Control of peripheral blood flow: responses in the human hand when extremities are warmed.

Previous investigators have concluded that sympathetic activity produces active vasodilatation (4, 6, 8, 10) and active vasoconstriction (6). The possibility that sweat gland activity might cause vasodilatation has also been investigated, but no such relationship has been demonstrated (4). However, it has been reported that indirect’ vasodilatation or vasoconstriction may occur in an extremity when other body segments are heated or cooled (7, 8, 10, 11). Occlusion of the venous return from such heated segments usually prevents the occurrence of this indirect vasodilatation, probably eliminating heat receptors and a nervous reflex as mediators (7, 10, 11). However, Pickering reported that venous occlusion of a cooled extremity does not prevent transient indirect vasoconstriction (12). Because the phenomenon of vasoconstriction appears in sympathectomized limbs, adrenaline has been postulated as a mediator (6). Stomach irrigations with cool water have also produced indirect vasoconstriction (9, 12). These previous studies indicate that average blood temperature (the true deep body temperature) probably affects peripheral vascular flow (9, 12, 15). In one of the initial studies, Roy and Brown, working with frogs, stated t.hat peripheral blood flow is dependent upon local tissue temperature and concentration of tissue metabolites (14). Freeman concurred with this hypothesis, but only for sympathectomixed extremities; in normally innervated hands, he found that the blood flow is modified reflexly in accordance with the need of the body as a whole for dispersion or for conservation of heat (6). Pickering, working with human beings, reported that central control is concerned with protection against cold or excessive heat (12). Although these studies indicate that average blood temperature probably affects peripheral vascular flow and that central control protects the body as a whole against cold or excessive heat, the nature of local control has not been clearly defined. Freeman initiated a different approach to this problem. He studied, at one ambient temperature (approximately 24”C.), the effect in one hand when the other was warmed and observed increases in blood flow and