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. Author manuscript; available in PMC: 2018 Oct 1.
Published in final edited form as: Drug Alcohol Depend. 2017 Aug 18;179:337–340. doi: 10.1016/j.drugalcdep.2017.07.031

Assessing electronic cigarette effects and regulatory impact: Challenges with user self-reported device power

Alyssa Rudy 1, Adam Leventhal 2, Nicholas I Goldenson 2, Thomas Eissenberg 1
PMCID: PMC5599371  NIHMSID: NIHMS900718  PMID: 28843084

Abstract

Background

Electronic cigarettes (ECIGs) aerosolize liquids for user inhalation that usually contain nicotine. ECIG nicotine emission is determined in part by user behavior, liquid nicotine concentration and electrical power. Whether users are able to report accurately nicotine concentration and device electrical power has not been evaluated. This study’s purpose was to examine if ECIG users could provide data relevant to understanding ECIG nicotine emission, particularly liquid nicotine concentration (mg/ml) as well as battery voltage (V) and heater resistance (ohms, Ω) – needed to calculate power (watts, W).

Methods

Adult ECIG users (N=165) were recruited from Los Angeles, CA for research studies examining the effects of ECIG use. We asked all participants who visited the laboratory to report liquid nicotine concentration, V, and Ω.

Results

Liquid nicotine concentration was reported by 89.7% (mean=9.5 mg/ml, SD=7.3), and responses were consistent with the distribution of liquids available in commonly marketed products. The majority could not report voltage (51.5%) or resistance (63.6%). Of the 40 participants (24.8%) who reported voltage and resistance, there was a substantial power range (2.2–32,670 W) the upper limit of which exceeds that of the highest ECIG reported by any user to our knowledge (i.e., 2,512 W). If 2,512 W is taken as the upper limit, only 30 (18.2%) reported valid results (mean 237.3 W, SD=370.6; range=2.2–1705.3 W).

Conclusions

Laboratory, survey, and other researchers interested in understanding ECIG effects to inform users and policymakers may need to use methods other than user self-report to obtain information regarding device power.

Keywords: Nicotine, Electronic cigarette, Voltage, Resistance, Wattage, Power

1. Introduction

Electronic cigarettes (ECIGs) use an electrically-powered heating element to aerosolize for user inhalation a liquid that usually contains nicotine (Breland et al., 2017). ECIG nicotine emission is determined in large part by three factors: (1) the device’s electrical power output (measured in watts or W); (2) liquid nicotine concentration; and (3) user behavior (i.e., puff number and duration; Talih et al., 2015). Early ECIG models delivered little nicotine to users (e.g., Vansickel et al., 2010; Bullen et al., 2010), possibly as a result of low electrical power (i.e., less than 10 W). However, when low-power devices (e.g., 7.3 W) are paired with high nicotine concentration liquid (e.g., 36 mg/ml nicotine), they can meet or exceed the nicotine delivery profile of a combustible tobacco cigarette (Ramôa et al., 2016). Recent ECIG models with higher voltage (V) batteries, lower resistance (Ω) heating elements, and more sophisticated electronics enable their power output to exceed 150 W (e.g., Wagener et al., 2016), allowing low nicotine concentration liquids to deliver nicotine effectively to users. In fact, 10 puffs from high power ECIGs (mean=70 W) filled with 4 mg/ml nicotine liquid (on average) can match the nicotine delivery of a tobacco cigarette (Wagener et al., 2016).

While Wagener and colleagues (2016) report devices powered as high as 162.4 W, there may be an upper limit to device power. An informal internet search on youtube.com of high power ECIG devices (using the search terms “high watt,” “high power,” “vaping,” and “ecigs”) revealed few mass-marketed ECIGs operating above 500 W, and the highest customized device that we could find for which operating characteristics were clearly identified involved a 14.7 V battery and a 0.086 Ω heating element (although these device characteristics could not be verified; V2/Ω=2,512 W; https://www.youtube.com/watch?v=6NKmBRIudQc). In a video depicting use of this device, the user described the experience: “As you can see, stupid and pointless.” and “…the limit of what a human can vape…”. The user’s description of the device indicates that devices with wattages at this level produce aversive sensory effects and are unlikely to be used by many ECIG users; therefore, 2,512 W may be the upper limit to device power.

