Sildenafil is a phosphodiesterase-5 inhibitor that has been approved for the treatment of pulmonary arterial hypertension with orphan drug designation. Sildenafil modulates the nitric oxide (NO) pathway in the vessel wall. Since this pathway is impaired in pulmonary arteries of patients with pulmonary hypertension (PH) associated with chronic obstructive pulmonary disease (COPD), we hypothesized that sildenafil might improve pulmonary hemodynamics and increase exercise tolerance in this condition. However, in COPD sildenafil may also impair gas exchange due to the inhibition of pulmonary hypoxic vasoconstriction. The research project is aimed to evaluate these effects.

It is a prospective, randomized, double-blind study to evaluate the acute effects of a single dose of 20 or 40 mg of sildenafil on gas exchange and pulmonary hemodynamics. Subjects: 20 patients (10 in each group). Measurements: pulmonary hemodynamics, arterial blood gasses and ventilation-perfusion distributions; at rest and during sub-maximal exercise.

Inclusion Criteria:

• COPD (FEV1/FVC<0.7)
• Age 40-75
• Pulmonary hypertension (Vmax TI>=2.8m/sec)

Exclusion Criteria:

• Treatment with CYP3A4 inhibitors, nitrates, PDE-5 inhibitors
• Coronary disease
• Ischemic optical neuritis