Sympathetic Influences on Cardiac Rate and Contractility During Acute Stress in Humans

ABSTRACT Experiments are reported concerning an evaluation of sympathetic influences on heart rate and cardiac contractility in normal young adult humans during a stressful reaction time task. During the preparatory interval only vagal influences on heart rate change could be found which were related to concomitant somatic activity. In expectation of the shock and for a more sustained period thereafter, sympathetic influences became manifested on both heart rate and contractility which were independent of concomitant somatic activity. In a follow‐up study, the relationship was evaluated between blood pressure, as measured directly from the radial artery, and both contractility and heart rate. Sympathetic influences on the heart were not found to be secondary to depressor effects, although appreciable phasic decreases in blood pressure were sometimes found to follow the onset of large increases in heart rate and contractility. The data suggest that sympathetic influences on the heart are normally very minimal but are evoked by intense stress when the organism attempts to cope with the stress.