[Which factors promote chronic alveolar hypoventilation in patients with obstructive sleep apnea?]

The pathogenesis of obesity hypoventilation is incompletely understood. We investigated 505 patients with sleep apnoea in respect of determinants that correlate with chronic hypercapnia. 14 patients (2.8 per cent) exhibited daytime hypercapnia (PCO2 greater than or equal to 45 mmHg). Compared with the entire group of patients, these patients showed heavier overweight (p less than 0.001) and their nightly respiratory dysregulation defined by the apnoea index was more severe (p less than 0.001). If these patients were compared with 14 normocapnic controls matched for apnoea index, weight and age, there was no difference in respect of lung function data. We conclude that overweight and the severity of sleep apnoea are determinants that predispose to chronic alveolar hypoventilation.