Hypoxic cutaneous vasodilation is sustained during brief cold stress and is not affected by changes in CO₂

Abstract

Hypoxia decreases core body temperature in animals and humans during cold exposure. In addition, hypoxia increases skin blood flow in thermoneutral conditions, but the impact of hypoxic vasodilation on vasoconstriction during cold exposure is unknown. In this study, skin blood flow was assessed using laser-Doppler flowmetry, and cutaneous vascular conductance (CVC) was calculated as red blood cell flux/mean arterial pressure and normalized to baseline (n = 7). Subjects were exposed to four different conditions in the steady state (normoxia and poikilocapnic, isocapnic, and hypercapnic hypoxia) and were cooled for 10 min using a water-perfused suit in each condition. CVC increased during all three hypoxic exposures (all P < 0.05 vs. baseline), and the magnitude of these steady-state responses was not affected by changes in end-tidal CO(2) levels. During poikilocapnic and hypercapnic hypoxia, cold exposure reduced CVC to the same levels observed during normoxic cooling (P > 0.05 vs. normoxia), whereas CVC remained elevated throughout cold exposure during isocapnic hypoxia (P < 0.05 vs. normoxia). The magnitude of vasoconstriction during cold stress was similar in all conditions (P > 0.05). Thus the magnitude of cutaneous vasodilation during steady-state hypoxia is not affected by CO(2) responses. In addition, the magnitude of reflex vasoconstriction is not altered by hypoxia, such that the upward shift in skin blood flow (hypoxic vasodilation) is maintained during whole body cooling.

No effect of systemic isocapnic hypoxia on α-adrenergic vasoconstrictor responsiveness in human skin

“…Systemic isocapnic hypoxia exposure in the current investigation did not elicit the same cutaneous vasodilator response that we have observed previously (Simmons et al 2007(Simmons et al , 2010. The reason for this is that one subject in this study responded to isocapnic hypoxia with a considerable vasoconstrictor response.…”

“…Hypoxic exposure was isocapnic in this study, and we have previously demonstrated the capacity of this breathing circuit to maintain isocapnia during changes in ventilation associated with hypoxia (Simmons et al 2010). Hypoxic exposure was isocapnic in this study, and we have previously demonstrated the capacity of this breathing circuit to maintain isocapnia during changes in ventilation associated with hypoxia (Simmons et al 2010).…”

Cold‐induced cutaneous vasoconstriction in humans: Function, dysfunction and the distinctly counterproductive

“…In a follow-up study using prolonged cooling, the magnitude of the cold-induced vasoconstrictor response was greater during hypoxia compared with normoxia, thereby eliminating the hypoxia-induced 'offset' in skin blood flow seen in the earlier (brief cooling) study (Simmons et al, 2010). Furthermore, this hypoxia-mediated increase in cold-induced vasoconstriction remained when noradrenergic receptors were blocked, suggesting that non-noradrenergic vasoconstrictor mechanisms mediate the increased cold-induced vasoconstriction during hypoxia.…”

“…Although the skin remained able to vasoconstrict in response to the cold stimulus, hypoxia caused a persistent vasodilatation throughout cooling, such that there was an 'offset' in skin blood flow with a similar reduction in response to cold (Simmons et al, 2010). Although the skin remained able to vasoconstrict in response to the cold stimulus, hypoxia caused a persistent vasodilatation throughout cooling, such that there was an 'offset' in skin blood flow with a similar reduction in response to cold (Simmons et al, 2010).…”

Effect of voluntary hypocapnic hyperventilation on cutaneous circulation in resting heated humans

“…Simmons et al (46) recently showed that CVC forearm during normothermia and whole body cooling did not differ under conditions of hypocapnic and eucapnic hypoxia, which suggests hypocapnia does not affect the cutaneous vascular response in those situations. A similar result was obtained in the forearm under normothermic, normoxic conditions in the present study.…”