Impairment of thermoregulatory control of skin sympathetic nerve traffic in the elderly

Background-Human aging is characterized by a marked increase in muscle sympathetic nerve traffic (MSNA). No information exists, however, on the effects of aging on skin sympathetic nerve traffic ( SSNA) and on its reflex modulation by thermoregulatory mechanisms. Methods and Results-In 13 young, 11 middle-aged, and 12 elderly healthy subjects, we measured arterial blood pressure (Finapres), skin temperature ( thermocouples), and resting MSNA and SSNA (microneurography). Measurements also included the SSNA responses to ( 1) an acute increase and reduction (+/-8degreesC) in room temperature, each lasting 45 minutes and ( 2) an acoustic stimulus capable to trigger an emotional arousal. Although resting MSNA was progressively and significantly (P < 0.05) increased from young to middle-aged and elderly groups, SSNA was significantly (P < 0.05) reduced in the latter compared with the former 2 groups. Cold exposure induced a SSNA increase that was significantly (P < 0.01) smaller in the elderly than in young and middle-aged subjects. Conversely, heat exposure induced a SSNA reduction that was significantly (P < 0.05) smaller in elderly than in young and middle-aged subjects. Compared with SSNA in young individuals, the SSNA change from cold to warm temperature was reduced by 61% in the elderly group. This was not the case, however, for the SSNA responses to the arousal stimulus, which were superimposable in the 3 groups. Conclusions-These data provide the first demonstration of a dichotomy in the MSNA and SSNA responses to aging. They also show that aging markedly impairs thermoregulatory control of SSNA and that this impairment might participate at the age-related SSNA decrease.