Vagal influences on respiratory mechanics, pressures, and control in rats

In eight spontaneously breathing anesthetized rats airflow, volume, and tracheal pressure were measured. The passive and active mechanical properties of the respiratory system, the shape of the tracheal occlusion pressure wave (Potr), the decay of inspiratory muscle pressure during expiration, and parameters related to the control of breathing were computed both before and after bilateral cervical vagotomy. Pre- and post-vagotomy values of passive elastance, resistance, and time constant were similar. Active mechanics disclosed an increase of elastance and a decrease in resistance and in the time constant after vagotomy. The time course of Potr showed a downward concavity and was not modified by vagotomy in the range of control inspiratory times, whereas the shape of inspiratory muscle pressure decay during expiration was changed. The present data help to explain why after vagotomy the load-compensatory mechanisms are less effective.