i 34 o 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 1 1 . The effect of body heating and of change of posture 

 on the oxygen saturation of deep and superficial forearm venous 

 blood. The black rectangle indicates the period of general body- 

 heating. The intervals between the dotted lines represent the 

 periods during which the subject's legs were passively raised. 

 O, Left forearm blood How, ■ oxygen saturation of superficial 

 venous blood in right forearm; •, oxygen saturation of deep 

 venous blood in right forearm. [From Roddie el al. (170).] 



On warming a rather cold subject, the blood flow 

 through the forearm, and hence through the skin of 

 the forearm, increases in two steps (171). The first 

 increase, from about 2 to about 4 ml per 100 ml per 

 min, is of the same order of size as the increase which 

 follows block of the superficial nerves to the forearm, 

 and may be assumed to be due to withdrawal of 

 vasoconstrictor activity. The subject is by now com- 

 fortably warm. If body heating is continued, there 

 is a further increase in forearm flow from 4 to 10 to 

 1 5 ml per 1 00 ml per min. This is accompanied by 

 sweating. The total forearm blood flow and the oxygen 

 saturation of the blood from superficial veins now far 

 exceed the levels seen after cutaneous nerve block. 

 Blocking the cutaneous nerves at this stage causes the 

 forearm blood flow to fall to about the level seen in 

 an unheated subject (72). Without block, the blood 

 flow through the skin of the forearm is now very large 

 indeed; Edholm el al. (71 ) give a figure of 165 ml per 

 100 ml of forearm skin per min, but do not claim 

 that this is more than an approximate figure. The 

 sweating can be prevented and the vasodilatation 

 delayed by the injection of atropine into the brachial 

 artery before the heating starts. Fox & Hilton (81) 

 have found that during sweating there is a fivefold 

 increase in the bradykinin-like activity in the per- 

 fusate of the subcutaneous tissue of the forearm, and 

 that a bradykinin-formintj enzyme is present in 

 sweat. Bradykinin is a very powerful vasodilator 



substance. Injected into the human brachial artery 

 it is more powerful, per molecule, than acetylcholine 

 or histamine, or indeed any other known substance 

 (80). It is suggested (81) that the vasodilatation in 

 the skin of the human forearm is produced in the main 

 by bradykinin resulting from sweat gland activity, 

 itself provoked by cholinergic sympathetic nerves. 



In the region of the wrist there must be a transi- 

 tion from the vasoconstrictor control of the hand 

 vessels to the predominantly vasodilator control of 

 the forearm vessels. The site, sharpness, and varia- 

 bility or constancy of the demarcation have not been 

 defined. 



other areas of the human body. The innervation 

 of the foot has been less completely examined than 

 that of the hand, but as far as is known, the pattern 

 is similar. Elsewhere, our knowledge is fragmentary 

 and incomplete. In the upper arm, calf of leg, and 

 thigh (36) the pattern of vasomotor innervation is 

 like that of the forearm, there being a weak vasocon- 

 strictor innervation operating when the subject is 

 cold, and a more powerful vasodilator innervation, 

 probably associated with sweat gland control, which 

 operates when the subject is hot. Vasodilator control 

 is also dominant in the forehead and chin, and cutane- 

 ous vasodilatation accompanies sweating in these 

 areas; vasoconstrictor control is important in the 

 glabrous portion of the lips, and in the skin of the 

 nose (78, 79). 



the skin of animals. Apart from the paws (138), the 

 skin of the limbs of cats and dogs lacks eccrine sweat 

 glands. In these species, heat vasodilatation results 

 from the reduction in the activity of vasoconstrictor 

 nerves, and there is no evidence for vasodilator 

 nerves (77, 102). 



late effects of sympathetic denervation. Goltz 

 & Freusberg (97) noted that the freshly denervated 

 leg of the dog was warmer than its fellow, but that 

 the difference does not persist. It has since been 

 shown by several groups of workers (18, 23, 101, 145, 

 184, 190) that the blood flow in a limb several weeks 

 after sympathectomy differs little from the preopera- 

 tive value. The blood flow in both hands and feet 

 reaches its highest value about the second day after 

 the operation, and then declines steeply during the 

 next few days (fig. 9). In the hand, the decline in flow- 

 is equally rapid whether a preganglionic section or a 

 postganglionic section with ganglionectomy has been 

 performed (184). In the forearm (63) the maximum 



