The aim of the present study is to investigate combined aortic stenosis and regurgitation of varying severity using numerical simulations. The numerical simulations will provide detailed data on the time dependent flow field. Moreover, the numerical simulations can be effectively utilized to isolate the governing factors and to develop (together with other tools of investigation) more reliable methodologies in the assessment of the severity of aortic stenosis and regurgitation.
Usually the simplified Bernoulli equation is used to calculate the pressure drop across heart valves. However, since the flow is viscous (rotational) and time dependent, this equation may not be valid or yield accurate results. This is especially true in the present case of stenotic lesions in combined aortic stenosis and regurgitation, where strong interaction and the vortical flow invalidates the underlying assumptions. Furthermore, the effect of stenosis severity on the color Doppler assessment of the regurgitant jet in these lesions was never studied in a controlled manner. Therefore it is of utmost importance to comprehend the resulting flow field and consequently to develop improved and simplified relationships (or correlations) for estimating more accurately the pressure drops in the case of combined aortic stenosis and regurgitation.
The present results confirm that the existing method for calculating the flow rate might be inaccurate for relatively large regurgitant holes or away from the hole. The study also shows that the Bernoulli approximation fails at small holes and therefore other means for approximating the pressure drop should be sought. It was found, however, that the static pressure drop is proportional to the square of the hole size. Subsequent research will study the combined effect of stenosis and insufficiency and modifications of the Bernoulli approximation will be attempted to increase the accuracy of the prediction of the pressure drop in clinical applications.
