Step I v/q and TB

[LizzyBoop]

Hey guys!

I have a question from a uworld q and I'm not sure if it's dumb but here goes--maybe you can help my little brain.

Ventilation is lower in the apex of the lung and greater in the base but since perfusion is a lot lower in the apex than in the base then v/q is higher in the apex. So why is reactivated tb in the apex "where it loves air" since ventilation is actually higher in the base?

Thanks for your help in advance!

 

[raynor123456]

Hey guys!

I have a question from a uworld q and I'm not sure if it's dumb but here goes--maybe you can help my little brain.

Ventilation is lower in the apex of the lung and greater in the base but since perfusion is a lot lower in the apex than in the base then v/q is higher in the apex. So why is reactivated tb in the apex "where it loves air" since ventilation is actually higher in the base?

Thanks for your help in advance!

My guess:

Since perfusion is lower, then there is less gas exchange--this means there is more O2 available, in terms of partial pressures, to M. tuberculosis, an obligate aerobe in the apex of the upper lobe, despite the lower ventilation.

 

[norealname]

Although it is true that ventilation in the upper lobes is less than that of lower lobes, perfusion in the lower lobes is much higher than in the upper lobes (V/Q upper lobe > V/Q lower lobe). Therefore, alvoelar oxygen in the lower lobes will be low because of higher levels of gas exchange, while alveolar O2 will be high in the upper lobes --> M. Tuberculosis heads up because of higher O2 there.