[Mechanisms of diurnal hypercapnia in sleep apnea syndromes associated with morbid obesity]

The prevalence and mechanisms of diurnal hypercapnia in subjects with sleep apnea syndrome are not well known, particularly in the morbidly obese.We studied a group of 24 subjects with sleep apnea syndrome and morbid obesity defined as a body mass index greater than 40 kg/m2 and free of chronic respiratory disease.Hypercapnia (PaCO242 mmHg) was found in 50% of the subjects. Age, body mass index, waist/hip ratio, apnea index, ratio of maximum forced expiratory volume in one second (FEV1) to vital capacity and expiratory reserve volume were not significantly different between hypercapnic and normocapnic subjects. Total pulmonary capacity, vital capacity and FEV1 were significantly lower in hypercapnic subjects than in normocapnic subjects.These findings suggest that ventilatory restriction plays an important role in the development of diurnal alveolar hypoventilation in subjects with sleep apnea syndrome and morbid obesity.