Three Dimensional Fluid Mechanics of the Sinus of Valsalva With a Bileaflet Mechanical Heart Valve

Fluid mechanics of the sinus of Valsalva is an underlying basis of aortic surgery. Bellhouse and Talbot first reported the closure mechanism of the human aortic valve in vitro, and found that a vortex motion in the sinus facilitates the initial closing response, thus minimizing the regurgitation [1]. Since their early study, a variety of researches have been conducted to gain systematic understanding of the flow in the sinus of Valsalva. Phase-contrast MRI technique in vivo and computational fluid dynamics in vitro are modern flow diagnostic tools, both of which potentially has a capability of characterizing the three-dimensional flow. However, the flow in reality is strongly affected by the opening and closing dynamics of the aortic valve, and vice versa. This fluid-structure coupling has yet to be understood systematically. This study aims to clarify the mechanism of the coupling in vitro with a bileaflet mechanical heart valve by means of 2D PIV and 3D Stereo PIV technique [2]. An emphasis is placed on the geometrical effect of the sinus of Valsalva, where three geometries, namely the Anatomical, Neosinus and Straight models, are compared on the flow dynamics and valve closing dynamics.

Wavelet Transforms in the Analysis of Mechanical Heart Valve Cavitation

Cavitation is known to cause blood element damage and may introduce gaseous emboli into the cerebral circulation, increasing the patient’s risk of stroke. Discovering methods to reduce the intensity of cavitation induced by mechanical heart valves (MHVs) has long been an area of interest. A novel approach for analyzing MHV cavitation is presented. A wavelet denoising method is explored because currently used analytical techniques fail to suitably unmask the cavitation signal from other valve closing sounds and noise detected with a hydrophone. Wavelet functions are used to denoise the cavitation signal during MHV closure and rebound. The wavelet technique is applied to the signal produced by closure of a 29-mm Medtronic-Hall MHV in degassed water with a gas content of 5ppm. Valve closing dynamics are investigated under loading conditions of 500, 2500, and 4500mmHg∕s. The results display a marked improvement in the quantity and quality of information that can be extracted from acoustic cavitation signals using the wavelet technique compared to conventional analytical techniques. Time and frequency data indicate the likelihood and characteristics of cavitation formation under specified conditions. Using this wavelet technique we observe an improved signal-to-noise ratio, an enhanced time-dependent aspect, and the potential to minimize valve closing sounds, which disguise individual cavitation events. The overall goal of this work is to eventually link specific valves with characteristic waveforms or distinct types of cavitation, thus promoting improved valve designs.