INVITRO VELOCITY-MEASUREMENTS IN THE VICINITY OF AORTIC PROSTHESES

A laser-Doppler anemometer was used for in vitro measurements of velocity profiles in the vicinity of aortic prostheses at steady flow rates of 167 cm3/sec to 417 cm3/sec. Results showed that at these high flow rates the wall shear stresses were about 1 × 103 dyn/cm2 in the near vicinity of the aortic prostheses studied. Also maximum turbulence-intensity levels of 25-50% were measured, and they decayed to about 15-20% at 120 mm downstream from the valves. The experimentally observed wall-shear stresses were of a magnitude that could damage the endothelial lining of the ascending aorta and the formed elements of blood, at least when they adhere to the wall of the aorta. In the near vicinity of the aortic prostheses, maximum values of bulk-turbulent-shear stresses estimated from turbulence-intensity measurements and simple flow models were in the range of 102-103 dyn/cm2. Turbulent shears in that range could damage red-blood cells and platelets and lead to thrombus formation. With pulsatile flow, where there is an acceleration phase, the shear stresses would even be larger. © 1979.