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We studied left ventricular (LV) pressure-diameter relations in 13 open-chest mongrel dogs to explore whether ventricular filling is passive, active, or a combination of both. Left ventricular internal diameter along the minor axis and thickness of the LV free wall were measured with ultrasonic dimension gauges. Pressures in the LV, left atrium (LA), and aorta were measured with catheter-tip micromanometers. Pressure in the LV during the rapid filling phase of diastole decreased from 13 +/- 1 mm Hg to 3 +/- 0.4 mm Hg (mean +/- SE). During this period, LV internal diameter increased from 32.6 +/- 1.5 to 36.7 +/- 1.5 mm, and this represented 49% of the total change of LV diameter that occurred during diastole. The pressure-diameter relation that we observed during the rapid phase of filling suggests that active enlargement rather than passive distension of the left ventricle occurred. Reduction of pressure within the left ventricle during rapid filling, while the ventricular diameter increased, appears to be due to forces within the LV wall that act to restore the LV to its diastolic dimensions. This allows the LV to draw blood from the atrium by creating a pressure in the LV that is lower than in the LA. On the other hand, during the latter part of diastole, following atrial contraction, the pressure-diameter relation suggests that the left ventricle undergoes passive distention.

Pressure-diameter relations during early diastole in dogs. Incompatibility with the concept of passive left ventricular filling.