Carbon monoxide

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"The inspiration of CO gas will result in"
A. An unchanged arterial pO2
B. A lowered arterial p)2
C. An increased pO2
D. an increased percentage of Hemoglobin saturated with O2

The answer was A. If CO competes with oxygen for binding to Hb, doesn't that mean that there would be more O2 displaced from Hb and dissolved in the blood, thus increasing pO2 concentrations in the blood?

 

[wizzed101]

The vast majority of O2 supplied to tissue is from Hb as the solubility of O2 in blood is very poor. Nobody cares about pO2 anywhere but within the pulmonary capillaries. So that question is kinda nonsensical for me.

But anyway, solubility of individual gase is only dependent on its partial pressure in the gas phase per Henry's law. In the pulmonary capillaries, O2 and CO and other gases are saturated in the liquid phase and blood from the pulmonary veins to the systematic arteries are the same. Thus, pO2 is the same at its saturated concentration.

However, this assumes that you don't inhale pure CO because in that case, per Henry's law, pO2 will decrease significantly. I guess the question gear toward cases where the air contaminated with CO still have the same %O2 as normal air, and thus will not affect O2 solubility in the pulmonary capillaries.