According to the oxygen-hemoglobin dissociation curve, PO2 in the lungs of 100 mm Hg results in Hb being 98% saturated. At high altitude, there is less O2. At a PO2 in the lungs of 80 mm Hg, Hb would be saturated. According to the oxygen-hemoglobin dissociation curve, PO2 in the lungs of 100 mm Hg results in Hb being 98% saturated. At high altitude, there is less O2. At a PO2 in the lungs of 80 mm Hg, Hb would be saturated. 95% 100% less than 50% 98%

Oxygen-hemoglobin dissociation curve is basically a sigmoid curve which relates between the saturation of oxygen (SO2) and partial pressure of oxygen in blood (PO2). It shows the affinity of oxygen with hemoglobin at different temperature and other factors. In the oxygen-hemoglobin dissociation curve; saturated oxygen is ploted on verticle axis and partial pressure of oxygen in mmHg on the horizontal axis.

Here in the above scenario at the high altitude oxygen is less and at 80 mmHg, Hb would be 95% saturated.