EXTRACORPOREAL PULSATILE PUMP OR FLOW MODULATOR TO BE ADDED TO AN EXTRACORPOREAL CONTINUOUS FLOW PERFUSION SYSTEM

Abstract: At present the extracorporeal systems (heart lung machine, called here HLM) use continuous flow pumps; but this continuous flow is completely different from the pulsatile flow produced by the natural heart, to which the human body is used to. Therefore, in many places, studies on extracorporeal systems using pulsatile blood pumps are going on. If a pulsatile pump replaces the HLM continuous flow pump (one pump system), there is a pulsatile flow in the oxygenator and in the cannula connecting the oxygenator to aorta. Therefore the cannula's inertance influence (which is greater than its compliance influence) and the oxygenator mechanical impedance make necessary high positive and negative peaks in the pump pressure, during the corresponding flow rate increase and decrease phases, to obtain the correct pulsatile flow waveform. But the positive peaks can be obtained while the negative are limited by the blood vapour tension. The consequence is the difficulty to generate the correct flow waveform (necessary to produce the correct aortic pressure waveform) and the possibility to damage the blood. Aim of this invention is the use of an active or passive device, that can be inserted at the end of an HLM, immediately before the connection to aorta (or also immediately after the oxygenator, but using a cannula with a proper distributed compliance in order to compensate its inertance) which allows to have pulsatile flow only in the terminal part of the cannula, so strongly reducing the negative effects of the inertance. This device periodically injects energy to the fluid, so to produce the pulsatility, taking it from an own energy source (active device), or using energy supplied by the continuous flow pump of the HLM (passive device made by a compliance plus an on-off valve).

Description: Description Extracorporeal pulsatile pump or flow modulator to be added to an extracorporeal continuous flow perfusion system General Description of the field of application of the invention In some cardiosurgery operations it is necessary the use of the HLM in which continuous flow pumps are used (Fig 1 a) But the human body is used to the pulsatile blood flow, produced by the heart Results obtained in total artificial heart and in ventricular assist devices applications, which generate pulsatile flow and allows survival more than one year, suggest that the pulsatile flow is definitely not dangerous and better than continuous flow Moreover the needs to use cardiopulmonary bypass during the always longer and complex surgery operations, suggest the opportunity to switch from continuous to pulsatile flow A way is to replace the continuous flow pump used in the HLM with a pulsatile pump Another way is to add a pulsatile pump in the terminal part of an HLM, matching the pulsatile pump behaviour to the HLM behaviour, to obtain that the average (on one or more periods) pulsatile pump flow could be equal to the flow of the continuous flow pump and that the pressures in the circuit between the pumps could be correct A third way is to use, always in the terminal part of an HLM, a flow modulator device which, properly filling and ejecting, produces a negative or positive flowrate that is subtracted or added to the continuous flow, so realizing the desired correct flow waveform and, as a consequence, the correct pressure waveform in aorta If the continuous flow pump has a pressure depending flow (for instance the centrifugal pump Medtronic Bio-Medicus), the flow modulator must be properly controlled in order to compensate the flow fluctuations of the continuous flow pump These are due to the pulsatility of the aortic pres- sure which, coming back through the aortic cannula, produces a pulsatile load to the output of the continuous flow pump. In all the solutions the flowrate of the pulsatile pump or of the modulator, which is given by HR*SV (HR=pump or modulator frequency; SN= pump or modulator stroke volume), can be regulated by modifying HR and/or SV. In the first solution, (one pump system), the pulsatile flow is present in the oxigenator and in the cannula connecting the oxigenator to aorta. Therefore the cannula' s inertance influence (which is greater than its compliance influence) and the oxigenator mechanical impedance make necessary high positive and negative pressure peaks in the pump, during the corresponding flow increasing and decreasing phases, to obtain the correct pulsatile flow waveform. But while it is possible to reproduce the increasing flow phase by proper positive pressure peak in the pump, it can result impossible to reproduce the decreasing flow phase if the negative pressure peak, which is necessary to reduce the blood velocity in the aortic cannula, is lower than the blood vapour tension. The consequence is the difficulty to generate the correct flow waveform (necessary to produce the correct aortic pressure waveform) and the possibility to damage the blood. To compensate this problem should be necessary to use a cannula (from oxigenator to aorta) having an increased distributed compliance, and to control the pump, according to the desired and the measured (immediatly before the input to aorta) flow waveforms and to the average flow value selected from the perfusionist. This principle could be applied also to the second and the third solution, allowing to put the pulsatile pump or the modulator immediatly after the oxigenator: in these cases the control system of the pulsatile pump