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Cardiovasc Eng Technol. 2019 Sep;10(3):520-530. doi: 10.1007/s13239-019-00419-0. Epub 2019 Jun 11.

Preload Sensitivity with TORVAD Counterpulse Support Prevents Suction and Overpumping.

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Windmill Cardiovascular Systems, Inc, Austin, TX, USA.
Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
Windmill Cardiovascular Systems, Inc, Austin, TX, USA.
Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
Department of Internal Medicine, UTHealth/McGovern Medical School, Houston, TX, USA.



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.


Counterpulse support; Physiological control; Starling response; Ventricular assist device

[Available on 2020-09-01]

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