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. Author manuscript; available in PMC: 2024 Mar 28.
Published in final edited form as: Curr Opin Physiol. 2021 Jun 11;22:100447. doi: 10.1016/j.cophys.2021.06.001

Table 2.

E-cigarette effects on lung physiology

Experimental Approach Species Nicotine Flavored Subjects Exposure Time Key findings Limitations Ref.
Unblinded randomized interventional trial Human Yes (5%) Yes (JUUL flavor of choice) E-cig users (n = 126)
Tobacco smokers (n = 61)
Age: 43 ± 12 40% women		 6 weeks

  • The e-cigarette group had significantly greater reductions in urine

  • NNAL (a pulmonary tobacco-specific carcinogen), eCO, respiratory symptoms, and number of cigarettes smoked in the past seven days among those still smoking than the cigarettes as usual group.

  • Lung function and BP were similar in the two groups.

  • Cotinine was not significantly different at week six.

 The six-week study period is insufficient to understand long-term effects of e-cigs. [36]
In vivo Mouse No Yes (vanilla) Six-week old C57BL/6 female mice. 2 hours/d for six weeks

  • Immunophenotyping of lung immune cells revealed an increased number of dendritic cells, CD4+ T cells, and CD19+ B cells in the VG/PG- exposed group compared to air, irrespective of the presence of vanilla flavoring.

  • Quantification of bioactive lung lipids demonstrated a >3-fold increase of 2-AG, an anti-inflammatory mediator, and a 2-fold increase of 12-

  • HETE, another inflammatory mediator, following VG/PG exposure, with or without vanilla flavoring.

 No difference in gene expression at six weeks in this study, contrary to the difference at 16 weeks in Madison et al. [9] [29]
n = 11–12/group 70%30% VG/PG, and 70%30% VG/PG + vanilla flavoring Take away: VG and PG disrupt immune homeostasis.
Randomized, investigator-blinded, three-period crossover study Human Yes Yes E-cig users (n = 30) whom were former tobacco smokers
Age: 38 ± 2 years 100% male

  1. Vaping of nicotine e-cigs for 5d

  2. Nicotine-free-vaping for 5d

  3. Cessation of vaping for 5d

  • Compared with nicotine-free-sessions and nicotine-free-sessions, a specific metabolomic signature characterized the stop-session.

  • Baseline serum club cell protein-16 was higher during the stop-session

  • Heart rate was elevated in nicotine-vaping session

  • Compared with acute sham-vaping in the stop-session, acute nicotine-vaping and acute nicotine-free vaping slightly decreased skin oxygen tension.

  • FEF-25% was higher in the stop-session compared to the nicotine-free-session.

  • No monitoring of vaping during the 5d before experimental sessions.

  • This study enrolled only male participants.

 [26]
Take away: Short-term e-cigarette cessation decreased baseline heart rate and increased CC16 and FEF-25%, suggesting slight improvement of airway status.
Interventional cohort study Human Yes Yes Cigarette smokers, e-cigarette users, dual users and controls
Age: 21.7 ± 2 years n = 30/group		 E-cig use with everyday habits for 5 min. Measurements done at 1 and 30 min following exposure.

  • Compared with controls, lower FeNO were found in cigarette smokers and dual users.

  • CO concentrations were lower in controls relative to inhalant users.

  • Smokers and dual users had decreased PEF and MEF75.

  • E-cigarette use was associated with decreased FeNO and airflow indices (PEF, MEF75), but increased airway temperature.

 Between-subject differences in device used in the experiment might have affected the group results. There were small numbers of subjects in each arm. [37]
*

Studies where findings were likely to be biased by funding and authors had significant conflicts of interest. eCO: exhaled carbon monoxide.