CA1187757A

CA1187757A - System for extracorporeal circulation of blood

Info

Publication number: CA1187757A
Application number: CA000386631A
Authority: CA
Inventors: Tsunekazu Hino
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-09-24
Filing date: 1981-09-24
Publication date: 1985-05-28
Also published as: CA1209672A

Abstract

ABSTRACT OF THE DISCLOSURE
An extracorporeal blood circulation system including a line for withdrawing the venous blood from the patient, an artificial lung provided on the line, a reservoir for the blood withdrawn, a blood supply line for sending out the blood from the reservoir to the artery of the patient, and a blood supply pump provided on the blood supply line and serving as an artificial heart. The amount of blood to be supplied is automatically controlled to maintain the arterial pressure of the patient in a suitable required range.
The blood supply pump is stopped when the arterial pressure of the patient measured is above a predetermined upper limit value, while the pump is driven when the arterial pressure has lowered to a level below a lower limit value. The amount of blood to be withdrawn is also controlled automatically to keep the central venous pressure of the patient approximately constant. The blood withdrawing line has a blood withdrawing pump.
The reservoir is connected to the inlet side of this pump by a shunt line having a valve which is usually opened. The valve is closed when the central venous pressure exceeds a predetermined upper limit level. A
vertical overflow tube detects the central venous pressure exceeding the upper limit level.

Description

The present invention rela-tes to a system for the extracorporeal circulation of -the blood for a patient undergoing an operation on the lung or heart to refresh -the blood of the patient and always circulate the blood through the body in place of the lungs and heart of the patient.
Systems for extracorporeally circula-ting the blood com-prise a blood withdrawing line for drawing off the venous blood Erom the patien-t, an artificial lung provided on the line, a reservoir Eor the withdrawn blood, a blood supply line for feeding the blood from the reservoir to the artery of the patient, and a blood supply pump provided on the blood supply line and serving as an artificial heart. With such systems, it is most critical to maintain the amount of the blood withdrawn from the body of the patient in balance with the supply of the blood to the body to keep the amount of the blood circulated through the body cons-tant at all times. In controlling the amount of blood circulation -through the body, bleeding from the site operated on, etc. must also be considered since bleeding reduces the amount of blood in the body. Conven-tionally the amount of blood circula-tion through .~-.. ~, ~

7 3 ~ 7 the body is controlled by the operator through manual procedures for driving the blood withdrawing pump and blood supply pump and replenishing the blood reservoir with transfusion blood. This mode of control involves many items of manipulation, and the system must be controlled item-wise promptly based on immediate judgment while watching incessantly changing conditions of the patient, i.e. arterial and venous blood pressures, measurement of amoun-t of bleeding, amount of blood in the reservoir and electro-cardiogram. Thus the operator must be trained for controlling the system. Additionally the operator suffers from much fatigue when the operation takes a prolonged period of time.
SUMMARY OF THE INVENTION
The invention provides a system for circulating the blood extracorporeally comprising: a blood withdrawing line, a reservoir for the blood withdrawn, means for detec-ting that the venous pressure has exceeded a prede-termined upper limit level, said means comprising first and second vertical tubes communicating with each other at their upper ends and being vertically adjust-able, at least one of the vertical tubes having an upper end open to atmosphere, and a blood sensor positioned to detect blood flowing over the communicating portion from one of the vertical tubes to the other; and means for increasing the amount of blood to be withdrawn when the venous pressure has exceeded the upper limit level.
The sys-tem for the extracorporeal circulation of the blood as disclosed herein is adapted to automatically control the blood supply to the body so that -the arterial pressure will be maintained suitably in a required range. The amount of blood -to be withdrawn from the body is automatically controlled so tha-t the venous pressure of the patient will be maintained at an approxi-mately constant level. The system is adapted to control the amount of blood to be supplied to the body of the patient and the amount of blood to be withdrawn therefrom to keep the amount of circula-tion of the blood through the body approximately constan-t. The system can smoothly effect a change from the spontaneous circula-tion of the blood by the cardiac force of the patient to the forced circulation of the blood by an extracorporeal system or a change reverse to the above.
The intracorporeal circulation of the blood is assisted by an extracorporeal circulation system while the blood is being spontaneously circulated through the body by the cardiac force of the patient so that the intracorporeal circulation of the blood will not be interrupted even when the heart stops temporarily.
The system for the extra-7~7 co~oreal circula.tlon oi~ the blood comprises a bloodithdra~ing line 7 an artlficial lun~ provi~ed on the line, a reservoir for the blood withdra~m, a blood suPpl,~ 'ine Lor sendin$ out the blood from the reservoir, a blood sup~ pump ~-rovided on the blood su-opl~T line and serving as an artificial heart, means for detecting that the venous pressure has exceeded a predeterilllned u~?per lil~li-t level, a blood ~reSsure transducer for measuring the arterial pressure, means for increasing the amoun-t of blood to be withdrawn when the venous pressure has exceeded the upper limit level, and means for controlling the blood su~pl~- ~ump in res~onse to an output frorrl the blood pressure transducer to main-tain the arterial pressure in a predetermined required range.
The venous pressure detecting means comprises a vertical tube having an u~er end opened to the atmosphere and a blood sensor provided at a positi.on of specified heigh-t for the vertical tube for detecting that the blood level has reached tne position. ~his arrangement detects the venous pressure more accurately than a blood pressure transducer used as the venous pressure detecting means. ~or the same purpose, t~o vertlcal tubes ma,~ be used which are in communication wi-th each other at upper portions thereofO ''i,hen the . ~ ~

