Development of "plug and play" TransApical to aorta VAD

Our TransApical to Aorta pump, a simple and minimally invasive left ventricular (LV) assist device, has a flexible, thin-wall conduit connected by six struts to a motor with ball bearings and a turbine extending into the blood path. Pulsatile flow is inherent in the design as the native heart contraction preloads the turbine. In six healthy sheep, the LV apex was exposed by a fifth intercostal left thoracotomy. The pump was inserted from the cardiac apex through the LV cavity into the ascending aorta. Aortic and LV pressure waveforms, pump flow, motor current, and pressure were directly measured. All six cannula pumps were smoothly advanced on the first attempt. Pump implantation was <15 minutes (13.6 +/- 1.8 minutes). Blood flow was 2.8 l/min to 4.4 l/min against 86 +/- 8.9 mm Hg mean arterial blood pressure at maximum flow. LV systemic pressure decreased significantly from 102.5 +/- 5.55 mm Hg to 58.8 +/- 15.5 mm Hg at the fourth hour of pumping (p = 0.042), and diastolic LV pressure decreased from 8.4 +/- 3.7 to 6.1 +/- 2.3 mm Hg (p > 0.05). The pump operated with a current of 0.4 to 0.7 amps and rotation speed of 28,000 to 33,000 rpm. Plasma free hemoglobin was 4 +/- 1.41 mg/dl (range, 2 to 5 mg/dl) at termination. No thrombosis was observed at necropsy.A left ventricular assist device using the transapical to aorta approach is quick, reliable, minimally invasive, and achieves significant LV unloading with minimal blood trauma.     

A pulsatile control algorithm of continuous-flow pump for heart recovery

The intra-aorta pump is a novel continuous flow (CF) left ventricular (LV) device. According to literatures, the pulsatile flow LV device can provide superior LV unloading and circulatory support compared with CF LV assist devices at the same level of ventricular assist device flow. Therefore, a pulsatile control algorithm for the intra-aorta pump is designed. It can regulate the pump to generate pulsatile arterial pressure (AP) and blood flow. A mathematic model of the cardiovascular-pump system is used to verify the feasibility of the control strategy in the presence of LV failure. The surplus hemodynamic energy (SHE), pulsatile ratio (PR), and pulsatile attenuation index (PAI) are used to evaluate the pulsatility of AP and blood flow. The SHE is 8,012.0 ergs/cm(3) by using the pulsatile control strategy (PCS) compared with 5,630.0 ergs/cm(3) by failing heart without support. The PR is 0.302 in the PCS vs. 0.315 in failing heart without support. Meanwhile, the PAI is 85.9% in the PCS compared with 69.7% in failing heart without support. The results demonstrate that the presented control strategy can maintain the pulsatility of AP and blood flow. Moreover, the pulsatile controller provides notably LV unloading. To test the response of the controller to the change of blood demand of patients, another simulation is conducted. In this simulation, the peripheral resistance is reduced to mimic the status of a slight physical active; the Emax is increased to simulate the ventricular contractility recovery. The simulation results demonstrate that the proposed control strategy can automatically regulate the pump in response to the change of the parameters of the circulatory system. To test the dynamic character of the intra-aorta pump, an in vitro experiment is conducted on an in vitro experiment rig. The experimental results demonstrate that the intra-aorta pump can achieve the pulsatile pump speed calculated by the pulsatile controller. The PCS is feasible for the intra-aorta pump. As a key feature, the proposed control strategy provides adequate perfusion in response to the change of blood demands of patients, while restoring the pulsatility of AP and blood flow.     

In vitro evaluation of the PUCA II intra-arterial LVAD

The "pulsatile catheter" (PUCA) pump is a minimally invasive intra-arterial left ventricular assist device intended for acute support of critically ill heart failure patients. To assess the hydrodynamic performance of the PUCA II, driven by an Arrow AutoCat IABP driver, we used a (static) mock circulatory system in which the PUCA II was tested at different loading conditions. The PUCA II was subsequently introduced in a (dynamic) cardiovascular simulator (CVS) to mimic actual in vivo operating conditions, with different heart rates and 2 levels of left ventricular (LV) contractility. Mock circulation data shows that PUCA II pump performance is sensitive to afterload, pump rate and preload. CVS data demonstrate that PUCA II provides effective LV unloading and augments diastolic aortic pressure. The contribution of PUCA II to total flow is inversely related to LV contractility and is higher at high heart rates. We conclude that, with the current IABP driver, the PUCA II is most effective in 1:1 mode in left ventricles with low contractility.     

