Association between daytime sleepiness and impaired expiratory lung function due to smoking in patients with mild-to-severe OSA: an observational study

PurposeThere are no studies about daytime sleepiness (DS) in patients with obstructive sleep apnea (OSA) and impaired expiratory lung function (IELF) due to the smoking habit. We aimed to evaluate the association between DS and IELF in patients with OSA and look for possible DS-related factors. MethodsIn a prospective study, 220 untreated patients with mild-to-severe OSA were divided into non-smokers (Group 1, N = 113), smokers without IELF (Group 2, N = 69) and smokers with IELF (Group 3, N = 38). Data about anthropometric characteristics, main comorbidities, spirometry, polygraphy, and DS (by Epworth Sleepiness Scale-ESS) were collected. ResultsCompared to other groups, patients in Group 3 had lower mean values and the lowest SpO2 (pulse oximetry oxygen saturation), with a greater ST90 (sleep time with SpO2 below 90%). In Group 3, DS was lower (ESS median 3) in comparison to Groups 1 (median 6; p = 0.043) and 2 (median 6; p = 0.005)(Kruskal-Wallis test p = 0.021). In Group 3, particularly in patients with moderate-to-severe IELF, there was a significant association between ESS values and nocturnal lowest heart rate (LHR) (r(2) = 0.436; p = 0.001). Finally, two multivariate linear regression-adjusted models, the second considering domiciliary treatment with bronchodilators, confirm the association between the nocturnal LHR and ESS (beta = -0.278; p < 0.001 and beta = -0.260; p = 0.001). ConclusionPatients with OSA and IELF are less sleepy than OSA patients without it, even if they are smokers. A probable effect of autonomic alteration may explain the lower perception of sleepiness in OSA patients with IELF.