O2 diffusion in exercise and high altitude

[Fallot101]

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During exercise and in high altitudes, is O2 diffusion still perfusion limited? As the equilibrium between Pa and PA is still eventually reached. Read somewhere that it became diffusion limited, but didn't agree, as to my understanding diffusion limited gases never equilibrate with alveolar partial pressure.

Anyone could shed a light?

 

[Merely]

Are you sure the Pa and PA equilibrate during exercise and high altitude?

 

[Fallot101]

Check out these images, one from FA and one from Costanzo:

https://postimg.org/image/evvffjpkv/
https://postimg.org/image/isdt8ngvz/

FA says "Gas does not equilibrate by the time blood reaches the end of the capillary." about diffusion limited gases, so I'm inclined to say O2 remains perfusion limited in those circumstances.

 

[Sharkanatomist]

During exercise and in high altitudes, is O2 diffusion still perfusion limited? As the equilibrium between Pa and PA is still eventually reached. Read somewhere that it became diffusion limited, but didn't agree, as to my understanding diffusion limited gases never equilibrate with alveolar partial pressure.

Anyone could shed a light?

well depends what you mean by "Limited" it certainly is an important factor

 

[Merely]

During exercise and in high altitudes, is O2 diffusion still perfusion limited? As the equilibrium between Pa and PA is still eventually reached. Read somewhere that it became diffusion limited, but didn't agree, as to my understanding diffusion limited gases never equilibrate with alveolar partial pressure.

Anyone could shed a light?

I don't think it equilibrates because during exercise I think that the blood reaching the alveoli is so deoxygenated that the oxygen from the alveoli is entering the blood as fast as it can and being picked up by the hemoglobin and so it cant raise the Pa high enough to equilibrate since the blood is so oxygen deficient and so it would be diffusion limited. For altitude, the partial pressure of oxygen in the alveoli is so low that all of the oxygen can enter the blood, be picked up by the Hb, and also not equilbrate since there's just not that much of it so it also can't raise the Pa high enough to equilibrate. Does that make sense?

 

[Jabbed]

Unless there's gross pathology, it's safe to assume that oxygen is always perfusion limited unless stated otherwise. Equilibration occurs 1/4 of the way through a normal capillary. Even with emphysema diffusion impairment is only modestly significant with heavy exercise.