Analysis of the relationship between left ventricular pressure and motor current for evaluation of native cardiac function during left ventricular support with a centrifugal blood pump

Control of the ventricular assist device (VAD) for native heart preservation should be attempted, and the VAD could be one strategy for dealing with the shortage of donors in the future. In the application of nonpulsatile blood pumps for ventricular assistance from the ventricular apex to the aorta, bypass flow and hence the motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous-flow pumps, in this study we investigated whether motor current could be used as an index for continuous monitoring of native cardiac function. In study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mmHg, afterload of 40 mmHg, and LV systolic pressure of 40 mmHg was used. The pump speed was fixed at 1300, 1500, and 1700 rpm, and LV systolic pressure was increased up to 140 mmHg by steps of 20 mmHg while the changes in LV pressure, motor current, pump flow, and aortic pressure were observed. In study 2, an in vivo experiment was performed using three sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LVP was varied through administration of dopamine while the changes in LV pressure, pump flow, and motor current at 1500 and 1700 rpm were observed. An excellent correlation was observed in both in vitro and in vivo studies in the relationship between motor current and LV pressure. In study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1300, 1500, and 1700 rpm, respectively. In study 2, they were 0.88 (animal no. 1), 0.83 (animal no. 2), and 0.88 (animal no. 3) for 1500 rpm, and 0.95 (animal no. 2) and 0.93 (animal no. 3) for 1700 rpm. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VAD for native heart preservation.     

Pulsatile ECMO in neonates and infants: first European clinical experience with a new device

This study presents the first European clinical experience with the Medos DeltaStream DP1, a new pulsatile flow pump, in neonates and infants. Between January 2002 and December 2004, 420 patients at our institution underwent congenital heart surgery on cardiopulmonary bypass. During this period, 10 patients required extracorporeal membrane oxygenation (ECMO) support for acute postcardiotomy heart failure. Seven patients (median age 7 days, range 1-70 days), were supported by a nonpulsatile Biomedicus centrifugal pump, whereas three patients (aged 1 month, 1 year, and 12 years) were supported by a pulsatile Medos DP1. The DP1 is an extracorporeal rotary blood pump. The pump features a diagonal-flow impeller, and can be used for both continuous and pulsatile output. Special characteristics include a small priming volume of approximately 30 ml and a high pumping capacity. A temperature sensor and speed sensors are integrated in the pump. The pump has a delivery rate of up to 8 l/min and a speed range of 100-10,000 rpm. Overall mortality was 40% (4 of 10 patients), and all four deaths were in the nonpulsatile Biomedicus group. In the nonpulsatile group, the median support duration was 95 hours with a range of 48-140 hours. Two patients assisted with the pulsatile pump system were successfully weaned after 36 and 53 hours, respectively; the 12-year-old patient was successfully transplanted on the eighth postimplant day and discharged from the hospital on the 32nd posttransplant day. Although this preliminary experience doesn't allow for statistical analysis, clinically it was possible to observe a better performance in pulsatile flow recipients with faster lactate recovery, reduced need for inotropic support, reduced assistance duration in bridge-to-recovery settings, and smoother intensive care management. ECMO for postcardiotomy heart failure in neonates and infants still carries high mortality and morbidity rates. Pulsatile flow with the Medos DeltaStream DP1 pump system improves results by producing more physiologic hemodynamics, reducing the duration of support in the case of bridge to recovery, and improving end-organ function.     

The enabler cannula pump: a novel circulatory support system.

