Ventilatory failure during resistive loaded breathing in the newborn primate

Previous investigations have shown that ventilatory failure during severe inspiratory resistive loading (IRL) in the 21-day-old infant primate occurs secondary to a decrease in respiratory frequency, that is, central failure. To examine the response of the more immature newborn to IRL, minute ventilation (V'E), arterial blood gases and pH, minute diaphragmatic electromyogram (EMG) activity, peak inspiratory airway pressure, and the centroid frequency (Fc) of the diaphragmatic EMG power spectrum were measured in four unanesthetized tracheotomized 2-day-old monkeys during various levels of IRL, until either 1) ventilatory failure occurred (ventilatory failure run) or 2) normocapnia was sustained for 1 hr (successful trial). During successful trials, minute ventilation, breathing frequency, tidal volume, Fc, and PaCO2 were sustained at baseline levels and an increase in minute EMG activity and peak inspiratory airway pressure were observed. In contrast, during ventilatory failure runs, minute ventilation and tidal volume fell and PaCO2 rose compared to their respective baseline values. Respiratory frequency did not change. The decline in tidal volume occurred despite significant increases in minute diaphragmatic EMG activity and peak inspiratory airway pressure. No shifts in Fc were noted, suggesting that peripheral diaphragmatic fatigue did not occur. We conclude that ventilatory failure during IRL in the 2-day-old monkey is due to the animal's inability to defend tidal volume as opposed to central failure.