At the beginning of the study, RIP bands will be placed around the infant's chest and abdomen. An Edi catheter will be placed and the current gastric catheter may or may not be removed. Infants will be ventilated with the Servo i ventilator equipped with NIV NAVA software {Maquet, Solna, Sweden}. Data will be continuously and simultaneously acquired using the MP100 Biopac data acquisition system. Data acquired will be as follows: heart rate, oxygen saturation, transcutaneous CO2 and O2, PIP, PEEP, rib cage and abdominal RIP signals, summed tidal volume, and Edi. Infants will receive 15 minute trials of NIV NAVA and NIPPV in random order with the first 10 minutes after changing to be considered a washout period and the last 5 minutes used for data collection. The data recorded from the two RIP bands will be used to calculate the phase angle (θ) as an estimate of WOB.