Non-invasive measuring of the circulatory effect of afterload reduction in order to monitor the pharmacodynamic effect of drugs in normal volunteers.

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Abstract
In order to measure the effect of a decrease in afterload on systolic time intervals, left ventricular end-systolic diameter and left ventricular wall stress, 8 healthy young persons underwent a randomized placebo controlled trial of terbutaline before and during atenolol treatment. Pre-ejection period index, left ventricular end-systolic diameter, and wall stress all decreased after terbutaline, the decrease being clearly dose-dependent. This was identical before and during atenolol administration. Consequently the observed changes were induced by .beta.2 elicited vasodilatation, possibly combined with some decrease of parasympathetic tone. A close correlation between changes in pre-ejection period index (PEPI) and changes in left ventricular end-systolic diameter (LVESD) and wall stress was shown both before and during atenolol treatment. When using non-invasive methods in the evaluation of changes in contractility, it is important to correct for changes in preload and afterload. For normal subjects, the relation between .DELTA.PEPI and .DELTA.LVESD as a percentage of the mean values should apparently be used for evaluation of afterload changes. A method is suggested for estimating changes in pre-ejection period index induced by changes in left ventricular end-systolic diameter or wall stress.