Are E Cigarettes a Safe Alternative to Smoking? Using Airway Cell Cultures to Assess Early Indicators of COPD Progression Inquiries Journal Chronic electronic cigarette exposure in mice induces features of COPD in a nicotine dependent manner Thorax Comparative study of lung toxicity of E cigarette ingredients to investigate E cigarette or vaping product associated lung injury ScienceDirect Older users of e cigarettes at greater risk of respiratory illness, study suggests CUNY Graduate School of Public Health & Health Policy National Emphysema Foundation E cigarettes are Poor Substitutes for Conventional Smoking in COPD Patients Links to E Cigarette Resources American Lung Association