Effect of static exercise and muscle ischemia on cardiac function as evaluated by the systolic time intervals

To determine the role of muscle chemoreflex in the cardiac response to static exercise the effect of the forearm muscle ischemia on systolic time intervals (STI), heart rate (HR) and blood pressure (BP) recovery following static handgrip was studied in 7 healthy men. During handgrip maintained for 4 min at 30% maximal voluntary contraction HR and BP increased significantly while duration of the pre-ejection period (PEP) and isovolumic contraction time (ICT) were shortened with a significant lowering in the ratio of PEP to the left ventricle ejection time (LVET). Occlusion of the circulation to the forearm muscles for 2 min after cessation of exercise did not prevent a rapid decline of HR or increment in PEP, ICT and PEP-to-LVET ratio while BP remained elevated for as long as blood flow to muscles was restricted. The study failed to demonstrate an appreciable effect of muscle chemoreflex on HR or myocardial contractility, suggesting that input from muscle afferents activated by metabolic stimuli induces the pressor response mainly by the peripheral vasoconstriction.