OXYGEN UTII.rZATION— ADOLPH 



45 



conclude that tliis theory of cold death has ahiiost no evidence in its favor and has 

 some evidence against it. Hut it will serve the purpose of focusing our discussion. 



Delivery of oxygen from the atmosphere to the intracellular enzymes that trade 

 it for electrons can he suhdivided into processes of (a) lireathing. (h) circulation 

 of blood, (c) transport in blood, (d) (jxygen ])ressure in tissues, and (e) oxygen 

 transfer in cells. I will mention each of the.se proces-ses in turn. 



Breathing. Oxygen consum])tion in unanesthetized animals such as rats (hg. 1 j 

 augments when body cooling begins. .\s soon as the core temperature drojjs below 

 2)2)° , however, the consumi)tion diminishes. It is linearly related to core temperature, 

 becoming zero at approximately the tem]ierature at which breathing ceases, which 

 is 15° for the rat (Adolph, l')50). just above this tem])erature the pulmonary 

 ventilation is very slow; nevertheless, in species tested (guinea pig. Gosselin ; dog, 

 Rosenhain and Penrod ; man. Dill and Forbes ) it is found to be more than adequate 

 to deliver oxygen to the lung alveoli, as indicated by high pO, and low pC( ). in 

 arterial blood. Therefore, it can be considered that breathing does not limit the 

 mammal's supply of oxygen until it ceases through paralysis by cold. Even then 

 artificial breathing alone does not allow animals to survive much lower body tem- 

 peratures, and specificallv does not. I infer, augment the oxvgen consumption 

 at 15° to 20° C. 



Circulation. The cardiac outi)ut of unanesthetized rats has been measured by 

 dye solution in this laboratory. It decreases linearly with body temperature (fig. 2). 

 The stroke volume of the heart is as large at 18° as it is at 38°, thus having a tem- 

 perature coefficient of 1. At each temperature the oxygen consumption may be 

 divided by the cardiac output to give the utilization fraction ; this fraction does not 

 increase at low temperatures. Evidently the blood delivers adequate oxygen to the 



0.8 



0.4 



0.2 



0.1 



RAT 



^ 



COLONIC TEMPERATURE 



0° 10° 2 0° 3 0° 4 0° 



Fig. 2. — Cardiac outputs and stroke volumes of hypothermic rats. Xew data of R. W . Bullard. 