'7'~'7 blood in one o~ the vertical tubes rises beyond the communicatin~ -oortion, the blood flows over this portion into -the o~er tube. 'Ihe overflow is detected by a sensor. If the vertical tube or sensor is movable upward or do-~nward, the upper limi~ level oc` the venous pressure is variableO ~he venous pressure to be etected is preferably the central venous pressure.
The means for controlli:ng t~e blood su.pply pump preferably comprlses an upper limit detecting clrcult for detectln~ that the arterlal pressure has exceeded a predetermined upper li.nit value, a lower limit detecting circuit for detec-ting th~t the arterial pressure has lowered belovr a predetermined lower limit value, and a control circuit for stopping the blood supply pump upon detectlng t'^e upper limit and for operatin~ -the blood supply pump upon detectin~ -the lower limit. It is preferable to use a pulsatile pump as the blood supply pump.
Other features and advantages of thls lnvention will become apparent from the followlng descrlptlon of an embodlment ':;lth reference to the accompan~Tlng ~rawings.
BRI~ DES~RIPTION O~''l'H~ DRA'IINGS
~i,3. 1 ls a diagram of a preferred embodiment o:c` the inventlon showlng a clrcult for e~tracorporeal 7~;~7 blood circulation and including a blocl~ diagram of ~art OI the electric circuit associated with the circuit;
~ig. 2 is a block diagram showing the construc-tion of a control unit in detail;
ig. 3 is a sectional view showing a cannula;
Eigs. 4, 5 and 6 show other examples of central venous pressure adjusting units;
Fig. 7 shows another example of blood supply line; and ~ig. 8 is a block diagram showing a system for adjusting tke pressure of the left atrium.
DES~RIPTION 0~ Th~ PR~l~'ERL~ED h~iBOD~'~'!ENT
The system of this invention for extracorporea blood circulation includes a blood withdrawin~ line 1, an overflow line 2, an asplration line 3 and a blood supply line 4. These lines 1 to 4 are each made of a flexible tube. The lines 1 to 3 are provided with rotary pumps 11 to 13 respectively. The rotary pump comprises rollers adapted for a circular motion to draw and forward the blood through the tube by squeezing the tube, forming a continuous flow of blood. The line 4 is provided with a pulsatile pump 14 which is operated by compressed air supplied thereto intermittently to intermittently force the blood throu~h the line 4 as a pulsating flow.

-.

77~i~

~ he line 1 for withdra~i1ing the venous blood fro~ tl~e body of the patient has two cannulas 15 connectea to one end t'~ereof. As seen in -~iig. 3, the cannula 15 comprlses an outer tube 16 having a slightly ta-pered I or~rard end, and an inner tube 17 having a forward end projecting outward from the forward end of the outer tube 16 and a rear end extending out~ard from -the outer tube 1~. The forward end oi^ the outer tube 16 i5 formea with a large n~er OI holes 18. The rear end of the outer tube 16 is connected to the line 1. The forward ends of the cannulas 15 are inserted into the superior and inferior venae cavae of the patient individually to draw the venous blood into the line 1 through the holes 18 and the outer tubes 16. The line 1 is provided with an oxygenerator and a heat exchanger 6. The oxygenerator f~L~c-tions as an artificial lung, in which the venous blood withdrawn from the body of the patient gives off ; carbon dioxide and takes up oxygen. The heat exchanger maintains the blood at the desired temperature and9 when needed, lowers the blood temperature. The blood thus refreshed is led in-to a blood r~servoir 7 and s-tored -therein. Alternatively the heat exchanger may be disposed between the reservoir 7 and the pump 14 on the blood supply line 4, or on a por-tion of the line 4 downstream from the pump 14. A collapsible bag 9 for '7~

