Restrictive spirometry (RS) and preserved ratio impairment spirometry (PRISm) are widely used conditions, assumed to be characterized by proportionate reductions in FEV1 (PRISm) and FVC (RS) in the presence of a non-obstructive FEV1/FVC ratio. Limited data are available to assess the assumption of symmetric reduction in FEV1 and FVC in population-based cohorts.

We assessed pre-BD RS (FVC<80%GLI and FEV1/FVC?70%) and PRISm (FEV1<80%GLI and FEV1/FVC?70%) as well as lung volumes (total lung capacity (TLC), RV/TLC, maximal mid-expiratory flow (MMEF) and specific airway conductance (sGAW)) in the general population within the LEAD study, a single-centered, observational, population-based cohort study including 11423 participants aged 6-82 years from Austria.

The study population included 9967 subjects with valid lung function and normal TLC (total lung capacity, LLN?TLC?ULN). FVC and FEV1%GLI are highly correlated in the study population (R=0.804, p<0.001). 452 and 380 participants were classified with PRISm and RS, respectively, and 237 fulfill the criteria of both. FVC %GLI is significantly higher in PRISm vs RS (78.8±6.9 vs 75.0±4.6; p<0.001), and TLC %GLI is higher in PRISm vs RS (94.2±8.6 vs 91.2±7.5; p<0.001) without changes in RV/TLC. MMEF %GLI and sGAW (1/sRAW) are significantly lower in PRISm versus RS (64.3±13.2 vs 81.5±24.0; p<0.001; 1.0±0.4 vs 1.2±0.5; p<0.001).

Generally assumed to be related to proportionate reductions in FEV1 and FVC in the presence of non-obstructive FEV1/FVC ratio, our study demonstrates concordant classification in only ~50% of affected subjects, with marked differences in MMEF and sGAW in PRISm. Further studies are needed to explore differences in the clinical spectrum in both conditions.