Variations in ECIG device power have implications for ECIG users and policymakers. With regard to users, higher power devices may increase abuse liability and nicotine dependence as higher power devices produce more nicotine-containing aerosol for inhalation (e.g., Sleiman et al., 2016; Talih et al., 2017) and may also increase adverse health effects as the aerosol produced by these higher power devices also can be more toxicant-laden than low power devices (Gillman et al., 2016; El-Hellani et al., 2016). With regard to policymakers, the availability of higher power devices limits the impact of regulations regarding nicotine liquid concentration. For example, the European Union’s (EU’s) Tobacco Products Directive 2014/40/EU limits ECIG liquids to no more than 20 mg/ml nicotine to allow “for a delivery of nicotine that is comparable to the permitted dose of nicotine derived from a standard cigarette…” (European Parliament and the Council, 2014). This intended effect will not be met when a 70 W device paired with only 4 mg/ml liquid can mimic a cigarette’s nicotine delivery profile (Wagener et al., 2016). Hence, regulating ECIG nicotine emissions requires accurate data on both power and liquid nicotine concentration.

While device power is clearly important to understanding ECIG effects, many studies of ECIG users have not reported data regarding the power of the devices that those ECIG users use regularly (e.g., Vansickel and Eissenberg, 2013; Spindle et al., 2017; Spindle et al., 2017; Christensen et al., 2014; Brown et al., 2014; Hitchman et al., 2015; Sutfin et al., 2015). Of those that did, sample size was small (e.g., Wagener et al., 2017; N=20) or more than 50% of respondents did not know the power (wattage) of their device (Harvanko et al., 2017). We are unaware of any published study examining the proportion of users who can report product parameters that are critical to understanding nicotine emissions (i.e., nicotine concentration, voltage, and resistance).

The purpose of this study was to examine the extent to which experienced ECIG users could provide data relevant to understanding ECIG nicotine delivery, particularly liquid nicotine concentration (mg/ml) as well as battery voltage and heater resistance. Based on previous reports and the internet search referred to above, we expected liquid nicotine concentration to range from 0–36 mg/ml (higher concentrations are available, but generally are diluted before use; Breland et al., 2017) and power to range from 7–2,512 W (this upper limit likely is extreme, but has been documented).

2. Methods

2.1. Participants

Adult ECIG users (N=165) were recruited from the Los Angeles, CA metropolitan area via online and physical advertisements announcing the opportunity to participate in research studies examining the effects of ECIG use. Eligibility criteria were: (1) current ECIG use (i.e., ≥1 day/week for ≥1 month); (2) no recent use of smoking cessation medication; (3) no plan to cut down or quit ECIGs in the near future; (4) not pregnant or breastfeeding; and (5) aged ≥18 years old. All participants provided written informed consent, and the USC IRB approved study protocols.

2.2. Procedures

In two of the studies, 121 young adult ECIG users (Study 1 n=101, Study 2 n=20; 57.5% current smokers) attended a single laboratory visit in which they self-administered experimenter-provided ECIGs (for details on the paradigm see Goldenson et al., 2016). In the other study, adult concurrent combustible cigarette and ECIG users (N=44) attended five visits in which they smoked their own preferred-brand cigarettes and used their own ECIGs. In all studies, the measures included in the current report were collected at the first laboratory visit.

2.3. Measures

All participants completed self-report questionnaires assessing e-cigarette nicotine concentration (“What nicotine concentration do you usually use in your e-cigarette?”), device voltage (“What voltage do you prefer?”; the use of the word “prefer” was chosen to account for variable voltage devices that allow the user to control this variable using circuitry internal to the device) and atomizer resistance (“What is the resistance of your atomizer?”). Response options for each question were open-ended. Participants also completed measures assessing demographics, ECIG use characteristics (i.e., puffs per day) and smoking characteristics (i.e., past 30-day smoking, cigarettes smoked per day).

