Alterations in cardiac contractility during classical aversive conditioning in dogs: methodological and theoretical implications.

An investigation of sympathetic influences on the heart was undertaken in dogs using classical aversive conditioning procedures. For this purpose, heart rate and cardiac contractile changes were measured, the latter using techniques assessing the rate of change or slope at which either the muscles of the left ventricle contract, or blood is accelerated in the ascending aorta, or the pulse pressure wave ascends from diastole to systole. Sympathetic influences were found to be more clearly manifest in contractile rather than heart rate changes as indicated by the greater attenuating influence of beta-adrenergic blockade on anticipatory and unconditioned responses. Anticipatory sympathetic influences on the heart were commonly acute, becoming minimal upon repeated exposure to the aversive procedures. The rate of change or slope measures appear to detect sensitively extrinsic sympathetic influences on contractility. They are minimally influenced by intrinsic effects on contractility such as heart rate as well as non-contractile events such as diastolic blood pressure. The slope of the ascending limb of the pulse pressure wave appears to offer a means of assessing contractility in human Ss.