69. DATA FOR CONSTRUCTING BLOOD O2 DISSOCIATION CURVES 



Lowest oxygen tension, in mm Hg, at which respiratory blood pigment (hemoglobin, unless otherwise indicated) is 

 95% or more saturated, is referred to as tension of saturation: that at which the pigment is 50% saturated (i.e., when 

 unoxygenated pigment equals oxygenated pigment) is called the tension of half- saturation and indicated as "t. 2 sat." 

 The tension of half- saturation for a specific pigment establishes the upper limit of tissue oxygen tension and the 

 lower limit of environmental oxygen for the function of that pigment. When per cent saturation is plotted as ordinate 

 against oxygen pressure as abscissa, the "position" (O^ pressure required to produce 50% saturation) of the resultant 

 dissociation curves differs from species to species, and varies greatly within the same species with changes in pH, 

 temperature, and dilution. The "shape" is not affected by these factors, in that the curves may be superimposed 

 upon each other by multiplying p02 (t. j sat.) of standard curve for man by a suitable factor "f"[ ij. This is true 

 only as a first approximation, for certain fish show some change in shape with changes in PCO2, and sheep hemo- 

 globin at low O2 pressures has definite changes in shape as pH is varied [ 2] . The figure below illustrates dissocia- 

 tion curves for two animals whose blood has a low affinity for oxygen, i.e., a high t. j sat. (pigeon, crocodile), and 

 for two others (arenicola, eel) showing a high affinity and low t. j sat. In the tables below, values in brackets are 

 calculated "f" factors. 



lOOr 



080 



X60 



«40 



■£20 



10 20 30 40 50 60 70 



Oxygen Pressure, mm Hg 



Part I; MAN 



80 



90 



/I/ Standard reference condition with an "f" factor taken as [ 1.00] . 



Part II: MAMMALS 



/I/ Values in parentheses are calculated. In calculations at 370C, pH = 6.15 + log- j .". — '-rrr;. — ^. 



where 6.15 and 0.0290 are the pK' and CO2 factors, respectively, for whole blood. 



66 



