Continuous-flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end-stage heart failure, even if continuous flow is different from physiological flow in that it has less pulsatility. A novel pump controller of continuous-flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous-flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit-Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80-90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse pressure, clamp/continuous/pulsatile, 25.0 ± 7.6/11.7 ± 6.4/22.6 ± 9.8 mm Hg, mean dp/dt max, 481.9 ± 207.6/75.6 ± 36.2/351.1 ± 137.8 mm Hg/s, respectively). In clamp condition, %EEP was 10% higher than mean AoP (P = 0.0078), while in continuous mode, %EEP was nearly equivalent to mean AoP (N.S.). In pulsatile mode, %EEP was 9% higher than mean AoP (P = 0.038). Our newly developed pulsatile mode of continuous-flow LVADs can produce pulsatility comparable to physiological pulsatile flow. Further investigation on the effect of this novel drive mode on organ perfusion is currently ongoing.

No abstract

A flow rate estimating method was investigated for a centrifugal blood pump developed in our institute. The estimated flow rate was determined by the power consumption, the rotating speed of the motor, and the hematocrit value. The power consumption and the rotating speed of the motor were measured with a wattmeter. The examinations were performed in a closed mock loop filled with goat blood with hematocrit values of 21.5%, 28%, 34%, and 42%. Measured values of blood viscosity were 2.47, 3.09, 3.71, and 5.07 mPa.s at a share rate of 37.5/s, respectively. A linear correlation between the power consumption and the pump flow rate was observed in all hematocrit values. But variations in hematocrit caused a difference in the flow rate up to 1.1 L/min at the same power consumption and rotating speed. Effects of blood viscosity on the flow estimation were corrected by the hematocrit value. The value of the coefficient of determination, R2, between the estimated flow rate and the measured flow rate was 0.988. These results may indicate that the flow estimating method calculated by the power consumption of the motor, the rotating speed, and the hematocrit value is useful in the clinical situation.

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.

In-body tissue architecture-a novel and practical regeneration medicine technology-can be used to prepare a completely autologous heart valve, based on the shape of a mold. In this study, a three-dimensional (3D) printer was used to produce the molds. A 3D printer can easily reproduce the 3D-shape and size of native heart valves within several processing hours. For a tri-leaflet, valved conduit with a sinus of Valsalva (Biovalve type VII), the mold was assembled using two conduit parts and three sinus parts produced by the 3D printer. Biovalves were generated from completely autologous connective tissue, containing collagen and fibroblasts, within 2 months following the subcutaneous embedding of the molds (success rate, 27/30). In vitro evaluation, using a pulsatile circulation circuit, showed excellent valvular function with a durability of at least 10 days. Interposed between two expanded polytetrafluoroethylene grafts, the Biovalves (N 5 3) were implanted in goats through an apicoaortic bypass procedure. Postoperative echocardiography showed smooth movement of the leaflets with minimal regurgitation under systemic circulation. After 1 month of implantation, smooth white leaflets were observed with minimal thrombus formation. Functional, autologous, 3D-shaped heart valves with clinical application potential were formed following in-body embedding of specially designed molds that were created within several hours by 3D printer.