Preload changes modify systolic pressure-diameter relations in the conscious .dog

sure-diameter relations in the conscious dog.-Am. J. Physiol. 240 (Heart Circ. Physiol. 9): H354-H360, 1981.-The behavior of the end-systolic ventricular diameter was examined during control state, atrial pacing, and acute volume loading (VL) followed by methoxamine infusion in conscious dogs instru-mented with a left ventricular micromanometer and ultrasonic crystals measuring internal diameter and wall thickness. Heart rate and systolic pressure were markedly increased by maximal VL but for moderate VL were minimally modified. Moderate VL increased end-diastolic diameter by 5 % and end-systolic diameter by 2.9 % with a significant increase of systolic stress. There was no common final pathway of shortening in the force-velocity-length diagram for different preloads. During methox-amine infusion, the end-systolic pressure-diameter points de-scribed a linear regression but points obtained during atria