 
occurrence of IN2 interrupt pulse to the occurrence of IN1 interrupt 
pulse. In this instance, a command signal to turn the solenoid valve 15 
off is applied to the output port p of the interface 33 (24), and the 
command signal to open the valve 20 or to energize the electrical coil of 
the solenoid valve 20 is applied to the output port n of the interface 33 
(25). 
As a result of the "switching control", the signals "33-p" and "33-n" shown 
in FIG. 5b are applied to the digitized pressure regulating circuits 37p 
and 37n, respectively. In response to these signals, the circuits 37p and 
37n regulate the pressure in the manner mentioned above. Thus, during the 
systole when the positive pressure flag is set, the solenoid valve 20 is 
closed while the solenoid valve 15 is opened and closed so that the 
pressure detected by the sensor 23 is equal to R-positive pressure (d). 
During the diastole when the negative pressure flag is set, the solenoid 
valve 15 is closed while the solenoid valve 20 is opened and closed so 
that the pressure detected by the sensor 23 is equal to R-negative 
pressure (g). In this manner, a constant positive and negative pressure 
control as well as a switching between a positive/negative pressure can be 
achieved by providing the single solenoid valve 15 or 20 in the positive 
or the negative pressure system, respectively. 
VII. During the execution of the "switching control" mentioned under the 
paragraph VI during which the artificial hearts 11R and 11L are being 
driven, any input entered on the operating board of the master unit 20 
causes such data to be transmitted to CPU 34 from CPU of the unit 20 in 
the similar manner as mentioned under the paragraphs I and II. CPU 34 
updates the content of the latches 36p and 36n with the data received, and 
CPU of the master unit 60 re-calculates the timing so as to modify the 
interrupt pulses in accordance with the re-calculated data. Accordingly, 
the "switching control" mentioned under the paragraph VI is based on such 
modified data and pulses. 
VIII. When an operator enters a "stop" command on the operating board of 
the master unit 60, CPU thereof transmits such command to CPU 34. Upon 
receiving such command, CPU 34 proceeds through steps 4, 6, 7, 8, 9, 10 
and 27, deenergizing the decompressor motor 19 (27), waiting for the 
transient stop period T.sub.2 to pass (28), whereupon the compressor motor 
14 is stopped (29), and after an associated transient stop period T.sub.3 
to pass (30), IN1 and IN2 interrupts are inhibited (31). Because IN1 and 
IN2 interrupt subroutines (FIGS. 2b and 2c) are no longer executed or the 
flags cease to be updated, the artificial heart 11R ceases to operate. 
Subsequently, CPU 34 turns the solenoid valve 15 on (32), waits for a 
transient period T4 associated with the energization of its coil to pass 
(33), and then turns the solenoid valve 20 on (34). As a result of the 
both solenoid valves 15 and 20 being turned on, the compressed air from 
the positive pressure accumulator 16 flows into the negative pressure 
accumulator 21, allowing the pressures within the both accumulators 16, 21 
to approach the atmospheric pressure. CPU 34 then clears the positive and 
the negative pressure flag (35), and waits for a sufficient time period 
T.sub.5 which allows the pressures of the both accumulators to neutralize 
(36) before advancing to the data demand step 3. 
As mentioned, the valve 15 is maintained open until the detected pressure 
reaches the first given value (a) during the systole, thus achieving a 
rapid rise in the pressure which is applied to the artificial heart 11R. 
When the first given pressure is exceeded, the valve 14 is opened and 
closed with a duty cycle of 75%, thus providing a more gentle pressure 
rise. When R-positive pressure (d) is exceeded, the valve 14 is opened and 
closed with a duty cycle of 25%, whereby the pressure which has been 
rising then begins to decline in a gentle manner. In this manner, it is 
possible to stabilize the pressure at R-positive pressure (d) smoothly 
without producing any excessive overshoot during the rising period of the 
positive pressure. Any significant pressure fluctuation is also avoided 
during the stable period which follows the rising period. This is because 
of the inertia of the valve 15 which involves a time lag in the opening 
and closing thereof with respect to the energization and deenergization of 
the associated coil. 
During the systole, when the region e immediately before the target 
pressure (d) which exceeds a first given value (e) is reached, the valve 
15 is opened and closed in an oscillating manner with a duty cycle of 75%, 
thus accompanying a reduced rate in the rise of the positive pressure. If 
the opening and closing operation of the valve 15 is switched to produce a 
declining pressure when the target pressure (d) is reached, the occurrence 
of an overshoot as in the prior art is eliminated. In the region 2 which 
has just exceeded the target pressure (d), the valve 15 is opened and 
closed in an oscillating manner with a duty cycle of 25%, producing a 
retarded declining rate in the positive pressure. Accordingly, if the 
opening or closing operation of the valve 15 is switched to the rising 
pressure when the target pressure (d) is reached, the occurrence of an 
excessive undershoot is experienced in the prior art is eliminated. Also 
during the diastole, the valve 20 is opened and closed in an oscillating 
manner in the regions 5 and 6 around the target pressure (g). 
It is to be noted that the solenoid valves 15 and 20 will be fully open 
when their associated coils are energized with a duty cycle of 100%. 
