ARTHUR B. OTIS 261 



ing, but whether the primary faihire is one of excitation, of conduction or 

 of synaptic transmission is not known. 



If the ventilation of tlie hmgs is maintained at an adequate vahie by 

 artificial means then dogs can sometimes survive for several hours at body 

 temperatures of 20°C or even lower and show no signs of permanent injury 

 on being re warmed (1, 3). 



DIFFUSION BETWEEN LUNG AND BLOOD 



In normal circumstances ventilation and perfusion of the lung are so 

 evenly distributed and transfer of carbon dioxide and oxygen by diffusion 

 is so adequate that the partial pressures of these gases in the systemic 

 arterial blood are close to being in equilibrium with those in the alveoli. 



If lowering of the body temperature were to interfere in some way with 

 this transfer, then a large arterial-alveolar gradient might be set up and 

 respiratory gas exchange could be inadequate even though ventilation of 

 the lungs were maintained. It has been suggested that some such impair- 

 ment does actually occur (4) but neither we (5) nor Severinghaus et at. 

 (6, 7) have been able to find any evidence for this point of view. 



In our investigation of this problem we first of all made simultaneous 

 measurements of alveolar and arterial partial pressures of carbon dioxide, 

 at body temperatures covering the range from 16° to 37°C. On the average 

 the values determined for arterial PcOo were 3 mm Hg higher than those for 

 the corresponding alveolar values. This apparent gradient, which may 

 reflect in part at least a small systematic error in one or both sets of 

 measurements, need not concern us here. What is of importance to the 

 present problem is that there was no significant or consistant difference 

 between the apparent gradients at different temperatures. 



Even though we found no evidence that low body temperatures jiro- 

 duced any significant barrier to the transfer of COo across the lung it was 

 conceivable that O2 transfer might be impaired because of the relatively 

 low solubility of the latter gas. In collaboration with Dr. Jude an attempt 

 was made to measure the diffusing capacity of the lung in dogs at normal 

 and reduced body temperatures, using a steady state carbon monoxide 

 method (5). 



The diffusing capacity of the lung for a given gas is defined as the 

 rate of transfer of that gas divided by the difference between its partial 

 pressures in the alveoli and in the blood flowing through the pulmonary 

 capillaries. The determination of diffusing capacities involves several as- 

 sumptions, and relatively small analytical errors can lead to large varia- 

 tions in the final value obtained. However our four experiments, each on 

 a different dog, were consistent in showing a drop in diffusing capacity 

 with lowering of the body temperature, the decrement per degree drop 



