Wall shear stress distribution along the cusp of a tri-leaflet prosthetic valve.

High levels of wall shear stress on the surface of valvular cusps can cause mechanical damage to the blood cells and the cusp surfaces. The shear stresses are also responsible for mechanical failure of prosthetic heart valves. Qualitative measurements of wall shear stress in the vicinity of the leaflets are thus essential for diagnosis of suspected complications and provide important information for the design and fabrication of bioprosthetic heart valves. For this purpose we measured the velocity distribution along the inside wall of the cusps of a tri-leaflet heart valve with a two colour laser Doppler anemometer system. The wall shear stresses on the cusp surface were computed and found to range from 80 to 120 N/m2 during the ejection phase. Wall shear stresses of up to 180 N/m2 were measured in loci of cusp flexure and the accelerated boundary layer. The results of this study show a correlation between the high shear stress loci and the clinically (animal) observed regions of cusp calcification.