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

Abstract

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 instrumented 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 methoxamine infusion, the end-systolic pressure-diameter points described a linear regression but points obtained during atrial pacing before VL were significantly shorter. We conclude that VL increases the total loading of the heart producing a lengthening of the end-systolic diameter when end-diastolic diameter is increased. This reduces the expression of the Starling mechanism and suggests caution when interpreting end-systolic pressure-diameter relations and derived indices for significantly different end-diastolic diameters.

The responses of left ventricular end‐systolic pressure‐diameter relationship to acute pressure overload induced by aortic constriction

“…Thus, it is possible that the baseline preload just prior to loading (constriction) and unloading (release), as well as the left ventricular contractile state, were among the factors determining ESPDR and its slope. Crozatier et al (1981) previously reported that an acute volume overload shifted ESPDR to the right in the conscious dog. Berko et al.…”

The step response of left ventricular pressure to ejection flow: A system oriented approach

“…One way of dealing with deviations encountered experimentally consists of defining additional state vec- tor components and thus making the model more accurate. As to the elastance model, it was shown in isolated ventricles (97), as well as in the intact animal (8,20,28,58,91), that deviations occur for greater stroke volumes and ejection fractions. This was also shown for extreme conditions on contractile state by Burkhoff et al (19).…”

“…A number of ejection parameters were claimed to influence the time course of elastance. Increasing stroke volume and/or ejection fraction (8,97), as well as the preload to the ventricle (8,28), were shown to result in a decrease of elastance. In contrast, after increasing afterload, the opposite occurred (8,31,84).…”

The Pressure—Length Loop

“…By extending the concept of time-varying elastance to pressure-length relationships, it can be shown that a linear relationship exists between pressure and diameter [4,16], and pressure and length at the end of systole (P-L es ) ( fig. 7) and that increases in inotropy increase its slope ( fig.…”

“…An early tenet of the analysis of end-systolic pressure-dimension relationships was that a constant volume or dimension intercept exists at zero pressure (figs 6, 8) [27]. This has been subse- quently disproved [4] and, at regional level, the intercept of the P-L es line with the length axis is not constant [8].…”