An in vivo method of measurement of the mechanical properties of vascular prostheses: the mechanical properties of saphenous vein bypass grafts

It seems likely that long term patency of small bore vascular prostheses is dependent upon, among other things, the mechanical properties of their walls. Arteries are visco-elastic but there is no accurate method of measuring the visco-elasticity of arterial substitutes in vivo. The most successful vascular substitute is autogenous saphenous vein and it is essential to know its elastic properties if we are to mimic them in prostheses. (veins rapidly lose their elasticity when excised and measurements made in vitro are unrealistic.) We describe an in vivo method which is based on measurements of pressure alone from which we calculate a propagation constant and phase speed, which characterises the visco-elastic behaviour of vein. Sixteen patients who had a femoro-popliteal bypass were studied. Measurements of pressure were used to calculate the phase speed of the pulse and the relationship of phase speed to frequency was calculated. The asymptotic phase speed for human saphenous vein was 13.6 m s-1.