Short halt in vaping modifies cardio-respiratory parameters and urine metabolome: a randomized trial.

Abstract
Background: Propylene glycol and glycerol are e-cigarette constituents that facilitate liquid vaporization and nicotine transport. As these small hydrophilic molecules quickly cross the lung epithelium, we hypothesized that short-term cessation of vaping in regular users would completely clear aerosol deposit from the lungs and reverse vaping-induced cardio-respiratory toxicity. Aims: To assess the acute effects of vaping and their reversibility on biological/clinical cardio-respiratory parameters (serum/urine pneumoproteins, hemodynamic parameters, lung-function test and diffusing capacities, transcutaneous gas tensions (primary outcome) and skin microcirculatory blood flow). Methods: Regular e-cigarette users were enrolled in this randomized, investigator-blinded, three-period crossover-study. The periods consisted of nicotine-vaping (nicotine-session), nicotine-free vaping (nicotine-free-session), and complete cessation of vaping (stop-session), all maintained for five days before the session began. Multiparametric metabolomic analyses were used to verify subjects' protocol compliance. Biological/clinical cardio-respiratory parameters were assessed at the beginning of each session (baseline) and after acute vaping exposure. Results: Compared to the nicotine- and nicotine-free-sessions, a specific metabolomic signature characterized the stop-session. Baseline serum club-cell protein-16 was higher during the stop-session than the other sessions (p<0.01) and heart rate was higher in the nicotine-session (p<0.001). Compared to acute sham-vaping in the stop-session, acute nicotine-vaping (nicotine-session) and acute nicotine-free vaping (nicotine-free-session) slightly decreased skin oxygen tension (p<0.05). Conclusion: In regular e-cigarette-users, short-term vaping cessation seemed to shift baseline urine metabolome and increased serum club-cell protein-16 concentration, suggesting a decrease in lung inflammation. In addition, acute vaping with and without nicotine decreased slightly transcutaneous oxygen tension, likely as a result of lung gas exchanges distrubances.