2.4. Data Analysis

Device wattage was calculated using W=V2/Ω.

3. Results

3.1. Participant Characteristics

Of the 165 participants in the pooled sample, the mean age was 27.7 years (SD=7.69); 65.5% were men; the ethnic distribution was 43.0% White non-Hispanic, 32.7% Black non-Hispanic, 8.5% Hispanic, 12.1% Asian, and 3.7% Other Race; 68.5% were past 30-day combustible cigarette smokers in addition to being ECIG users. Of the 161 participants who reported daily ECIG puff number, the mean was 81.1 (SD=131.9) ECIG puffs/day. Of the 113 participants who reported being past 30-day cigarette smokers, 95 reported that their mean daily cigarette consumption was 10.5 cigarettes/day (SD = 7.2).

3.2. Liquid Nicotine Concentration, Battery Voltage, Heating Element Resistance, And Power

Table 1 provides descriptive statistics for reported liquid nicotine concentration, battery voltage and heater resistance as well as wattage as calculated based on available data. Nearly all of the participants (89.7%) reported liquid nicotine concentration, and all their responses were consistent with values available in most marketed products (Breland et al., 2017), but the majority did not report device voltage (51.5%) or resistance (63.6%) by leaving the answer option blank, and some values were nonsensical (e.g., two reported 0 V and one reported 0 Ω). Of the participants (24.8%) who reported both voltage and resistance, calculated wattage revealed a substantial range (2.2–32,670 W), the upper limit of which exceeds that of the highest custom-made ECIG we could identify (i.e., 2,512 W, see Introduction).

Table 1.

Self-reported liquid nicotine concentration, battery voltage, heater resistance (N=165), and calculated wattage.

Reported Nicotine Concentration
(mg/mL; n=148)		 Reported Voltage
(V; n=80)		 Reported Resistance
(Ω; n=60)		 Calculated Wattage
(W=V2/Ω; n=40)*
Mean 9.5 24.5 1.5 3926.5
SD 7.3 28.3 1.8 8343.5
Median 6.0 8.2 0.5 204.9
Range 0.0–30.0 0.0–110.0 0.0–7.0 2.2–32670.0
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*

One participant reported 3.7 V and 0.0 Ω; these data were not included in calculated wattage.

4. Discussion

We conducted this study to evaluate the ability of ECIG users to report valid information regarding factors that influence ECIG nicotine delivery: (1) liquid nicotine concentration; and (2) battery voltage and heater resistance that, together, yield device power output. In this analysis of experienced ECIG users, most participants (89.7%) reported liquid nicotine concentration and their reports were consistent with the range of products on the market (Breland et al., 2017) and commonly used liquid nicotine concentrations reported elsewhere (e.g., median liquid nicotine concentration=12/mg/ml, N=2,807; Etter, 2016). The majority of participants could not report battery voltage and heater resistance (125/165 or 75.8%). Of the 40 participants who reported both, the validity of some of the information was suspect, with 10 (25%) reporting voltage/resistance information that yielded calculated device power > 3500 W. If 2,512 W is taken as the upper limit of possible wattage for ECIG users in this study, only 30 (18.2%) of this sample of 165 ECIG users reported valid wattage results (Mean=237.3 W, SD=370.6; range=2.2–1,705.3 W). Of the remaining 10, the mean wattage was 14,993.9 W (SD=10,943.2; range=3,600–32,670 W). Thus, even when experienced ECIG users report device operating characteristics, there is some question regarding the validity of the results.

These results suggest that researchers and others interested in understanding ECIG user device characteristics, including power, may need to use methods other than user self-report to obtain valid results. For clinical laboratory work (e.g., Ramôa et al., 2016; Spindle et al., 2017), a user’s battery voltage easily can be measured with a voltmeter, and mass-marketed products exist to measure conveniently the resistance of ECIG heating elements (e.g., https://www.coil-master.net/product/coil-master-ohm-meter). These tools may be essential for any work in which researchers have an opportunity to come into contact with ECIG users and their devices. For survey work, including large-scale surveillance projects such as the Population Assessment of Tobacco and Health study (Hyland et al., 2016), other methods beyond standard self-report may be necessary to characterize optimally product parameters that determine individual-level and population-level exposure to nicotine ECIG emissions. For example, for online surveys, there may be an opportunity for users to upload pictures of their battery and heating element. If brand and other specifications are visible in the picture, voltage/resistance may be identifiable through internet searches. In other scientific domains, pictures of food are uploaded in order to calculate calorie intake (e.g., Martin et al., 2012); adapting these applications to calculate ECIG device characteristics may be valuable for future ECIG surveys.

