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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.

Author information

1
Windmill Cardiovascular Systems, Inc, Austin, TX, USA. jgohean@windmillcvs.com.
2
Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA. jgohean@windmillcvs.com.
3
Windmill Cardiovascular Systems, Inc, Austin, TX, USA.
4
Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
5
Department of Internal Medicine, UTHealth/McGovern Medical School, Houston, TX, USA.

Abstract

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.

KEYWORDS:

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

PMID:
31187397
PMCID:
PMC6717040
[Available on 2020-09-01]
DOI:
10.1007/s13239-019-00419-0

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