Obstructive sleep apnoea and lung function, and their association with nocturnal hypoxemia: results from the Swedish CArdioPulmonary bioimage Study (SCAPIS) - a cross-sectional study.

Unlabelled: Obstructive sleep apnoea (OSA) and its associations with lung function.

Background: OSA is highly prevalent and characterised by abnormal respiration during sleep. This large, population-based study aimed to investigate the associations between OSA and lung function in subjects aged 50-64 years.

Method: The population-based Swedish CArdioPulmonary bioimage Study includes information on anthropometry, comorbidities and spirometry. The current analysis included data from three centres (Gothenburg, Umeå and Uppsala) on whole-night respiratory polygraphy as a meta-analysis examining the overall effect size of lung function on sleep apnoea severity, expressed as ß-coefficient after stratifying for sex and adjusting for age, waist circumference and smoking status.

Results: Data from 9016 participants (54% women, age 58±4 years, body mass index 27±4 kg/m ) with sleep recordings of good quality were included in the final analysis. Forced expiratory volume during 1 s (FEV ) (ß=-0.10 (95% CI -0.16 to -0.03)), forced vital capacity (FVC) (-0.15 (-0.21 to -0.10)) and diffusion capacity for carbon monoxide (DL ) (-0.08 (-0.10 to -0.05)) were all negatively associated with the oxygen desaturation index (ODI) and also with per cent of registration with nocturnal oxygen saturation <90% FVC (-0.44 (-0.87 to -0.01)), FEV (-0.86 (-1.36 to -0.36)) and DL (-0.47 (-0.60 to -0.35)). Additionally, a positive association was observed between FEV (0.13 (0.05 to 0.22)) and DL (0.07 (0.04 to 0.09)) with the mean nocturnal saturation. There was a negative association between DL and apnoea-hypopnoea index, AHI, (ß=-0.04 (95% CI-0.06 to -0.03)), while no associations were found between FEV or FVC and AHI.

Conclusion: In OSA, lower lung function is more distinctly associated with the nocturnal hypoxic burden than AHI. Potential lung function impairment should be investigated in OSA patients with a high ODI relative to AHI.