To examine vascular reactivity and inflammatory biomarkers via quantitative magnetic resonance imaging (MRI) and blood serum, respectively, in a crossover study where active vapers (electronic cigarette users) and smokers will undergo three separate acute exposure-episodes of electronic cigarette +/- nicotine and tobacco-cig. The MRI exams and blood draws will be performed pre- and post-exposure. The results will be compared against baseline values derived from a group of non-smokers/non-vapers, who will also undergo a blood draw and MRI.

This work is an extension of prior funded work on the acute effects of nicotine free electronic cigarette aerosol on vascular function and inflammatory biomarkers in healthy non-smokers. Here, the investigators will examine vascular reactivity and inflammatory biomarkers using quantitative magnetic resonance imagine (MRI) and blood serum in a crossover study, with active vapers (electronic cigarette users) and smokers undergoing three, separate-day, acute exposure-episodes of smoking a tobacco cigarette, an electronic cigarette without nicotine, and an electronic cigarette with nicotine. Participants will undergo an MRI exam and a blood draw pre- and post-exposure-episode.

The investigators hypothesize that all three paradigms will cause a transient response but greatest for tobacco and nicotinized electronic cigarettes. The results will be compared against baseline values derived from a group of non-smokers/non-vapers, who will undergo a blood draw and MRI only. Eligible participants will be healthy, males and females, current, habitual users of electronic or tobacco cigarettes (except for the non-smoking/non-vaping comparison group), 21 to 45 years of age, and without co-morbidities.

Inclusion Criteria:

• BMI: 18.5 to 30
• Current users of electronic cigarettes or tobacco cigarettes with a use history of six months or greater.

Exclusion Criteria:

• Cancer
• HIV
• Mental illness in which the participant is not of proper cognizance
• Overt cardio- or neurovascular disease (prior heart attack, stroke, transient ischemic attacks)
• Serious arrhythmias
• Bronchospastic disease
• Upper respiratory tract infection within the past six weeks
• Medication affecting vascular function
• Antibiotics
• Magnetic resonance imaging contraindications (metallic implants/intraocular foreign bodies, claustrophobia, cardiac/cochlear implantable electronic devices, etc.)

Blinding to nicotine and placebo containing standardized electronic research cigarettes and standardized tobacco research cigarettes.