Non-Invasive Positive Pressure Ventilation (NIPPV) provides un-synchronized positive pressure and considered to be superior to nCPAP in preventing extubation failure. Recently, Non-Invasive Ventilation Neurally-Adjusted Ventilatory Assist (NIV-NAVA) was introduced to NICU. NAVA is a ventilation mode that uses the electrical activity of the patient's diaphragm (Edi-signal) to guide both timing and magnitude of the support. However, it is unknown whether NIV-NAVA is superior to NIPPV in preventing extubation failure and preventing BPD.

Hence, the investigators aim to compare the effect of NIPPV and NIV-NAVA on diaphragm function in premature infants with RDS or evolving BPD. Our hypothesis is that infants treated with NIV-NAVA will have improved diaphragmatic function and lung scoring.

STUDY POPULATION Premature infants with respiratory distress syndrome who are admitted to Mount Sinai NICU and are supported with NIPPV or NIV-NAVA.

Inclusion criteria

1. Infants that were born at 22 0/7 to 29 6/7 weeks gestation and admitted to the NICU at Mount Sinai Health System.
2. Infants that are on NIPPV or NIV-NAVA respiratory support for at least 24 hours at the time of enrolment.

Exclusion criteria

1. Infants with congenital anomalies.
2. Infants with known genetic disorder.
3. Infants with known lung malformation or diaphragm dysfunction.
4. Infants of whom parents declined consent.

Study Design and settings:

This is a prospective cohort study that includes premature infants born at 22 0/7 to 29 6/7 weeks GA in Mount Sinai Hospital and admitted to the NICU. Written consent will be obtained from parents or guardians prior to enrolment in the study. Enrolment of eligible infants will start after obtaining approval from Mount Sinai Research Ethics Board and parent's consent. Recruitment will be done over one year, and the investigators are expecting to recruit about 30 infants in the NIPPV group and similar number in the NIV-NAVA group.

Time of assessment; Eligible infants will be identified by a member of the infant's circle of care. Parents of infants who are eligible for the study will be approached for consent. Chest ultrasound (lung ultrasound and diaphragmatic function assessment) will be performed at > 7 days postnatally, provided that the infant is supported by either NIPPV or NIV-NAVA for at least 24 hours. CUS will be done prior to feeding to avoid any concerns of a full stomach on diaphragmatic assessment.

Study procedure: Functional assessment of the diaphragm combined with lung ultrasound examination will be done by one of the investigators.

Lung ultrasound assessment technique; Lung ultrasounds will be performed in a standardized manner. A longitudinal scan of the anterior and lateral chest walls will be performed. Three chest areas for each side (upper anterior, lower anterior, and lateral) will be assessed. Each area will have a score of 0 to 3 points with a total score between 0 to 18, which inversely correlates with lung aeration.

Diaphragmatic assessment technique; Diaphragm assessment will be performed in the supine position. To measure diaphragmatic excursion, the curvilinear probe will be placed on the lower intercostal spaces between the mid-clavicular and anterior axillary lines on the right side and between the anterior and mid-axillary lines for the left side. Using the B mode, the proper exploration line of the diaphragm will be detected by directing the beam perpendicular to the posterior third of the right hemidiaphragm. By M mode, the cyclic caudal diaphragmatic displacement with respiration will be measured as the perpendicular distance between the most caudal point of the liver or spleen at the end of expiration and the end of inspiration. The average of three respiratory cycles will be taken.

The assessment of the diaphragmatic efficiency as a pressure generator will be evaluated using the diaphragmatic thickness fraction. Diaphragmatic thickness will be measured at the apposition zone which can be obtained by placing the linear transducer above the 10th rib in the mid-axillary or anterior axillary lines in the right intercostal spaces. By B mode, three distinct layers will be seen, the diaphragm as a hypo-echoic area bordered by two clear echogenic lines of the pleural membrane (upper line) and the peritoneal membrane (lower line). Using M-mode tracing, inspiratory diaphragmatic thickness will be measured as the maximum perpendicular distance between pleural and peritoneal layers and by the same way expiratory diaphragmatic thickness will be recorded. diaphragmatic thickness fraction will be calculated using the following formula:

diaphragmatic thickness fraction = [(inspiratory thickness - expiratory thickness)/expiratory thickness] x 100.

The average of the calculated diaphragmatic thickness fraction from three respiratory cycles will be estimated. The higher scores the better the diaphragmatic function. All Chest ultrasound assessments will be undertaken using a standard aseptic technique.

Inclusion criteria

1. Infants that were born at 22 0/7 to 29 6/7 weeks gestation and admitted to the NICU at Mount Sinai Health System.
2. Infants that are on NIPPV or NIV-NAVA respiratory support for at least 24 hours at the time of enrolment.

Exclusion Criteria:

1. Infants with congenital anomalies.
2. Infants with known genetic disorder.
3. Infants with known lung malformation or diaphragm dysfunction.
4. Infants of whom parents declined consent.

Infants that were born between 22 0/7 to 29 6/7 weeks gestation and were admitted to the NICU at Mount Sinai Health System will be eligible for the study. Infants will be enrolled after obtaining parents' consent and Research Ethics Board approval