Preload Sensitivity with TORVAD Counterpulse Support Prevents Suction and Overpumping

  • Jeffrey R. GoheanEmail author
  • Erik R. Larson
  • Raul G. Longoria
  • Mark Kurusz
  • Richard W. Smalling



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.


Ventricular assist device Counterpulse support Starling response Physiological control 



Research reported in this publication was supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health (NIH) under award No. R44HL117446.

Conflict of interest

All authors have equity interests in Windmill. JG and EL are employees of Windmill, RL and MK consult with Windmill, and RS receives no financial support other than travel reimbursement.

Ethical Approval

This article does not contain any studies with human participants or animals performed by any of the authors.


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Copyright information

© Biomedical Engineering Society 2019

Authors and Affiliations

  1. 1.Windmill Cardiovascular Systems, IncAustinUSA
  2. 2.Department of Mechanical EngineeringThe University of Texas at AustinAustinUSA
  3. 3.Department of Internal MedicineUTHealth/McGovern Medical SchoolHoustonUSA

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