Hypoxic Pulmonary Vasoconstriction and Gas Exchange During Exercise
To patients with chronic obstructive pulmonary disease (COPD) studied at rest, nifedipine releases hypoxic pulmonary vasoconstriction (HPV), diverts blood flow to poorly ventilated lung units, and worsens gas exchange. During exercise, release of HPV in COPD by nifedipine blunts the increase in pulmonary artery pressure (Ppa) and lowers the severity of pulmonary hypertension. However, the effects of this lower pulmonary vascular tone on ventilation- perfusion (Va/Q) relationships under exercise conditions are still poorly understood. This investigation was aimed at analyzing the role of hypoxic vasoconstriction in modulating pulmonary gas exchange during exercise in COPD. We used the multiple inert gas elimination technique to determine the Va/Q distributions of eight patients with COPD at rest and during exercise, before and after releasing HPV by nifedipine. We elected to include subjects with advanced COPD but without overt clinical cor pulmonale on the assumption that HPV might predominate in these patients more than in those with end-stage vascular disease, who presumably have more irreversible structural damage. vardenafil 20 mg
