CIRCULATION THROUGH THE SKIN 



'343 



• 



OCIRCULATION OCCLUDED- NO HEAT 

 ©HEAT-CIRCULATION OCCLUDED 

 • HEAT- NO OCCLUSION 



60 ^.---....e 120 



SECONDS 



fig. 13. Changes in hand blood flow during heating of the 

 front of the legs. Each curve is the mean of three runs. [From 

 Kerslake & Cooper (129).] 



and while this is in progress the heat loss may be 

 several times greater than the heat gain during 

 exposure to heat. 



When a nude person is chilled, the temperature of 

 the skin and the loss of heat from it fall to much lower 

 levels over the limbs, and particularly the hands and 

 feet, than they do over the head, neck, and trunk. 

 This difference is partly accounted for by the more 

 vigorous vasoconstriction in the skin of the limbs, and 

 partly by the more favorable opportunities in the 

 limbs for economizing heat loss by exchange of heat 

 between arteries and veins. Thus there are poor 

 defenses against heat loss from the head and trunk, 

 and these regions are particularly dependent on 

 clothing for insulation. The loss of heat from the 

 uncovered head may be very large (85), amounting 

 to about one-half the resting heat production of the 

 body when the ambient temperature is — 4 C. 



emotion. In the middle ranges of flow, the circulation 

 through the hand is often very sensitive to slight emo- 

 tional stimuli; it may suffer a considerable transient 

 reduction, lasting a minute or more, when a person 

 enters the room, if a remark is made or a question in 

 mental arithmetic posed (2), or if there is an unex- 

 pected noise. For this reason it is important to reduce 

 disturbance to a minimum in experiments in which 

 the blood flow to the hand (or foot) is measured. A 



more prolonged emotional stimulus, such as is pro- 

 vided by mental arithmetic for 10 min under trying 

 conditions, causes in persons with hyperhidrosis and 

 in some normal persons an increase in the blood flow 

 through the hand; this is associated with emotional 

 sweating (10). All these responses are prevented by 

 division of the sympathetic nervous outflow. It is, 

 however, possible that during more severe emotional 

 upsets, the circulation through the skin may be 

 affected by adrenal gland activity. In the forearm, 

 the circulation through the skin is little affected by 

 the emotional stress of mental arithmetic (76). 



fainting. In posthemorrhagic fainting the blood flow 

 through the hand was found by Barcroft & Edholm 

 (21) to be more reduced than would be expected 

 from the fall in arterial blood pressure. This indicated 

 vasoconstriction in the hand. Other observations have 

 indicated little change or vasodilatation. It seems very 

 probable that the response is a variable one, de- 

 pending perhaps on the degree of associated emo- 

 tional sweating. Little is known about the precise 

 changes in blood flow in other areas of skin. 



general sensory stimuli. Transient reduction in 

 hand or finger blood flow has been described in re- 

 sponse to a great range of mildly unpleasant stimuli 

 such as immersing another part of the body in cold 

 water (160), pinching (2), or inflating a pneumatic 

 cuff around the arm. On the other hand, Lynn & 

 Simeone (146) were unable to provoke reflex vaso- 

 constriction in anesthetized dogs by electrical stimu- 

 lation or by distention of the femoral vein. 



response to a deep inspiration. After a deep in- 

 spiration there is a transient decrease in finger volume 

 (38, 94). The size of the arterial pulsations diminishes 

 and the rate of blood flow falls sometimes to a very 

 low level (116, 189). The blood flow can be seen to 

 slow in the capillary loops of the nail bed (153). The 

 blood flow is similarly transiently decreased in the 

 hands and feet (138) but not in the more proximal 

 parts of the limbs. The response is lost after nerve 

 block or sympathectomy. 



Gilliatt (90) found that the vasoconstrictor response 

 in the finger could be elicited by a sufficiently fast 

 and deep expansion of the lungs, whether brought 

 about by passive inflation or voluntary inspiration. 

 It did not follow obstructed inspiratory or expiratory 

 efforts, nor deep expiration. The response has been 

 observed in the fingers and toes of persons with a 

 complete break in the functional continuity of the 