BACKGROUND: The enabler circulatory support system is a catheter pump which expels blood from the left or right ventricular cavity and provides pulsatile flow in the ascending aorta or pulmonary artery. It is driven by a bedside installed pulsatile driving console. The device can easily be implanted by a minimal invasive approach, similar to the Hemopump. PURPOSE: To demonstrate the hemodynamic performance of this new intracardiac support system. METHODS: In a series of 9 sheep, hemodynamic evolutions were recorded in various conditions of myocardial contractility (the non-failing, the moderately failing and the severely failing heart). Heart failure was induced by injection of microspheres in the coronary arteries. RESULTS: Introduction of the cannula through the aortic valve was feasible in all cases. Pump flow by the enabler was gradually increased to a maximum of 3.5 L/min. Diastolic (and mean) aortic blood pressure is significantly increased in the non-failing and moderately failing condition (counterpulsation mode). In heart failure, cardiac output is significantly increased by the pump (p < 0.0001). A drop in left atrial pressure (indicating unloading) is achieved in all conditions but reaches significant levels only during heart failure (p=0.0068). CONCLUSIONS: This new circulatory support system contributes to stabilization of the circulation in the presence of cardiac unloading. In heart failure it actually supports the circulation by increasing cardiac output and perfusion pressure.     

Comparison of four different pediatric 10F aortic cannulae during pulsatile versus nonpulsatile perfusion in a simulated neonatal model of cardiopulmonary bypass

We compared four commercially available 10F pediatric aortic cannulae with different geometric designs (DLP-Long tip, DLP-Short tip, RMI-Long tip, and Surgimedics-Short tip) during pulsatile versus nonpulsatile perfusion in terms of pressure drops and surplus hemodynamic energy (SHE) levels in an in vitro neonatal model of cardiopulmonary bypass. The pseudo patient was subjected to seven pump flow rates at 100 ml/min increments in the 400-1,000 ml/min range. A total of 44 experiments (n = 22, nonpulsatile; n = 22, pulsatile) were performed at each of the seven flow rates. Surgimedics had significantly higher pressure drops than the other three cannulae at various flow rates during nonpulsatile and pulsatile perfusion, respectively. When the perfusion mode was changed from nonpulsatile to pulsatile flow, SHE levels at both precannula and postcannula sites increased seven to nine times at all flow rates in all four cannulae. Surgimedics generated a significant lower SHE level when compared with the other three cannulae at all flow rates at both precannula and postcannula sites. The results suggest that different geometries of aortic cannulae have a significant impact on pressure drops of the cannulae as well as hemodynamic energy generation and delivery. Pulsatile perfusion generates more "extra" hemodynamic energy when compared with the nonpulsatile perfusion mode with all four cannulae used in this study.     

A novel counterpulsation mode of rotary left ventricular assist devices can enhance myocardial perfusion

The effect of rotary left ventricular assist devices (LVADs) on myocardial perfusion has yet to be clearly elucidated, and several studies have shown decreased coronary flow under rotary LVAD support. We have developed a novel pump controller that can change its rotational speed (RS) in synchronization with the native cardiac cycle. The aim of our study was to evaluate the effect of counterpulse mode, which increases the RS in diastole, during coronary perfusion. Experiments were performed on ten adult goats. The EVAHEART LVAD was installed by the left ventricular uptake and the descending aortic return. Ascending aortic flow, pump flow, and coronary flow of the left main trunk were monitored. Coronary flow was compared under four conditions: circuit-clamp, continuous mode (constant pump speed), counterpulse mode (increased pump speed in diastole), and copulse mode (increased pump speed in systole). There were no significant baseline changes between these groups. In counterpulse mode, coronary flow increased significantly compared with that in continuous mode. The waveform analysis clearly revealed that counterpulse mode mainly resulted in increased diastolic coronary flow. In conclusion, counterpulse mode of rotary LVADs can enhance myocardial perfusion. This novel drive mode can provide great benefits to the patients with end-stage heart failure, especially those with ischemic etiology.     

Development of a novel drive mode to prevent aortic insufficiency during continuous-flow LVAD support by synchronizing rotational speed with heartbeat

Aortic insufficiency (AI) is a serious complication for patients on long-term support with left ventricular assist devices (LVAD). Postoperative aortic valve opening is an important predictor of AI. A system is presently available that can promote native aortic flow by reducing rotational speed (RS) for defined intervals. However, this system can cause a reduction in pump flow and lead to insufficient support. We therefore developed a novel “delayed copulse mode” to prevent AI by providing both minimal support for early systole and maximal support shortly after aortic valve opening by changing the RS in synchronization with heartbeat. To evaluate whether our drive mode could open the aortic valve while maintaining a high total flow (sum of pump flow and native aortic flow), we installed a centrifugal LVAD (EVAHEART^®; Sun Medical) in seven goats each with normal hearts and acute LV dysfunction created by micro-embolization of the coronary artery. We intermittently switched the drive mode from continuous (constant RS) with 100 % bypass to delayed copulse mode with 90 % bypass. Total flow did not significantly change between the two modes. The aortic valve opened when the delayed copulse mode was activated. The delayed copulse mode allowed the aortic valve to open while maintaining a high total flow. This novel drive mode may considerably benefit patients with severe heart failure on long-term LVAD support by preventing AI.     

