Effect of hypohydration and altitude exposure on skin blood flow responses to local heating

It is unknown whether hypohydration (HYPO) or hypobaric hypoxia alter skin blood flow (SkBF) responses to local heating. We hypothesized that HYPO (4% of body weight) and acute altitude (ALT, 3,048 m) would decrease forearm SkBF responses to local heating and that ALT‐HYPO together would result in a further decline. Four healthy young men (23 ± 6 years, 175 ± 5 cm, 74 ± 5 kg) completed 4 trials each: a) sea‐level–euhydrated (SL‐ EUH); b) SL‐HYPO; c) ALT‐EUH; and d) ALT‐HYPO. Local thermal control of cutaneous vascular conductance (CVC) was assessed by local heating to 42°C for 30 min. CVC was calculated as laser‐Doppler flow/mean arterial pressure and analyzed for initial peak (~2–4 min after onset of warming), and plateau (last 3–5 min of warming). Initial peak CVC values were 1107 ± 593, 673 ± 273, 619 ± 241 and 784 ± 440 % of baseline for SL‐EUH, SL‐HYPO, ALT‐EUH, and ALT‐HYPO, respectively. Plateau CVC values were 1585 ± 797, 1340 ± 609, 962 ± 396 and 1082 ± 869 % of baseline. There were no significant influences of HYPO or ALT (P > 0.05 for all), although HYPO and ALT reduced initial peak SkBF by 29–44% and plateau SkBF by 15–39%. Based on these pilot data, 14–18 subjects would be required to give 80% power to detect statistical differences in initial peak and plateau SkBF responses during local heating as a result of hypohydration and altitude exposure. The opinions contained herein are not official and do not reflect Army/DOD views