Infants without nasal cannula will have a nasal cannula placed in their nares. After a 15-minute baseline period and during quiet sleep, the infant will then be exposed to 30 seconds of 100% oxygen (O2) by increasing FiO2. This test will be repeated 3 times, with at least 3 minutes between tests to allow for return of oxygen saturation (SpO2) to baseline values. If oxygen saturations increase to 99% for 15 seconds or the infant is apneic for greater than 5 seconds following initiation of 100% oxygen (O2), the test will be stopped and FiO2 brought back to baseline. Infants in the NICU will be monitored continuously with heart rate, respiratory rate, and SpO2% for 12 hours after Carotid Body Function Test according to NICU standards. Infants discharge who return for Carotid Body Function Test at 40 and 52 weeks PMA will be monitored continuously for 1 hour after the test is finished.

Infants receiving nasal cannula high flow support 3 liters per minute (LPM) or less with or without supplemental O2 at 36 weeks PMA will be eligible. After a 15-minute quiet sleep period, infants' FiO2 will be weaned, in 0.20 decrements for 5 min intervals. Flow then decreased in 10 min intervals, initially in 1 Liter Per Minute (LPM) decrement until nasal cannula flow is 1LPM, and then decreased by 50% decrements to 0.125 LPM then off. If the infant is weaned to room air alone for 15 minutes, not meeting failure criteria, he/she has passed the RAC. Failure of the RAC is defined as occurring when SpO2% falls below 80%, even briefly, or remains less than 90% for 5 consecutive minutes any time during the test, bradycardia (Heart rate [HR] < 80 bpmx 10 sec) or persistent apnea despite stimulation. Infant is returned to the level of support provided before the RAC begun if meets any failure criteria.

A physician investigator will review 30 minutes of continuous recording made 24 hours prior to test scheduled to identify infants that are at high risk for significant oxygen desaturations during Hypoxemia Challenge.

If subject passes the screening test, the hypoxic challenge will be performed. For the hypoxemia test, a nasal cannula will be placed prior to a 15 minute period of quiet sleep recorded to confirm antecedent stability of ventilatory pattern and SpO2%. During the 15 minutes of quiet sleep, the infant is required to maintain a SpO2 of > 92% in order to undergo the HCT. After the 15-minute baseline recording, HCT will begin using FiO2 = 0.18 for 5 minutes, unless failure criteria is met: SpO2% < 80% even briefly, or SpO2% 80% to 85% for 15 seconds. If infant does not meet failure criteria, infant will be given FiO2 0.15 for 10 minutes. If an infant meets even a single criterion for failure, Hypoxic mixture will be stopped.

Infants will have nasal catheter in place (NeoTech Premature RAM Cannula). A 15-minute baseline recording of physiologic study parameters prior to initiation. Tested in three groups of infants.

1. 28 and 32 weeks PMA flow rates increased after a 15-minute baseline period to 3LPM, or by 1LPM to a max of 5LPM for 15 minutes. Infant on Bubble CPAP will be increased 1cm H2O to max 8 cm H2O for 15 minutes.
2. Infant's that fail the RAC or HCT at 36 weeks with periodic breathing, high flow at 3LPM will be started for 2 minutes or until periodic breathing stops. Infants on Bubble CPAP will not undergo the RAC or HCT. Their pressure is increased by 1cm H20 to max of 8 cm H2O for 15 minutes.
3. Infant on RA at 40 and 52 weeks PMA with periodic breathing lasting longer than 1 minute during the 15-minute baseline period, flow at 3LPM will be started for 2 minutes or until periodic breathing stops.

A non-sedating MRI scan will be performed on 3 subsets of infants at 37-40 weeks Post Menstrual Age (PMA), or when infant is within one week of discharge from the NICU. Standard images as well as research images will be obtained. The research images use the same MRI scanner and collection techniques as standard clinical imaging, but provide a more detailed examination of brain anatomy and injury. Collection of these sequences using our standard non-sedated acquisition practices for infants is well tolerated. Infants will be placed in scanner by registered nurse accompanied by radiology technician to assure infants' comfort during scan. Infant will remain on cardio-respiratory monitor during MRI via a pulse oximetry probe. It will take no longer than one hour to complete MRI scan including transportation to radiology unit.

An echocardiogram (referred to as an ultrasound of the heart on the consent form) will be performed to assess cardiac structure and function. Echocardiograms are performed routinely in premature newborns in the NICU. The Echocardiogram will be performed at the infant bedside and will be coordinated with bedside nurse. The infant will remain on a cardio-respiratory monitor during the echocardiogram for approximately 15 minutes.

Infants that have echocardiograms will have a blood sample collected near the time the echocardiogram is obtained, 3-blood samples total. The blood sample will only be collected with parental permission on an opt-in or out-basis and collected only with routine clinical labs.