Purpose

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.

Methods

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.

Results

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.

Conclusions

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.

中文翻译：

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带有 TORVAD 反脉冲支持的预载灵敏度可防止吸入和过度泵送。

目的

本研究比较了连续流 (CF) VAD 支持的预载敏感性与使用 Windmill 环形 VAD (TORVAD) 的反搏。TORVAD 是一种双活塞旋转泵，可在舒张早期排出 30 mL，从而增加心输出量，同时保持主动脉瓣流量。

方法

使用心血管系统的两个集总参数模型比较了 CF 与 TORVAD 反搏支持的前负荷敏感性：(1) 使用体循环的开环模型通过隔离体循环并规定前负荷和后负荷来获得心室功能曲线边界条件，以及 (2) 闭环模型用于测试对肺血管阻力、全身血管阻力、心率、正性肌力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吸气的风险。

结果

在 5 mmHg 的低预负荷下，与 TORVAD 反搏支持相比，CF 支持过度泵送循环（健康心脏的心输出量为 3.3 L/min，CF 支持为 4.7，TORVAD 反搏支持为 3.5）并且灵敏度远低于反搏支持（健康心脏为 0.342 L/min/mmHg，CF 支持为 0.092，TORVAD 反搏支持为 0.306）。在闭环模型中，当 PVR 增加超过 0.035 mmHg·s/mL 时，CF 支持过度泵送循环并引起心室抽吸事件，但 TORVAD 反搏支持维持足够的心室容积并且不会引起抽吸。

结论

TORVAD 的反脉冲支持可保持主动脉瓣流量，并在所有预载条件下提供生理敏感性。这应该可以防止过度泵送并将吸入的风险降至最低。