Studies in a cardiovascular model on the arterial dilution curve of valvular regurgitation

Abstract

Many methods for assessing valvular regurgitation, including techniques which attempt to quantify backward flow, are based on analysis of deformities characteristically observed in arterial dilution curves. The present study was designed to ascertain what these methods actually measure. Dye was injected into the atrium, and dilution curves were recorded continuously from the elastic aorta of a pulsating two-chambered cardiovascular model. Forward flow, backflow, ventricular stroke and end-systolic volumes, and atrial size, shape, and elasticity were systematically varied. One hundred and seventeen experiments were performed. In 61 experiments the atrioventricular valve was made incompetent, with backward flows ranging from 8 to 73 per cent of total ventricular output. With forward flow and central volume held constant, enhancement of mixing, produced by altering atrial geometry or the distribution of fluid between atrium and ventricle, reproduced the earlier appearance, lower peak, flatter downslope, and wider spread seen with valvular regurgitation. Qualitatively and quantitatively indistinguishable dilution curves were produced in the presence and absence of regurgitation by appropriate manipulation of mixing. For a given forward flow, with or without regurgitation, the spread of dilution curves was related to Newman's mixing volume by a single regression line, but to Hamilton's central volume by a family of such lines, each uniquely determined by the ratio of mixing volume to central volume. With forward flow and mixing volume held constant, the dilution curve was unaltered by the introduction of valvular regurgitation. These results demonstrate the following: (1) The parameters of dilution curves obtained downstream to a valve, after injection upstream, are functions of forward flow and of a volume, real or virtual, in which indicator has effectively mixed, whether or not valvular regurgitation is present. (2) Methods which assess valvular regurgitation by analysis of such curves do not measure regurgitant flow. They are merely indices of an enhanced mixing which usually, but not inevitably, accompanies regurgitation.