Introduction and objective:
Reduced maximal mid-expiratory flow between 25% and 75% of forced vital capacity (MEF25- 75) may indicate small-airway impairment, but its relationships with inhalational exposure and symptoms are uncertain. We compared exposure histories, respiratory symptoms and spirometric patterns in adults with reduced MEF25-75 and controls.

Material and methods:
Adult spirometry records (1 January 2023–31 May 2026) were reviewed retrospectively. Reduced MEF25-75 was defined operationally as <70% predicted. The final cohort included 172 adults (100 cases, 72 controls). Propensity-score matching on age, sex, body mass index, smoking and previous respiratory disease yielded 47 matched pairs. Paired tests and false-discovery-rate adjustment were applied.

Results:
After matching, broad binary inhalational exposures, including pesticides and bleach/chlorine, did not differ significantly between groups. Post-exposure cough was more frequent among cases (63.8% vs 34.0%; matched odds ratio 3.80, 95% confidence interval 1.37–13.02; p=0.007; q=0.046). Sputum and chest tightness were nominally associated but not significant after adjustment (both q=0.090). Conventional spirometric impairment occurred in 37/47 (78.7%) matched cases versus 6/47 (12.8%) matched controls; 10/47 (21.3%) matched cases had isolated reduced mid-expiratory flow. MEF25-75 correlated with FEV1 (rho=0.862) and FEV1/FVC (rho=0.820).

Conclusions:
Reduced MEF25-75 frequently accompanied conventional impairment but occurred in isolation in approximately one-fifth of matched cases. Binary exposure variables were not discriminatory after matching. The <70% cut-off was a study classification rather than a stand-alone diagnostic threshold.