Effect of electronic cigarette use on the urge-to-cough sensation

Introduction: Electronic cigarettes (e-cigs) have attained common usage worldwide, yet knowledge of their physiological effects remains minimal. The aim of this study was to evaluate the effect of a single exposure to e-cig vapor on the urge-to-cough (UTC) threshold and C₅. Methods: Seventeen healthy nonsmokers underwent C₅ measurement employing capsaicin cough challenge at baseline, 15 minutes, and 24 hours after e-cig exposure (30 puffs 30 seconds apart). The endpoint of cough challenge is C₅, the concentration of capsaicin inducing five or more coughs. The UTC threshold (C_u) is defined as the lowest concentration of capsaicin inducing UTC without an associated motor cough. Results: The C_u and C₅ were significantly inhibited (Cu and C₅ increased) 15 minutes after e-cig use. Mean log C_u rose from -0.035 ± 0.08 (SEM) to 0.21 ± 0.12 (P = .005). Mean log C₅ increased from 0.60 ± 0.11 to 0.92 ± 0.16 (P = .001). By 24 hours after e-cig exposure, C_u and C₅ had returned to baseline levels. Conclusions: A single session of e-cig use, approximating nicotine exposure of one tobacco cigarette, induces significant inhibition of the C_u, as well as C₅. Previous studies implicate nicotine as the agent responsible for suppression of C₅, and we hypothesize a similar role for nicotine in the suppression of the C_u. Given our observation of the effect of a single e-cig exposure, studies of the respiratory physiologic implications of repeated or chronic e-cig use are warranted. Implications: This is the first study to demonstrate that a single exposure to an e-cig significantly inhibits the C_u as measured by capsaicin cough challenge testing. These findings add to the growing body of evidence that e-cig vapor is not a physiologically benign substance, and support further investigation of the effects of repeated or chronic use of e-cigs on cough sensitivity and other respiratory parameters.