World-first implantable aortic valvo-pump (IAVP) with sufficient haemodynamic capacity

For better anatomic and physiologic fitting, a novel implantable aortic valvo-pump (IAVP) has been developed. A valvo-pump is a micro axial flow impeller pump, which has the same dimensions and function, as well as the same location, of a valve. Therefore, IAVP needs no inlet and outlet tubes, no additional anatomic occupation, and has less physiologic disturbance to natural circulation compared with the traditional bypass left ventricular assist device (LVAD). The device has a stator and a rotor. The stator consists of a motor coil with an iron core and an outflow guide vane; the rotor includes driven magnets and impeller. There is neither bearing nor strut in both the pump and the motor. In order to reduce the attractive force between the rotor and the stator, so as to enhance the durability of the performance, the rotor magnets were minimized without reducing the driving torque and efficiency of the motor. The impeller vane was designed according to a three-dimensional and analytical method, for preventing stasis and turbulence. The largest outer diameter is 24.7 mm and the length at this point is 12.4 mm. The total weight is 40 g (including the rotor of 11 g). The consumed power is 7 W (14 V x 0.5 A) at 15 000 rpm. This rotating speed stays unchanged during haemodynamic testing together with a pulsatile centrifugal pump, which imitates a failing ventricle. The maximal flow cross IAVP reaches over 10 l min(-1) and the pressure head at 0 l min(-1) can be as large as 80 mmHg. At flow rate of 4 - 8 l min(-1), IAVP enlarges the flow c. 1 l min(-1) and meanwhile increases the pressure about 10 mmHg. The pressure pulsatility generated by the pulsatile centrifugal pump remains 40 mmHg after passing IAVP. By first animal experimental trial the device was sewed in aortic position of an 80 kg pig without harm to adjacent tissue and organs. IAVP promises to be a viable alternative to natural donor heart for heart transplantation in the future.     

完全磁悬浮心室辅助装置的体外模拟循环系统实验研究

目的研究我国自主研发的第3代完全磁悬浮心室辅助装置(CH-VAD)对于心衰患者的循环辅助效果。方法建立一套体外模拟循环系统(mock circulatory system,MCS)。该系统能够模拟人体健康休息状态以及心力衰竭状态,并与CH-VAD协同工作,测试CH-VAD在连续流状态下的辅助效果。另外,对CH-VAD的搏动流控制方法进行测试,该模式采用正弦波速度波形,使CH-VAD的运行与MCS心室周期同步。结果 CH-VAD在正常连续流状态下能够使心衰状态的血流动力学参数(动脉压、心排量)恢复到正常范围。初步的搏动流测试结果显示,当前的速度搏动幅值对血流动力学影响较小,搏动流状态下与连续流状态所对应的平均动脉压、动脉脉压、平均心排量与心排量波形等差异不大。结论 CH-VAD能够通过搏动控制器产生一定程度的速度搏动,提供足够的心室辅助,并可以进一步改良优化,提供符合生理条件的搏动血流。所研制的MCS能够提供心室辅助装置以及其他机械循环辅助装置一个有效、可控的体外测试平台,是机械循环辅助装置设计、优化和验证的重要工具。     

Hemodynamic and pressure-volume responses to continuous and pulsatile ventricular assist in an adult mock circulation

