[Pulmonary artery hypertension and nocturnal hypoxemia in chronic obstructive bronchopneumopathy]

Permanent and marked hypoxemia (PaO2 less than or equal to 60 mmHg) is a major cause of pulmonary hypertension (PH) in patients with chronic obstructive lung disease (COLD). In these patients PH, although mild to moderate (with a mean pulmonary artery pressure generally comprised between 20 and 35 mmHg), is by itself an indicator of poor prognosis. During sleep, hypoventilation and exaggerated ventilation/perfusion ratio inequalities can induce severe desaturation dips responsible for sudden peaks of PH. However, in hypoxemic COLD patients, the prognostic value of sleep-related desaturation (and resulting PH) has not been demonstrated. In COLD patients without marked daytime hypoxemia (PaO2 greater than or equal to 60 mmHg) permanent PH in rather rare. Ventilatory changes during sleep may account for nocturnal desaturation and transient PH. Do these repeated transient pulmonary hypertensive peaks finally lead to permanent PH? This attractive hypothesis supposes that significant sleep desaturation can develop in patients without pronounced daytime hypoxemia, which has not been demonstrated yet. In fact very few studies have been devoted to the occurrence of nocturnal desaturation (and PH) in such patients and the above mentioned hypothesis could not be confirmed. Long-term oxygen therapy (greater than or equal to 16-18 h/day) is generally prescribed in COLD patients with marked and persistent daytime hypoxemia. Oxygen therapy including sleep time and several studies have shown that usual O2 flows (1, 5-3 l/mn) are efficient and increase O2 saturation during sleep over 90%, with a resulting improvement of nocturnal PH. It has been demonstrated that daytime PH is stabilized (or improved) in patients receiving long-term O2 therapy. In COLD patients with less severe daytime (and nighttime) hypoxemia, almitrine could be of interest. The benefit of isolated nocturnal oxygen therapy has not been yet clearly established.