The pO 2 at 50% SO 2 (expressed as P 50) measures the O 2-affinity for Hb, which is about 26 mmHg for normal adult human Hb (HbA) ( Fig. The primary function of Hb is to transport oxygen (O 2) from the lung to tissues, binding and releasing O 2 in a cooperative manner, as demonstrated by the oxygen equilibrium curve (OEC), which represents O 2 saturation of Hb (SO 2) at varying partial pressures of O 2 (pO 2) ( Fig.
