The obesity-hypoventilation syndrome revisited - A prospective study of 34 consecutive cases

Study objectives: Obesity has many detrimental effects on the respiratory function and may lead to chronic hypoventilation in some patients, an association known as the obesity-hypoventilation syndrome (OHS). In many cases, patients with OHS also have sleep apneas. Hereafter, we describe several features of a cohort (n = 34) of patients with OHS and show the comparisons with a large cohort (n = 220) of patients with obstructive sleep apnea syndrome (OSAS). We compare also OHS patients with a group of patients with the association of OSAS and COPD, also known as overlap patients. Design: Descriptive analysis of prospectively collected clinical data. Setting: Respiratory care unit and sleep laboratory of university hospital. Results: In OHS patients, OSAS was present in most of the cases (23 of 26 patients). However, in three patients, OHS was not associated with OSAS, showing that obesity per se may lead to chronic hypoventilation. As expected by definition, OHS patients had, on average the worst diurnal arterial blood gas measurements, compared to the other groups. For the OHS patients, the mean diurnal Pao(2) was 59 +/- 7 min Hg, which was significantly different from the Pao(2) of the OSAS patients (75 +/- 10 mm Hg; p = 0,001) but also from the overlap patients (66 +/- 10 min Hg; p = 0.015). Pulmonary hypertension (ie, mean pulmonary artery pressure > 20 min Hg) was more frequent in OHS patients than in pure OSAS patients (58% vs 9%; p = 0.001). Conclusion: Patients with OSAS and chronic respiratory insufficiency had in most cases an associated OHS or COPD. Patients with OHS were older than patients with pure OSAS. They had mild-to-moderate degrees of restrictive ventilatory pattern due to obesity. Severe gas exchange impairment and pulmonary hypertension were quite frequent. The association of OHS and OSAS was the rule. However, in three patients, OHS was not associated with OSAS, suggesting that OHS is an autonomous disease.