checking whether or not the blooa is being withdrawn smoothly is provided on the blood withdrawing line 1 at a location between the shunt line 5 to be de~cribed later ana the cannulas 15. ;~hen the withdrawn blood is f`lowing smoothly through the line 1, the bag 9 is filled ith the blood and is thereby inflated. If thè line 1 is collapsed somewhere between the cannulas 15 and the 'oag 9, or if the blood is no-t withdrawn from the body for one reason or another, no blood is supplied to the bag 9. Since -the blood in the line 1 is drawn bv the pump 11 which is in operation at all times, the bag 9 is emptied of the blood and collapses. A sensor 27 is provided for detecting the state of the bag 9, i.e.
whether the bag 9 is inflated or collapsed. The detect-ing signal of the sensor 27 is fed to a con-trol uni-t 40.
If the bag 9 collapses, an alarm goes on, informing the operator of the trouble occurring in -the blood with-dra~!ing line 1. When necessary 9 the blood supply pump 14 may be brought out of operation in the event of the line 1 malfunctionin~. In the present embodiment, however, the pump 14 need not be sto~ped even if the line 1 is blocked since the blood is withdrawn through the overflow line 2 provided in parallel with the line 1.
A bottom portion of the blood reservoir 7 is 5 connected by a shunt line 5 to a portion of the line 1 7~

