Background: Although well documented in tobacco smokers, there is little empirical
evidence on self-titration (i.e. adjusting puffing patterns to obtain desired blood nicotine
levels) in e-cigarette users. The primary aim was to explore the inter-relationships
between e-cigarette puffing topography, nicotine concentrations and e-cigarette
characteristics. Other aims were to identify the possible predictors of smoking cessation
in smokers attempting to quit using an e-cigarette.
Methods: Study 1 (N = 12 experienced e-cigarette users) employed a within-participants design and measured how puffing topography differs between high (24
mg/mL) and low (6 mg/mL) nicotine concentrations in 2 separate ad lib vaping
sessions. Study 2 used a mixed-participants design in which e-cigarette naïve smokers
(N = 70; 62.9% female) were randomly allocated to a cigalike (18mg/mL) or a tank
containing either 18 or 6 mg/mL nicotine concentrations to obtain profiles of puffing
topography characteristics associated with each of the aforementioned conditions and
how these evolve over a 2-week period (in 3 separate 20-minute ad lib vaping sessions).
Puff duration, number and inter-puff intervals (IPI) were recorded along with exhaled
carbon monoxide (CO), cigarette dependence, craving and withdrawal, and subjective
effects at each session. Participants were given the e-cigarette to take home and asked
to record cigarettes smoked per day (CPD) and subjective symptoms. In Study 3, Study
2 participants were followed up at 1, 3 and 6 months. Logistic regression analyses
explored whether device type, nicotine concentrations, craving reduction, mean puff
duration, cigarette dependence and motivation to quit could predict cessation.
Results: Study 1: Liquid consumption and puff number were higher and puff duration
longer in the low nicotine concentrations condition (all ps < 0.01). There were no
statistically significant differences between conditions in self-reported craving,
withdrawal symptoms, satisfaction, hit or adverse effects. Nicotine plasma levels was
significantly higher in the high nicotine concentration condition. Study 2: Puff duration
significantly increased one week post e-cigarette initiation whilst puff numbers and IPI
decreased. Cigalikes were associated with longer puff duration, shorter IPI and greater
number of puffs; the use of Tank 18 led to longer IPI and shorter puff duration but this
was not statistically significant when compared to Tank 6. The Tank 18 and cigalikes
were more efficient in reducing craving compared to the Tank 6 at baseline.
Participants rated both Tanks (18 and 6 mg/mL) as more satisfying at baseline and Time
1 compared with the cigalike. CPD, CO and nicotine dependence reduced significantly
at week 1 then plateaued between week 1 and 2, but did not differ between conditions.
Study 3: Lower cigarette dependence, greater craving reduction with e-cigarette use
reported at baseline and reports of tank use at follow up were significant predictors of
cessation at 1, 3 and 6 months respectively. Nicotine concentrations, mean puff
duration and motivation to quit at baseline were not significant predictors.
Conclusion: Consistent with the self-titration theory, e-cigarette users engaged in
compensatory puffing with lower (6 mg/mL) nicotine concentration liquids, nearly
doubling their consumption. Although self-titration was incomplete with significantly
higher plasma nicotine levels in the high condition, compensatory puffing was sufficient
to reduce craving and withdrawal discomfort. The rapid adjustment in puffing
topography and the more erratic puffing regimen in the cigalike condition both lend
support to the self-titration theory. Whilst higher nicotine concentrations are more
effective in reducing craving, tank systems are preferable in achieving satisfaction. This
suggests an important role for device type in providing satisfaction and equally
important role for nicotine concentrations to reduce craving. Delineating the
mechanisms by which device types play a role in providing satisfaction and its subtle
difference with craving should be one area to concentrate for future research. Those
with lower cigarette dependent scores were more likely to quit at 1 month, whilst those
who reported greater craving reduction following e-cigarette use in the lab were more
likely to have quit at 3 months; the predictive utility of measures of craving reduction at
first use can be fostered to inform smoking cessation programmes. The odds of quitting
at 6 months were higher for those using a tank device at the time of follow-up compared
to those using a cigalike, which is in line with previous studies suggesting that tank
systems are associated with greater likelihood of successful cessation. Key findings
suggest that e-cigarettes have good potential in helping reduce tobacco smoking.