Question

The plateau portion of the $O_2-Hb$ curve________

• A. Is in the blood-PPO₂ range that exists at the pulmonary capillaries.
• B. Means that hemoglobin becomes almost nearly saturated in the lungs unless the pulmonary capillary PPO₂ falls below 60 mmHg.
• C. Is in the blood-PPO₂ range that exists at the systemic capillaries.
• D. Both (b) and (c) above are correct.
• E. Both (a) and (b) above are correct.

Answer 1

The correct option is E

Both (a) and (b) above are correct.

The plateau region is where $O_2$ is being loaded onto Hb. In this region $PP{O}_2$ is 100 mm Hg. Looking at the $O_2-Hb$ curve, note that at a blood $PP{O}_2$ of 100 mmHg, Hb is 97.5% saturated. Therefore Hb in the systemic arterial blood normally is almost fully saturated. If the alveolar and consequently the arterial , fall below normal. There is little reduction in the total amount of $O_2$, transported by the blood until the, falls below 60 mmHg, because of the plateau region of the curve. Even if the arterial $PP{O}_2$ falls from 100 to 60 mmHg, The % Hb saturation is still remarkably high at 90% .