
The relationship between the $\rho O_{2}$ and the percent saturation of haemoglobin when represented on a graph is called as oxygen haemoglobin dissociation curve. It is sigmoid in shape. Rise in $\rho CO_{2}$, $H^{+}$ ions (fall in pH), temperature and diphosphoglyceric acid shifts the $HbO_{2}$ dissociation curve to the right. (As more $O_{2}$ dissociate from the oxyhaemoglobin)