Prevalence of restrictive lung function in children and adults in the general population

Background: Restrictive lung function (RLF) is characterized by a reduced lung expansion and size. In the absence of lung volume measurements, restriction can be indirectly assessed with restrictive spirometric patterns (RSP) by spirometry. Prevalence data on RLF by the golden standard body plethysmography in the general population are scarce. Therefore, we aimed to evaluate the prevalence of RLF and RSP in the general population by body plethysmography and to determine factors influencing RLF and RSP. Methods: Pre-bronchodilation lung function data of 8891 subjects (48.0% male, age 6-82 years) have been collected in the LEAD Study, a single-centered, longitudinal, population-based study from Vienna, Austria. The cohort was categorized in the following groups based on the Global Lung Initiative reference equations: normal subjects, RLF (TLC < lower limit of normal (LLN)), RSP (FEV1/FVC >= LLN and a FVC < LLN), RSP only (RSP with TLC >= LLN). Normal subjects were considered those with FEV1, FVC, FEV1/FVC and TLC between LLN and ULN (upper limit of normal). Results: The prevalence of RLF and RSP in the Austrian general population is 1.1% and 4.4%. Spirometry has a positive and negative predictive value of 18.0% and 99.6% to predict a restrictive lung function. Central obesity was associated with RLF. RSP was related to smoking and underweight. Conclusions: The prevalence of true restrictive lung function and RSP in the Austrian general population is lower than previously estimated. Our data confirm the need for direct lung volume measurement to diagnose true restrictive lung function.