Calculation of atrioventricular compliance from the mitral flow profile: analytic and in vitro study

The quantitative assessment of ventricular diastolic function is an important goal of Doppler echocardiography. Hydrodynamic analysis predicts that the net compliance (C_n) or the left atrium and ventricle can be quantitatively predicted from the deceleration rate (dv dt) of the mitral velocity profile by the simple expression: C_n = - A ρ{variant} dv dt where A is effective mitral valve area and ρ{variant} is blood density. This formula was validated using an in vitro model of transmitral filling where mitral valve area ranged from 0.5 to 2.5 cm² and net compliance from 0.012 to 0.023 cm³/(dynes/cm²) (15 to 30 cm³/mm Hg). In 34 experiments in which compliance was held constant throughout the filling period, net atrioventricular compliance was accurately calculated from the E wave downslope and mitral valve area (r = 0.95, p < 0.0001). In a second group of experiments, chamber compliance was allowed to vary as a function of chamber pressure. When net compliance decreased during diastole (as when the ventricle moved to a steeper portion of its pressure-volume curve), the transorifice velocity profile was concave downward, whereas when net compliance increased, the velocity profile was concave upward. Application of the preceding formula to these curved profiles allowed instantaneous compliance to be calculated throughout the filling period (r = 0.93, p < 0.001). Numeric application of a mathematic model of mitral filling demonstrated the accuracy of this approach in both restrictive and nonrestrictive orifices. It is concluded that 1) net compliance can be calculated noninvasively and quantitatively from mitral valve area and E wave downslope, and 2) the time course of net compliance determines the shape of the downslope: concave downward profiles indicate decreasing compliance whereas concave upward profiles indicate increasing compliance.