Deflation-related variability of breathing pattern persists with intact upper airway

In anesthetized, tracheotomized rats continuous negative airway pressure (CNAP) augments breath-to-breath variability of the respiratory pattern compared to that during continuous positive airway pressure (CPAP). To test the hypothesis that loss of airflow regulation by the upper airway was responsible for this increased variability during CNAP we measured respiratory pattern regularity in rats with intact airways subjected to steady inflating and deflating transrespiratory pressures. The coefficients of variation of tidal volume, peak inspiratory flow, and rate of change of flow at end-inspiration were larger during deflation maneuvers than during inflations, whereas the coefficients of variation of inspiratory and expiratory durations were not different. A variable degree of expiratory flow retardation often was observed during deflation. We conclude that breathing through the upper airway does not prevent the increase in variability of the respiratory pattern associated with deflation.