Acute Controlled Wood Smoke Exposure Induces Sensory Airway Irritation Without Detectable Changes in Small Airway Mechanics in Healthy Adults: A Randomized Crossover Study.

BACKGROUND: Residential wood combustion is a major source of ambient particulate matter in Northern Europe and is associated with adverse respiratory health outcomes. However, the acute effects of short-term wood smoke exposure on small airways remain incompletely characterized. OBJECTIVE: To investigate the acute effects of controlled wood smoke exposure on airway function in healthy adults, with specific emphasis on small airway mechanics, spirometry, and respiratory symptoms. METHODS: In a randomized, double-blind crossover-designed study, 14 healthy non-smoking adults (11 men, 3 women; mean age 26 years) underwent 2-hour chamber exposures, under two occasions, to wood smoke (PM1: 453 ± 13 μg/m3) and to filtered air separated by a three-weeks washout period. Lung function was assessed before and after each session using Forced Oscillation Technique (FOT, tremoFlo®) and spirometry. Symptoms were recorded on a modified Borg scale at 30-minute intervals. RESULTS: Exposure to wood smoke significantly elicited nasal irritation (p = 0.003) and showed trends toward increased cough and unpleasant odor perception. No exposure-specific changes were detected in spirometric parameters or oscillometric resistance parameters (R5, R5-R19, R5-R20). Reactance (X5) and resonant frequency (Fres) showed significant time-dependent changes irrespective to exposure condition (p < 0.001 and p = 0.022, respectively). CONCLUSIONS: Short-term controlled wood smoke exposure induced sensory upper airway irritation without detectable changes in small airway mechanics in healthy adults. Peripheral airway mechanical changes may require higher exposure concentration, longer durations, or susceptible populations. Furthermore, reliance on spirometry may underestimate early health effects, as irritative symptoms precede measurable mechanical dysfunction. TRIAL REGISTRATION: ClinicalTrials.gov NCT03302117.