Impact of Body Positioning on EndoFLIP Measurements: A Comparative Study of Supine and Left Lateral Decubitus Positions

Inclusion Criteria: * must be between 5 years and 21 years of age at the time of the procedure, which is within the FDA-approved age range for EndoFLIP use. * participants must be scheduled to undergo a clinically indicated EndoFLIP procedure at Johns Hopkins Children's Center. * participants must have a parent or legal guardian who is able to provide written informed consent in English, or with the assistance of translation services for non-English speakers. * participants who are of appropriate age and developmental capacity must be able to provide assent for study participation. * participants must be candidates for general anesthesia as determined by the anesthesia team. Exclusion Criteria: * patients younger than 5 years of age or 22 years of age and older will be excluded. * patients who have contraindications to EndoFLIP will be excluded, including situations where upper endoscopy is generally contraindicated such as known or suspected gastrointestinal perforation, hemodynamic instability, severe coagulopathy, or inability to safely undergo general anesthesia. * patients who cannot be safely positioned in both supine and left lateral decubitus positions due to medical or anatomical considerations will be excluded. * pregnant patients will be excluded. Pregnancy status will be determined by patient or guardian report and, when clinically indicated, by urine or serum pregnancy testing per institutional protocols for patients of childbearing potential. * patients whose parent or legal guardian declines to provide informed consent or patients who decline to provide assent when age-appropriate will be excluded. * patients for whom the proceduralist or anesthesia team determines that participation in the research protocol would pose additional risk beyond routine clinical care will be excluded.