Hypoxemia in COPD but not other lung diseases?

[Daitong]

Hi,

Could someone explain to me why in COPD (and sleep apnea), we get hypoxemia resulting in pulmonary hypertension (and ultimately cor pulmonale), but hypoxemia rarely occurs in other obstructive lung diseases, and not restrictive diseases (they probably do, but to a lesser extent).


Best,

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[Kazaki]

Great question but you already sort of answered it yourself towards the end!
Hypoxemia is present in obstructive disease due to air being trapped inside the lung. Hypoxemia in restrictive disease is mainly due to V/Q mismatch, which is caused by pulmonary fibrosis in intrinsic lung disease. Extrinsic causes of restrictive lung disease, lets sayyy obesity, cause a decrease in lung volumes, therefore less gas exchange etc..
To clarify, obstructive diseases of the lung are COPD (chronic bronchitis and emphysema) bronchiectasis, and obstructive sleep apnoea.
Asthma has an obstructive pattern, but only during an attack, and with proper management does not lead to any permanent damage in the airways I believe. For a detailed explanation behind ABG during an asthma attack, check out the post below, thehundredthone explained it beautifully!

http://forums.studentdoctor.net/threads/blood-gases-in-asthma.1179366/#post-17448479

 

[Instatewaiter]

Hi,

Could someone explain to me why in COPD (and sleep apnea), we get hypoxemia resulting in pulmonary hypertension (and ultimately cor pulmonale), but hypoxemia rarely occurs in other obstructive lung diseases, and not restrictive diseases (they probably do, but to a lesser extent).


Best,

In restrictive lung diseases (ILD) you do get hypoxia induced pulmonary hypertension. Many of these diseases (IPF for instance) do not allow you to live long enough for the pulm HTN to get severe.