Hydrogen bubble visualization of the flow past aortic prosthetic valves.

The hydrogen bubble technique was used to visualize flow past two different aortic valve prostheses. The results reported in this paper clearly show the efficacy of the method and its main advantage, namely that tracers can be produced at any position and at a completely controlled rate. This fact allows the study of either selected moments or regions of the flow field, thus enhancing contrast and therefore increasing the signal-to-noise ratio of the picture. The possible perturbations introduced by the cathode may be decreased to a minimum by using small-diameter wires or wall flush-mounted thin plates. On the other hand, the buoyant velocity of the bubbles may be only a few percent of the fluid velocity and therefore not substantially affect the results. Within the limited scope of the present investigation, the xenographic valve seems to disturb the flow significantly less than the Björk-Shiley prosthesis, both for steady and pulsatile flow, as shown by the traverse velocity profiles or through turbulent stress mapping.