Pressure-flow relations across the normal mitral valve.

The stenotic mitral valve area is a major determinant of the atrioventricular pressure-flow relation, and mean atrioventricular pressure gradient is proportionate to the square of mean flow rate. In the absence of obstruction, this relation is linear. The effect of the normal mitral valve area on this pressure-flow relation has not been previously examined. Pulsed Doppler studies of transmitral flow were performed simultaneously with thermodilution cardiac outputs in 25 patients in sinus rhythm and with no valvular disease. Mean flow rate was determined as thermodilution stroke volume/diastolic filling period measured by Doppler. Several instantaneous pressure gradients were estimated from multiple velocity measurements using the modified Bernoulli equation and were plotted against time. Mean pressure gradient was estimated by dividing the area under the pressure-time curve by the diastolic filling period. Average and standard deviation of mean flow rate and pressure gradient was 223 +/- 70 ml/s and 1.4 +/- 0.8 mm Hg, respectively. There was an excellent linear correlation between these 2 parameters (r = 0.91, SEE = 30 ml/s). This confirms the linear relation of mean pressure gradient to mean flow rate in the absence of obstruction. The excellent correlation, obtained without considerations of individual variations of valve area, suggests that this relation is independent of valve area, under normal physiologic conditions.