This paper presents a novel mock circulation for the evaluation of ventricular assist devices (VADs), which is based on a hardware-in-the-loop concept. A numerical model of the human blood circulation runs in real time and computes instantaneous pressure, volume, and flow rate values. The VAD to be tested is connected to a numerical-hydraulic interface, which allows the interaction between the VAD and the numerical model of the circulation. The numerical-hydraulic interface consists of two pressure-controlled reservoirs, which apply the computed pressure values from the model to the VAD, and a flow probe to feed the resulting VAD flow rate back to the model. Experimental results are provided to show the proper interaction between a numerical model of the circulation and a mixed-flow blood pump.

The current article presents a novel physiological control algorithm for ventricular assist devices (VADs), which is inspired by the preload recruitable stroke work. This controller adapts the hydraulic power output of the VAD to the end-diastolic volume of the left ventricle. We tested this controller on a hybrid mock circulation where the left ventricular volume (LVV) is known, i.e., the problem of measuring the LVV is not addressed in the current article. Experiments were conducted to compare the response of the controller with the physiological and with the pathological circulation, with and without VAD support. A sensitivity analysis was performed to analyze the influence of the controller parameters and the influence of the quality of the LVV signal on the performance of the control algorithm. The results show that the controller induces a response similar to the physiological circulation and effectively prevents over- and underpumping, i.e., ventricular suction and backflow from the aorta to the left ventricle, respectively. The same results are obtained in the case of a disturbed LVV signal. The results presented in the current article motivate the development of a robust, long-term stable sensor to measure the LVV.

Various physiological controllers for left ventricular assist devices (LVADs) have been developed to prevent flow conditions that may lead to left ventricular (LV) suction and overload. In the current study, we selected and implemented six of the most promising physiological controllers presented in literature. We tuned the controllers for the same objectives by using the loop-shaping method from control theory. The in vitro experiments were derived from literature and included different preload, afterload, and contractility variations. All experiments were repeated with an increased or decreased contractility from the baseline pathological circulation and with simulated sensor drift. The controller performances were compared with an LVAD operated at constant speed (CS) and a physiological circulation. During preload variations, all controllers resulted in a pump flow change that resembled the cardiac output response of the physiological circulation. For afterload variations, the response varied among the controllers, whereas some of them presented a high sensitivity to contractility or sensor drift, leading to LV suction and overload. In such cases, the need for recalibration of the controllers or the sensor is indicated. Preload-based physiological controllers showed their clinical significance by outperforming the CS operation and promise many benefits for the LVAD therapy. However, their clinical implementation in the near future for long-term use is highly dependent on the sensor technology and its reliability.

Couch tracking with the Protura treatment couch is achievable. To reliably track all possible respiration patterns without prediction filters a short lag time below 100 ms is needed. More scientific work is necessary to extend our prototype to tracking of internal motion.

Turbodynamic blood pumps are used clinically as ventricular assist devices (VADs). They are mostly operated at a constant rotational speed, which results in a reduced pulsatility. Previous research has analyzed pulsing pump speeds (speed modulation) to alter the interaction between the cardiovascular system and the blood pump. In those studies, sine- or square-wave speed profiles that were synchronized to the natural cardiac cycle were analyzed in silico, in vitro and in vivo. The definitions of these profiles with respect to both timing and speed levels vary among different research groups. The current paper provides a definition of the timing of these speed profiles such that the resulting hemodynamic effects become comparable. The results published in the literature are summarized and compared using this definition. Further, applied to a turbodynamic VAD, a series of measurements is conducted on a hybrid mock circulation using a constant speed as well as different types of square-wave speed profiles and a sine-wave speed profile. When a consistent definition of the timing of the speed profiles is used, the hemodynamic effects observed in previous work are in agreement with the measurement data obtained for the current paper. These findings allow the conclusion that the speed modulation of turbodynamic VADs represents a consistent tool to systematically change the ventricular load and the pulsatility in the arterial tree. The timing that yields the minimal left ventricular load also yields the minimal arterial pulse pressure.

The clinical importance of pulsatility is a recurring topic of debate in mechanical circulatory support. Lack of pulsatility has been identified as a possible factor responsible for adverse events and has also demonstrated a role in myocardial perfusion and cardiac recovery. A commonly used method for restoring pulsatility with rotodynamic blood pumps (RBPs) is to modulate the speed profile, synchronized to the cardiac cycle. This introduces additional parameters that influence the (un)loading of the heart, including the timing (phase shift) between the native cardiac cycle and the pump pulses, and the amplitude of speed modulation. In this study, the impact of these parameters upon the heart-RBP interaction was examined in terms of the pressure head-flow (HQ) diagram. The measurements were conducted using a rotodynamic Deltastream DP2 pump in a validated hybrid mock circulation with baroreflex function. The pump was operated with a sinusoidal speed profile, synchronized to the native cardiac cycle. The simulated ventriculo-aortic cannulation showed that the level of (un)loading and the shape of the HQ loops strongly depend on the phase shift. The HQ loops displayed characteristic shapes depending on the phase shift. Increased contribution of native contraction (increased ventricular stroke work [WS ]) resulted in a broadening of the loops. It was found that the previously described linear relationship between WS and the area of the HQ loop for constant pump speeds becomes a family of linear relationships, whose slope depends on the phase shift.

Over the last few decades, the left ventricular assist device (LVAD) technology has been tremendously improved transitioning from large and noisy paracorporeal volume displacement pumps to small implantable turbodynamic devices with only a single transcutaneous element, the driveline. Nevertheless, there remains a great demand for further improvements to meet the challenge of having a robust and safe device for long-term therapy. Here, we review the state of the art and highlight four key areas of needed improvement targeting long-term, sustainable LVAD function: (1) LVADs available today still have a high risk of thromboembolic and bleeding events that could be addressed by the rational fabrication of novel surface structures and endothelialization approaches aiming at improving the device hemocompatibility. (2) Novel, fluid dynamically optimized pump designs will further reduce blood damage. (3) Infection due to the paracorporeal driveline can be avoided with a transcutaneous energy transmission system that additionally allows for increased freedom of movement. (4) Finally, the lack of pump flow adaptation needs to be encountered with physiological control systems, working collaboratively with biocompatible sensor devices, targeting the adaptation of the LVAD flow to the perfusion requirements of the patient. The interdisciplinary Zurich Heart project investigates these technology gaps paving the way toward LVADs for long-term, sustainable therapy.

Turbodynamic left ventricular assist devices (LVADs) provide a continuous flow depending on the speed at which the pump is set, and do not adapt to the changing requirements of the patient. The limited adaptation of the pump flow (PF) to the amount of venous return can lead to ventricular suction or overload. Physiologic control may compensate such situations by an automatic adaptation of the PF to the volume status of the left ventricle. We evaluated two physiologic control algorithms in an acute study with eight healthy pigs. Both controllers imitate the Frank-Starling law of the heart and are based on a measurement of the left ventricular volume (LVV) or pressure (LVP), respectively. After implantation of a modified Deltastream DP2 blood pump as an LVAD, we tested the responses of the physiologic controllers to hemodynamic changes and compared them with the response of the constant speed (CS) mode. Both physiologic controllers adapted the pump speed (PS) such that the flow was more sensitive to preload and less sensitive to afterload, as compared with the CS mode. As a result, the risk for suction was strongly reduced. Five suction events were observed in the CS mode, one with the volume-based controller and none with the pressure-based controller. The results suggest that both physiologic controllers have the potential to reduce the number of adverse events when used in the clinical setting.