Mechanism of augmented rate of left ventricular filling during exercise.

At rest, most of left ventricular (LV) filling occurs early in diastole. This LV filling occurs in response to the pressure gradient produced as LV pressure falls below left atrial (LA) pressure. Because mitral valve flow occurs in response to an LA to LV pressure gradient, augmented diastolic mitral valve flow during exercise may be due to an increased mitral valve pressure gradient resulting from a rise in LA pressure and/or a fall in LV early diastolic pressure. Accordingly, we studied 13 conscious dogs, instrumented to measure micromanometer LV and LA pressures, and determined LV volume from three ultrasonic dimensions during exercise. The animals ran on a treadmill for 8-15 minutes at 5-8 miles/hr. With reflexes intact, during exercise, the heart rate increased from 116 +/- 20 to 189 +/- 24 beats per minute (mean +/- SD, p less than 0.01), the maximum rate of change of LV volume (dV/dtmax) increased from 185 +/- 44 to 282 +/- 76 ml/sec (p less than 0.01), the ejection fraction and cardiac output incr...