The purpose of this voluntary research study is to evaluate the extent to which infants with Gastroesophageal Reflux (GER) exhibit oxygen desaturation (low oxygen levels in their blood) and bradycardia (slow heart rate) in supine (lying flat on back) and inclined positions.

Mothers will bring their infants to the Clinical Research Center where they will be escorted to a private room. Participants will proceed to feed their infant a typical liquid meal (i.e. breastmilk or formula). Within 15 minutes of completion of the feed, infants will be placed in the prototype infant reclining device at either 0, 10, 18, or 28 degrees of incline. Infants will spend 15 minutes at each level of incline in a randomly assigned order. During this time period that each infant is under observation the infant may be entertained/distracted/comforted with white noise, music or other forms of distraction as determined by the mother or study team. Mothers may touch/caress their infant or use a pacifier to soothe infant as needed so long as each 15 minute segment is completed. Following each 15 minute segment, a "washout" period will be used such that the next 15 minute segment will not begin for a minimum of 1 minute to a maximum of 5 minutes in duration before the next incline position is begun. This allows for a clean start and stop period for each 15 minute segment that is not impacted by either the prior position or the change to the new position. This also allows mothers or study staff to pick up and comfort the infant.

During each of the four 15 minute segments, infants will be monitored using the Masimo RAD-97 pulse oximeter with data continuously collected regarding oxygen saturation and heart rate in 2-second intervals. The oxygen saturation probe will preferably be attached to a big toe, but can be placed in alternative spots consistent with usual clinical care such that a consistent reading of heart rate and oxygen saturation are recorded. A study coordinator will complete a data collection form for each segment characterizing whether GER occurred (spit-up into mouth or outside of mouth), the number of GER episodes as well as a subjective assessment of degree crying/fussing, hiccups, back arching, and breathing difficulty. The coordinator will also have a timer to measure the duration of crying in each position. Infants will be video recorded as a backup method for symptom assessment and for qualitative assessments by the study sponsor.

Inclusion Criteria:

• born at >= 34 weeks gestation
• weight for age >= 10th percentile
• No serious medical conditions
• English-speaking parent capable of consenting
• Diagnosis of GER from healthcare provider (not necessary for controls)
• 4 or more visible spit-ups (mouth or nose) per day for at least 5 days OR 2 or more spit-ups out of the nose per day for at least 5 days OR I-GERQ score >=16 (not necessary for controls)
• If applicable, parent willing to refrain from giving medication for GER for 12 hours prior to study participation

Exclusion Criteria:

• Signs of a more serious or complex illness including weight loss, lethargy, fever, excessive irritability/pain, bulging fontanelle, seizures, macro/microcephaly, bilious vomiting, hematemesis, chronic diarrhea, rectal bleeding, suspicions of GI obstruction
• History of a Brief Resolved Unexplained Event (BRUE)
• Use of a Home Apnea Monitor prescribed by a healthcare provider

Participants will be identified through providers in the Divisions of Academic General Pediatrics, Hospital Pediatrics, and Pediatric Gastroenterology. The Department of Family and Community Medicine may also refer participants to the study.