RESPIRATORY PHYSIOLOGY— SKX'F.RIXGHArS and STUPFEL S3 



formula. (Note: this is not 34 ])er cent divided l)y 13°, since the decrease is a frac- 

 tion of the tension for each increment, lience a los^aritlimic decrease.) For CO., a 

 greater experimental scatter was noted, and the average change ohserved, 3 per cent 

 per degree, is not considered reliahle. There is no reason to douht the accuracy of 

 the calculated \'alues, based on well established factors. 



COv tension was also comi)Uted from pil measured on whole blood and plasma 

 COo content, S and pK' using the Ilenderson-Hasselbalch ecjuation, solved for Poo.,- 



p _ COo content 

 •''»^- S(10(PH-PK' + 1) 



S may be ol)tained by multiplying the values for alpha of CO. in water, in standard 

 handbooks, by the figm-e 0.0544, giving 0.0301 at c>8° C. 



Determination of pK'. It has been assumed since 1928 that ])K' is 6.105 at 38° 

 and 6.19 at 20°. varying in linear fashion between these temperatures. These data 

 are based on an averaging of several investigators' data compiled by Hastings ct al.,^ 

 and the determination of temperature sensitivity by Cullen et al.* To our knowdedge, 

 subsequent reports at variance with these have not been incorporated into investiga- 

 tive procedure. Robinson ct al:' reported a large number of pK' determinations on 

 human sera in 1934, averaging 6.092. Furthermore, if data on horse sera are omitted 

 from Hastings ct al., the average is 6.094. With regard to temperature variations 

 in pK, Rossier and Mean'' in 1941 reported variations twice as great as those ob- 

 served by Cullen ct al. Dill ct a I.' noted changes in pK' with the pH of the serum in 

 which the determination was made, corresponding to a rise of 0.03 for a fall in pH 

 of one unit. With these conflicting data at hand, it seemed w^ise to determine the 

 ])K' variations with temperature and pH. as they would affect our observations. A 

 further reason was that pH standards have been changed through the years, and 

 that most of the data were obtained with hydrogen electrodes, whereas most investi- 

 gative work is now done with the glass electrode. 



Our 41 determinations, on 9 sera, agree well with Robinson, suggesting that pK' 

 is 6.090 at 37.5°, pH 7.4. We found the increase of .pK with falling pH to be slightly 

 greater than Dill et al, our slope being .042. At 24° this slope was increased to .062, 

 and the rise of pK' at pH 7.4 agreed with Cullen, a value of —0.005 per degree 

 being found (fig. 1 ). These data have been incorporated into a nomogram (fig. 2) 

 for the calculation of human serum pK' at various temperatures and pH values. 



Physiology of pulmonary function during hypothermia. Hypothermia de- 

 presses the spontaneous respiratory exchange. The magnitude of this depression and 

 the temperature of its end point, apnea, depend greatly on the depth of anesthesia, 

 the type and amount of premedication, and individual variations, precluding an\- 

 valid prediction of these quantitative ventilatory responses to hypothermia. It is 

 usually assumed that assistance to or control of respiration is desirable during 

 hypothermia. 



Whenever artificial respiration is used, questions arise concerning its effect on the 

 blood gas tensions, the pH and the circulation. At 2)7° the problem is the mainte- 

 nance of normal values. At reduced temperatures an additional problem presents 

 itself: What are the most desirable values of pH and Pco.,. there being no normal? 

 If one holds pH or Pco., constant, CO. is retained. In other species pH may rise 



