Short-Term Cardiovascular Effects of E-Cigarettes: Influence of Device Power

Inclusion Criteria: * Use e-cigarettes on at least 25 days in the past 30 for at least 3 months and have not used another tobacco product in the past 30 days * Healthy on the basis of medical history and limited physical examination (screening visit), as described below: * Heart rate \< 105 beats per minute (BPM)\* * Systolic Blood Pressure \< 160 and \> 90\* * Diastolic Blood Pressure \< 100 and \> 50\* * Body Mass Index (BMI) ≤ 38.0 (at investigator's discretion for higher BMI if no other concurrent health issues) \*Considered out of range if both machine and manual readings are above/below these thresholds. * Any race/ethnicity Exclusion Criteria: * Used tobacco products other than e-cigarettes in past 30 days * Expired carbon monoxide of over 5 ppm at screening * The following unstable medical conditions: * Heart disease * Uncontrolled hypertension * Thyroid disease (not hypo or hyper, controlled with medication) * Diabetes * Hepatitis B or C or Liver disease * Glaucoma * Prostatic hypertrophy * Psychiatric conditions: * Current or past schizophrenia, and/or current or past bipolar disorder * Adult onset attention deficit hyperactivity disorder (ADHD) (if being treated) * Participants with current or past depression and/or anxiety disorders will be reviewed by the study physician and considered for inclusion * Psychiatric hospitalizations are not exclusionary, but study participation will be determined as per study physician's approval * Drug/Alcohol Dependence: * Alcohol or illicit drug dependence within the past 12 months with the exception of those who have recently completed an alcohol/drug treatment program * Positive toxicology test at the screening visit (THC \& prescribed medications okay) * Opioid replacement therapy * Positive urine cannabis is not exclusionary but participant must report use of cannabis in any form on not more than 2 times per week to be eligible * Psychiatric medications: * Current regular use of any psychiatric medications with the exception of Selective Serotonin Reuptake Inhibitor (SSRI) and serotonin-norepinephrine reuptake Inhibitor (SNRIs) and current evaluation by the study physician that the participant is otherwise healthy, stable, and able to participate. * Medications * Use of medications that are inducers of nicotine metabolizing enzyme CYP2A6 (Example: rifampicin, dexamethasone, phenobarbital, and other anticonvulsant drugs). * Concurrent use of nicotine-containing medications * Other/Misc. Chronic Health Conditions * Oral thrush * Fainting * Untreated thyroid disease * Other "life threatening illnesses" as per study physician's discretion * Pregnancy * Pregnancy (self-reported and urine pregnancy test) * Breastfeeding (determined by self-report) * Concurrent participation in another clinical trial * Inability to communicate in English * Planning to quit smoking or vaping within the next 60 days