Characteristics of Mechanical Heart Valve Cavitation in a Pneumatic Ventricular Assist Device

Abstract

In previous studies, we investigated the mechanism of mechanical heart valve (MHV) cavitation and cavitation intensity with a nonsynchronized experiment system. Our group is currently developing a pneumatic ventricular assist device (PVAD), and in this study we investigated MHV cavitation intensity in the PVAD using a synchronized analysis of the cavitation images and the acoustic signal of cavitation bubbles. A 23-mm Medtronic Hall valve with an opening angle of 70 degrees was mounted in the mitral position of the PVAD after removing the sewing ring. A function generator provided a square signal, which used the trigger signal of the electrocardiogram R wave (ECG-R) mode of the control-drive console for circulatory support. This square signal was delayed by a delay circuit and was then used as the trigger signal for a pressure sensor and a high-speed video camera. The data were stored using a digital oscilloscope at a 1-MHz sampling rate, and then the pressure signal was band-pass filtered between 35 and 200 kHz using a digital filter. The band-pass filtered root mean squared (RMS) pressure and cavitation cycle duration were used as an index of cavitation intensity. The cavitation bubbles were concentrated at the valve stop, and the cavitation cycle duration and RMS pressure increased as the heart rate and driving pressure increased. At the low valve-closing velocity, bubble cavitation was observed near the valve stop. However, at the fast valve-closing velocity, cloud cavitation was observed. A high-frequency signal wave was generated when the bubbles collapsed. The cavitation cycle duration and RMS pressure increased as the valve-closing velocity increased linearly.

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“…Assuming blood is an incompressible Newtonian liquid, blood behaves as a Newtonian fluid for the condition of reasonable shear stresses, as expected in the LEV-VAD, and shear rates above 100/s [17]. When the normal temperature of the human body is 37 • C, blood density is 1055 kg/m 3 , viscosity is 0.0035 Pa*s, blood gas density is 0.5542 kg/m 3 , and viscosity is 0.0000134 Pa*s, whose vaporization pressure at the corresponding temperature is −715 mmHg [18,19]. The detailed settings of the boundary conditions are shown in Table 2.…”

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“…Hwansung Lee and Yoshiyuki Taenaka (16) of the National Cardiovascular Center, Osaka, Japan investigated mechanical heart valve (MHV) cavitation intensity in their pneumatic ventricular assist device (PVAD) using a synchronized analysis of the cavitation images and the acoustic signal of cavitation bubbles. A 23‐mm Medtronic Hall valve with an opening angle of 70 degrees was studied in the mitral position.…”