Blunted increases in skin sympathetic nerve activity are related to attenuated reflex vasodilation in aged human skin

Abstract

Reflex cutaneous vasodilation in response to passive heating is attenuated in human aging. This diminished response is mediated, in part, by age-associated reductions in endothelial function; however, the contribution of altered skin sympathetic nervous system activity (SSNA) is unknown. We hypothesized that 1) healthy older adults would demonstrate blunted SSNA responses to increased core temperature compared with young adults and 2) the decreased SSNA response would be associated with attenuated cutaneous vasodilation. Reflex vasodilation was elicited in 13 young [23 ± 1 (SE) yr] and 13 older (67 ± 2 yr) adults using a water-perfused suit to elevate esophageal temperature by 1.0°C. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry) in the innervated dermatome (the dorsum of foot) were continuously measured. SSNA was normalized to, and expressed as, a percentage of baseline. Cutaneous vascular conductance (CVC) was calculated as flux/mean arterial pressure and expressed as a percentage of maximal CVC (local heating, 43°C). Reflex vasodilation was attenuated in older adults (P < 0.001). During heating, SSNA increased in both groups (P < 0.05); however, the response was significantly blunted in older adults (P = 0.01). The increase in SSNA during heating was linearly related to cutaneous vasodilation in both young (R = 0.87 ± 0.02, P < 0.01) and older (R = 0.76 ± 0.05, P < 0.01) adults; however, slope of the linear regression between ΔSSNA and ΔCVC was reduced in older compared with young (older: 0.05 ± 0.01 vs. young: 0.08 ± 0.01; P < 0.05). These data demonstrate that age-related impairments in reflex cutaneous vasodilation are mediated, in part, by blunted efferent SSNA during hyperthermia.

Chronic statin therapy is associated with enhanced cutaneous vascular responsiveness to sympathetic outflow during passive heat stress

“…The local heater was clamped at 33°C during baseline and heating in order to specifically isolate reflex mechanisms of cutaneous vasodilatation (Stanhewicz et al . , ).…”

“…, , b ; Stanhewicz et al . , ; Greaney & Kenney, ). Briefly, a unipolar tungsten microelectrode was inserted percutaneously through intact unanaesthetized skin and positioned into skin nerve fascicles of the peroneal nerve near the fibular head.…”

“…; Stanhewicz et al . ). This reflex cutaneous vasodilatation is substantially blunted in healthy older adults (>∼60 years), a defect mediated by impairments in both central sympathetic outflow directed to the cutaneous circulation and cutaneous microvascular endothelial function (Kenney et al .…”

“…; Stanhewicz et al . ). Recent work from our laboratory suggests that, in healthy ageing, the transduction of skin sympathetic nervous system activity (SSNA) to the cutaneous microvasculature during heat stress is impaired due to reductions in both the sensitivity (slope) and range of the vasodilatory response (Stanhewicz et al .…”

“…Recent work from our laboratory suggests that, in healthy ageing, the transduction of skin sympathetic nervous system activity (SSNA) to the cutaneous microvasculature during heat stress is impaired due to reductions in both the sensitivity (slope) and range of the vasodilatory response (Stanhewicz et al . ). Moreover, targeted intervention strategies to improve microvascular endothelial function result in greater increases in skin blood flow during heat stress in older individuals, in part, via improvements in the sensitivity of the cutaneous microvasculature to sympathetic outflow (Stanhewicz et al .…”