Nicotine e-cigarette use exposes the upper airway to repeated inhalation of complex aerosols containing propylene glycol, glycerol, nicotine, flavourants, thermal degradation products, metals, and ultrafine particulates. These constituents can alter mucosal properties, inflammatory responses, and microbial community structure, with potential downstream effects on airway function and immune homeostasis. However, acute biological consequences of cessation remain poorly characterized. This dissertation examined rapid changes across pulmonary function, nasal inflammation, and nasal microbiome composition during the critical 72-hour period following e-cigarette cessation in young adult vapers. Using a within-participant repeated-measures design, 24 participants (mean age 23.3 years; 54% male) completed baseline assessments (Visit 1) and follow-up assessments at 24, 48, and 72 hours of instructed abstinence (Visits 2–4). Primary analyses focused on the baseline-to-72-hour contrast (Visit 1 vs. Visit 4). Adherence was verified by significant urinary cotinine decline and persistently low exhaled carbon monoxide. Outcomes included spirometry, impulse oscillometry, exhaled biomarkers, nasal pro-inflammatory mediators quantified in nasal epithelial lining fluid via electrochemiluminescence immunoassay, and 16S rRNA gene sequencing of nasal brush samples for microbiome analysis. Paradoxically, spirometry showed small but significant declines in percent-predicted FEV1 (0.96 percentage points, p=0.001) and FVC (1.06 percentage points, p<0.001), while the FEV1/FVC ratio remained unchanged. In contrast, impulse oscillometry demonstrated improved small-airway mechanics, with significant increases in reactance (X5) and X5 z-score (both p<0.001). Nasal inflammation increased selectively for IL-1β and IL-6 (both p<0.05). Nasal microbiome diversity increased significantly, with Simpson index rising from 0.78 to 0.83 (p=0.03), alongside concordant Shannon diversity trends (p=0.07). Taxonomic shifts were heterogeneous, consistent with ecological rebalancing. Baseline microbiome diversity showed limited predictive value for physiological changes and inflammatory responses, with a modest positive association observed for IL-6 change only (r=0.23, p=0.04). These findings demonstrate that 72-hour e-cigarette cessation triggers rapid, compartment-specific changes spanning airway physiology, nasal inflammation, and microbial community structure. Future longitudinal studies incorporating extended follow-up, quantitative microbiome profiling, and functional genomics are essential to determine whether early shifts are transient or long-standing (assuming longer abstinence periods).
Tina Afshar (Thu,) studied this question.