DEFLATION-RELATED VARIABILITY OF BREATHING PATTERN PERSISTS WITH INTACT UPPER AIRWAY

In anesthetized, tracheotomized rats continuous negative airway pressu re (CNAP) augments breath-to-breath variability of the respiratory pat tern 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 su bjected 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 defla tion maneuvers than during inflations, whereas the coefficients of var iation of inspiratory and expiratory durations were not different. A v ariable degree of expiratory flow retardation often was observed durin g deflation. We conclude that breathing through the upper airway does not prevent the increase in variability of the respiratory pattern ass ociated with deflation.