Methods

Participants and Study Design. Adult EC users (≥ 18 years old) were identified amongst a pool of regular Vape Shops customers. Vape shop owners who helped in a previous study22 were instructed to ask their regular clients a few questions about smoking history and EC use patterns. Customers who had never smoked or who reported having smoked less than 100 cigarettes in their lifetime were defined as never smokers23 and considered for inclusion. They also had to be daily EC users of≥ 3 months. They were invited for a free medical check-up at the Centro per la Prevenzione e Cura del Tabagismo (CPCT) of the University of Catania. Age-and sex-matched non-smoking controls (and not using ECs) were selected from hospital staff and included as a reference (control) group. Subjects were recruited from June 2013 to September 2013 and data collection completed in March 2017. Participants came to the CPCT in the mornings for their check-up visits during which vital signs (blood pressure-BP, heart rate-HR, body weight) as well as measurements of lung function, respiratory symptoms, and airway inflammation (eNO and eCO levels) were recorded. Details of EC-related products purchased (ie ECs hardware, e-liquid nicotine strengths and flavours) were also noted. Three additional follow-up visits were scheduled yearly for up to 3.5 years; follow-up visits 1 (F/up1), 2 (F/up2) and 3 (F/up3) were carried out at 12 (±1), 24 (±2) and 42 (±2) months after baseline visits, respectively. At F/up3, EC users were offered the additional option of undergoing lung HRCT. All these tests and measurements were carried out in accordance with relevant guidelines and regulations. University of Catania Ethics Review Board approved the study protocol and subjects gave informed consent prior to participation.

BP, HR, and Body Weight. After a 5-minute rest, BP and HR measurements were obtained by a semi-automated oscillometric sphygmomanometer (Smart Pressure, CA-MI Snc, Parma, Italy). Two measurements in the sitting position, spaced 1–2 min apart, were obtained at each visit. Measurements were taken in the morning, and participants were instructed not to vape or consume caffeinated drinks for at least 60 min prior to each visit. The average of two measurements was considered for analysis. Participants removed shoes and heavy clothing and were weighed at each visit by using a mechanical scale (Seca, Intermed Srl, San Giuliano Milanese, Italia).