ups-Gr2am from the pump 11. The line 5 has an electro-magne~ic valve 32. The valve 32 and the electromagnetic valve 33 to be clescribed later are each a pinch valve.
i~hen Ihe valve 32 is open, the blood in the reservoir 7 is aspirated b~r the p~ 11 through the line 5 and returned to the reservoir 7 by ~ay OI the oxygenerator ana heat e~changer 6. Since a major portion of the blood arawn and for~Narded b~T the pump 11 is supplied via the line 5, the amount of venous blood withdrawn from the body is small when the valve 32 is open. When the valve 32 is closed, no blood is su-oplied through the line 5, with the result that the suction by the pump 11 acts entirely on the cannula 15 to withdraw an increased amount of venous blood from the patient.
The overflow line 2 is provided with a uni-t 20 for adjusting the central venous pressure (hereinafter referred to as "~VP"), v~hich is the mean pressure of the superior vena cava pressure and the inferior vena cava pressure and is given by -the inner tubes 17 of the pair of cannulas 15. The CVP aajusting unit 20 com~rises a support member 23 the position of which is vertically adjustable, and two vertical tubes 21 and 22 mounted on the support member 23. The vertical tube 21 is connected at i-ts lower end to the inner tubes 17 OI
the -two cannulas 15, while the lower end of the other 5'~
ld vextical tube 22 is in co:nmunication ~!ith the inlet of the p~p 12. T'~le u~per enG OI the ver-tical tube 21 communicates throu~l a horizontal tube ~ith an upper ~ortion of the vertical tube 22, ~.hich ha~ an u?per end extending u~ ard beyond the communicating portion and opened to the atmosphere. A sensor 24 for detec-ting an overflo~ of blood is disposed at a loca-tion sligh-tly below the communicating portion of the vertical tube 22.
Each of the sensor 24, the above-mentioned sensor 27, and the sensors 25, 26 to be described later is a photo-electric detector, for which infra.rec. rays are preferably used as the beam to be projected. Other sensors, s-uch 2S those utilizing ultrasonic waves or capacitance, are of cou-rse usable.
~ince the forward ends of the inner tubes 17 of the cannulas 15 are inserted into the superior and inferor venae cavae individually as already stated, portions of the venous blood flow into the inner tubes 17 individually from the -two venae cavae and join togeth-er, whereby the blood pressures of the two veins are averaged. The venous blood rises through the ver-tical tube 21 in accordace with the mean blood pressure, i.e.
the CVP. The level of the blood in the ver-tica.l tube 21 represents the CVP. The up~er limit level of CVP is determined by the height of the upper end of the vertical tube 21 from the heart OI the patient. 'ilhen -the ~JP i5 higher than the up,er limit level, the blood v,i-thin the vertical tube 21 overflo~Js the tube 21 into the vertical tube 22, so that this is detected by the sensor 24. The overflo~;r of bloocl is aspira~ed by the pump 12 and led in-to the reservoir 7. The unper li,mi-t level of CVP can be set to a desired value by adjustin~ the level of the support member 23.
The as~iration line 3 is provided for aspirating the blood released from the site of the patient operated on. The blood is sent to the reservoir 7 by the pump 13. The blood through the lines 2 and 3, although led directly into the rese-rvoir in ~ig. 1, may be fed to the oxygenerator and heat-exchanger 6 and then for~/arded to the reservoir 7 when so required.
The blood supply line 4 has one end connected to a bottom portion of the reservoir 7 and the other end connected to a cannula ~f~hich is inserted into the ascendin~ aorta of the patient. ~he refreshed blood stored in -the reservoir 7 is passed through the line 4 into the aorta by the pulsatile p~p la which is an arti~icial heart. The blood through the line 4 is pulsatile and therefore resembles the arterial blood forced out from the heart to produce a physiologically favorable influence on the patient. A reservoir 8 :-aisposed above the blood reservoir 7 for storing theblood to be transI`used has a bottom portion connected to an u-oper portion of the reservoir 7 by a tube 37.
The tube 37 has an electromagnetic valve 33. The sensor 25 detects that only a small amount of blood remains in the reservoir 7, while the sensor 26 detects that t~e reser~rolr 7 is filled with the blood to i-ts upper limit level. ~iYhen the small amount of blood remaining in the reservoir 7 is detected b~ the sensor 25, the electromagnetic valve 33 is opened to supply the blood from the re~ervoir 8. When the sensor 26 detects that the reservoir 7 has been filled with the blood to its upper li~it level, the valve 33 is closed to discontinue the supply of blood. The blood in the reservoir 8 may be supplied to the reservoir 7 by way of the oxygenerator and heat exchanger 6. The reservoir 8 may be connected to the aspiration line 3. Ringer's solution and other solutions or 2.rugs needed for the patient under opera-tion are admixed wi-th the blood in the reservoir 7.
Preferably an artificial kidney (not shown) is provided for filtering off such components from the blood in the reservoir 7 when the blood is diluted with these solu-tions -to an excessive volume.
The compressed air for ~riving the pulsatile pump 14 is supplied from an air source through a line 34, 7~5 ].3 which is ~ro~ided v~!ith ~ -pressure re~ulator 36, -tank 35 a.nd electroma~netic va.lve 31. As will be s-ta-ted later, -the valve 31 is controlled to open and close in.ermittently.
The control unit ~0 controls the electromagne-tic valves 31, 32 and 33. The u~i~ 40 receives detecting signals from the sensors 24, 25, 26 and 27, output si~nals from blood pressure transducers 41 and 42 for detecting the venous blood pressure and the arterial blood pressure (hereinafter referred to as "VP" and "AP" respectivel.y) of the patient, output signals from an electrocardio-~raph 43 for preparing an electrocardiogram for the patient, and output pulses from a heat rate generator 44. The blood pressure tranoducers 41 and 42 measure the blood pressures of the vena c va and the aorta res.pectively. ~'Ihen desired, the blood pressures of the superior and inferor venae cavae ma~- be measu-red individually, and the mean value of the measurements may be used as the VP (i.e. CVP).
~ig. 2 shows the construction of the control unit 40 in detail. The si~nals of the transducer 42 representin the AP and those of the electrocardiograph 43 are sent to a monito-r 45 equipped with a cathode-ray tube (CRT), on which the waveform of AP and the electro-cardio~ram are displayed. While the heart of the patient '5 7 is in operation, the blood is circulated through the body by the force of cardiac contraction. This mode of blood c rculation is termed "spontaneous circulation."
On the other hand, the intracorporeal circulation of the blood by the e~tracorporeal system of this invention, rarticularly by the pulsatile ump 14, is termed "forced circulation." The forced circulation can be effected by the pump 14 also during -the spontaneous circulation because there is the need to assist in the bloo~ circula-tion by the pump 14 when the spontaneous circulation isto be changed over to the forced circulation and vice versa, whereb~- the change-over can be accomplished smoothly. ~he AP signal from the blood pressure trans-ducer 42 and the output signal from the electrocardio-graph 43 are used as triggers for starting -the pump 14 during the spontaneous circulation. A trigger generating circuit 46 produces a trigger pulse when the AP signal waveform has reached a pea~. A trigger generating circuit 47 produces a trigger pulse upon the rise of R wave in the electrocardiogram. ''lith reference to the AP waveform and electrocardiogram on the monitor 45, the operator can select one of the two trig~er pulses by 2 selecting switch 48. ~he selected trigger pulse is sent to an AND circuit 54 and to a timer 51.
For the forced circulation, the heart rate 7'~5~