Accurate measurement of liquid nicotine concentration and device power is more than an academic exercise. There is substantial variability regarding the extent to which ECIG use, as assessed in cross-sectional and longitudinal surveys, is associated with smoking cessation rates (Kalkhoran and Glantz, 2016). One potential factor underlying the variability in associations with smoking cessation may be that ECIGs generally are treated in these studies as a product class that is largely homogenous. In fact, with liquid nicotine concentration varying from 0 to 36 mg/ml or more, batteries ranging from 3.3 to 14.7 V, and heating element resistance ranging from 0.09 to 2.5 Ω, there is considerable heterogeneity within ECIG products with regards to nicotine emissions (e.g., Breland et al., 2017; https://www.youtube.com/watch?v=6NKmBRIudQc). Given that liquid nicotine concentration and device power influence nicotine delivery to the user (e.g., Ramôa et al., 2016; Wagener et al., 2017) and that the magnitude of nicotine delivery may impact the extent to which ECIGs suppress nicotine withdrawal symptoms and other determinants of smoking behavior (e.g., Hiler et al., in press), this heterogeneity may influence the magnitude of associations of ECIG use with cessation outcomes in survey research. The fact that user behavior such as puff number and duration also influences ECIG nicotine delivery (e.g., Hiler et al., under review) adds an additional source of variability. Thus, the impact of future cross-sectional and longitudinal survey work regarding ECIG effects may be improved by rigorous assessment of user liquid nicotine concentration, device power, and, to the extent possible, user behavior. As ECIGs continue to evolve, research methods must adapt in order to evaluate ECIG effects and inform policy regarding them.

Limitations of this study were that it was a small convenience sample of some exclusive ECIG users and some dual ECIG users and cigarette smokers who were recruited to participate in laboratory studies. These participants likely are not representative of all ECIG users. The items designed to elicit information regarding device power and liquid nicotine concentration were not validated and may not be designed optimally for this purpose. Also, no attempt was made to verify liquid nicotine concentration via analytic chemistry or device V and Ω. Future studies addressing the issue of ECIG nicotine delivery would benefit from independent verification of these important liquid/device characteristics and formative work to develop accurate, multi-method measures of ECIG product parameters that impact nicotine emissions (e.g., user provides pictures of device for classifying device power based on publicly available product data in addition to self-reported power).

This study provides evidence that experienced ECIG users may not be able to report their ECIG device operating characteristics accurately. Researchers may need to use methods other than user self-report to obtain valid information regarding device power.

Highlights.

  • We examined how well electronic cigarettes (ECIG) users could report liquid and device characteristics.

  • Most users reported liquid nicotine consistent with marketed concentrations.

  • Most participants could not report voltage or resistance.

  • Only 18.2% of participants reported a valid ECIG wattage.

  • Researchers need methods other than self-report to obtain ECIG characteristics.

Acknowledgments

Dr. Eissenberg is a paid consultant in litigation against the tobacco industry and is named on a patent application for a device that measures the puffing behavior of electronic cigarette users.

Role of Funding Source

This research was supported by the National Institute on Drug Abuse of the National Institutes of Health under Award Number P50DA036105 and P50CA180905 and the Center for Tobacco Products of the U.S. Food and Drug Administration. The content is solely the responsibility of the authors and does not necessarily represent the views of the NIH or the FDA.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Contributors

TE and AL contributed to the conceptualization and design of the study. TE and AR conducted data analyses. All authors contributed to the writing and editing of this paper. All authors have read and approve the final submission.

Conflict of Interest

No conflict declared.

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