This study investigated the hemodynamic and left ventricular (LV) pressure-volume loop responses to continuous versus pulsatile assist techniques at 50% and 100% bypass flow rates during simulated ventricular pathophysiologic states (normal, failing, recovery) with Starling response behavior in an adult mock circulation. The rationale for this approach was the desire to conduct a preliminary investigation in a well controlled environment that cannot be as easily produced in an animal model or clinical setting. Continuous and pulsatile flow ventricular assist devices (VADs) were connected to ventricular apical and aortic root return cannulae. The mock circulation was instrumented with a pressure-volume conductance catheter for simultaneous measurement of aortic root pressure and LV pressure and volume; a left atrial pressure catheter; a distal aortic pressure catheter; and aortic root, aortic distal, VAD output, and coronary flow probes. Filling pressures (mean left atrial and LV end diastolic) were reduced with each assist technique; continuous assist reduced filling pressures by 50% more than pulsatile. This reduction, however, was at the expense of a higher mean distal aortic pressure and lower diastolic to systolic coronary artery flow ratio. At full bypass flow (100%) for both assist devices, there was a pronounced effect on hemodynamic parameters, whereas the lesser bypass flow (50%) had only a slight influence. Hemodynamic responses to continuous and pulsatile assist during simulated heart failure differed from normal and recovery states. These findings suggest the potential for differences in endocardial perfusion between assist techniques that may warrant further investigation in an in vivo model, the need for controlling the amount of bypass flow, and the importance in considering the choice of in vivo model.     

World-smallest LVAD with 27 g weight, 21 mm OD and 5 l min-1 flow with 50 mmHg pressure increase

To investigate the feasibility of a long-term left ventricular assist device (LVAD) placed in the aortic valve annulus, an implantable aortic valve pump (21 mm outer diameter, weighing 27 g) was developed. The device consists of a central rotor and a stator. The rotor assembly incorporates driven magnets and an impeller. The stator assembly has a motor coil with an iron core and outflow guide vanes. The device is to be implanted identically to an aortic valve replacement, occupying no additional anatomic space. The pump delivers the blood directly from left ventricle to the aortic root, like a natural ventricle, therefore causing less physiologic disturbance to the natural circulation. Neither connecting conduits nor 'bypass' circuits are necessary. The pump is designed to cycle between a peak flow and zero net flow to approximate systole and diastole. Bench testing indicates that the pump can produce a blood flow of 5 l min(-1) with 50 mmHg pressure increase at 17,500 rpm. At zero net flow rate, the pump can maintain a diastole aortic pressure against 80 mmHg at the same rotating speed.     

Shifting the pulsatility by increasing the change in rotational speed for a rotary LVAD using a native heart load control system

We have previously developed a native heart load control system for a continuous-flow left ventricular assist device (LVAD) ((EVAHEART^®; Sun Medical) and demonstrated that the rotational speed (RS) in synchronization with the cardiac cycle can alter pulsatility and left ventricular (LV) load under general anesthesia. In this study, we assessed the effects of different levels of increase in RS on pulsatility and LV load in the chronic awake phase. We implanted the EVAHEART via left thoracotomy in 7 normal goats (59.3 ± 4.6 kg). Two weeks after implantation, we examined the effects of co-pulse mode (increased RS in the systolic phase) and counter-pulse mode (increased RS in the diastolic phase), as well as shifting the change in RS from 250 to 500 rpm, and 750 rpm in both modes on pulsatility and LV load. Pulsatility was assessed using pulse pressure and mean dP/dt max of aortic pressure. LV load was assessed using stroke work and left ventricle end-diastolic volume determined from LV pressure–volume loops. In the co-pulse mode, pulsatility values increased as the change in RS increased. By contrast, in the counter-pulse mode, these values decreased as the change in RS increased. LV load increased significantly in the co-pulse mode compared with the counter-pulse mode, but there were no significant differences among the three levels of RS increase in either mode. Increasing RS to varying degrees with our newly developed system could contribute to pulsatility. However, it appeared to have little effect on LV load in normal hearts.     

