The position of the oxy-hemoglobin dissociation
curve is not fixed & can vary by a few factors. These
variations in the position of the curved are described as
changes in the affinity of hemoglobin for O2.
The position of the curve can be defined by the PO2 at
which 50% of Hb is bound to oxygen, P50. At normal body
temperature of 37°C, arterial blood with a pH of 7.4, a
PCO2 of 40 mmHg, P50 » 27 mmHg. When the affinity of
hemoglobin for oxygen decreases (P50 increases) the curve
is shifted to the right & unloading of oxygen to the tissues is
enhanced.