ARTHUR B. OTIS 



263 



judged by the maintenance of a normal arterial-venous oxygen difference 

 at body temperatures down to 20°C. 



Fig. 2. Magnitude of various 

 functions in the anesthetized 

 dog at a body temperature of 

 20°C relative to those at nor- 

 mal body temperature. Circles 

 indicate the means and the ver- 

 tical lines the ranges of values 

 obtained from measurements on 

 10 dogs. 



LV Work 



Cardiac Output 



Total LV Oxygen 

 Consumption 



Total Body Oxygen 

 Consumption 



Coronary Flow/ 

 100 Gm LV 



Mean Aortic B.P 

 Mean Pulse 



H O 1 



H o 1 



10 20 30 40 50 60 70 80 

 Percent Normothermic Value 



AVAILABILITY OF OXYGEN TO TISSUES 



Although it appears that the circulation carries plenty of oxygen to the 

 tissues, the question remains as to whether the tissue cells are able to 

 extract as much oxygen as they need from the capillary blood. The left- 

 ward shift of the dissociation curve that favors the loading of oxygen in 

 the lungs also hinders the unloading in the tissues. If, as has been men- 

 tioned above, the percentage saturation of the venous blood with oxygen 

 is similar at low and at normal temperatures, then the venous Poo must be 

 lower at low temperatures because of the decreased dissociation. This means 

 that there is either a diminution in the diffusion gradient for oxygen from 

 capillary blood to tissue cells or in the Poo of the cells themselves. How- 

 ever, unless the reduction in diffusion gradient is proportionately no 

 greater than the decrease in the requirement for oxygen by the cells, then 

 ample oxygen will be supplied the cells and at a partial pressure similar 

 to that which normally exists, provided that the diffusing capacity of the 

 tissue is not diminished. 



In some experiments by Hegnauer (10), oxygen was substituted for air 

 as the inspired gas of hypothermic dogs. Although this must have in- 

 creased the diffusion head for oxygen, no increase in oxygen consumption 

 could be measured. Bigelow (1) kept dogs at 20°C for several hours and 

 then rewarmed them, measuring oxygen consumption continuously. There 

 was no evidence during the rewarming period that an oxygen debt was 

 being repaid. 



These measurements seem to show that the diffusion gradients in the 

 tissues are on the whole adequate at temperatures as low as 20° C. However, 

 they may not be sensitive enough to detect small changes and it is pos- 



