1 Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, University of Pittsburgh, Pittsburgh, PA.
2 Department of Emergency Medicine, University of Pittsburgh, Pittsburgh, PA.
3 University of Maryland School of Medicine, University of Maryland, Baltimore, MD.
4 Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, University of Pittsburgh, Pittsburgh, PA; Electronic Cigarette Research Initiative, University of Pittsburgh, Pittsburgh, PA. Electronic address: [email protected].