Utilizing the energization with a duty cycle of 75% and at the frequency 
of 200 Hz, the on/off energization which causes the energization to be 
interrupted before the valve reaches its fully open position causes the 
valve opening to be on the order of 70% as viewed in a time sequence. The 
valve opening will be on the order of 20% for the energization with a duty 
cycle of 25%. 
Third Embodiment 
In a third embodiment shown in FIG. 7, a positive pressure system includes 
a positive pressure regulating solenoid valve 15, a positive pressure 
accumulator 16 and a positive pressure open/close solenoid valve 17 while 
a negative pressure system includes a negative pressure regulating 
solenoid valve 20, a negative pressure accumulator 21 and a negative 
pressure open/close solenoid valve 22, generally in the similar manner as 
disclosed in U.S. Pat. No. 4,546,760. A first pressure sensor 23 detects 
the pressure in the accumulator 16 while a second pressure sensor 24 
detects the pressure within the accumulator 21. In this embodiment of the 
invention, both the positive and the negative pressure accumulator 16, 21 
have a reduced capacity on the order of 300 cc. 
In the third embodiment, the solenoid valves 17 and 22 are connected 
through associated solenoid drivers 30 and 29, respectively, so as to be 
energized with a systole signal "33-p" appearing on an output port p and a 
diastole signal "33-n" appearing on an output port n of an interface 33. 
Digitized pressure regulating circuits 37p and 37n are illustrated in FIG. 
8 where it will be noted that the signals "33-p" and "33-n" are not 
applied thereto. Consequently, the digitized pressure regulating circuit 
37p delivers signals appearing on the upper half of the table shown in 
FIG. 5c to the solenoid driver 27 in a manner corresponding to the 
pressures (1 to 4) shown in FIG. 5b detected by the first pressure sensor 
23 without regard to the systole or the diastole period. Also the digitzed 
pressure regulating circuit 37n delivers the signals appearing on the 
lower half of the table of FIG. 5c to the solenoid driver 28 in a manner 
corresponding to the pressures (4 to 7) shown in FIG. 5b detected by the 
second pressure sensor 24, again without regard to the systole or the 
diastole period. 
The operation of the master unit 60 and CPU 34 remains entirely the same as 
the operation of the second embodiment described above in connection with 
FIG. 4, with a similar effect. 
In either the second or the third embodiment, regions 3 and 5 in which the 
pressure is gently increased as well as regions 2 and 6 in which the 
pressure is gently decreased are established across the target pressures 
(g,g) in order to suppress an overshoot or undershoot which might occur 
immediately below or above the target pressures and to achieve a pressure 
which is equivalent to a selected target pressure in an accurate and 
precise manner. It will be noted that in the prior art practice, maximum 
pressure deviations are manifest as an overshoot during a pressure rise 
when switching from the diastole to the systole and an undershoot (which 
is equivalent to an overshoot as viewed in terms of the absolute magnitude 
of the pressure) during a pressure fall when switching from the systole to 
the diastole, both of which represented a significant problem, and the 
suppression of which would provide a great advantage. This end may be 
attained by providing D/A converters 40p and 40n in the digitized pressure 
regulator circuits 37p and 37n which directly deliver target pressures 
d=Prp and g=Prn; comparators 41p and 41n, and AND gate A3 and OR gates R1 
and R2 may be omitted so that an output from the gate A2 is directly 
applied to AND gate A4; target pressures d=Prp and g=Prn may be fed to the 
comparators 42p and 42n, respectively while the first given value a and 
the second given value f may be fed to the comparators 43n and 43p, 
respectively. With this arrangement, when the pressures in the region 2 
and 6 are detected, the valves 15 and 20 will be closed. Since the rate of 
pressure rise in the regions 3 and 5 is low, an overshoot when switching 
from the diastole to the systole or vice versa can be suppressed. 
The compressor 13 is provided with a relief valve which establishes a 
communication between its discharge port and the atmosphere at a pressure 
which is by a given amount higher than the target pressure (d). The 
decompressor 13 is provided with a relief valve which establishes a 
communication between its suction port and the atmosphere at a pressure 
which is by a given value less than the target pressure (g). In the second 
embodiment, these bleed valves may comprise solenoid valves, which can be 
served by the pressure regulator solenoid valves 15 and 20. In this 
instance, the "closed/open condition of solenoid valve 15" is equivalent 
to "establishment/interruption of a communication of the discharge port of 
the compressor 13 with the atmosphere"; and the "closed/open condition of 
the solenoid valve" is equivalent to the "establishment/interruption of a 
communication of the suction port of the decompressor 18 with the 
atmosphere". 
As described, it will be seen that the arrangement of both the second and 
the third embodiments allow the capacity of the accumulators to be reduced 
and are also capable of suppressing a variation in the magnitude of a 
positive/negative pressure fed to the pumping unit (11R). 
In the above description, the pumping unit has been illustrated as an 
artificial heart. However, it should be understood that the invention is 
equally applicable to other pumping units used in connection with a living 
human body or industrial pumping units which operate in the similar manner 
as the artificial heart 11R.