Borderline pulmonary hypertension associated with chronic hypercapnia in chronic pulmonary disease

Pulmonary hypertension (PH) due to lung diseases is classified as group 3 by the Dana Point classification. Given the basic pathophysiological conditions of group 3 lung diseases and the previously well-known concept of hypercapnic pulmonary vasoconstriction, chronic hypercapnia besides alveolar hypoxia might be another causative factor to increase mean pulmonary arterial pressure (PAm). Two hundred twenty-five subjects with chronic pulmonary diseases were assessed by a right heart catheterization and blood gas parameters. The subjects were classified into the following 4 groups: Hypercapnic Hypoxia (HCHX), Hypercapnic Normoxia (HCnx), Normocapnic Hypoxia (ncHX), and Normocapnic Normoxia (ncnx). Compared with ncnx, the HCHX, HCnx and ncHX groups all showed significantly higher PAm and met the criteria of borderline PH. Multiple regression analysis showed that PaCO₂, as well as SaO₂, was an independent variable for PAm. Given the poor prognosis with borderline PH, the elimination of excess pulmonary carbon dioxide in hypercapnia could be a considerable treatment strategy in chronic pulmonary disease.