CIRCULATION THROUGH THE SKIN' 



J335 



in the level of blood flow at the height of the vaso- 

 dilatation (113, 135)- In such subjects, kept warm to 

 release sympathetic vasoconstrictor tone, the reactive 

 hyperemic blood flow with the hands at 40 C, and 

 the resting blood flow with the hands at 40 C, 20 C, 

 and 10 C is no different from that in normal controls 

 (135). The improved circulation in the hands of cold- 

 habituated persons reported by other observers may 

 depend more on general adaptation of the circula- 

 tion than on a local adaptation in the periphery. 



PROLONGED EXPOSURE TO COLD: TRENCH FOOT AND 



immersion foot. Prolonged local cooling to tempera- 

 tures above the freezing point is capable of causing 

 serious injury. Although in many recorded cases the 

 parts have been wet as well as cold, the main factor 

 is the cooling of the extremities in a chilled subject 

 (183). The feet are particularly liable to injury, and 

 most cases have been seen after exposure for many 

 hours or days in war time. 



The four stages of the condition have been well 

 described by Ungley (183). 



/) During exposure, the limb is numb, power is 

 reduced, and movement is clumsy. Pain is unusual. 

 Swelling is common, the limb often looks bright red, 

 and there may be periods of warmth, presumably due 

 to cold vasodilatation, but the chilling of the subject 

 reduces this to small proportions. 



2) Immediately after rescue and return to warmth 

 and shelter there is a prehyperemic stage, which may 

 last for 2 to 5 hours. The limb is cold and either 

 pale with cyanotic patches or cyanosed. The arterial 

 pulsations cannot be felt. There is a partial or com- 

 plete '"stocking" sensory loss. 



3) A hyperemic stage follows, the part becoming 

 red, swollen, painful, and sometimes blistered. When 

 the arterial pulses return, they are very strong, and 

 the temperature of the skin is as high as that of the 

 axilla or groin. The hyperemia is judged clinically 

 to be at least as great as that following sympathec- 

 tomy, and it is often much more persistent, lasting as 

 long as 14 weeks. There is partial anesthesia, and 

 vasomotor and sudomotor paralysis, indicating nerve 

 damage. In addition there is direct vascular damage. 



4) In mild cases there is a return from the hy- 

 peremic state to normal, but in severe cases a post- 

 hyperemic state follows. The circulation decreases 

 greatly, and although vasomotor reflexes to heating 

 and cooling the rest of the body return, the response is 

 slow and incomplete. There is often an increased 

 sensitivity to cold, reduction of the blood flow for 

 many hours sometimes following immersion in water 



at a temperature as high as 24 C. Once constricted 

 or dilated, the vessels tend to remain so for a long 

 time. The cause of this altered vascular reactivity is 

 not known. 



Although the vascular damage may not be an es- 

 sential feature (183) it may sometimes be severe (84) 

 with dilatation and engorgement of vessels, rupture, 

 and thrombus formation. Exposure for many days 

 to water at as high a temperature as 21 C has been 

 sufficient to cause the feet to become swollen, hy- 

 peremic, and painful (186). Of nine volunteers 

 living for 5 days in a covered raft in arctic waters, 

 seven developed hyperemic swollen feet, a condition 

 which in two cases persisted for several weeks; the 

 lowest toe temperature recorded during exposure 

 was 1 1 C, and the temperatures were usually 13 C to 

 15 C. (44). The vascular changes during exposure 

 have not been followed in man. It is presumed that 

 cold vasodilatation subsides after a time, perhaps 

 because the subject becomes generally chilled, and 

 that there is an extremely low blood flow for a long 

 time. 



exposure to severe cold, frostbite. Exposure to a 

 temperature sufficiently low to cause freezing of the 

 tissues may cause frostbite, which is commonly 

 followed by gangrene and loss of tissues. During 

 exposure there is arterial spasm and capillary stasis. 

 On rewarming, there is an intense hyperemia, and 

 the capillary permeability is greatly increased, lead- 

 ing to edema and to blockage of the vessels with blood 

 cells. There is frequently thrombosis in some vessels 

 and this may lead to a permanent reduction in blood 

 flow (149). 



The freezing point of living fingers is about —0.6 C, 

 but supercooling is usual so that fingers immersed in 

 brine at —1.9 C, the freezing point of sea water, do 

 not always freeze (128). Supercooling to —1.9 C 

 does not cause the tenderness, redness, and warmth 

 which persist for several days after freezing at that 

 temperature. The damage on freezing the tissues is 

 probably caused partly by the formation of ice 

 crystals, and partly by the concentration of the dis- 

 solved substances in the liquid water that remains 



(i5°)- 



In dogs, after immersion of the hind leg in an 



alcohol and dry ice mixture at —25 C for 30 min, 



or — 4 C to — 8 C for 2 1 o min, the blood flow, on 



rewarming the limb, is increased for several hours 



to several times the level in the contralateral control 



limb (125) and this vasodilatation appears to depend 



on the integrity of sympathetic outflow (126). 



