Abstract Rationale Vaping is increasingly prevalent, yet its long-term pulmonary effects remain poorly understood. We hypothesized that vapers exhibit early structural lung changes detectable via quantitative computed tomography (Q-CT), particularly in tissue heterogeneity metrics. This pilot study aimed to identify differences in lung density patterns between vapers and matched non-vaping controls. Methods We recruited 10 vapers (≥1 year use) and 10 non-vaping controls. Participants underwent low-dose chest CT. Lung segmentation was performed on inspiratory and expiratory CT images. Quadtree Decomposition (QtD) was applied to quantify regional heterogeneity in lung tissue density. QtD recursively subdivides axial slices into squares until pixel intensities within each square fall within a 100 HU range. The final number of squares, normalized by total pixels, yields the QtD metric—higher values indicate greater heterogeneity. QtD was calculated for all lung tissue (QtDFull), and separately for medium-density (−900 to − 750 HU; QtDMD) and low-density ( −900 HU; QtDLD) regions. Spirometry and oscillometry assessed lung function and airway mechanics. Group differences were evaluated using effect sizes, bootstrap confidence intervals, and p-values. Results No QtD metric reached conventional statistical significance (p 0.05), reflecting limited power. However, effect size estimates revealed consistent trends. Expiratory QtDFull (Controls: 0.18 ± 0.05; Vapers: 0.23 ± 0.06) showed a moderate-to-large group difference (g = -0.80; 95% CI -1.77 to 0.19), with vapers exhibiting greater heterogeneity. QtDMD (Controls: 0.14 ± 0.04; Vapers: 0.17 ± 0.04) also showed moderate differences (g = -0.48; 95 % CI -1.42 to 0.48). Negative directionality indicated more patchy and asymmetric lung tissue in vapers. Spirometry z-scores showed slightly higher FVC and FEV1 in vapers (FVC: 1.22 ± 1.03 vs. 0.52 ± 1.20; FEV1: 0.89 ± 0.83 vs. 0.61 ± 0.78), though these differences were not statistically significant. The FEV1/FVC ratio z-score was lower in vapers (-0.42 ± 1.18 vs. 0.16 ± 0.85; p = 0.23), suggesting a trend toward airflow limitation. Oscillometry revealed significantly less negative X5 in vapers (-0.07 ± 0.02 vs. -0.10 ± 0.03; p = 0.015), suggesting reduced elastic recoil. D5-20 (%) showed a trend toward higher values in vapers (29.57 ± 11.68 vs. 16.99 ± 13.09; p = 0.056), consistent with increased small airway resistance. Conclusions This pilot study shows that expiratory QtD metrics highlight early ventilation heterogeneity and air-trapping in vapers. Combined with altered oscillometry measures, these findings suggest QtD may be a sensitive marker of microstructural lung changes. Larger studies are needed to validate these observations. This abstract is funded by: Royal Society of New Zealand, James Cook Fellowship
Burrowes et al. (Fri,) studied this question.