The heart-pump interaction: effects of a microaxial blood pump

BACKGROUND: When we use rotary blood pumps as an assist device, an interaction takes place between the pump performance and the native heart function (native heart influences pump performance and vice versa). The interaction between native heart and rotary blood pump can be useful to predict recovery of the failing heart. METHODS: The rotary blood pumps used were microaxial catheter-mounted pumps with an external diameter of 6.4 mm (Impella, Aachen, Germany). The pump-heart interaction was studied in five juvenile sheep with a mean body weight of 68.5 +/- 8.7 kg. The pumps were introduced via the left carotid artery and placed in transvalvular aortic position. Recorded parameters were pump speed (rpm), generated flow (L/min) and differential pressure (mm Hg) obtained at high frequency rate of data recordings (25 sets of data per second). This allowed continuous analysis of the pump performance during cardiac cycle. Under clinical conditions the interaction was studied in a 60-year-old male, in whom the device was applied due to postcardiotomy heart failure after myocardial infarction. RESULTS: Heart-pump interaction was analyzed based on pump flow differential pressure. This relationship, analyzed continuously during cardiac cycle, presents as a loop. The dynamic contribution of the heart to the flow generated by the pump leads to continuous fluctuation in the pressure head and the creation of hysteresis. The improved function of the failing heart under clinical conditions after seven days of mechanical support was expressed by: increased hysteresis of the loop caused by increased gradient of flow generated during cardiac cycle, a more pronounced venticular ejection phase that indicates more dynamic heart contribution to the generated flow, and finally increased gradient of the differential pressure during cardiac cycle, caused predominantly by increased aortic pressure and decreased left ventricle pressure during diastolic phase. CONCLUSIONS: The heart-pump interaction based on the pump flow-differential pressure relationship can be useful in predicting the possibility to wean the patient from the device.     

Numerical simulation of the influence of a left ventricular assist device on the cardiovascular system

The PUCA (pulsatile catheter) pump is a left ventricular assist device (LVAD) capable of unloading the left ventricle (LV) and improving coronary flow by providing a counterpulsation effect. It consists of an extracorporeal located membrane pump, coupled to a transarterial catheter that enters the body via a superficial artery and ends in the LV. Blood is aspirated from the LV and pumped in the ascending aorta through the same catheter guided by a valve system. Timing and frequency of the PUCA pump influence its efficacy. To study the influence of several pump parameters a numerical model of the device and the circulatory system has been developed. Results of animal experiments were used to validate the model. Optimization studies resulted in a pump configuration with a stroke volume of 50 cc and pump:heart frequency mode of 1:2 that starts ejection at the beginning of diastole.     

Myocardial hemodynamics, physiology, and perfusion with an axial flow left ventricular assist device in the calf

The Jarvik 2000 axial flow left ventricular assist device (LVAD) is used clinically as a bridge to transplantation or as destination therapy in end-stage heart disease. The effect of the pump's continuous flow output on myocardial and end-organ blood flow has not been studied experimentally. To address this, the Jarvik 2000 pump was implanted in eight calves and then operated at speeds ranging from 8,000 to 12,000 rpm. Micromanometry, echocardiography, and blood oxygenation measurements were used to assess changes in hemodynamics, cardiac dimensions, and myocardial metabolism, respectively, at different speeds as compared with baseline (pump off, 0 rpm) in this experimental model. Microsphere studies were performed to assess the effects on heart, kidney, and brain perfusion at different speeds. The Jarvik 2000 pump unloaded the left ventricle and reduced end-diastolic pressures and left ventricular dimensions, particularly at higher pump speeds. The ratio of myocardial oxygen consumption to coronary blood flow and the ratio of subendocardial to subepicardial blood flow remained constant. Optimal adjustment of pump speed and volume status allowed opening of the aortic valve and contribution of the native left ventricle to cardiac output, even at the maximum pump speed. Neither brain nor kidney microcirculation was adversely affected at any pump speed. We conclude that the Jarvik 2000 pump adequately unloads the left ventricle without compromising myocardial metabolism or end-organ perfusion.     

In vitro evaluation of left ventricular assistance by cannulation of both femoral arteries

