Premature babies often require breathing support during their neonatal intensive care unit stay. This is because their lungs are not fully developed to perform the work of breathing on their own. Although breathing support can be provided via a breathing tube, it is preferable to provide breathing support non-invasively from a breathing machine which is then connected to a mask or prongs placed on the baby's nose. In premature babies born under 32 weeks gestation, a commonly used mode of non-invasive breathing support is called Non-Invasive Positive Pressure Ventilation (NIPPV). In this mode, the breathing machine provides 2 levels of support: one is the constant distending pressure to keep the lungs open and the other provides additional 'breaths' on top of that distending pressure. This is to mimic regular breathing. These breaths are set at a fixed rate and pressure. Although NIPPV protects the lungs from injury caused by a breathing tube, the breaths are not in sync with the baby's own breathing effort. Another mode of non-invasive breathing support recently being used in premature infants called Neurally Adjusted Ventilatory Assist (NAVA). When NAVA is provided non-invasively using a mask or prongs similar to NIPPV, it is called Non-invasive NAVA (NIV-NAVA). During NIV-NAVA a special feeding tube is used that detects the baby's own breathing movement from the electrical signal of the baby's diaphragm and feeds back to the machine which then provides a 'top-up' to the baby's own breath. This top-up breath also provides only as much pressure as the baby needs on top on their own breathing effort. Therefore, this is thought to be in sync with the baby's own breathing effort. However, it is not known if this mode of ventilation leads to improved sleep, improved brain oxygen levels, reduced discomfort and improved functioning of the diaphragm. The investigators aim to examine these indices in this research project.

Rationale: It is imperative to find the optimal method of supporting not only lung development, but also brain development during this critical period of brain growth and development. NIV-NAVA is a more physiologically compatible method of supporting respiration. The investigators hypothesize that this compatibility may increase comfort and restful periods compared to standard NIPPV, and thus, may be more neuroprotective.

Objective and outcomes assessed: The objective is to compare sleep-wake cycling, cerebral oxygenation, heart rate variability and diaphragm function during standard NIPPV and NIV-NAVA modes in preterm neonates born at <32 weeks' gestation who are stable on NIPPV or NIV-NAVA for at least 24 hours and are a minimum of 3 days old.

Inclusion Criteria:

• Preterm infants born between 22+0 and 31+6 weeks' GA
• Weight > 500 g at the time of approach for consent
• A minimum of 3 days of age
• Clinically stable for > 24 hours while receiving NIPPV or NIV-NAVA

Clinical stability will be defined as meeting all the following criteria for a 24 hour period prior to recruitment:

1. differences in maximum and minimum fractions of inspired oxygen (FiO2) of <20%
2. differences in maximum and minimum MAP <4 cm H2O
3. no active infection
4. no hypotension
5. no use of cardioactive medications or medical therapy for patent ductus arteriosus.

Exclusion Criteria:

• Infants with IVH of grade 3 or 4
• Birth weight < 3rd percentile
• Genetic or congenital abnormalities

Preterm infants at tertiary NICU at Mount Sinai Hospital (Toronto, Ontario).