Heart contractility at pressure loads induced by ischemia of exercised muscle in humans

Abstract

During one- or two-leg bicycle exercise in three subjects the exercised limb(s) were made ischemic by occlusion cuffs inflated to 300 Torr immediately at, or 30 s before, end of 7-min exercise and kept inflated for 3 min of recovery. Mean arterial pressure (MAP) remained elevated during occluded recovery, whereas heart rate (HR) and forearm blood flow tended to recover at the same rate as in the control situation without occlusion. Systolic time intervals (STI) were negatively correlated to HR in the interval 60–120 beats/min. In spite of a variation in afterload of 30 Torr induced by occlusion the correlation between HR and STI fitted the same equations. The involvement of different size of muscle mass did not change these relationships. The elevation of MAP during ischemia of exercised muscles is due to an increased vascular tone reflexly induced from muscle chemoreceptors and not cardiac in origin. The results also demonstrate that heart contractility adapts well to the induced afterload.