enerator 44 produces t-rigger pulses of ~requency set b~ its setting device 44a. The heart rate can be set as desired by the setting device 44a. The trigger pulse from the gener2tor 44 is fed to an AND circuit 55.
.~ switch 49 is used for setting the forced circulatlon.
When the forced circula-tion is set by the switch 49, a high (H) level signal is given to an OR clrcuit 52.
It is likely that the heart of the patient will stop temporarily without u~dergoin~ periodic contraction when spontaneous circulation is changed to forced circulation and vice versa. If the heart fails to function for spontaneous circulation, the blood will not circulate through the body, so that the circulation mode must be changed over to forced circula-tion tempo-rarily. The timer 51 is reset by the trigger pulse ofthe generating circuit 46 or 47. If the timer 51 is not reset again upon lapse of a predetermined period of time, e.g. 2 seconds, after resetting, the timer produces an H level signal, which is fed to the OR
circui-t 52. li~lhen forced circulation is set by the switch 49, or when the heart of the patient does not repeat contraction even upon the lapse of 2 seconds, the OR
circuit 52 produces an H level signal, which is deli~ered tothe AND circuit 55. Accordingly the trigger pulse from the heart rate generator 44 passes through the 77~'i' A~ ci-rcuit 55 and then th-rough an OR circuit 56 and ls fed to a delay circuit 57. The r.1 level signal from the OR clrcuit 52 is inverted by a ~OT circuit 53 to a low (~) level signal, which is given to the A~D
5 circuit 54. Accordin~ly the AND circuit 54 inhibits passage of the trigger p-ulse from the sv~itch 48. If forced ci-~culation is not set, a~d the heart is repeat-ing contraction with a period of ~7iu~in 2 seconcls, the output of the OR circuit 52 is at Ilevel, and the output of the NOT circuit 53 is at H level. In this case, the -trigger pulse from the generating circuit 46 or 47 passes through the AND circuit 54 and is fed to -the delay circuit 57 through tl1e OR clrcuit 56.
The AND circuit 55 prevents passage of the tri~ger 15 pulse from the generator 44.
The delay circuit 57 delays the trigger pulse fed thereto for a predetermined period of time. This is of importance durin~ spontaneous circulation. In the case of spontaneous circulation, the pump 14 for supplying the blood assists the heart of the patient in supplying the blood, so that the two blood supplies must be in synchronism. It is preferable that the pump 14 supply the blood with a time delay after the arterial blood is supplied by the heart. This is 25 termed "counter pulsation." The delay circuit 57 77~7 determines this delay time, rlhich is preferably so determined as to be dependent on the period of systole of the heart. ~he delay -time is obtained, for example~
by multiplying the previous pe-riod OI systole measured or the mean value of preceding periods of systole by a sui-table percentage. ~he measurement of the period and the calculation of the dela-y~ time can o~ course be performed automatically by a control circuit (not sho~m).
The percenta.ge is variable as desired.
The ~ridth of the delayed trigger pulse is shaped to resemble the systole time of the heart by a pulse width setting circuit 58. ~he control pulse delivered from the circuit 58 is sent throu~h A~D
circuits 59 and 60 to the electromagnetic valve 31 to open the valve. The valve 31, when opened, permi-ts supply of compressed air to the pump 14 to contract the pump 14 and supply the blood. Accordin~ly the ~idth of the output pulse of the circuit 58 determines the contraction time of the pump 14. Prefarably the contraction time corres~onds to the s~-stole time of the heart. ~he pulse wid-th is calculated also based on the period of systole of the heart. In the case of forced circulation, the delay time of the circuit 57 and the pulse width of the circuit 58 are determined preferably ill accordance with the heart rate set by the ~enerator ~4.

