In Aim 1 of the study, enrolled infants will be randomly assigned to a sequence of either: oxygen hood, followed by 1 L/min NC, ½ L/min NC, ¼ L/min NC, 1/8 L/min NC, and then oxygen hood, OR oxygen hood followed by 1/8 L/min NC, ¼ L/min NC, ½ L/min NC, 1L/min NC, and then oxygen hood. Infants will remain on each flow for a minimum of 30 minutes with 5 minute interval readings of transcutaneous PCO2 , heart rate, and respiratory rate. The "optimal" nasal cannula flow rate will be defined as the lowest flow rate that consistently maintains a SaO2 >85% with FiO2≤ 0.5 without increasing transcutaneous PCO2 more than 5 mm Hg above the oxygen hood PCO2.