so normally in a copd pt, you have vasoconstriction of capillaries near areas of poor ventillation due to copd pathophys

so then you get vasoconstriction of those areas, and relative vasodilation of the well ventilated areas this helps focus the blood where it matters bioth

but then you give someone too much oxygen, and the oxygen reaches the otherwise poorly ventilated areas

this causes the blood vessels in those areas to dilate, and therefore steal some of the blood from the well ventilated areas

the result is … the oxygen exchange in the poorly ventillated areas is worse than it would’ve been had the blood still been largely shunted towards the well ventilated areas

Open Evidence verified