The effect of blood O2 affinity on the efficiency of O2 transport in blood at hypoxic hypoxia.

An index of the efficiency of O2 transport in blood and delivery to tissues, the capacitance coefficient beta, was theoretically analyzed as a function of the position of the blood O2 dissociation curve (ODC). The P50 at which beta reaches its maximum is high at normoxia and decreases with lowering the ambient PO2. At very deep hypoxia this value becomes lower than the normal P50 of human blood. An increase of blood O2 capacity enlarges beta, particularly at deep hypoxia, and also increases the P50 at which maximal beta is reached. Changes of (a-v)O2 have ambivalent effects, depending on both P50 and PaO2. The capacitance coefficient beta was further calculated as a function of PaO2 at three values of P50, simulating the effect of a shift of the ODC. The capacitance coefficient is several times higher at deep hypoxia than at normoxia at all values of P50 used. A shift of the ODC to the left results in a moderate decrease of beta at mild hypoxia but in a large increase at severe hypoxia; a shift to the right has a reverse effect.