Intermittent non-invasive (or nocturnal mechanical ventilation) eliminates symptoms of hypoventilation and improves gas exchange in patients with chronic respiratory failure. Performing right heart catheterisation we studied the influence of nocturnal mechanical ventilation on pulmonary hemodynamics. We investigated 20 patients with restrictive thoracic diseases (Post-TBC: n = 9, scoliosis: n = 11, PaCO2: 59.8 +/- 7.6 mmHg) and 13 patients with COPD (n = 13, PaCO2: 58.5 +/- 7.8 mmHg). All patients were mechanically ventilated in controlled mode. During the study the medication was not changed; COPD patients with long-term oxygen maintained this therapy. Right-heart catheterisation was performed immediately before and after 1 year nocturnal mechanical ventilation. In patients with thoracic restriction NMV induced a marked reduction of pulmonary artery pressure (PAP) from 33.2 +/- 10.0 mmHg before to 24.8 +/- 6.2 mmHg after 1 year nocturnal mechanical ventilation. In the COPD group PAP increased from 25.3 +/- 6.0 mmHg before to 27.5 +/- 6.0 mmHg after 1 year nocturnal mechanical ventilation. In contrast to the COPD group in patients with chronic respiratory failure due to thoracic restriction nocturnal mechanical ventilation causes substantial reduction in pulmonary artery pressure after a one year application.