Lung Volumes in Tobacco-Exposed Individuals with Preserved Spirometry: An Overlooked Pointer of Respiratory Health?

Spirometry, the standard for diagnosing chronic obstructive pulmonary disease, has limited sensitivity for early identification of tobacco-exposed individuals with preserved spirometry (TEPS) at risk for respiratory decline. We aimed to determine whether abnormalities in residual volume to total lung capacity ratio (RV/TLC) and total lung capacity (TLC) identify TEPS at higher risk of subsequent spirometric decline.

1986 tobacco-exposed individuals (≥ 25 years, ≥ 10 pack-years) with preserved spirometry (FEV₁/FVC ≥ lower limit of normal, z-scores, ≥ - 1.645) over ≥ 4 years follow-up from the population-based Austrian LEAD study were analysed. Participants were stratified by into four groups according to RV/TLC and TLC abnormalities.

High RV/TLC (≥ upper limit of normal, ULN, z-scores > + 1.645) was present in 6.5% of TEPS, predominantly with normal TLC (87.6%) and associated with greater smoking intensity. Notably, elevated RV/TLC associated with disproportionate declines in FEV1/FVC driven by discordant reductions in FEV₁ and increases in FVC. While FEV₁ z-scores remained largely normal, RV/TLC variability was pronounced, suggesting its potential as an early marker of pre-COPD progression.

These findings underscore the limitations of spirometry alone and advocate for routine lung volume assessment in at-risk smokers.