Continuous positive airway pressure (CPAP) is used in premature infants to maintain lungs open and facilitate gas exchange. When ventilation/perfusion (V/Q) mismatch is present, areas of the lung that are open for gas exchange do not match up with the areas of the lung that are receiving blood for gas exchange. This study measure the responsiveness of V/Q mismatch to changes in the amount (or level) of CPAP.

Inclusion Criteria:

1. Born at 27-35 weeks gestational age (GA) by best obstetric estimate, determined by the clinical obstetric team during antepartum admission.
2. Age limits: 24 hours of age - 35 weeks corrected gestational age.
3. On continuous CPAP support between 4-8 cm H2O for greater than 24 hours, as document on the bedside infant flow sheet.
4. Supplemental oxygen requirement, with a fraction of inspired oxygen (FiO2) 0.25 for at least 2 consecutive hours, as documented on the bedside infant flow sheet.

Exclusion Criteria:

1. Congenital anomalies, as determined by the clinical supervising physician.
2. Current or prior air leak syndrome, as determined by the clinical supervising physician.

48 hours after intervention

Adverse event monitoring limited to air leak syndromes (pneumothorax, pulmonary interstitial emphysema, pneumomediastinum; as determined by the clinical supervising physician during routine clinical care) and respiratory deterioration, defined as an increase in baseline FiO2 greater than 0.10 in the 48 hour following the study intervention,