Interactions of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress

We examined the interactive effects of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress. Eight male lowlanders performed, in a counterbalanced order, a normoxic and a hypoxic (partial pressure of oxygen: ~12 kPa) hand cold provocation (consisting of a 30-min immersion in 8°C water), while immersed to the chest either in 21°C [cold trials; 0.5°C fall in rectal temperature (T_rec) from individual preimmersion values], or in 35.5°C water, or while exposed to 27°C air. The duration of the trials was kept constant in each breathing condition. Physiological (T_rec, skin temperature, cutaneous vascular conductance, oxygen uptake) and perceptual (thermal sensation and comfort, local pain, affective valence) reactions were monitored continually. Hypoxia accelerated the drop in T by ~14 min (P = 0.06, d = 0.67). In the air-exposure trials, hypoxia did not alter finger perfusion during the local cooling, whereas it impaired the finger rewarming response following the cooling (P < 0.01). During the 35.5°C immersion, the finger vasomotor tone was enhanced, especially in hypoxia (P = 0.01). Mild hypothermia aggravated finger vasoconstriction instigated by local cooling (P < 0.01), but the response did not differ between the two breathing conditions (P > 0.05). Hypoxia tended to attenuate the sensation of coldness (P = 0.10, r = 0.40) and thermal discomfort (P = 0.09, r = 0.46) in the immersed hand. Both in normoxia and hypoxia, the whole body thermal state dictates the cutaneous vasomotor reactivity to localized cold stimulus.