The AP is used also for controlllng the start and discontinuance of the operation of the pulsatile pump 14. The AP
signal from the blood pressure transducer 42 is applied to a peak hold circuit 61 and a mean value calculating circuit 62. While the heart ~f the patient is in operation and also while the pump 14 is in operation, the arterial blood is pulsating. Accordingly the AP signal has a pulsatile waveform. The peak value of the pulsatile AP signal, corresponding to the systolic pressure, is held by and sent out from the hold circuit 61. The systolic pressure signal is fed to an upper limit detecting circuit 63 and a lower limit detecting circuit 64. An upper limit value (e.g.
150 mm Hg) for the systolic pressure is set on the upper limit detecting circuit 63. When the systolic pressure input signal is in excess of the upper limit value, the circuit 63 emits an H level signal. A lower limit value (e.g. lO0 mm Hg) ~or the highest blood pressure is set on the lower limit detecting circuit 64. If the systolic pressure input signal is below the lower limit value, the circuit 64 delivers an H level signal. The upper limit value and the lower limit value are variable.
The detecting signal from the upper limit ~ -18-~L~7~757 detectin~ circuit 63 is sent throu~h an OR circuit 67 to the se-t input terminal of a flip-flop 69. The detect~
ing si~nal ~rom the lower llmit detectinr~ circuit 64 is sent through an OR circuit 68 to the reset input terminal of the flip-flop 69. The flip flop 69 is initially reset. 'i~hen the flip-flop 69 is reset, the inverted output thereof is at H level, and at this time, the cont-rol pulse of -the circuit 58 is sent throu~h the ~D ci-cuit 59 to the valve 31. When the flip-flop 69 is set, the inverted output the-reof is at ~ level, so that the passa~e of the control pul~e is prevented.
Consequently the pump 14 is brour~ht out of operation ,rhen the hi~hest AP value exceeds t~le upper limit value, ~lhereas the pump 14 is initiated into operation when the value drop~ below the lower limit value. The high-es-t AP value is alwa~-s maintained a-t a level between the upper limit value and the lo-ver limit value.
While the pump 14 is heid out of operation, no peak appears in the AP si~nal. ~Ihen the blood supply pump is not a pulsatile pump but a rotary pump, -the blood is continuously forced into the artery of -the patient, so that no peak appears in the AP sir~nal. The mean value calculatin~ circuit 62 is provided to meet such a situation. The peak hold circuit 61 has the function of producin~ a no-peak si~nal when no pulse _ 1 9 ~'7~ 5'7 appears in the AP signal for a specified periocl of til~e. The llo-pea.k signal i9 applied to the calculatln circuit 62, whereupon the circuit 62 functions to calculate and deliver the mean value of the ~P si~nal everJ specified periocl of time. The mean value signal is sent to upper and lower limit detectin~ circuits 65 and 66, on which upper and lower limit values are set respectively. `~ihen the mean value signal e~ceeds the upper limit value and when the si~nal drops below the lower limit value, the circuits 65 and 66 each produce an H level detectin_ signal, which is fed to the flip-flop 69 in the same manner as above.
The detecting signal (H level) from the sensor 24 of the ~VP adjusting unit 20 has its ~aveform shaped by a waveform shapin~ circuit 73 and then applied to the set input terminal of a flip-flop 74. The ~P
si~nal from the blood pressure transducer 41 is fed to a mean value calculating circuit 71, in which the mean value thereof is calculated every specified time interval. The mean value signal is delivered to a lower limit detecting circuit 72, on which a lower limit value for the venous blood pressure is set. When the mean YP value drops below the lower limit value, the circuit 72 emits an H level detecting signal, which is given to the reset inpu-t terminal of the flip-flop 74.

~t~ 5~f The flip-llop 74 is initiall~ reset. ~3/hile the flip-lop 74 is reset, the inver-ted output si~nal thereof is at H level. The ~ level signal opens the electro-ma~netic valve 32. blhen the flip-flop 74 is set by an overflow de-tecting signal fro~the sensor 24, the flip-flop delivers an inverted output at I level to close the valve 32. ~onsequently the pump 11 withdraws an increased amount of blood as already described.
Thus, if the C~P exceeds the upper limit level (e.g.
10 to 20 mm Hg),for example, due to the con~estion of blood in the body, the valve 32 closes, whereas if the mean VP value drops below the lo-ier limit value (e.g.
several mm ~g), the valve 32 opens. The ~VP is there-fore maintained at an approximately constant level at all times.
The blood pressure transducer 41 and the ci-rcuits 71 and 72 are not always necessary; the valve 32 may be controlled only with the detecting signal of the sensor 24. In this case 7 the electroma~netic valve 32 is held open at all times and is closed only while the sensor is detecting an overflow, ~hereby the CVP
can be kept appro~ima-tely constant if the upper limit for the CVP is set at a suitable level.
The detectin~ signals from the sensors 25 and 26 are fed to a valve control circuit 81. When the ~ ~7~

