Association between e-cigarette exposure and ventilation homogeneity in young adults: a cross-sectional study.

Background: The number of young people who use e-cigarettes is rising. It remains unclear whether e-cigarette use impairs lung function. We aimed to compare ventilation distribution between young adults exposed to e-cigarettes and an unexposed group.

Methods: Study participants included otherwise healthy young adults (18-24 years) who self-reported e-cigarette use and unexposed participants who had no history of e-cigarette, tobacco or cannabis exposure. Exposure to e-cigarettes was defined using three measures: 1) ever-exposed, 2) daily use and 3) puff frequency, which includes none (unexposed), minimal (<2 puffs·h^-1), moderate (3-4 puffs·h^-1) and heavy (≥5 puffs·h^-1). Ventilation distribution was measured using the multiple-breath washout test and reported as lung clearance index (LCI).

Results: A total of 93 participants were recruited; 38 unexposed and 41 exposed participants had LCI measures. The exposed group consisted predominately of participants who used flavoured e-liquids (94.5%) that contained nicotine (93.5%). The magnitude and direction of the difference in LCI across the exposure definitions was similar. Compared with the unexposed group, in the unadjusted models LCI was higher in those with any e-cigarette use (mean difference 0.15, 95% CI -0.004-0.31), daily users (mean difference 0.10, 95% CI -0.08-0.28) and heavy users (mean difference 0.22, 95% CI 0.03-0.41).

Conclusion: This preliminary work suggests that LCI may be a useful biomarker to measure the effects of e-cigarette use on ventilation distribution and to track early functional impairment of the small airways.