Age Difference In Muscle Sympathetic Nerve Activity During Passive Leg Raising In Females

Sympathetic vasomotor outflow to skeletal muscle (muscle sympathetic nerve activity: MSNA) at rest increases with advancing age. Moreover, the increase in MSNA with aging is steeper in females than in males. Acute increases in central blood volume (CBV) inhibit sympathetic activity by loading of cardiopulmonary baroreceptors, but the influence of aging in females is unknown. PURPOSE: To elucidate age-related differences in sympathoinhibiton during cardiopulmonary baroreceptors loading in females. METHODS: Healthy older females (OF, n = 8, 69 ± 2 yrs, means±SE) and younger females (YF, n = 8, 21 ± 1 yrs) participated in two experimental visits on separate days. On day 1, participants performed a passive leg raising (PLR) test with measurement of left radial MSNA. On day 2, participants repeated the PLR test with measurements of estimated central venous pressure (eCVP; right large antecubital vein) as an index of CBV. During each PLR test, participants rested in a supine position (0°), and then the lower limbs were lifted passively and gradually at 10°, 20°, 30°, and 40°, each held for 3 minutes. RESULTS: Baseline mean arterial blood pressure (MAP) and MSNA burst frequency (BF) and burst incidence (BI) were higher in OF than YF. MSNA BF and BI decreased during the PLR test in both OF (Δ -4.1 ± 0.5 bursts/min at 40°) and YF (Δ -6.8 ± 0.3 bursts/min at 40°). The decrease in MSNA BF during the PLR test was smaller in OF than in YF (P < 0.01). The eCVP increased during the PLR test in both OF (Δ +3.2 ± 0.4 mmHg at 40°) and YF (Δ +2.9 ± 0.4 mmHg at 40°) but did not differ between the two groups (P = 0.90). Heart rate and MAP remained unchanged throughout the PLR test in each group. CONCLUSIONS: These results suggest that the sympathoinhibitory effects caused by cardiopulmonary baroreceptors loading could be impaired with advancing age in females. Supported by JSPS KAKENHI #22H03479 JSPS KAKENHI #22H03479