[Differentiated evaluation of heart valve stenosis by expanded Bernoulli equation--in vitro studies of model stenoses].

A suitable measure for the hydrodynamic assessment of heart valve stenoses must be independent of flow and should correspond to the morphology of the stenoses. The effective orifice area according to Gorlin does not fulfil this requirement, generally, because it is constant only under special conditions. This suggests the development of a multidimensional stenosis model. The idea for doing so is based on hydrodynamic evaluation of different elementary stenosis types in comparison with a valve that behaves like Gorlin's theory. The Bernoulli equation can than be expanded definitely and one gets a set of unknown stenosis parameters corresponding to the elementary stenoses. The clinical relevance of these must be evaluated by morphological evidence and by similarity of the flow-pressure drop characteristics as compared to real heart valve stenoses. A suitable reference valve is the Bjork-Shiley valve. This valve was combined with evident elastic and stiff obstacles to opening with the result of flow-pressure drop characteristics similar to biological valves written in terms of flow q : Δ p = c 2 . q 2 + c 1 . q + c 0 where q and q 2 are mean flow and mean square flow through the valve, respectively. Empirical results reported in the literature can be explained as special cases of the stenosis model as demonstrated by examples. The proposed equation can be interpreted in physically founded terms in contrast with an empirical one. It gives rise to a differentiated evaluation of heart valve stenosis by orifice area (c 2 ), elastic properties of shape and material (c 1 ) and pre-stress (c 0 ) independent on flow. The model can be extended step by step as required.