Prevalence and Spirometric Transitions of PRISm and Obstruction: A Population-Based Study

Background and Objective: This study aims to assess the prevalence and longitudinal transitions of spirometric patterns defined by the lower limit of normal (LLN) criteria: normal airflow (FEV ₁/FVC≥LLN, FEV ₁ ≥ LLN); preserved ratio impaired spirometry (PRISm; FEV ₁/FVC≥LLN, FEV ₁ < LLN); or obstruction (FEV ₁/FVC<LLN). Methods: Post-bronchodilator values of pulmonary function tests in the transitional states of these spirometric patterns were examined in the population-based Austrian LEAD study at visits 1 (V1) and 2 (V2). 7232 (aged ≥ 18 years) were re-examined after 4.3 ± 0.6 years and categorized into different spirometric patterns. Changes in static lung volumes and flow rates were additionally examined to better characterize changes in spirometric patterns and associated spirometric measurements. Results: Whilst abnormal spirometry was found in 6.7% individuals at baseline, the prevalence of PRISm (2.2% and 1.6%), but not obstruction (4.5% and 6.1%), remained consistent over time (V1 and V2 respectively). Individuals with PRISm-V1 exhibited substantial rates of transition (48.9%) whilst individuals with obstruction-V1 remained relatively stable (77.8%). Most individuals who reverted from obstruction to improved spirometry had baseline FEV1/FVC values closer to the LLN threshold (optimal cut-off: 64.5%) while those who progressed to obstruction had an optimal predicted threshold of approximately 75%. Changes in pulmonary function tests over time were substantially different between transitional states, and notably more so in those with incident PRISm compared to incident obstructive individuals. Conclusion: We demonstrate the changes in lung function in different transitional states of spirometric patterns over time which thereby illustrate the need for repeated spirometric assessments combined with lung volume measurements for accurate monitoring and diagnosis.