Arterial PO2 decreases with chronic lung disease because physiologic shunt decreases O2 extraction ratio

[DoctorB]

I'm not sure I understand this. In FA it says "Arterial PO2 decreases with chronic lung disease because physiologic shunt decreases O2 extraction ratio"

Can anyone explain this?

[Mondoshawan]

click image to enlarge

I think because there is a V/P mismatch; normal perfusion with less ventilation (from fluid, chronic inflammation, tissue destruction, or whatever). The "shunt" is the blood going from pulmonary artery to pulmonary vein without ever getting oxygenated.

[DoctorB]

That makes complete sense! Awesome pic. Thank you so much It is clear now.

[JSA-mant]

@Mondoshawan

You are awesome