Effect of aging on arm and leg muscle sympathetic nerve activity in humans

Abstract

Aging is associated with heterogeneous changes in sympathetic nervous system outflow to various organs. Previous studies have consistently reported pronounced increases in leg muscle sympathetic activity (MSNA) at rest with age. We tested the hypothesis that aging is associated with similar increases in arm and leg MSNA at rest. Moreover, we tested the hypothesis that baroreflex unloading elicits similar increases in arm and leg MSNA in older adults. To address these hypotheses we simultaneously measured arm and leg MSNA using microneurography in young (N=7; 23±1 years old; mean±SE) and older adults (n=5: 63±2) at rest and in response to lower body negative pressure (LBNP of ‐10, ‐20, and ‐40 mmHg) (older subjects only). MSNA at rest increased similarly with age in the arm (8±2 vs. 34±6 bursts/min for young and older, respectively; P<0.05) and leg (9±2 vs. 35±6 bursts/min; P<0.05). Moreover, LBNP elicited similar increases in leg (Δ4±2, Δ8±4, and Δ16±6 bursts/min, change from baseline for ‐10, ‐20, and ‐40 mmHg LBNP, respectively; main effect P<0.05) as well as arm MSNA (Δ4±2, Δ2±2, and Δ15±6; main effect P<0.05) in older adults. Collectively, these data indicate that aging is associated with similar increases in arm and leg MSNA at rest. Moreover, parallel increases in leg and arm MSNA occur during baroreflex unloading in older humans.Support: NIH AG24420, HL77670, M01 RR10732