sensor 25 ~etects that the blood in the reservoir has reduced to below a specified level, the circuit 81 emits an H level signal to open the valve 33 until the sensor 26 gives an u~e-r limit level detec-ting si~nal.
~he ~ level signal is sent through a NOT circuit 82 to -the A~1D circuit 60. Accordingly when the blood remaining in the rese-rvoir is found to be in a small a~ount, tne control pulse from the circuit 58 does not pass- the AND circuit 60 9 and the motor 14 comes to a stop. This prevents air from flo~ring into the artery of the patient. However, if the level to be detected by the sensor 25 is set at a relatively high level, the pu~p 14 need not alwa~s be stopped even if the sensor 25 emits a detecting signal.
Figs. 4, 5 and 6 show other examples o~ CVP
adjusting units. With reference to Fig. 4, a vertical tube 21 has an extension 21a extending vertically beyond the portion thereof communicating with a vertical tube 22. The extension 21a communicates at its upper end with the tube 22. When the CVP increases abruptly beyond its upper limi-t level, the pressure in excess of the upper limit level can be measured by the extension 21a. A sensor 24 may be disposed in the vicinity of the com~unicating portion of the vertical tube 21.
~i~. 5 shows pairs of vertical tubes 21A, 22A;

~7t7~,t;, 21~, 22~; and 21C, 22C. The vertical tubes 21A to 21C
have communica-ting portions at different levels. The other vert~ca,l tubes 22A to 22C are provided with sensors 24A to 24~ for detectin~ an overflow of the blood, res;oectively. A plurality of ~VP measurin~, levels can be set on this CVP ad~us-ting unit. l~`/hen the detecting signals from the sensors 24A -to 24~ are used for controllin~ the openin~ de~ree of the valve 32, the C~P is controllable in a finer more accurate manner.
With the arrangement of Fig. 5, the vertical tubes 22A, 22~ are provided with electroma~netic valves 38A, 38~, respectively. These valves 38A, 38~ are open usually and are closed when the corresponding sensors 24A, 24 have detected an overflow of blood. The valves are opened again when the ~VP lowers to eliminate the over-flow.
The overflow line 2 shown in ~ig. 6 is provided only wi-th a vertical tube 21 the upper end of which is open to the atmosphere. The line 2 has an electro-magnetic valve 39 positioned closer to the pump 12. Thevertical tube 21 is fi~ed in place, while a sensor 24 is movable upward or downward along the tube 21 as suppor-ted onthe tube. The valve 39 is closed usually but is opened when the sensor 24 detects the blood reachin~ the level of the sensor. Thus the blood is ~ ~ ~7'75~

aspirated throu~h the line 2 as is the case with an overflow. ~he u~per limit level for the CVP is settable as desired by varyin the level of the sensor 24.
Fi~. 7 shovJs another example of blood supply line. ~etween a blood reservoir 7 and a pump 14, the blood su~-ply line 4 is provided with a rotary pump 91 and an electromagnetic valve 93 positioned downstream from the pu~p 91. In parallel with the rotary pump 91.
a return line is connected to tne line 4, with another electromagnetic valve 92 provided on the return line.
For forced circulation, the p~p9 91, 14 operate, and the valve 92 is closed with the valve 93 opened, whereby the blood in the reservoir 7 is aspirated by the p~p 91 and intermittently forced out by the pump 14. If the hi~hest AP value exceeds an upper li~it value, the valve 92 is opened and the valve 93 is closed, so that the blood circulates throu~h the return line and the pump 91 without flovrin~ into the pump 14. At this time, the pu~p 14 may be in or out of operation~
When the hi~hest AP value drops below a lower limit value, the valve 92 is closed again and the valve 93 is opened.
While the heart of the patient is in operation to circulate the blood spontaneously, the pressure of the left atrium (hereinafter referred to as "~AP") can ~'7~ 5 be measured. Accordin21y the blood circulation can be so controlled that -the left side s~y-stem of the heart and the risht side s~-stem of the heart wlll function in sood balance. The ~AP reflects the function of the left heart system, vrhile the ~VP reflects the function ol the right heart system. The range of desire~ values of ~AP (e.g. 8 to 15 mm Hg) is p-recLetermined, and the CVP is so adjusted that the IAP ~lill be maintained in this range at all times.
With reference to Fig. 8, the TAp is detected by a pressure transducer 101. The means IAP value is ca~culated at a specified time interval by a mean value calculating circuit 102. The u~per limit value (e.g.
15 mm ~g) of the desired range of ~AP values is set on an upper limit detecting circuit 103. Vlhen the output from the circuit 102 e~ceeds the upper limit value, tL~le circuit 103 emits an up~er limit detecting signal. The lower limit value (e.g. 8 mm Hg) of the desired ~AP
range is se-t on a lower limit detecting circuit 104.
When -the ~AP drops belo~v the lovler limit value, the circuit 104 emits a lower limit detectin~ signal. ~evel control means 105 raises or lowers the upper limit level of CVP in the CVP adjusting unit 20. With the unit 20 shown in ~i~. 1, the vertical tubes 21, 22 and the support member 23 are raised or lowered. With the ~77~'~

