To determine the effect of filling pressure on the pattern of left ventricular filling in humans, the mitral flow velocity profile was measured by pulsed wave Doppler echocardiography during right and left heart catheterization in 11 patients before and during nitroglycerin infusion. Nitroglycerin reduced mean arterial pressure from 90 ± 9 to 80 ± 11 mm Hg (p < 0.001) and mean pulmonary capillary wedge pressure from 9 ± 4 to 4 ± 2 mm Hg (p < 0.001). Cardiac output fell from 6.6 ± 1.5 to 5.5 ± 1.4 liters/min (p < 0.001) and heart rate increased from 60 ± 13 to 65 ± 14 beats/min (p < 0.002). The time constant of isovolumic relaxation (TL.) decreased from 51 ± 9 to 46 ± 8 ms (p < 0.01), indicating faster left ventricular relaxation.
Nitroglycerin altered the Doppler characteristics of the early filling (E) wave but not those of the atrial contraction (A) wave. Peak velocity of the E wave decreased from 56 ± 14 to 44 ± 9 cm/s (p < 0.001), peak velocity of the A wave did not change and the ratio of peak velocities of the E and A waves decreased from 0.97 ± 0.33 to 0.77 ± 0.20 (p < 0.02). The deceleration of the E wave decreased from 289 ± 138 to 186 ± 71 cm/s2 (p < 0.02). The ratio of velocity-time integral of the A wave to total velocity-time integral (that is, contribution of atria) contraction to total filling) increased from 0.31 ± 0.09 to 0.36 ± 0.08 (p < 0.03). Crossover pressure correlated positively with peak velocity of the E wave (p < 0.007, r = 0.56).
These results indicate that the pattern of left ventricular filling, measured by the Doppler mitral flow velocity profile, is dependent on left ventricular filling pressure. A reduction in the filling pressure changes the flow velocity profile in a manner that mimics the abnormalities previously reported with impairment of left ventricular diastolic function. Therefore, when interpreting Doppler-derived indexes of left ventricular diastolic function, the influence of preload must be taken into account.
