Carbon Dioxid Dissociation Curve. 



7 



The dissociation curve in severe anemia is more nearly hori- 

 zontal and lies at a higher level than does the normal dissociation 

 curve at carbon dioxid tensions that exist in the body. This is 

 due to the diminution of the hemoglobin, which has the power, 

 according to Parsons 1 and Henderson 2 , of combining with a 

 part of the alkali of the blood. The diminution of hemoglobin 

 renders a larger proportion of the alkali of the blood available for 

 combination with carbon dioxid at low tensions of CO2. This 

 reduces the "buffer" action of the blood against carbon dioxid 

 so that for a given change of C0 2 -tension the corresponding change 

 in hydrogen-ion concentration is greater than normal. This is 

 offered as a partial explanation of the exertional dyspnea found 

 in these cases. 



The P H of blood exposed to a carbon dioxid-air mixture of 

 the same C0 2 -tension as that existing in the alveolar air obtained 

 by the Haldane method was calculated from the H 2 C0 3 /BHC0 3 

 ratio and found to vary between 7.42 and 7.29, with an average 

 of 7.35. In general the alveolar carbon dioxid, dissociation curve 

 and alveolar P H during rest vary in different individuals but are 

 constant and characteristic for any given individual. 



The arterial CCVtension, as determined in three normals, 

 is also a characteristic of the individual, as is the arterial P H . 

 The limits of variation of the arterial P H are, however, greater 

 than those of the alveolar P H , being 7.23 to 7.45. As a natural 

 corollary to this it is found that, contrary to general opinion, the 

 alveolar tension is not always the same as that of the arterial blood. 

 The arterial tension may be as much as 10 or 11 mm. Hg. higher 

 than the alveolar even in normal resting persons. 



An empirical equation to correct the carbon dioxid tension of 

 the arterial and venous blood for oxygen-unsaturation is proposed. 

 It assumes that the action of oxygen on the carbon dioxid com- 

 bining capacity of whole blood is a function of the concentration 

 of hemoglobin in the blood and the ratio of reduced to oxy-hemo- 

 globin. The equation employed was: 



Parsons, Journ. Physiol., 191 7, li, 440, 1920, liii, 340. 

 Henderson, L. J., Journ. Biol. Chem., 1920. li, 401. 



