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UWorld, in QID# 1219, says, in the second paragraph of the explanations, that the aerophilic TB prefers the apices (for secondary infection) because ventilation is greatest there.
That's wrong. Both perfusion and ventilation increase from apex --> base. I wrote them a comment (not that it matters).
But that also got me thinking: ventilation is less at the apices, so why does TB still prefer to grow there? Is it because the lesser perfusion means that less O2 diffuses into the capillaries (due to earlier saturation), so increased deadspace means increased O2 available to the TB?
Cheers,
That's wrong. Both perfusion and ventilation increase from apex --> base. I wrote them a comment (not that it matters).
But that also got me thinking: ventilation is less at the apices, so why does TB still prefer to grow there? Is it because the lesser perfusion means that less O2 diffuses into the capillaries (due to earlier saturation), so increased deadspace means increased O2 available to the TB?
Cheers,