Physical and physiological determinants of transmitral velocity: numerical analysis

The Doppler transmitral velocity curve is commonly used to assess left ventricular diastolic function. Recent investigations, however, relating Doppler mitral indexes to ventricular compliance, relaxation, and preload have been inconclusive and at times contradictory. We used a mathematical formulation to study the physical and physiological determinants of the transmitral velocity pattern for exponential chamber pressure-volume relationships with active ventricular relaxation (2,187 combinations investigated). We showed that transmitral velocity is fundamentally affected by two principal physical determinants, the transmitral pressure difference and the net atrioventricular compliance, as well as the impedance characteristics of the mitral valve. These physical determinants in turn are specified by the compliance and relaxation parameters of physiological interest. We found that the peak mitral velocity is most strongly related to initial left atrial pressure but lowered by prolonged relaxation, low atrial and ventricular compliance, and systolic dysfunction. Peak acceleration varies directly with atrial pressure and inversely with the time constant of isovolumic relaxation, with little influence of compliance, whereas the mitral deceleration rate is approximately valve area divided by atrioventricular compliance. We then used these data to suggest possible strategies for improved analysis of noninvasive data (Doppler indexes, planimetered valve area, and isovolumic relaxation time) to estimate ventricular compliance and relaxation and atrial pressure.