22 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



tions of inulin space were made with a single injection before the cooHng had begun 

 and again after the animal had been cooled. They interpreted their results as indi- 

 cating that, while the circulating blood volume was reduced by cooling, the reduc- 

 tion was not due to shift of fluid outside of the circulation. The decreased plasma 

 volume appeared to be due to a trapping of blood in various areas of the vascular 

 bed as a result of the cooling procedure. However, these results do not account 

 for the frequent reports of increases in the hematocrit,*"' *'^' '^^ which could only be 

 due to a loss of fluid from the circulating blood or to an addition of cells from the 

 spleen. Swan et fl/.*° found an increased hematocrit but little change in the plasma 

 volume, which they believed might have been the result of splenic discharge of 

 red cells. 



D'Amato and Hegnauer"^ noted a transitory rise in plasma protein concentration 

 in dogs at rectal temperatures of 25° C. which was reversed when the cooling con- 

 tinued to 20° C. The consistent decrease in plasma volume observed at the latter 

 temperature suggested that whole plasma was removed from the circulation either 

 by sequestration in constricted vessels or loss to extravascular spaces. D'Amato"^ 

 later reported a temporary shift of water from the plasma to the tissues of the hypo- 

 thermic dog. Simultaneously water was found to move from the interstitial com- 

 partment of skeletal muscle into the cells. This was associated with shivering. At 

 lower body temperatures, where shivering had ceased, the water movement was 

 reversed. This agrees well with the previous observations of Barbour ct al/'^" and 

 with what is known concerning increased intracellular water in skeletal muscle in 

 response to increased activity.''"' - ' 



It thus appears that during the initial stages of hypothermia, and associated with 

 the muscular activity of shivering, there is a shift of water out of the vascular sys- 

 tem and a concomitant increase in interstitial and intracellular water. As hypo- 

 thermia progresses and shivering ceases these water shifts are reversed. The avail- 

 able evidence indicates further that at lower body temperatures the reduction in 

 blood volume is the result of a loss of plasma from the circulation, either by periph- 

 eral sequestration in constricted blood vessels or by loss of whole plasma to the 

 extravascular space, or as a response to dehydration and body weight loss. 



SUMMARY 



A review of metabolic processes during the development and maintenance of the 

 state of hypothermia has been made. Although some general statements could be 

 made it is obvious that the available data are too conflicting to permit much assur- 

 ance as to the validity of such conclusions. A profound reduction in metabolic 

 processes is agreed to occur. In order for more specific details of the relationship 

 of temperature to metabolic processes to be obtained, a more precise experimental 

 approach nmst ])e instituted. .Such an a])i)r()ach should incori)orate, as a minimum, 

 standardization of at least the following factors: (a) ventilation; (b) anesthesia : 

 (c) nutritional status of the experimental animals; ( d) ])resence or al)sence of 

 shivering; and (c) rate of cooh'ng, tlic method employed in cooling, and the final 

 attainment of a steady state. 



