Cardiac valve orifice equation independent of valvular flow intervals: application to mitral valve area computation in mitral stenosis and comparison with the Gorlin formula and direct anatomical measurements.

An orifice equation is developed which relates the effective mitral valve area (A), the average mitral valve pressure gradient (dP), the cardiac output (Q) and the heart frequency (f) through considerations of momentum conservation across the mitral valve. The form of the new equation is A = (4.75 X 10(-5)Qf/dP, where A, Q, and dP are expressed in cm2, ml X min-1 and mmHg respectively. Mitral valve areas computed with the new orifice formula are found to correlate with those computed by the Gorlin formula in conditions of equilibrium associated with the resting state at a level of r = 0.95, SE = 0.15 cm2, with autopsy measurements at a level of r = 0.85, SE = 0.18 cm2 and with direct anatomical measurements of excised valves at a level of r = 0.78, SE = 0.41 cm2. The results suggest that the new formula may be considered as an independent orifice equation enjoying a similar domain of validity as the Gorlin formula. The new equation offers the possibility of deriving additional useful haemodynamic relationships when used in combination with established cardiological formulas.