arran~ement sho-im in PiT. 6, the blood sensor 24 is raised or lowered. When the detected IAP value is above the upper limit settin~, the upper limit level for CVP is slowly lowered until the LqP lowers below the u~per limit value. Conversely if the detected ~AP
value is below the lower limit, the upper limit level for the CVP is slowly raised. The rise of the CVP u~er limit level is stopped when the IAP exceeds the lower limit value. In this wa~-, the IAP is maintained in the desired ran~e at all times.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A system for circulating the blood extracorporeally comprising:
a blood withdrawing line, a reservoir for the blood withdrawn, means for detecting that the venous pressure has exceeded a predetermined upper limit level, said means comprising first and second vertical tubes communicating with each other at their upper ends and being vertically adjustable, at least one of the vertical tubes having an upper end open to atmosphere, and a blood sensor positioned to detect blood flowing over the communicating portion from one of the vertical tubes to the other; and means for increasing the amount of blood to be withdrawn when the venous pressure has exceeded the upper limit level.

2. A system as defined in claim 1 wherein the venous pressure detected is the central venous pressure.

3. A system as defined in claim 1 wherein the blood amount increasing means comprises a blood withdrawing pump provided on the blood withdrawing line, a shunt line connecting the reservoir to the inlet side of the blood withdrawing pump, a valve provided on the shunt line and usually open, and a valve control circuit for closing the valve when the venous pressure has exceeded the upper limit level.

4. A system as defined in claim 1, further comprising:
an overflow line, a reservoir for the blood withdrawn and overflowed, a cannula comprising an outer tube having a slightly tapered forward end being formed with a number of holes and rear end connected to the withdrawing line, and an inner tube having a forward end being opened at the forward end of the outer tube and rear end extending outward from the outer tube, and blood overflowing means having two vertical tubes communicating with each other at their upper ends, at least one of the vertical tubes being opened to the atmosphere at its upper end, wherein one of the vertical tubes being connected at its lower end to the rear end of the inner tube of the cannula and the other being connected at its lower end to the overflow line.

5. A system as defined in claim 4 including a pump for leading the overflow of blood into the reservoir.

6. A system as defined in claim 4 or 5, including:
two said cannulae, and means for adjusting the central venous pressure said means comprising said blood overflowing means, wherein the outer tubes of said cannulae are connected at their rear ends to the withdrawing line and the inner tubes of said cannulae are connected at their rear ends to said vertical tube of said blood overflowing means.

7. A system as defined in claim 1 further comprising:
a blood supply line for sending out the blood from the reservoir, a blood supply pump provided on the blood supply line and serving as an artificial heart, a blood pressure transducer for measuring the arterial pressure, and means for controlling the blood supply pump in response to an output from the blood pressure transducer to maintain the arterial pressure in a predetermined required range.

8. A system as defined in claim 7 wherein the means for controlling the blood supply pump comprises an upper limit detect-ing circuit for detecting that the arterial pressure has exceeded a predetermined upper limit value, a lower limit detecting circuit for detecting that the arterial pressure has lowered below a pre-determined lower limit value, and a control circuit for stopping the blood supply pump upon detecting the upper limit and for oper-ating the blood supply pump upon detecting the lower limit.

9. A system as defined in claim 7 wherein the blood supply pump is a pulsatile pump.

10. A system as defined in claim 1, including an artificial lung provided on the blood withdrawing line, a blood supply line for sending out blood from the reservoir, and a blood supply pump provided on the blood supply line and serving as an artificial heart, an apparatus for adjusting the pressure of the left atrium comprising:
means for detecting that the venous pressure has exceeded an upper limit level, means for increasing the amount of blood to be withdrawn when the venous pressure has exceeded the upper limit level, means for detecting the pressure of the left atrium, and means for varying the upper limit level for the venous pressure in accordance with the pressure of the left atrium to maintain the pressure of the left atrium in a predetermined range.