Increased duration of postinspiratory inspiratory activity during augmented breaths in cats.

The duration of diaphragm electrical activity in augmented breaths during early expiration (postinspiratory inspiratory activity, PIIA) was assessed in 12 pentobarbital-anesthetized cats. There were significant prolongations of expiratory time (P less than 0.001) and PIIA (P less than 0.001) during augmented breaths compared to cupneic breaths, but no alteration in the portion of expiratory time during which the diaphragm was electrically silent. Furthermore, significant linear correlations were found between control and augmented breaths for the duration of PIIA (r = 0.95) and for the ratio of PIIA to expiratory time (r = 0.88). These results suggest that during augmented breaths there is not only an increased motor output to the diaphragm during inspiration, but that the early expiratory activity of the diaphragm is greater as well.