DAVID L. DRABKIN 



methaemoglobin may be used interchangeably for the haemoglobins 

 and myoglobins of man, dog and horse. The iron content of the dif- 

 ferent haemoglobins is identical, within the error of the method, and the 

 nitrogen content closely similar. The spectrophotometric determina- 

 tion of MHbCN (total pigment) is actually equivalent to a determina- 

 tion of the haemin iron. 



The direct determination of p0 2 and pC0 2 of arterial blood — R. L. 

 Riley et al z * had adapted the Roughton and Scholander syringe 

 analyzer 35 for the direct micro volumetric analysis of blood p0 2 and 

 pC0 2 . C. J. Lambertsen and P. L. Bunce have greatly increased the 

 precision of this technique by (1) use of a larger syringe, which accom- 

 modates a 5 ml blood sample instead of 1 ml, and (2) attachment of 

 a 200 mm long capillary (with 200 scale divisions) to the syringe, thereby 

 materially reducing the reading error. The analyses are performed in 

 duplicate upon whole arterial blood at 37°C. Meticulous attention to 

 details, which cannot be discussed here, in the handling and preparation 

 of the samples is necessary. The error of the Lambertsen and Bunce 

 modified technique is, in terms of the standard deviation, ± 2 mm of 

 Hg for both p0 2 and pCO 2 . 



Experimental and Results 



The oxygen dissociation data (solid circles in Figure 4) were obtained 

 by the application of the above methods for percentage of Hb0 2 

 (direct spectrophotometric) and for the tensions of 2 and C0 2 to 

 44 separate arterial samples. The latter were drawn by femoral punc- 

 ture from 16 healthy, young adult males, non-smokers, and from one 

 older subject, comfortably recumbent and who had subjectively come 

 to a steady state of relaxation while breathing appropriate gas mixtures, 

 containing different amounts of oxygen. A 15-minute period was 

 allowed for adjustment before drawing the blood. Obviously nervous 

 individuals were not used as subjects. Other determinations, including 

 pH, were also done on the blood samples. 



In Figure 4 each solid circle (and one open circle) represent a point, 

 whose position was determined by our raw, uncorrected data for per- 

 centage Hb0 2 against corresponding p0 2 . Correction to constant pC0 2 

 or to constant specified /?H was purposely not attempted, although 

 data for pC0 2 and pH were available. Such corrections, as well as 

 others which might have been applied, would not materially alter the 

 picture, and were thought to be inadvisable for a number of reasons. 

 They would imply, for pC0 2 , a ' baseline ' not existent in vivo. The 

 order of magnitude of the various corrections was well within the 

 margin of uncertainty imposed by the error range of ± 2 mm of Hg in 

 the p0 2 and pC0 2 determinations. It may be mentioned, at this point, 



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