I need some help clearing up this concept in PE, since I 've seen it come up 3 times in UWorld so far

USMLE USMLE 1
#1

I need some help clearing up this concept in PE, since I 've seen it come up 3 times in UWorld so far.

The explanation says that redistribution of blood happens and that results in a lot of blood rushing in to the normally perfused capillaries.

  1. Since O2 is perfusion limited (normal alveolar and capillary membrane thickness and area), why does PaO2 fail to equilibrate? Is it due to blood perfusion now being disproportional to the ventilation (low V/Q units) like during exercise?

  2. “No further O2 can bind since Hb is fully saturated in normal V/Q areas” - Agree, but didn’t they just say that there is hypoxemia? So Hb saturation is low and the redistribution of blood causing low V/Q units should stir the V/Q ratio towards normal. So why is not hypoxemia not corrected at all by hyperventilating here?