Laser Doppler anemometry study of bidimensional flows downstream of three 19 mm bileaflet valves in the mitral position, under kinematic similarity.

Abstract

Three small-size (nominal size: 19 mm) bileaflet valves, CarboMedics R (CM), St Jude Standard (SJ) and Sorin Bicarbon (SB), have been tested by means of a two-component laser Doppler anemometry (LDA) system, in the mitral position, in order to assess the potential damage to blood elements entailed by the turbulent flow through them. A high regime (6 l/min cardiac output) was chosen to perform measurements for the worst case in generated turbulence. Two half-diameter profiles, at 13 and 26 mm downstream of the valve plane, have been investigated for each model. Besides velocity profiles, turbulence shear stresses (TSS) are reported, after the application of the stress analysis technique, in order to assess the maximum values of TSS (TSSmax) exerted on blood particles. Results show the typical bileaflet-type velocity profile for SB and SJ, with three jets exiting the valve, whereas CM lacks the central jet, due to instabilities of its flow field. As for TSSmax, CM reaches the highest values, presumably due to leaflets fluttering. SJ's TSSmax profiles maintain similar shapes at the two downstream locations, whereas SB presents an unexpected increase in the peak value of TSSmax, from 13 to 26 mm downstream of the valve plane, probably due to the curved leaflet design. The three prosthetic heart valves (PHVs) tested show many differences as for their turbulence properties, although they are similarly constructed.