Analysis of the responses evoked in the cutaneous circulation of one hand by heating the contralateral hand

Abstract

In 9 healthy human subjects, cutaneous red cell flux in the thenor eminence of the left hand was measured by a Laser Doppler meter, while the right hand was transferred sequentially from water at 33°C, to water at 42°C for 5 min, to water at 33°C (first experimental run) and then to water at 42°C for 2 min (second experimental run). Red cell flux increased significantly by the end of the 2nd min of heating and had increased further by the end of the 5th min. Mean arterial pressure, measured by sphygmomanometry from the left arm, had not changed at either times indicating that the changes in red cell flux reflected progressive cutaneous vasodilatation. Meanwhile heart rate was significantly increased by the 5th min. By contrast, when these experiments were carried out on 8 subjects with a cuff on the right arm inflated to approximately 60 mm Hg to impede venous outflow from the heated limb, red cell flux in the contralateral hand showed a significant increase by the 5th min of heating, but this was accompanied by a fall in arterial pressure and no change in heart rate. By the 5th min after release of the occlusion and while the right arm was still in warm water, there was a further increase in red cell flux in the contralateral hand, but arterial pressure was not significantly different from the original control level and heart rate was significantly increased. Occlusion per se had no effect on red cell flux. Thus, we propose that heating one hand evokes reflex cutaneous vasodilatation in the contralateral hand which is partly mediated by peripheral thermoreceptors in the warm hand and partly by core thermoreceptors that are affected by blood temperature. We suggest that this cutaneous vasodilatation is part of a widespread peripheral vasodilatation which tends to reduce arterial pressure if not counteracted by an increase in cardiac output. We suggest that an increase in heart rate contributes to the latter and that this is initiated predominantly by core thermoreceptors.