Assessment of Small Airways Function in Eosinophilic Preserved Ratio Impaired Spirometry

Preserved ratio impaired spirometry (PRISm) is an important phenotype of pulmonary function in clinical and public health practice. It is possible for some patients to have chronic obstructive pulmonary disease (COPD) at an early stage. At present there is little research on the association of PRISm with type 2 (T2) inflammation biomarkers. The blood eosinophilia and impairment of small airway function in PRISm have not been fully assessed. This study investigated the eosinophilic phenotype in PRISm.

Between January 2019 and September 2022, a retrospective assessment was conducted in a single pulmonary function unit in China. PRISm was defined as forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ≥ 70% and FEV1 < 80% predicted. Two groups were formed among the PRISm participants: eosinophilic PRISm, blood eosinophil count (BEC) ≥ 150/µL; non-eosinophilic PRISm, BEC < 150/µL. Differences were analyzed between eosinophilic and non-eosinophilic PRISm.

The study included 313 participants, of whom 135 were assigned to the eosinophilic PRISm group. After adjusting for potential confounders, compared to non-eosinophilic PRISm, eosinophilic PRISm remained correlated with lower natural logarithm (ln) MEF25% predicted (- 0.161 [- 0.267, - 0.054], P = 0.003) and elevated fractional exhaled nitric oxide (FeNO) (10.616 [6.384, 14.849], P < 0.001).

Eosinophilic phenotype was common in individuals with PRISm. Compared to participants with non-eosinophilic PRISm, those with eosinophilic PRISm tended to have impaired MEF25% predicted and elevated FeNO.