Is there an optimal P50 of haemoglobin? Considerations about the significance of a left- or right-shift of the oxyhaemoglobin dissociation curve.

The effect a permanent change in the oxygen-haemoglobin affinity would have on the oxygen transport system is considered theoretically. The calculations were based on Hill's equation and its derivative. It was demonstrated that in normoxia and at normal oxygen consumption the position of the oxyhaemoglobin dissociation curve of the human adult (P50 3.53 kPa) differs from the optimal position calculated and that a right-shift (increase in P50) would be favourable. However, the higher the oxygen consumption and therefore the saturation change, and/or the more pronounced the hypoxia, the more the P50 found in vivo coincides with the theoretical optimum.