In the longitudinal results shown, before and after using oxygen for 1 month, hypoxemic patients did not have on average increased levels of HIF-1α, but after oxygen therapy, the HIF-1α decreased in COPD and OSA but not in fibrosis, which may be related to the course of deterioration that is common in pulmonary fibrosis or to the pathogenesis of the disease. Here, HIF1A is linked to chronic obstructive pulmonary disease.