Inhibition of sympathetic vasomotor outflow during low-intensity leg cycling is attenuated in healthy older females.

Abstract

The purpose of the present study was to elucidate the impact of age on muscle sympathetic nerve activity (MSNA) during dynamic leg exercise in females. Nine older females (71±2 years, mean±SD) and ten younger females (21±2 years) completed the study. The participants performed two 4 min leg cycling at 10% of their heart rate reserve using a cycle ergometer in a semirecumbent position [MSNA and estimated central venous pressure (eCVP) trials]. MSNA was recorded via microneurography of the left radial nerve. The CVP was estimated based on peripheral venous pressure, which was monitored using a cannula in the right antecubital vein. The magnitude of the change in mean arterial blood pressure during exercise was larger (P<0.001) in older females (+11.6±4.7 mmHg) compared with younger females (+4.1±3.2 mmHg). MSNA burst frequency (BF) was decreased during cycling in both groups, but the magnitude of the decrease in MSNA BF was smaller (P=0.004) in older females (-5.6±1.8 bursts/min) than in younger females (-9.1±2.5 bursts/min). The eCVP increased during exercise in both groups, and there was no difference in the changes in eCVP between the two groups (older, +0.80±0.27 vs. younger, +1.02±0.51 mmHg, P=0.462). From these results, it is possible that the cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow, elicited by the muscle pump, may be attenuated with advancing age in females.