External Carotid Blood Flow in Individuals With Post-Bariatric Hypoglycemia

Inclusion Criteria: * Age 18-70 years of age, inclusive at screening. * Individuals able to provide informed consent and follow all study procedures, including complete daily food, activity, and symptom diaries, and willingness to provide access to medical record review. * For healthy control group: individuals without a history of upper gastrointestinal surgery and without reported symptoms of hypoglycemia. * Individuals with access to personal iPhone running operating system 16 (iOS) or later versions (not feasible for Android platform users) and a password-protected home Wi-Fi network. Exclusion Criteria: * History of coronary artery disease or presence of 2 or more risk factors including diabetes, uncontrolled hypertension, uncontrolled hyperlipidemia, and active tobacco use. * History of myocardial infarction, unstable angina or revascularization within the past 6 months. * History of syncope (unrelated to hypoglycemia) or diagnosed cardiac arrhythmia. * Documented hypoglycemia occurring in the fasting state (\> 12 hours fast). * Concurrent administration of β-blocker therapy. * Vigorous physical activity within 24 hours prior to assessment. * Seizure disorder (other than with suspect or documented hypoglycemia). * Hematocrit \< 33% (women) or \<36% (men) within the past 6 months. * History of insulinoma. * Use of central nervous system-active medications, including: antidepressants, anxiolytics, antipsychotics, stimulants, antiepileptics, sedatives and opioids. * His…