Question

As the partial pressure of oxygen is increased from 70 to 90, the percentage saturation of haemoglobin

• A. Increases
• B. Decreases
• C. Remains the same
• D. Increases initially but gradually decreases

Answer 1

The correct option is C Remains the same

The partial pressure of oxygen does not have a direct effect on the percentage saturation of haemoglobin. The factors which affect haemoglobin affinity for oxygen are partial pressure of carbon dioxide, pH, temperature, and 2,3-bisphosphoglycerate. All these shift the oxygen dissociation curve to the right, indicating decreased affinity of haemoglobin for oxygen. As the oxygen partial pressure increases, more haemoglobin molecules bind to oxygen, until the maximum amount that can be bound is reached. As this limit is approached, very little additional binding occurs and the dissociation curve levels out as the haemoglobin becomes saturated with oxygen. This gives the curve a sigmoidal or S-shape. At pressures above about 60 mmHg, the dissociation curve is relatively flat, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure.