Medullary post-inspiratory neuronal and diaphragm post-inspiratory activities during spontaneous augmented breaths in anesthetized rats

Abstract

To test the hypothesis that during augmented breaths the prolonged expiratory time is correlated with the activity of medullary post-inspiratory neurons, changes in diaphragm electromyogram and post-inspiratory neuronal activities were examined in pentobarbital anesthetized rats. During augmented breaths, the mean total expiratory time significantly increased (from 0.57 ± 0.02 to 1.20 ± 0.07 s, P < 0.01), but the mean duration of post-inspiratory inspiratory activity (PIIA) was significantly decreased (from 0.08 ± 0.01 to 0.02 ± 0.003 s, P < 0.01) compared to control breaths. The mean time which the diaphragm was electrically silent was observed to be significantly prolonged during augmented breaths (from 0.48 ± 0.02 to 1.19 ± 0.07 s, P < 0.01). During significant prolongations of expiratory time in augmented breaths, most of the recorded neurons ( 9 10 ) in the medulla showed sustained discharges. The mean duration of discharges was longer than that of PIIA (0.02 ± 0.003 vs.0.50 ± 0.10 s, P < 0.01). The mean firing frequency/breath significantly increased compared to control breaths (9.45 ± 1.69 vs 37.6 ± 7.13 imp/breath, P < 0.01). These results suggested that during augmented breaths, the prolonged expiratory period may not be mediated by persisting post-inspiratory neuronal activity in the medulla.