Affiliations: Institute of Medical & Dental Bioengineering, University of Liverpool, P.O. Box 147, Liverpool, U.K.
Abstract: The haemodynamic disturbances which may exist downstream of a constriction have been implicated in the poor performance of small diameter prostheses which have a high rate of occlusion by thrombus formation at or near the anastomoses to the host vessels. Because the presence of turbulence in blood flows can be detrimental to the blood elements, factors which reduce or eliminate turbulence at these sites should be considered. This study forms part of an ongoing investigation into the role of wall compliance and vessel geometry on the development of post-stenotic flow disturbances in arterial prostheses and arterial reconstructions. The prostheses were fabricated with two degrees of compliance corresponding roughly to that of a ‘rigid’ knitted Dacron prosthesis and that of a naturally-compliant peripheral vessel (femoral artery). Flow disturbances were measured in both cylindrical and 0.75° tapered prostheses using a 20 MHz rangegated ultrasound Doppler velocimeter. The instantaneous centreline velocity (from which the disturbance intensities were calculated) was measured in steady flow downstream of 50% and 75% stenoses which were positioned, in turn, at the inlet to each conduit as a model of a proximal anastomosis. Experimental data obtained at physiological Reynolds numbers between 375 and 1500 showed that the flow disturbance intensity measured in the compliant prostheses was always greater than in the corresponding rigid conduits – a surprising result as it has been shown that a compliant wall can delay the onset of turbulent flow in cylindrical tubes. In contrast, the magnitude of poststenotic flow disturbances measured in the tapered prostheses was significantly lower for both rigid and compliant systems when compared with the data for the cylindrical conduits.
