Differential effects of female aging on sympathetic blood pressure regulation at rest and during stress in humans

Abstract

Older female (OF) adults exhibit blunted resting sympathetic blood pressure (BP) transduction compared with young female (YF) adults, affecting BP regulation. However, studies often lack control over health factors like body composition or habitual physical activity. Therefore, we compared resting sympathetic BP transduction and neurovascular responses during cold pressor test (CPT) and end-expiratory apnea between YF (n = 12) and OF (n = 9) matched for several health factors. We measured beat-to-beat hemodynamics and muscle sympathetic nerve activity (MSNA). OF exhibited higher resting supine BP and MSNA (p_s < 0.001) than YF. OF exhibited blunted increases in mean BP and diastolic BP following spontaneous MSNA bursts at rest. During the CPT, OF exhibited a smaller percent increase in total MSNA (interaction effect: p = 0.001) but not MSNA burst frequency responses. Mean BP increases were not different between groups, but OF exhibited a higher ∆mean BP/∆MSNA burst frequency ratio (p = 0.003). During apnea, OF experienced a smaller percent MSNA increase in total MSNA (p < 0.05), larger mean BP increases (interaction effect: p = 0.031), and higher ∆mean BP/∆total MSNA ratio (p = 0.003). These findings suggest attenuated signal-averaged sympathetic BP transduction at rest but increased time-averaged sympathetic transduction to mean BP during cold and apneic laboratory stressors in OF.

Keywords: aging; apnea; cardiovascular; cold pressor test; sympathetic transduction.

FIGURE 1

Resting Sympathetic Transduction to Blood Pressure (BP) following Spontaneous Sympathetic Bursts. (a) Mean BP increased following spontaneous bursts of muscle sympathetic nerve activity (MSNA) in both groups, with greater increases in young females (YF) during cardiac cycles 4–10. (b) Peak mean BP responses were higher in YF compared to OF. (c) Diastolic BP increased following spontaneous bursts of MSNA in both groups, with greater responses in YF during cardiac cycles 4–7. (d) Peak diastolic BP responses were higher in YF than in OF.

FIGURE 2

Resting Sympathetic Transduction to Blood Pressure (BP) following Non‐Burst Cardiac Cycles. (a) Reductions in mean BP during non‐burst cardiac cycles were greater in OF during cardiac cycles 7–10. (b) The nadir mean BP was lower in OF compared to YF. (c) Reductions in diastolic BP following non‐burst cardiac cycles were greater in OF during cardiac cycles 7–10. (d) The nadir diastolic BP was lower in OF than in YF.

FIGURE 3

Autonomic Cardiovascular Reactivity to the Cold Pressor Test (CPT). Absolute MSNA burst frequency was higher in OF during baseline and CPT. There was no interaction effect; however, the partial eta‐square value of 0.170 indicates a medium effect size (a). The mean blood pressure (BP) during baseline and CPT was higher in OF, but there was no interaction effect of age and condition (baseline vs. CPT) (b). Heart rate (HR) increased more in YF (c). The relative muscle sympathetic nerve activity (MSNA) during CPT was greater in young females (YF) compared to older females (OF) (d). The ∆mean BP/∆relative MSNA ratio was not different between groups (e). The ∆mean BP/∆MSNA burst frequency ratio was higher in OF (f).

FIGURE 4

Autonomic Cardiovascular Reactivity to End‐Expiratory Apnea (EEA). Absolute MSNA burst frequency was higher in OF during baseline and CPT, but there was no interaction effect (a). The mean blood pressure (BP) during baseline and CPT was higher in OF, with an interaction between group (YF vs. OF) and condition (baseline vs. EEA) (b). Heart rate (HR) did not differ between groups (c). The relative muscle sympathetic nerve activity (MSNA) during CPT was greater in young females (YF) compared to older females (OF) (d). The ∆mean BP/∆relative MSNA ratio was higher in OF (e). The ∆mean BP/∆burst frequency ratio was not different between age groups (f).