DAVID L. DRABKIN 



3 An examination of our data, in comparison with classical dis- 

 sociation curves obtained in vitro by means of gasometry, discloses 

 that they agree more closely with the earlier results of Bock, Field 

 and Adair 20 upon the blood of one subject, Bock (open curve, 

 Figure 4), than with the more recent composite data (closed curve, 

 Figure 4) of Dill 36 . If we had chosen to draw a curve through our 

 points, it is obvious that it would fall consistently slightly above 

 the curve of Bock and his colleagues. 

 Many years ago L. J. Henderson 37 pointed out that it was not 

 possible to represent correctly the alterations which occur in the body 

 in the change from arterial to venous blood by conventionally plotting 

 two oxygen dissociation curves, each at different pC0 2 (arterial and 

 venous), on ihe same two-dimensional graph. The difficulty was clear ; 

 physiologically, p0 2 and pC0 2 were interdependent. I have tried to 

 meet this need for an adequate graphic portrayal of the changes in 

 oxygen saturation in vivo. The result is embodied in Figure 5, a ' three- 

 dimensional ' graph, in which the percentage of Hb0 2 is treated as a 

 function of the two variables, p0 2 and/?C0 2 . In constructing the figure, 

 * separate ' graphs of oxygen dissociation for each pC0 2 have been 

 appropriately aligned. Definitive values for percentage of Hb0 2 , p0 2 

 and/>C0 2 in normal arterial and venous blood are given in the legend. 



Discussion and Criticism 



Towards the completion of this phase of the work we began to be 

 assailed by grave doubts as to how well we had met our primary objective 

 of establishing the dissociation curve of arterial blood in vivo. Our 

 concern with the value of the measurements had led us, as already 

 stated, to choose haemolyzed blood for the analysis of oxygen satura- 

 tion, whereas pQ 2 and pCOo had been determined on non-haemolyzed 

 blood. Furthermore, the spectrophotometric measurements were done 

 at a temperature of 25 to 27 °C, while the gas tensions were measured 

 at 37°C, the temperature of the body. The consequences of having 

 done one set of determinations upon a ' one phase ' system (haemolyzed), 

 the other upon a ' two phase ' system (non-haemolyzed) were many 

 and disturbing. Consideration made it evident that haemolysis (pro- 

 ducing a mixture of the cellular and plasma phases) would induce 

 alterations inp0 2 and/?C0 2 , and consequently in percentage saturation 

 and in pH. The difference in temperature would also operate (and in 

 the same direction). In effect, our measurements of percentage of Hb0 2 

 were not precisely at thep0 2 and pCO z which we had determined. It 

 was clear from the flatness of the dissociation curve at high/?0 2 , where 

 little change in per cent Hb0 2 accompanies relatively large changes in 

 p0 2 , that in this region there was no real need for doubt. However, 



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