With this study, it is expected to learn more about preterm babies on breathing support with nasal continuous positive airway pressure (nCPAP). To gain more information on how much oxygen is actually delivered to the baby from the nCPAP machine.

This study will tell more about a specific method of breathing support used frequently with preterm babies called nasal continuous positive airway pressure (nCPAP). It helps the baby breathe by providing air pressure and a certain amount of oxygen. It is very important for the baby's health to provide only as much oxygen as they need.

With this study, it is expected to learn if the amount of oxygen ordered by a doctor on the nCPAP machine changes when it reaches the baby's airway, and if the amount of oxygen changes depending on how much air pressure the doctor provides. The answers to these questions, are not known, because special measurements are required that are difficult to know while a baby is on nCPAP. This study will collect these special measurements

Inclusion Criteria:

• Gestational age at birth must be less than 35 weeks of completed gestation as documented in the subject's initial history and physical
• The infant must be stable while receiving nasal CPAP at any pressure level at the time of study
• The infant must be receiving 22-40% at the time of the study

Exclusion Criteria:

• Oxygen requirements greater than 40% at time of enrollment
• currently receiving invasive ventilation or not requiring ventilatory support
• Major congenital anomalies of the heart and/or lungs

Coded IPD will be shared with a collaborator once data collection is complete for the purpose of statistical analysis. All shared IPD will be de-identified and individual patients will be given an identifying code. Shared information will include gestational age, date of birth, postnatal age, race/ethnicity, vital signs, prior medical history, current respiratory support, complications during pregnancy, medical problems and diagnoses that the infant receives during hospitalization, and the inspired oxygen and lung volume values gathered during the study itself.

Beginning once data collection is complete and for three months afterward to afford time for statistical analysis.

Only primary investigators will be able to access de-coded IPD. One single collaborator will have access to coded IPD for the purpose of statistical analysis.