Relationship between body weight and daytime sleepiness in patients with untreated OSA: The role of hypoventilation due to obesity

To evaluate the relationship between body weight and daytime sleepiness (DS) in patients with obstructive sleep apnoea (OSA). We prospectively evaluated 353 untreated patients with OSA, categorised by body mass index (BMI) as normal weight, overweight, grade 1, grade 2, or grade 3 obesity. Patients with OSA and obesity hypoventilation syndrome (OHS) were analysed as a separate group. Demographic and anthropometric data, nocturnal polygraphy parameters, and DS (by the Epworth Sleepiness Scale-ESS) were collected. Excessive DS was defined as ESS > 10. Patients were classified as normal weight (13%), overweight (26%), grade 1 obesity (28%), grade 2 obesity (16%), grade 3 obesity (6%), and OHS (11%). DS did not differ significantly across body weight categories, whereas patients with OHS exhibited higher ESS scores and a greater prevalence of excessive DS. In patients with OSA, DS is not related to body weight or obesity per se. Instead, disease severity and the depth of nocturnal hypoxaemic events were the main determinants of excessive sleepiness, particularly in patients with concomitant OHS.