BACKGROUND: Population studies that assess lung function usually exclude results of individuals with poor-quality measurements, which often means excluding many subjects. Impaired cognition is frequently associated with poor-quality spirometry; excluding such subjects may introduce a selection bias in studies with lung function as either outcome or exposure. We investigated the association between poor-quality spirometry and impaired cognitive function and whether poor-quality spirometry is associated with future mortality risk independently of cognitive function. METHODS: We used data from a prospective cohort in three Central and Eastern European countries; 12,087 individuals aged 45-75 years (54% females) with complete information on variables of interest were included. Standard memory, verbal fluency, and executive cognitive domain tests were converted into latent variable z-scores and divided into quartiles. Spirometry tests were classified into two categories based on repeatability criteria: good- (71%) vs. poor-quality spirometry (29% of participants). Those with good-quality spirometry were further classified, using forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1), as healthy spirometry (63%) or impaired spirometry (8%). Multinomial logistic regression was used to assess the association between poor-quality spirometry and cognitive function, and a Cox proportional regression was used to analyze the risk of total mortality over a 17-year follow-up. RESULTS: After controlling for a range of covariates, higher cognitive function predicted lower odds of poor-quality spirometry. In the highest cognitive function quartile, compared with the lowest quartile, the odds ratio of poor-quality spirometry was 0.82 (95%CI: 0.72-0.92). Impaired spirometry was associated with higher mortality risk even after adjusting for cognition (adjusted hazard ratio 1.63, 95%CI: 1.45-1.84), but mortality risk was similar in subjects with poor- vs. good-quality (HR 1.02, 95%CI: 0.93-1.10). CONCLUSION: Higher cognitive function was associated with a lower risk of poor-quality spirometry. The lack of independent association of poor-quality spirometry with mortality suggests that excluding poor-quality spirometry measurements from analyses is unlikely to introduce a major bias. However, discarding poor-quality spirometry from epidemiological analyses might imply the exclusion of vulnerable subjects. These findings should be confirmed in future studies representing other populations.

Department of Epidemiology and Population Studies Institute of Public Health Faculty of Health Sciences Jagiellonian University Medical College Kraków Poland

Institute of Cardiology Lithuanian University of Health Sciences Kaunas Lithuania

National Institute of Public Health Prague Czech Republic

RECETOX Faculty of Science Masaryk University Kotlarska 2 Brno Czech Republic

Research Department of Epidemiology and Public Health University College London London UK

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