V/Q question -

[medsurf83]

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I'm confused... How is it that the base of the lungs have a higher Q and V compared to the Apex, yet the base has a lower PO2? It seems like a paradox.

Also, are inspiratory/expiratory lung sounds louder at the base since they have higher Ventilation?

 

[Evil_Abed]

The alveoli are more compressed at the base (due to gravitational forces), so they can expand more during inspiration whereas the alveoli at the apex don't expand as much.

 

[image187]

by PO2 do you mean PaO2? the total V and Q are.both the greatest at the bottom zones of the lung and least at the top zones, but the relative vent to flow (V/Q) ratio is higher in the too zones, leading to more oxygenation of the blood up there in that region and higher PaO2. This only makes up a very minor part of the total pulmonary circulation though while most comes from the lower region, so there's an overall Q/V discrepancy. This is why tuberculosis is usually found in the upper lobes, due to the higher O2 environment

 

[evilbooyaa]

Higher V and higher Q in the base = lower V/Q ratio --> Lower PAO2

Slight lower V and much lower Q in the apex during rest = higher V/Q ratio --> Higher PAO2