Local thermal control of the human cutaneous circulation

The level of skin blood flow is subject to both reflex thermoregulatory control and influences from the direct effects of warming and cooling the skin. The effects of local changes in temperature are capable of maximally vasoconstricting or vasodilating the skin. They are brought about by a combination of mechanisms involving endothelial, adrenergic, and sensory systems. Local warming initiates a transient vasodilation through an axon reflex, succeeded by a plateau phase due largely to nitric oxide. Both phases are supported by sympathetic transmitters. The plateau phase is followed by the die-away phenomenon, a slow reversal of the vasodilation that is dependent on intact sympathetic vasoconstrictor nerves. The vasoconstriction with local skin cooling is brought about, in part, by a postsynaptic upregulation of α2c-adrenoceptors and, in part, by inhibition of the nitric oxide system at at least two points. There is also an early vasodilator response to local cooling, dependent on the rate of cooling. The mechanism for that transient vasodilation is not known, but it is inhibited by intact sympathetic vasoconstrictor nerve function and by intact sensory nerve function

Cardiovascular responses to orthostatic and other stressors in men and women are independent of sex

1. Cardiovascular responses to the stress of orthostasis, forearm (FA) ischaemia (reactive hyperaemia) and FA exercise (postexercise hyperaemia) are well described. Although sex differences in responses to orthostatic stress have been reported, few studies have examined the impact of sex on reactive hyperaemia and none has commented with regard to postexercise hyperaemia. 2. We investigated 11 men (mean (±SEM) age 18.5 ± 0.3 years) and 10 women (18.8 ± 0.8 years), all of whom were sedentary, with women being studied in the mid-follicular phase of their menstrual cycle. We measured blood pressure (BP), heart rate (HR) and forearm blood flow (FBF) in response to a fixed sequence of orthostatic, ischaemic and exercise stressors. 3. Orthostatic stress (10 min at −50 mmHg lower body negative pressure; LBNP) induced presyncopal signs in one man and three women. In all other subjects, BP was well maintained, with FBF decreasing and HR increasing similarly in both sexes. The tachycardia was earlier in onset in men and reached significantly higher absolute levels in women during the final 5 min of LBNP, but the percentage changes and integrated responses of both HR and FBF were not different between sexes. 4. The increases in FBF following either 10 min FA ischaemia or 10 min FA exercise were similar in men and women in terms of peak blood flow, percentage change, rate of recovery and total blood flow response. 5. In conclusion, although women were less tolerant of orthostatic stress than men, the cardiovascular responses to this and the other stressors appeared essentially independent of sex