It is commonly caused by chronic alveolar hypoventilation or air way mucus plugging.

究其原因，可能为肺泡慢性足或道分物阻塞。

Chronic hypoventilation is a marker of disease severity in asthma and chronic obstructive pulmonary disease (COPD).

哮喘COPD出现慢性低是疾病严重标志之一。