Cutaneous Vascular Responses of the Hands and Feet to Cooling, Rewarming, and Hypoxia in Humans.

Introduction: This study investigated skin vasomotor responses in the fingers and toes during cooling and rewarming with and without normobaric hypoxia.

Methods: Fourteen volunteers (8 males and 6 females) were exposed to gradual air cooling (mean±SD: -0.4±0.1C·min) followed by rewarming (+0.5±0.1C·min) while breathing normoxic air (FO 0.21 at 761±3 mm Hg) or hypoxic gas (FO 0.12, at 761±3 mm Hg, equivalent to ~5000 m above sea level). Throughout the gradual cooling and rewarming phases, rectal temperature was measured, and skin temperatures and laser Doppler skin blood flow were measured on the thumb, little finger, and great and little toe pads.

Results: During gradual cooling, skin temperature but not deep body temperature decreased. No differences in cutaneous vascular conductance were found for the toes or thumb (P=0.169 great toe; P=0.289 little toe; P=0.422 thumb). Cutaneous vascular conductance was reduced in the little finger to a greater extent at the same mean skin temperatures (34.5-33.5C) in the hypoxic compared with normoxic conditions (P=0.047). The onset of vasoconstriction and release of vasoconstriction in the thumb and little finger occurred at higher mean skin temperatures in hypoxia compared with normoxia (P<0.05). The onset of vasoconstriction and release of vasoconstriction in the toes occurred at similar skin temperatures (P=0.181 and P=0.132, respectively).

Conclusion: The earlier vasoconstrictor response and later release of vasoconstriction in the finger during hypoxic conditions may result in a greater dose of cold to that digit, taking longer to rewarm following the release of vasoconstriction.