Model studies of the aortic pressure rise just after valve closure

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Abstract
Model experiments are performed in a long, thin-walled, fluid-filled, latex tube in which the fluid is locally suddenly stopped, starting from a steady flow, thus simulating the wave phenomenon generated by the final closure of the aortic valve. The resulting waveform is determined as it propagates upstream. The effect of a local step-wise change in compliance close to the valve, representing the aortic sinus section, is investigated. The observed phenomena are analysed by means of a quasi-one-dimensional model, solved by the method of characteristics, taking into account the influence of nonlinearities, wall shear stress, viscoelastic wall properties and wave reflections. The theoretical computations are well confirmed by the experimental results. The pressure jump, induced by the valve closing, appeared to be slightly affected by nonlinearities. The decrease of the pressure jump while propagating upstream and the gradual pressure increase that follows the pressure jump are caused by the effect of wall shear stress. The local change in compliance generates the expected wave reflections and has a strong influence on the rise-time of the wave front. The experiments confirmed the prediction that wall viscoelasticity is the dominant factor in the gradual decay of the slope of the wave.