This was a single center prospective study. Inclusion criteria: Any preterm with respiratory distress requiring CPAP but not mechanical ventilation or NIPPV was eligible for the study. 12 preterm infant more than 48 hours old and stable on bubble CPAP were recruited for the study Exclusion criteria: Infants with major congenital anomalies, neuromuscular disorders, upper airway anomalies, critically sick infants