B26-12 E-cigarette Users With Prior Combustible Cigarette Exposure Had Increased Small Airway Resistance, Unlike Exclusive E-cigarette Users: A Pilot Study in the BreathePA Cohort

Rationale The acute airway impacts of electronic cigarette (e-cigarette) use is under-characterized. A small cohort suggested that acute e-cigarette exposure increases small airways resistance (Jung, 2024). However, the airway impact of e-cigarette exposure in patients who have years of combustible cigarette use remains unknown. This pilot study aimed to characterize lung function, and airway inflammation with acute e-cigarette use in patients with and without combustible cigarette exposure. Methods E-cigarette users were defined as those using any e-cigarette >1x/week for >3 months and were stratified by prior combustible cigarette exposure. Non-users (controls) had never inhaled e-cigarettes or combustible cigarettes. E-cigarette users withheld e-cigarette use for 12 hours before the first visit and used the e-cigarette within 3 hours of the second visit. Non-users underwent no first visit intervention and inhaled nebulized saline at the second visit. We compared respiratory symptoms, exhaled nitric oxide (FeNO), peripheral blood and sputum cell counts, and lung function between e-cigarette users and controls at both the abstinence and acute use conditions. Results Nine e-cigarette users and six non-users have been enrolled. E-cigarette users were younger than non-users (mean age 27.8 vs. 45.3 yrs, p=0.005). E-cigarette users reported having vaped for an average of 4.1±1.9 years. Three (33%) of the e-cigarette users had prior combustible cigarette exposure, averaging 2.9±1.4 pack years. E-cigarette users with previous combustible cigarette exposure had lower FEF 25-75%-predicted compared to e-cigarette users without combustible cigarette exposure in both the e-cigarette withhold (p=0.03) and e-cigarette acute use (p=0.009) timepoints. At the e-cigarette withhold timepoint, FEV1%-predicted was also decreased in e-cigarette users with prior combustible cigarette exposure (p=0.04). There were no significant differences in dyspnea scores, other spirometry, FeNO, peripheral blood counts, and sputum cell counts between e-cigarette users and non-users at baseline, nor between e-cigarette withhold vs acute visits. Nebulized normal saline decreased FeNO (p=0.01) and monocyte counts (p=0.04) in non-users but did not impact other outcomes. Conclusions E-cigarette users with prior combustible cigarette exposure had more small airway resistance in both conditions. The combined and potentially synergistic impact of inhalational exposures warrants future physiologic and mechanistic exploration. References: Jung, L et al. “The Impact of Heat-Not-Burn, E-Cigarettes, and Cigarettes on Small Airway Function.” Tobacco use insights vol. 17. 19 Sep. 2024, doi:10.1177/1179173X241271551 This abstract is funded by: BreathePA Foundation