TABLE 3

Methodological characteristics of clinical studies

Clinical studies[References]
Electronic cigarette use status
 Never users[39–43, 58, 88, 89]
 Active users[58, 90, 91]
Tobacco cigarette smoking status
 Never smokers[39, 41–43, 62, 87, 91]
 Active smokers[40, 62, 87–90]
 Former smokers[58, 90]
Health status
 Healthy[39–43, 58, 62, 87, 88, 90, 91]
 Asthmatic[39, 40]
Period of electronic cigarette use in the study
 Up to 1 h inclusively[39, 40, 42, 43, 62, 87]
 1 h to 1 day inclusively
 1 day to 1 week inclusively[88]
 1 week to 1 month inclusively[41, 90]
 1–6 months inclusively[89]
 6 months to 1 year inclusively
 >1 year
 Undisclosed or self-reported[58, 91]
Number of study participants
 <50[39–43, 58, 62, 87]
 51–100[91]
 >100[88, 89]
Flavour used
 Tobacco[87, 89]
 Menthol[89]
 Dessert flavours[62]
 Unflavoured[39–43]
 User's choice (multiple flavours)[58, 90, 91]
Nicotine concentration used
 Low nicotine <6 mg·mL−1[40, 89]
 Medium nicotine 6–18 mg·mL−1[87]
 High nicotine >18 mg·mL−1[88]
 No nicotine[39–41, 43, 62]
 User's choice (multiple nicotine concentration)[58, 90, 91]
 Unknown[42]
Tissue collected or analysis performed
 Bronchoalveolar lavage[41, 42]
 Nasal epithelial cells[58]
 Sputum[90]
 Bronchial brushings[41, 42, 91]
 Lung function assessment[39, 40, 42, 62, 87–89]
 Cardiac function assessment[88]
 Blood analysis[40, 43, 87, 89]
 Urine analysis[41, 42]