Haemodynamic and rheological aspects of vascular grafts.

1. We now know that although the basic relationship of pressure, flow and resistance as expressed by the Poiseuille equation is useful in understanding basic regional haemodynamics, it cannot be applied to pulsatile flow and particularly if any measurements are to be made in the study of graft haemodynamics. Measurements of pressure wave velocity, and flow wave velocity with calculations of wall compliance and impedance are more appropriate. 2) The clinical performance of a graft depends on the mechanical properties of the graft and the response of the body to the prosthesis in terms of fibrous tissue reaction and thrombus deposition. 3) We should aim for grafts with low thrombogenicity, and a compliance which after implantation matches that of the arterial wall of the patient. 4) Although the animal experiments of the 1980s have given us enough indications of what we should aim for, and no doubt they will continue to be the ground for preclinical assessment, the time has come for us to develop techniques that will allow us to do the same measurements in our patients noninvasively. The high resolution M-mode and B-mode echographic vascular imaging and Doppler ultrasonic techniques with real-time fast Fourier analysis are with us and should form the spearhead for such an approach. By measuring graft compliance, thrombus deposition and flow velocities in the grafts implanted in our patients we shall bridge the gap between animal experiments and clinical evaluation, providing the manufacturers with enough information that points the direction towards more efficient grafts.