Analysis of Fluid Mechanical Energy Losses in Aortic Valve Stenosis

Abstract

Abstract Aortic valve stenosis occurs when the aortic valve does not open fully during systole, thus creating an obstruction to blood flow leaving the left ventricle. Maximum orifice pressure drop and valve orifice area are the primary clinical indicators of the severity of aortic stenosis. Pressure drop can be measured by catheter insertion or calculated with the modified Bernoulli equation from Doppler ultrasound velocity measurements. Unfortunately there are discrepancies between the two techniques that are often attributed to pressure recovery downstream of stenotic aortic valves [Levine et al, 1989]. The relationship between orifice pressure drop and left ventricular function is ambiguous. This has been emphasized in a recent paper by Vandervoort et al [1996], which states, “Although maximum, transvalvular, and net pressure gradients are all different gradients that physically exist, it is currently not known which of these gradients is most relevant to reflect the work load imposed on the heart”. Since it has been shown that left ventricular function has a significant effect on post-operative recovery [Ross, 1985], it is imperative that the severity of aortic valve stenosis be evaluated in terms of left ventricular work capacity. Therefore, the purpose of this study was to determine the relationship between left ventricular work and pressure drop measurements in aortic stenosis. The hypothesis that motivated this study was that the left ventricle performs work to overcome energy losses caused by aortic valve stenosis, and the pressure drop that most accurately represents this work should be used for clinical assessment of aortic stenosis.