or of the modulator has to compensate only the cannu- la These solutions, however, seem to be complex and expensive, particularly the first one which requires to compensate not only the cannula, but also the oxigenator Aim of the invention is the development of an active or passive device, which can be added at the end of any continuous flow HLM, immediatly before the connection to aorta (or immediatly after the oxigenator, but using a cannula having a radial elasticity, and as a consequence a proper distributed compliance, plus a proper control system), so that the flow at the output of this device, going to aorta, is pulsatile according to a physiological or, anyway, adequate waveform These systems can be active or passive type The active systems use any rotational or linear motion electric motors, by which it is possible to produce a reciprocating movement of a piston The passive systems use the energy supplied by the continuous flow pump of the HLM In this case the basic elements of the device are a compliance and an electrovalve When the electrovalve is closed, blood coming from the continuous flow pump is stored in the compliance, where - as a consequence - the pressure increases When the electrovalve opens, in the output there is a flow to aorta that is the sum of the continuous flow coming from the HLM and of the flow produced by the discharge of the compliance If a proportional electrovalve is used, it is possible to control the instantaneous flow to aorta according to the desired waveform These devices can operate and be controlled in different ways, according to the desired performances If the device is a pulsatile pump (active, pulsatile system having input and output unidirectional valves) it can operate as an artificial ventricle, moreover an artificial atrium is needed at its input in order to adapt the continuous (or about continuous) flow coming from the oxigenator to the pulsatile filling flow of the pulsatile pump The stability of the system (average flowrates balance between the continuous or about continuous flow and the pulsatile flow) and proper values for the artificial atrium pressure, can be obtained by using 75 the artificial atrium pressure as a control variable of the pulsatile pump average flow (particularly of HR when the pump is working with a fixed SN), operating similarly to the natural heart (Starling law) According to this, the pump flowrate is a function of the atrial pressure and increases (decreases) when atrial pressure increases (decreases) So, when the value of the continuous flow is modified by the perfusionist (for instance increases), in the 80 atrium starts an increase of pressure, till a value -which for- the increasing pulsatile pump average flowrate is equal to the continuous or to the average of the about continuous flow This device allows different operation modes tipical is the "full fill - full empty" mode When the ventricle is completely filled, starts its ejection with a duration which is depending on its previous filling time and on the systole/ diastole ratio The sum of the ejection time 85 and of the filling time is the period, from which is derived HR In this approach the possible available knowledge of the flowrate, selected by the perfusionist, is not necessary to the control system of the pulsatile pump (Fig 1 b) If the device is a flow modulator (active, pulsatile system without input and output unidirectional valves), it fills with a flowrate equal to that one coming from the continuous 90 flow pump, so annulling the flow to aorta; then it ejects the filling volume with a proper flow waveform that, combined with the flow coming from the continuous flow pump, produces the physiological or, anyway, adequate flow waveform to aorta If the modulator is working with a fixed stroke volume SV and flowrate waveform, its fre- quency, (that, for instance, can be varied between 60 and 120 beats/min) depends on the average flowrate of the continuous flow pump In this solution it is necessary to measure the instantaneous flowrate at the input or output section of the modulator (better if in the section of the cannula, immediatly before the input to aorta) and use this information to 75 control the motion of the piston and the frequency HR (Fig 1 c) If the continuous flow pump is a roller pump (approximately its flow rate is not depending on its pressure load) and if limited performances are accepted, the control system can be semplified using an approximate knowledge of the roller pump flowrate to control the HR of the modulator In this case, if the used HR is a little lower (higher) than the correct value, there is a little flow 80 from modulator to aorta (from aorta to modulator) during the time interval in which the the flow should be zero This system is more simple than the pulsatile pump there are no valves, no artificial atrium, moreover the necessary ejected volume (stroke volume) is lower than the one in the pulsatile pump 85 Fig 2 shows the basic fluid-dynamic properties of the two systems An interesting characteristic of these devices is that it is possible to stop them while the HLM is working, so restoring the continuous flow, if desired The proposed devices can operate correctly with any extracorporeal system using any type of continuous (constant or about constant) flow pump Another relevant characteristics are 90 the reduced dimensions of the device, as this must be positioned near the patient for a better operation mode, and a reduced priming volume Description of the preferred embodyment The preferred, but not the only, layout