Question

1. A patient has fibrosis. How can hypoxemia occur in the absence of hypercapnia?

Answer 1

Fibrosis of lungs can occur is disease like Interstitial lung disease (ILD). There is generalized and diffuse fibrosis of lung parenchyma especially the alveolar tissues.

This is a restrictive type of lung disease where there is difficulty in the lungs to inflate properly since the alveoli are damaged. The damage to the alveoli is due to uncontrolled repair mechanism of the lungs after an injury.

As the alveoli are damaged, the inspired air cannot diffuse effectively into the pulmonary circulation resulting in decreased oxygenation of blood (hypoxemia).

ILD is called restrictive lung disease since the individual suffering from it is restricted from fully expanding his lungs. It is an inspiratory phase defect.

Although there is not much difficulty in exhalation and therefore carbon dioxide is not accumulated and the lungs can deflate properly. Hence, hypercapnia is not seen in fibrosis of lungs.

Hypercapnia is seen in obstructive lung diseases like asthma, chronic bronchitis and bronchiectasis as there is difficulty for alveoli to deflate resulting in accumulation of carbon dioxide. It is an expiratory phase defect.