Individual Differences in Cardiac and Vascular Components of the Pressor Responses to Isometric Handgrip Exercise in Humans

Abstract

The aim of this study was to test the hypotheses that, in humans, cardiac output (CO) and total peripheral vascular resistance (TPR) responses to isometric exercise vary among individuals, and that the individual differences are related to the muscle metaboreflex and the arterial baroreflex functions. Healthy subjects (n = 32) performed 1‐min isometric handgrip exercise (HG) at 50% of maximal voluntary contraction, followed by a 4‐min period of post‐exercise muscle ischemia (PEMI) to selectively maintain activation of the muscle metaboreflex. In 11 subjects the pressor response to HG occurred solely by the increase in CO, but in 18 subjects it occurred due to both the increases in CO and TPR, and further it occurred solely via the increase in TPR in 3 subjects. Thus the pressor components varied widely among subjects. The CO and TPR responses during HG were positively correlated with those responses during PEMI, respectively. In addition, the CO response to PEMI was negatively correlated with the PEMI‐induced changes in an index of cardiac vagal tone and cardiac baroreflex sensitivity. We conclude that CO and TPR responses to HG vary among individuals, and that the individual differences in components of the pressor response could be attributed in part to the variations in the muscle metaboreflex and the arterial baroreflex functions. This study was supported by the grants from Japan Society for the Promotion of Science.