Mechanism of Self‐Regulation and In Vivo Performance of the Cleveland Clinic Continuous‐Flow Total Artificial Heart

Abstract

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) provides systemic and pulmonary circulations using one assembly (one motor, two impellers). The right pump hydraulic output to the pulmonary circulation is self-regulated by the rotating assembly's passive axial movement in response to atrial differential pressure to balance itself to the left pump output. This combination of features integrates a biocompatible, pressure-balancing regulator with a double-ended pump. The CFTAH requires no flow or pressure sensors. The only control parameter is pump speed, modulated at programmable rates (60-120 beats/min) and amplitudes (0 to ±25%) to provide flow pulses. In bench studies, passive self-regulation (range: -5 mm Hg ≤ [left atrial pressure - right atrial pressure] ≤ 10 mm Hg) was demonstrated over a systemic/vascular resistance ratio range of 2.0-20 and a flow range of 3-9 L/min. Performance of the most recent pump configuration was demonstrated in chronic studies, including three consecutive long-term experiments (30, 90, and 90 days). These experiments were performed at a constant postoperative mean speed with a ±15% speed modulation, demonstrating a totally self-regulating mode of operation, from 3 days after implant to explant, despite a weight gain of up to 40%. The mechanism of self-regulation functioned properly, continuously throughout the chronic in vivo experiments, demonstrating the performance goals.

Analysis of Cleveland Clinic continuous‐flow total artificial heart performance using the Virtual Mock Loop: Comparison with an in vivo study

“…One possible explanation for the lower correlation in right pressure rise and atrial pressure difference may be the numerical modeling method of the autoregulatory function of the CFTAH. As previously described, our CFTAH automatically regulates atrial pressure differences by axial movement of the rotating assembly, which changes the right pump performance . While bench testing the CFTAH pump with a position sensor for the rotating assembly, we found that the position of the rotating assembly has a linear correlation with the “normalized gradient difference,” which is calculated from the atrial pressure difference (LAP–RAP) and the arterial pressure difference (AoP–PAP), empirical weighting factor, and pump speed.…”

“…The investigational device prototype dimensions are: 60 mm diameter and 100 mm in length, with a priming volume of 37 mL (Figure ) . As previously described, this pump has a novel self‐regulating feature that allows for a degree of axial movement of the rotating assembly, caused primarily by inlet pressure differences . Through this axial movement of the rotating assembly, the size of the right pump aperture, which influences the right pump performance, changes to correct the inlet pressure imbalance without changing left pump performance.…”

“…In each test, data were recorded across the full range of operation. To evaluate the pump performance in bench testing with that of VML and in vivo, pump performance curves, in which flow was normalized by speed and pressure rise was normalized by speed squared, were plotted …”

Use of a Mechanical Circulatory Support Simulation to Study Pump Interactions With the Variable Hemodynamic Environment

“…An obvious disadvantage of such a hybrid system is that the user needs total command of all elements: the physical mock loop, control system, and a pre-existing MCS device. In contrast, the significant advantage of our approach is that the Virtual Mock Loop is fully portable, allowing exploration of the interactions between a variety of support devices (8)(9)(10)(11), proposed or currently under development, and the hemodynamic environment. The Virtual Mock Loop can receive numerous inputs to test for a wide combination of disease conditions and patient sizes that are beyond practical experimentation.…”

“…The ovine is a frequently used preclinical animal model for the assessment of cardiovascular device function and biocompatibility (1)(2)(3)(4)(5)(6)(7)(8)(9). Adult ovines have hearts that are similar in size to the human heart for evaluation of implantable devices such as ventricular assist devices (VAD).…”