Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system (CNS), disrupting autonomic function. PURPOSE: The aim of this study was to test the hypothesis that individuals with MS have blunted control of thermoregulatory reflex increases in sweat rate (SR) and cutaneous vasodilation compared to controls during a passive whole-body heat stress (WBH). METHODS: Eighteen individuals with relapsingremitting MS and 18 healthy controls (CON) participated in the study. Core temperature (Tcore), skin temperature, heart rate, arterial blood pressure (10 min intervals), skin blood flow (laser-Doppler flowmetry: LDF), and SR were continuously measured during normothermic baseline (34 °C water perfusing a tube-lined suit) and WBH (increased Tcore 0.8 °C via 48 °C water perfusing the suit). Following WBH, local heaters were warmed to 42 °C, inducing maximal cutaneous vasodilation at the site of LDF collection. Cutaneous vascular conductance (CVC) was calculated as the ratio of LDF to mean arterial pressure and expressed as a percentage of maximum. RESULTS: Individuals with MS had attenuated SR responses to WBH (∆SR from baseline: CON: 0.65±0.27; MS: 0.42±0.17 mg/cm 2 /min, p=0.003), while ∆%CVCmax from baseline was similar between groups (CON: 42±16%; MS: 38±12 %, p=0.39). SR responses were blunted as a function of Tcore in MS (interaction: group*Tcore, p=0.03), of which differences were evident at ∆Tcore 0.7 °C and 0.8 °C (p<0.05). No interaction was observed in ∆%CVCmax. CONCLUSION: Taken together, MS blunts sweating responses, while control of the cutaneous vasculature is preserved in response to WBH.

Tattooing of the skin involves repeated needle insertions to deposit ink into the dermal layer of the skin, potentially damaging eccrine sweat glands and the cutaneous vasculature. This study tested the hypothesis that reflex increases in sweat rate (SR) and cutaneous vasodilation are blunted in tattooed skin (TAT) compared to adjacent healthy skin (CON) during a passive whole-body heat stress (WBH). Ten individuals (5M, 5F) with a sufficient area of tattooed skin participated in the study. Intestinal temperature (Tint), skin temperature (Tskin), skin blood flow (laser-Doppler flux; LDF), and SR were continuously measured during normothermic baseline (34 °C water perfusing a tube-lined suit) and WBH (increased Tint 1.0 °C via 48 °C water perfusing suit). SR throughout WBH was lower for TAT compared to CON (p=0.033). Accumulated sweating responses during WBH (area under curve) were attenuated in TAT relative to CON (23.1±12.9, 26.9±14.5 mg×cm-2, p=0.043). Sweating threshold, expressed as the onset of sweating in time or Tint from the initiation of WBH were not different between TAT and CON. Tattooing impeded the ability to obtain LDF measurements. These data suggest that tattooing functionally damages secretion mechanisms, affecting the reflex capacity of the gland to produce sweat, but does not appear to affect neural signaling to initiate sweating. Decreased sweating could impact heat dissipation especially when tattooing covers a higher percentage of body surface area and could be considered a potential long-term clinical side effect of tattooing.

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