CIRCULATION THROUGH THE SKIN 



l 339 



failed to detect any contributions from vasodilator 

 nerves. Thus Pickering (161) during body heating 

 found equal rates of heat elimination from the two 

 hands, the ulnar nerve conveying part of the sym- 

 pathetic supply to one hand having been blocked. 

 In a more sensitive test, Arnott & Macfie (15) meas- 

 ured the heat elimination from the fifth fingers during 

 body heating. The sympathetic supply to one was 

 entirely interrupted by ulnar nerve block, but the 

 rates of heat elimination were equal. Warren et al. 

 (185) found that paravertebral block of the sym- 

 pathetic outflow increased rather than decreased the 

 blood flow through the hand of a heated subject. 

 Gaskell (87) compared the rates of blood flow through 

 the two hands by venous occlusion plethysmog- 

 raphy, which is probably the most accurate method. 

 He heated the subject, and then blocked on one 

 side near the elbow the radial, ulnar, and median 

 nerves which probably convey the great majority 

 of sympathetic fibers to the hand. This caused no 

 alteration in the rate of blood flow. Roddie et al. 

 (172) found no difference between the rates of blood 

 flow through the two hands in similar experiments 

 in which the nerve block on one side preceded the 

 body heating; this eliminated the possibility that in 

 GaskelTs experiments (87) a stable chemical vaso- 

 dilator substance was released by sympathetic nerves 

 before they were blocked. The most probable ex- 

 planation of these observations is that in the ade- 

 quately heated subject there is a complete cessation 

 of activity in the vasoconstrictor nerves to the hand, 

 and no activity in vasodilator nerves. The less prob- 

 able alternative is that in the hand of a heated subject 

 there is a balance of vasoconstrictor and vasodilator 

 activity, and that the vessels are unaffected when both 

 activities are abolished by nerve block. 



Although there is no evidence for the participation 

 of vasodilator nerves in the response to body heating 

 in normal persons, a vasodilatation dependent on an 

 intact sympathetic nerve supply may accompany 

 the sweating in the hand which is provoked by emo- 

 tional stress. The direct and immediate effect of 

 emotion is to reduce the blood flow through the hand 

 (2) by increasing the activity in vasoconstrictor nerves. 

 If, however, the emotional stress is continued, as by 

 mental arithmetic, the vasodilatation consequent on 

 sweating may outweigh the constriction even in 

 normal persons, and in persons suffering from ex- 

 cessive sweating the vasodilatation may be very 

 large indeed (10), the flow rising from 5 to over 

 30 ml per 100 ml per min (fig. 10). 



30 



20 --5. 



10 



Minutes 10 



fig. 10. Results showing the marked increase in hand blood 

 flow (•) during mental arithmetic in a hyperhidrotic subject. 

 There was little change in the forearm blood flow (O) or 

 arterial blood pressure. Plethysmograph temperature 36 C. 

 [From All wood et al. (10).] 



the human forearm. Both vasoconstrictor nerves, 

 and nerves which directly or indirectly cause vaso- 

 dilatation (vasodilator nerves) regulate the circula- 

 tion through the skin of the forearm. Of these, the 

 vasodilator nerves, first described by Grant & Holling 

 (100), are by far the more important. The role of the 

 two sets of nerves is clearly displayed during the 

 response of total forearm blood flow to general body 

 heating. 



This response has recently been shown, by several 

 methods, to be confined to the skin, the muscle cir- 

 culation remaining unchanged. Thus Edholm et al. 

 (71) found that intensive iontophoresis of adrenaline, 

 sufficient to arrest the circulation in the skin of the 

 forearm, prevented the normal increase in total 

 forearm blood flow with body heating. Barcroft et al. 

 (20) found that when a person is heated the total 

 blood flow through the calf of the leg, measured 

 plethysmographically, increases, but that through 

 the muscle, measured by a heated thermocouple 

 method, does not; the increase must have been in the 

 skin. The rate of clearance of radioactive sodium 

 from muscle is unchanged or reduced (154). Roddie 

 et al. (170) found that during general body heating 

 there was a gradual increase, from an initial 40 to 

 72 per cent to a final 85 to 99 per cent, in the oxygen 

 saturation of the blood in the superficial veins of the 

 forearm predominantly draining skin, but no change 

 in the deep veins mainly draining muscle (fig. 11); 

 the changes in the superficial blood closely paralleled 

 the increase in total forearm blood flow in the op- 

 posite arm. 