is shown in Fig 3 The piston, which can't rotate, is is moved in a reciprocating fixed linear stroke mode by three cams having a proper profile, 95 producing the ejection motion and the filling motion The actuator is an electric motor whose angular velocity is properly reduced by a gear set A constant angular velocity of the motor, and then of the three cams on which are rolling three standard bearings, produces a fixed flow profile If desired it is possible to modify the flow profile by using a proper angular velocity profile, so to obtain the physiological or - more generally - the adequate to 100 the patient, flow profile for the different working modes The piston squeezes and releases a deformable blood chamber, made by biocompatible material, connected to the oxigenator and to the patient In the chamber, blood is continuously coming from the oxigenator, pushed by the continuous or about continuous flow pump located before the oxigenator, and from the chamber is coming out blood -with a pulsatile flow- which is going to the patient 105 The frequency HR of the modulator, having a properly selected constant stroke volume SVm, is correlated to the average flowrate Q of the HLM pump, selected by the perfusionist, with a relation as HR = k*Q If, for instance, 4<=O <=8 liters/min and k=15 (beats/min)/(liters/min), the frequency is ranging from 60 to 120 beats/min Moreover if the systole/diastole ratio of the pulsatility is assumed equal to 0 5 and constant for semplicity, it 110 follows that S Vm= about 45 ml Fig 4 shows the profiles of three possible cams, having a relative mechanical angular phase relation equal to 2 π / 3 In Fig 5 it is shown the inner of the mechanism of Fig 3, which produces the motion law indicated in Fig 4 It is possible to combine the three cams in one (reducing the angular velocity to 1/3 of the previous value), so obtaining a more compact 115 device For semplicity in the following we name ECP the continuous flow pump (peristaltic pump, roller, centrifugal or similar) of the extracorporeal systems (HLM) used in cardiosurgery, and we name PulsaDev our device (active systems as pulsatile pump or modulator, or passive systems)

Claims: Claims 1) PulsaDev (pulsatile device) located between the output of the oxigenator and the input to the patient, converts the continuous -or about continuous- flow, coming from the oxigenator into a pulsatile physiological -or more generally adequate to the patient- flow, going to the patient, using a variable volume chamber without valves (flow modulator); the modulator has a flow transducer located at its input or output section (in this case it is better immediatly before the connection to aorta) and a control system which matches the PulsaDev operation mode to the ECP flow, selected by the perfusionist, and to the need of correct flow (and, as a consequence, pressure) waveform in aorta. 2) PulsaDev, as in claim 1, has its average flow selected directly from the perfusionist or automatically from the ECP. 3) PulsaDev, as in clai 1, uses a variable volume chamber with valves (pulsatile pump), having a compliance at its input (artificial atrium made by an elastic chamber), and is controlled by the artificial atrium pressure, realizing the Starling law as in a natural ventricle; the artificial atrium compliance and the "flowrate- artificial atrium pressure " relation are adequate to the modulator and the extracorporeal system characteristics. This device allows different operation modes: tipical is the "full fill-full empty" mode. When the ventricle is completely filled, starts its ejection, with a duration which is depending on its previous filling time and on the systole/diastole ratio. In this way the pulsatile pump frequency HR is the consequence of the ECP flowrate. ) PulsaDev is located between the output of the oxigenator and the input to the patient, and produces pulsatile flow by using energy supplied by ECP and available by the blood. The energy is stored in a compliance (made by an elastic chamber), in the phase during which the flow to the patient is zero and the pressure in the compliance increases. This is obtained by a closed valve located between the compliance and the patient. The energy is then released by the opening of this valve to realize the ejection to aorta. In this way the flow to aorta is the sum of the ECP continuous flow and the flow due to the discharge of the compliance. A control system calculates the opening and the closing phases durations of the valve; and it can also control the opening and the closing waveforms of the (proportional) valve, in order to obtain the instantaneous flow to aorta desired waveform. 5) PulsaDev, as in claims 1-3, has the piston motion generated mechanically by the rotation of a proper cam, which produces the desired motion law using a motor, working with constant angular velocity, whose value depends on the required average flowrate in the cycle. 6) PulsaDev, as in claims 1-3, has the piston motion generated by a velocity controlled motor, connected to the piston by any mechanism, whose characteristics are compensated to obtain the desired motion law. 7) PulsaDev, as in claims 1-3, has the piston motion generated by a linear motion motor - controlled in position or in position&velocity- connected directly to the piston, to obtain the desired motion law.

Inventors: ARABIA MAURIZIO, DANIELI GUIDO A, ARABIA, MAURIZIO, DANIELI, GUIDO, A.
Applicants: ARABIA MAURIZIO, DANIELI GUIDO A, ARABIA, MAURIZIO, DANIELI, GUIDO, A.
Application year: 2000
Main classification: A61M1
IPC codes: A61M1