Obesity and lung volumes, sleep disordered-breathing and respiratory failure – a cross-sectional observational study

<bold>Introduction:</bold> Obesity is associated with an increased risk of sleep-disordered breathing (SDB) and obesity hypoventilation syndrome (OHS). <bold>Aims and Objectives:</bold> The aim was to assess the prevalence of SDB and OHS in different degrees of obesity severity and to identify predictors for these. <bold>Methods:</bold> In a cross-sectional analysis of an observational study, obese patients (BMI≥30 kg/m2) undergoing an assessment with an in-laboratory sleep study, arterial blood gas analysis and pulmonary function test in the University Hospital Zurich, Switzerland between July 2016 and June 2023 were included. Analysis of variance was used for comparisons of obesity groups and multivariate regression analysis to identify predictors. <bold>Results:</bold> In 1065 obese adults (39% female; 48% obesity WHO I, 24% WHO II, 28% WHO III), the prevalence of OSA (apnoea-hypopnoea-index (AHI)≥5/h), severe OSA (AHI≥30/h), sleep hypoventilation and OHS was 77%, 29%, 21% and 8%, respectively. The likelihood of severe OSA and sleep hypoventilation increased with obesity class, while the presence of OSA in general and OHS did not differ across groups. Forced vital capacity (FVC %) and expiratory reserve volume (ERV %) correlated with BMI and were significantly lower in obesity WHO III. In multivariate regression models including BMI, neck circumference, age, sex, AHI, bicarbonate and ERV, bicarbonate and AHI were independent predictors of both sleep hypoventilation and OHS, and neck circumference of severe OSA. <bold>Conclusions:</bold> Three quarter of obese patients have OSA and the likelihood of severe OSA and sleep hypoventilation increases across obesity severity groups. Bicarbonate has a high diagnostic accuracy for OHS.