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

Assessment of ocular blood flow in continuous-flow ventricular assist device by laser speckle flowgraphy

Although the influence of continuous-flow left ventricular assist device (CF-LVAD) support on peripheral circulation has been widely discussed, its monitoring modalities are limited. The aim of this study was to assess the peripheral circulation using the laser speckle flowgraph (LSFG) which can quantitatively measure the ocular blood flow. We implanted a centrifugal CF-LVAD (EVAHEART^®; Sun Medical Technology Research Corporation, Nagano, Japan) in five adult goats (body weight 44.5 ± 2.9 kg) under general anesthesia. The waveform of the central retinal artery using the mean blur rate (MBR) for ocular blood velocity and fluctuations as a parameter of pulsatility were obtained before LVAD implantation and after LVAD full-bypass support. The MBR waveform and LSFG fluctuation data were compared with the waveform and pulsatility index of the external carotid artery using an ultrasonic flow meter to evaluate circulatory patterns at different levels. The MBR waveform pattern of the central retinal artery was pulsatile before LVAD implantation and less pulsatile under LVAD full bypass. The fluctuation was 14.7 ± 1.86 before LVAD implantation and 3.85 ± 0.61 under LVAD full bypass (p < 0.01), respectively. The fluctuations of LSFG showed a strong correlation with the pulsatility index of the external carotid artery meaning that similar changes in circulatory pattern were observed at two different levels. Measuring the ocular blood flow using LSFG has potential utility for the assessment of the status of the peripheral circulation and its pulsatility during CF-LVAD.

Dynamic motion analysis of impeller for the development of real-time flow rate estimations of a ventricular assist device

Implantable ventricular assist devices are used in heart failure therapy. These devices require real-time flow rate estimation for effective mechanical circulatory support. We previously developed a flow rate estimation method using the eccentric position of a magnetically levitated impeller to achieve real-time estimation. However, dynamic motion of the levitated impeller can compromise the method's performance. Therefore, in this study, we investigated the effects of dynamic motion of the levitated impeller on the time resolution and estimation accuracy of the proposed method. The magnetically levitated impeller was axially suspended and radially restricted by the passive stability in a centrifugal blood pump that we developed. The dynamic motions of impeller rotation and whirling were analyzed at various operating conditions to evaluate the reliability of estimation. The vibration response curves of the impeller revealed that the resonant rotational speed was 1300-1400 revolutions per minute (rpm). The blood pump was used as a ventricular assist device with rotational speed (over 1800 rpm) sufficiently higher than the resonant speed. The rotor-dynamic forces on the impeller (0.03-0.14 N) suppressed the whirling motion of the impeller, indicating that the dynamic motion could be stable. Although the temporal responsiveness should be determined based on the trade-offs among the estimation accuracy and time resolution, the real-time estimation capability of the proposed method was confirmed.

Varying speed modulation of continuous-flow left ventricular assist device based on cardiovascular coupling numerical model

Continuous-flow left ventricular assist devices (CFLVADs) routinely operate at a constant speed for the support of a failing heart, which decreases the pulsatility in the arteries. Some late complications could be related to a long-term lack of pulsatility. Modulating the CFLVAD speed is a solution to enhance the pulsatility. The purpose of this study is to modulate multiple varying speed patterns and investigate their effects on the ventricle and vascular system. A cardiovascular coupling numerical model is developed to provide a simulation platform for testing the varying speed patterns. The varying speed patterns are modulated by combining the shape, amplitude, frequency, phase shift, and pulsatile duty cycle of the speed profile. The influence of varying speed support is examined by analyzing the indexes of pulsatility, indexes of ventricular unloading, and hemodynamic variables. The results show that the synchronous counterpulsation pattern can effectively reduce the ventricular unloading indexes, whereas the low-frequency asynchronous pattern can effectively increase the vascular pulsatility indexes. Also, the hemodynamics with synchronous varying speed support is more physiological than that with asynchronous varying speed support. This study provides valuable insight for further optimization of varying speed modulation by weighing vascular pulsatility, ventricular unloading, and hemodynamics.

COMPARISON OF THREE CONTROL STRATEGIES FOR AXIAL BLOOD PUMP

Facing the gradually increased prevalence of heart failure (HF) and the shortage of donated hearts, the blood pump is widely used to prolong the life of end-stage HF patients: however, the pump generates continuous flow under constant rotational speed, declining the arterial pulsatility and causing related complications. Previous studies show that synchronous copulsation might be the best control strategy for restoring pulsatility, but synchronous strategies are needed to monitor the phase of the heartbeat, which will make the controller complex and impair its robustness. Here, we compare constant speed, synchronous copulsation in a model of a cardiovascular system with a blood pump, which shows that copulsation offers more arterial pulsatility, less pump power-consumption, and thus better battery endurance, and constant speed offers a greater ventricular unloading effect. Meanwhile, we design a strategy based on transforming left ventricular pressure, which is easier to implement and has similar effect to synchronous copulsation.