Table 1

Topography in e-cigarette users

Reference	Study characteristics Study product/sample Size	Traditional cigarette	Use duration e-cigarette	Use duration traditional cigarette	Results e-cigarette topography	Traditional cigarette topography	Other topography measures
Etter and Bullen26	Varied brands	N/A	Mean=3 months	N/A	120 puffs/day	N/A	N/A
Hua et al28	Preferred e-cigarette, flavour, nicotine concentration/64-e-cigarette users; 9 traditional cigarette users	Preferred traditional cigarette flavour, nicotine concentration	Ad libitum	Ad libitum	Puff duration 4.3 s, SD ±1.5; exhalation duration 1.7 s, SD 1.1	Puff duration 2.4 s, SD ±0.8; exhalation duration 1.6 s, SD 0.7	Observational data; e-cigarette users showed large variation in puff duration
Farsalinos et al 3	eGo-T battery, Epsilon atomiser, Nobacco 9 mg/mL nicotine/45 e-cigarette users; 35 traditional cigarette users	2 cigarette cigarettes (brand not identified)	Ad libitum for 20 min for experienced users; ad libitum for 10 min for naïve users	2 cigarette cigarettes ad libitum, 00.7 mg nicotine	E-cigarette user puff duration 4.2±0.7, inhalation 1.3±0.4 s; puff number=43; traditional cigarette users using e-cigarettes puff duration 2.3±0.5, inhalation 2.1±0.4 s	Puff duration 2.1±0.4 and inhalation 2.1±0.4 s	Observational data; nicotine absorption was not measured
Trtchounian et al14	Liberty Stix, Crown Seven Hydro Kit, NJOY, Smoking Everywhere Gold	Merit Ultra Lights, Marlboro Ultra Lights, Marlboro Lights, Marlboro Reds, Camel unfiltered, Camel Lights, Camel filtered, Pall Mall unfiltered	First 10 puffs of an e-cigarette	7–11 puffs; puffs were 2.2 s long every minute; 3 series	Average vacuums ranged from 25±3 mm H₂O to 153±12 mmH₂O	Average vacuums ranged from 30 mm H₂O±3 to 80 mm H₂O±5	Machine yield data from non-standardized, non-validated topography equipment
Trtchounian et al14	Liberty Stix, Crown Seven Hydro Kit, NJOY, Smoking Everywhere Gold, VapCigs	N/A	Vacuum and aerosol density measured until each cartridge was exhausted, 3 series	N/A	Average vacuums ranged from 34±6 mm H₂O to 174±23 mmH₂O; puffs ranged from 177±15 to 313±115.	N/A	Machine yield data from non-standardized, non-validated topography equipment
Williams and Talbot30*	Liberty Stix #1, Liberty Stix #2, VapCigs, Crown Seven Hydro Imperial, Smoking Everywhere Platinum	N/A	First 10 puffs of an e-cigarette	N/A	Pressure drop, flow rate and aerosol density remained constant for a given e-cigarette but varied among brands. Liberty Stix had the lowest pressure drop (20 mm H₂O) and Liberty Stix #2 had the highest pressure drop (150 mm H₂O)	N/A	Machine yield data from non-standardized, non-validated topography equipment
Williams and Talbot30*	VapCigs #2, Crown Seven Hydro Imperial, Smoking Everywhere Platinum	N/A	Aerosol density measured until each cartridge was exhausted, 3 series	N/A	Puffs ranged from 160±6 to 400±10.	N/A	Machine yield data from non-standardized, non-validated topography equipment
Williams and Talbot30*	Liberty Stix #1, Liberty Stix #2	N/A	11 puffs, 3 series	N/A	Aerosol density remained similar for the first e-cigarette so performed quite uniformly from trial to trial. In contrast, pressure dropped significantly during trial 3 for the second cigarette with a drop in aerosol density	N/A	Pressure drop was consistent for Liberty Stix #1 so performed uniformly; Liberty Stix #2 did not perform uniformly; machine yield data from non-standardized, non-validated topography equipment

*One Liberty Stix and one VapCigs e-cigarette from prior study (Trtchounian et al14) were included in this study. The original purchases are designated Liberty Stix #1 and VapCigs #1; the purchases used only in this study are designated Liberty Stix #2 and VapCigs #2.