DAVID L. DRABKIN 



When normal arterial blood was haemolyzed in a closed system 

 (tonometer), the following characteristic changes were found : p0 2 

 decreased about 4 mm, pC0 2 increased about 8 mm, and pH fell 0-07 

 to 0-1 pH unit. A superficial view of the p0 2 and pC0 2 changes could 

 lead into a morass of inconsistencies unless it is remembered that we 

 were dealing with a closed gas space. Since we were interested in the 

 effect of the changes on the oxygen saturation, only the change in p0 2 

 was pertinent. A decrease in p0 2 could only mean here that oxygen 

 had been taken up by the haemoglobin, freed from cellular confinement. 

 This was the thing we had feared. We were, therefore, relieved to find 

 that a change (decrease) in 5 mm of pQ 2 (equivalent to 0-015 volumes 

 per cent of the dissolved gas) corresponds to only a surprisingly small 

 change (and increase of 0-07 per cent) in the percentage of HbOo at 

 high levels of saturation. 



Though not pertinent in the present considerations, the change in 

 pH in haemolysis is interesting. The pH of the new, one phase system 

 is lower, but haemoglobin is now at a higher pH than it had been 

 intracellularly. Also, our dependence on a special reference point 

 leads us into descriptive inaccuracy. Classical dissociation curves are 

 referred to a pH of 7-4, the pH of whole blood, which is really the pH 

 of the plasma, but haemoglobin, responsible for the oxygen saturation, 

 functions in a cellular environment of appreciably lower pH. The 

 futility of empirically applying certain corrections becomes obvious. 



The human subject — With the above issues out of the way, an un- 

 certainty of a different character arose. Lambertsen and Bunce dis- 

 covered that we had been over-sanguine in the subjective judgement 

 of the steady state of relaxation of our subjects. They used the Pauling 

 oxygen meter 39 as a ' lie detector ' of the steady respiratory state. This 

 ingenious instrument, which affords a continuous record of p0 2 through 

 the unique paramagnetism of oxygen, was introduced into the respira- 

 tory equipment, permitting periodic sampling at ' end expiration '. At 

 five minutes of accommodation to a gas mixture with the composition 

 of air, when overbreathing (owing to excitement) was visually not 

 evident, but detected by the meter, arterial p0 2 was up, higher than 

 100 mm, pC0 2 was down. Full adjustment was not reached objectively 

 until about 30 minutes, when arterial pO z fell to a steady 96 mm and 

 pC0 2 rose, at times to as high as 45 mm. Again, we had been fortunate 

 in our experiments to use an adjustment period of at least 15 minutes. 

 With a similar gas mixture our subjects had yielded a mean value of 

 95 mm for arterial p0 2 , or only 1 mm below that found at complete 

 relaxation, judged objectively. 



Thus, although our measurements were not made under the con- 

 ditions which exist in the circulation, we believe that our data permit 



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