Flow Pattern and Velocity Field Distal to Human Aortic and Artificial Heart Valves as Measured Simultaneously by Ultramicroscope Anemometry in Cylindrical Glass Tubes

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Abstract
The flow phenomena distal to isolated fresh human aortic valves and different types of aortic valve prostheses mounted in straight glass tubes of (he corresponding aortic diameter, were investigated under steady flow conditions at physiological flow rates. The influences of different valves on flow were compared quantitatively on the basis of the following criteria: 1.) magnitude of energy loss due to the effective stenosis produced by the artificial valves, 2.) appearance of a thrombogenic flow pattern (stagnation point flow bordering large deadwater regions). Liquids used were water and a non-Newtonian fluid (polyacrylamide). The wall pressure was measured at opposite points of the tube circumference at various distances proximal and distal from the valve orifice. A laser-ultramicroscope-anemometer (7) was used to record the velocity field simultaneously over a length of 40 mm distal and proximal to the valve with a spatial resolution comparable to the thickness of a microthrombus (≅ 10 μm). The effect of bioprostheses on the hemodynamics approximates that of the fresh aortic valve only in respect to avoiding a thrombogenic flow pattern, whereas the energy loss is still remarkably high. Artificial valve prostheses show the opposite deviation from the behavior of the fresh valve. A new valve design which combines both of these beneficial properties would lead to a satisfactory valve substitution.

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