Expiratory Flow Limitation by FOT in a General Population and Comparisons with Matched Controls

Conventional lung function measures are effort dependent and may be insensitive to changes, particularly in the peripheral airways where small airway disease may originate or manifest. Forced oscillometry technique (FOT) is a noninvasive, objective and effort-independent method to measure airway mechanics. The aim of this study is to evaluate the prevalence of expiratory flow limitations (EFL) in an adult general population. Adults (≥18 years) from the population-based Austrian LEAD cohort with validated FOT (Resmon Pro Full, Restech, Italy), spirometry and body plethysmography measurements were analyzed for EFL, by a mean inspiratory minus mean expiratory reactance of the respiratory system >2.8 cmH2O·s·L−1 [Dellacà et al. Eur Resp J 2004]. Matched subgroups with a ratio of 2:1 were generated based on similarities in age, height, weight and FOT minute ventilation and the two groups compared by lung function and fractional exhaled nitric oxide measurements (FeNO) and diagnosed lung diseases. From a total of 5299 adults, 1.3% (n=29) of male and 1.8% (n=54) of female participants, with a median age of 69 years, showed EFL. Comparison with the matched subgroup without EFL (n=166) resulted in significant differences (p<0.001) of resistances (FOT-5Hz and (s)Raw), forced expiratory flows (PEF and MEFs) volumes (FEVs and FVC), and residual volume, whereas total lung capacity and FeNO values were similar (p>0.8). Prevalence of asthma and airflow obstruction was >3-fold greater in participants with EFL. Participants with EFL evaluated by FOT showed impaired spirometric expiratory patterns, signs of hyperinflation and higher prevalence for asthma and airflow obstruction with similar FeNO levels.