Q Transport of carbon monoxide (CO) is diffusion limited because:
A. High affinity of CO for haemoglobin
B. Alveolar membrane is less permeable to CO
C. CO crosses epithelial barrier slowly
D. On exposure to air there is sudden increase in partial pressure
Explanation
Correct Answer: A. High affinity of CO for haemoglobin
(Ref. Johnson’s Essential Medical Physiology, 3rd edn. pp 304)
Diffusion-limited gas: CO is an example.
CO binds with hemoglobin 210 times faster than oxygen. So, partial pressure of CO in capillary blood does not raised (partial pressure depends on dissolve form, not chemically bound form). Diffusion equilibrium between alveoli and pulmonary capillary never comes. The uptake of a gas that does not achieve diffusion equilibrium could obviously increase if the diffusing capacity increased.
A. High affinity of CO for haemoglobin B. Alveolar membrane is less permeable to CO C. CO crosses epithelial barrier slowly D. On exposure to air there is sudden increase in partial pressure Explanation
Correct Answer: A. High affinity of CO for haemoglobin
(Ref. Johnson’s Essential Medical Physiology, 3rd edn. pp 304)
Diffusion-limited gas: CO is an example.
CO binds with hemoglobin 210 times faster than oxygen. So, partial pressure of CO in capillary blood does not raised (partial pressure depends on dissolve form, not chemically bound form). Diffusion equilibrium between alveoli and pulmonary capillary never comes. The uptake of a gas that does not achieve diffusion equilibrium could obviously increase if the diffusing capacity increased.