Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Number of cigarettes smoker per day at baseline, follow-up visit 1 (12 ± 1.5 months), visit 2 (24 ± 2.5 months), visit 3 (48 ± 3 months) and visit 4 (60 ± 3 months) separately for COPD electronic cigarettes users (closed triangles) and COPD controls (closed circles). All data expressed as mean and error bars are standard deviation of the mean.
COPD, chronic obstructive pulmonary disease; EC, electronic cigarette.
