Pulmonary hypertension in hypoventilation syndromes.

In this issue of the European Respiratory Journal, HELD et al. [2] report on 18 patients with severe pulmonary hypertension due to alveolar hypoventilation, who were markedly improved after 3 months of noninvasive bi-level positive-pressure ventilation (NIPPV). Mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR) were 50 mmHg and 6–7 Wood units, respectively, at baseline, and decreased to 30 mmHg and 3–4 Wood units with NIPPV; this was accompanied by improved catherisation and echocardiographic indices of right ventricular (RV) function. The N-terminal pro-brain natriuretic peptide (NT-proBNP) levels also decreased, and the 6-min walk distance (6MWD) improved by 80 m. These results are in striking contrast with the ‘‘borderline’’ (mPAP 20–25 mmHg) or mild (mPAP 25–30 mmHg) pulmonary hypertension generally seen, but with rare exceptions, in patients with respiratory conditions. Borderline or mild pulmonary hypertension due to respiratory conditions is of uncertain clinical relevance, exhibits slow progression controlled by supplemental oxygen and is refractory to drugs targeting the pulmonary circulation [3, 4].