Among 30 patients with obstructive sleep (OSA) syndrome in 15% (50%) chronic alveolar hypoventilation developed; chronic hypercapnia was found in patients with mildly (7), moderately (2) and severely (6 patients) impaired lung ventilatory function. All patients with chronic hypercapnia were morbidly obese (BMI 44 +/- 12). Nocturnal polysomnography showed similar mean apnea duration in the groups of hypercapnic and eucapnic patients, longer duration of the longest apneas in hypercapnia (88 +/- 42 s) than in eucapnia (38 +/- 19 s), p < 0.01 and more severe desaturation during sleep (the mean of the lowest SaO2 during apneas 0.46 +/- 0.17 mol/mol) in hypercapnic and 0.71 +/- 0.11 mol/mol in eucapnic patients, p < 0.001). Polycythemia was found in 14 patients, exclusively in hypercapnia.
Conclusions: Chronic alveolar hypoventilation develops in some obese patients with impaired-even mildly or moderately-lung ventilatory function and with the most severe OSA syndrome, in which apneas may occasionally be extremely long and lead to very low saturation during sleep. Polycythemia occurs in most patients with chronic alveolar hypoventilation and OSA syndrome.