The possibility of achieving effective mechanical ventricular assistance without the need for thoracotomy provides great clinical advantages. Two in vitro systems were used to assess left ventricular unloading by means of a small-diameter cannula inserted retrograde into the left ventricle by cannulation of the femoral artery. This cannula is connected to the inlet of a centrifugal blood pump (CP) that delivers the blood into the contralateral femoral artery. Steady-flow test circulation was used to pump fluid in a closed loop from a reservoir through the test cannula back into the reservoir. Pressure drops over cannulae with inner diameters of 4, 5, 6, 7, and 8 mm at flows of 2, 2.5, 3 L/min, against a pressure of 60, 80, 100, and 120 mmHg were calculated. A stationary pressure drop of 120 mmHg was measured at a flow of 3 L/min through a 100 cm cannula with an inner diameter of 6 mm. The second system was a pulsatile mock circulation composed of an atrial and an arterial reservoir linked by a pneumatic prosthetic ventricle. This system was coupled with a 100 cm cannula, 6.1 mm inner diameter, which was passed across the outflow valve of the pulsatile prosthetic ventricle and connected to a CP. Fluid was withdrawn from the ventricle and pumped back into the arterial reservoir. Pulsatile pressure drop over the cannula was measured at different CP flows for increasing systolic ventricular pressure; heart unloading was quantified as a function of CP flow under baseline and failing conditions of the prosthetic left ventricle model. At a constant CP flow the pressure drop over the cannula increased with the pulsatility inside the ventricle. The work of the prosthetic ventricle was reduced by more than 50% when the CP pump was set to 3 L/min; at the same flow setting, when the situation of a failing left ventricle was simulated, the CP was able to take over all the work of the prosthetic ventricle, establishing a stationary flow and a 25% higher mean aortic pressure. This approach to left ventricular assistance may have significant clinical relevance.     

Pitfalls in the development of a rotary blood pump controller

The controller presents a major obstacle in the development of the rotary blood pump as a left ventricular assist device (LVAD). Clinically, LVAD flow is a good indicator in the regulation of circulatory conditions and pump flow changes, depending on pump preload and afterload. Many investigators have tried estimating pump flow by referencing the motor current. There have been pitfalls in in vitro experimental settings, however. Using a test loop with a pneumatically driven LV chamber and a centrifugal pump as an LVAD, we monitored pump flow and pressure head to evaluate the pump performance curve (H-Q curve). Under pulsatile LV conditions, the H-Q curve was a loop that changed, depending on LV contractility. The pneumatically driven LV chamber cannot mimic the Starling phenomenon, so the developed LV pressure does not change according to the LV preload. Rotary pump flow estimation is the most effective control method. In pulsatile conditions, however, the H-Q curve is a loop that changes under various LV contractility conditions, complicating determination of linear equation for calculating flow. In addition, the LV chamber in the test loop cannot mimic native heart contractility as described by Starling's law. This finding can lead to a misanalysis of the H-Q curve under pulsatile conditions.     

How to produce a pulsatile flow with low haemolysis?

It is evident that a pulsatile flow is important for blood circulation because the flow pulsatility can reduce the resistance of peripheral vessels. It is difficult, however, to produce a pulsatile flow with an impeller pump, since blood damage will occur when a pulsatile flow is produced. Further investigation has revealed that the main factor for blood damage is turbulence shear, which tears the membranes of red blood cells, resulting in free release of haemoglobin into the plasma, and consequently leads to haemolysis. Therefore, the question for developing a pulsatile impeller blood pump is: how to produce a pulsatile flow with low haemolysis? The authors have successively developed a pulsatile axial pump and a pulsatile centrifugal pump. In the pulsatile axial pump, the impeller reciprocates axially and rotates simultaneously. The reciprocation is driven by a pneumatic device and the rotation by a dc motor. For a pressure of 40 mm Hg pulsatility, about 50 mm axial reciprocating amplitude of the impeller is desirable. In order to reduce the axial amplitude, the pump inlet and the impeller both have cone-shaped heads, and the gap between the impeller and the inlet pipe changes by only 2 mm, that is the impeller reciprocates up to 2 mm and a pressure pulsatility of 40 mm Hg can be produced. As the impeller rotates with a constant speed, low turbulence in the pump may be expected. In the centrifugal pulsatile pump, the impeller changes its rotating speed periodically; the turbulence is reduced by designing an impeller with twisted vanes which enable the blood flow to change its direction rather than its magnitude during the periodic change of the rotating speed. In this way, a pulsatile flow is produced and the turbulence is minimized. Compared to the axial pulsatile pump, the centrifugal pulsatile pump needs only one driver and thus has more application possibilities. The centrifugal pulsatile pump has been used in animal experiments. The pump assisted the circulation of calves for several months without harm to the blood elements and the organ functions of the experimental animal. The experiments demonstrated that the pulsatile impeller pump is the most efficient pump for assisting heart recovery, because it can produce a pulsatile flow like a diaphragm pump and has no back flow as occurs in a non-pulsatile rotary pump; the former reduces the circulatory resistance and the latter increases the diastole pressure in aorta and thus increases the perfusion of coronary arteries of the natural heart.