Gohean Jeffrey R, Larson Erik R, Longoria Raul G, Kurusz Mark, Smalling Richard W
Windmill Cardiovascular Systems, Inc, Austin, TX, USA.
Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
Cardiovasc Eng Technol. 2019 Sep;10(3):520-530. doi: 10.1007/s13239-019-00419-0. Epub 2019 Jun 11.
This study compares preload sensitivity of continuous flow (CF) VAD support to counterpulsation using the Windmill toroidal VAD (TORVAD). The TORVAD is a two-piston rotary pump that ejects 30 mL in early diastole, which increases cardiac output while preserving aortic valve flow.
Preload sensitivity was compared for CF vs. TORVAD counterpulse support using two lumped parameter models of the cardiovascular system: (1) an open-loop model of the systemic circulation was used to obtain ventricular function curves by isolating the systemic circulation and prescribing preload and afterload boundary conditions, and (2) a closed-loop model was used to test the physiological response to changes in pulmonary vascular resistance, systemic vascular resistance, heart rate, inotropic state, and blood volume. In the open-loop model, ventricular function curves (cardiac output vs left ventricular preload) are used to assess preload sensitivity. In the closed-loop model, left ventricular end systolic volume is used to assess the risk of left ventricular suction.
At low preloads of 5 mmHg, CF support overpumps the circulation compared to TORVAD counterpulse support (cardiac output of 3.3 L/min for the healthy heart, 4.7 with CF support, and 3.5 with TORVAD counterpulse support) and has much less sensitivity than counterpulse support (0.342 L/min/mmHg for the healthy heart, 0.092 with CF support, and 0.306 with TORVAD counterpulse support). In the closed-loop model, when PVR is increased beyond 0.035 mmHg s/mL, CF support overpumps the circulation and causes ventricular suction events, but TORVAD counterpulse support maintains sufficient ventricular volume and does not cause suction.
Counterpulse support with the TORVAD preserves aortic valve flow and provides physiological sensitivity across all preload conditions. This should prevent overpumping and minimize the risk of suction.
本研究比较了连续流（CF）心室辅助装置（VAD）支持与使用风车环形VAD（TORVAD）进行反搏时的前负荷敏感性。TORVAD是一种双活塞旋转泵，在舒张早期射出30 mL血液，可增加心输出量，同时保持主动脉瓣血流。
使用两个心血管系统集总参数模型比较CF与TORVAD反搏支持的前负荷敏感性：（1）通过分离体循环并规定前负荷和后负荷边界条件，使用体循环开环模型获得心室功能曲线；（2）使用闭环模型测试对肺血管阻力、体血管阻力、心率、心肌收缩状态和血容量变化的生理反应。在开环模型中，心室功能曲线（心输出量与左心室前负荷）用于评估前负荷敏感性。在闭环模型中，左心室收缩末期容积用于评估左心室抽吸风险。
在5 mmHg的低前负荷下，与TORVAD反搏支持相比，CF支持使循环过度泵血（健康心脏的心输出量为3.3 L/min，CF支持时为4.7 L/min，TORVAD反搏支持时为3.5 L/min），并且其敏感性远低于反搏支持（健康心脏为0.342 L/min/mmHg，CF支持时为0.092，TORVAD反搏支持时为0.306）。在闭环模型中，当肺血管阻力增加超过0.035 mmHg·s/mL时，CF支持使循环过度泵血并导致心室抽吸事件，但TORVAD反搏支持维持足够的心室容积且不会导致抽吸。
TORVAD反搏支持可保持主动脉瓣血流，并在所有前负荷条件下提供生理敏感性。这应可防止过度泵血并将抽吸风险降至最低。
