Neurally adjusted ventilatory assist (NAVA) has been shown to improve patient- ventilator interaction and reduce asynchronies. This is a short-term physiologic comparison between PSV (pressure support ventilation) and NAVA in delivering noninvasive ventilation through a nasal cannula, in premature infants postextubation. Patients will undergo a 30-min crossover trial of noninvasive PSV and NAVA, 15 minutes each. Diaphragm electrical activity (EAdi)and airway pressure (Paw) are recorded to derive neural and mechanical respiratory rate and timing, inspiratory trigger delays time of synchrony between diaphragm contraction and ventilator assistance, and the asynchrony index (AI).