REVIEW AND APPRAISAL OF PARTS I AND II 



J. W. SEVERINGHAUS 



This synopsis will aUenipt lo present the more important concepts which may 

 now l)e assumed to he suhstantiated in this field. Mention will he made of mis- 

 leading or improl)ahle statements contained within the nianuscri])ts of the various 

 participants, lest these otherwise l)e acce])ted as valid. Contradictory results will 

 he contrasted and some areas needing further research will l)e noted. Ohviously, 

 much that is important and undisputed cannot he summarized here, since many 

 of the participants have prepared comprehensive reviews and summaries of work 

 in their particular field. 



The fields of emphasis which emerged at the conference differed slightly from 

 the organization of the agenda. Therefore, this discussion will he organized to high- 

 light several suhjects not specifically mentioned by title : such as Temperature 

 gradients, Temperature regulation. Endocrine and Electrolytes. 



Metabolism. It now seems generally agreed that body metabolism diminishes 

 as a direct effect of low temperature, and that none of this fall represents oxygen 

 or substrate deprivation in the cellular environment. For the whole body the extent 

 of this decrease in metabolism at 30° C. appears to vary from 25-50%. It was 

 suggested that cold may stimulate metabolism by some non-shivering mechanism in 

 the dog. It seems possible that occult shivering and/or vasoconstriction have not 

 been eliminated as contributing factors in the partially poikilothermic animal. The 

 inference drawn by the reviewer is that the lowest metabolic rates will obtain when 

 sympathetic nervous system activity and epinephrine release, as well as shivering. 

 are blocked. In general, the metabolic activity of each organ studied was found to 

 diminish at about the same rate. However, the effect of this on the organ function 

 varies. For example, liver oxygen consumption at 24° was reported as 40% of 

 normal, but the half life of morphine was increased from 2).7 to 94 minutes. Con- 

 versely, water and sodium excretion b}- the kidney are not depressed at low- teni- 

 peratures, since their reabsorption by the distal tubule appears to be depressed first. 

 Furthermore, nerve action potentials are actually increased at low temperatures, 

 and certain aspects of the central nervous system may be hyper-reactive. The 

 heart was reported to exhibit a greater efficiency and a near normal stroke volume 

 at 28° C. Thus, it cannot be said that all body functions are uniformly depressed 

 by low^ temperatures. Whereas a few reports suggest that metabolism falls linearlv 

 with temperature, leading to the unlikely conclusion that metabolism is zero at 10°, 

 most reports suggest the expected exponential fall off, the hibernators retaining 

 4-10% of their normal rate at 4° C. 



A comment on the frequent observation of RQ values below 0.7 during hypo- 

 thermia is needed. The marked changes in solubility of CO., respiration, pH and 

 blood bicarbonate levels have often not been adequately considered. It must be 

 recognized that COo is gradually stored in the body instead of being eliminated. 

 It seems douljtful that any true tissue RQ falls below .70. although the respiratory 

 exchange ratio. R, may be very low for long periods of time. 



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