Functional mechanism of expiratory pattern generator

Tidal expiratory activity and the time to its peak (TEa, i.e., time of active expiration) were measured from the integration curve of external oblique muscle activity in rabbits. The rabbits were spontaneously breathing under urethan-chloralose anesthesia in the prone position. CO2 rebreathing was performed, and the changes in the temporal profile of the integrated expiratory activity were studied. Hypercapnia increased the tidal expiratory activity before and after bilateral vagotomy. Before vagotomy, the rate of rise (tidal expiratory activity/TEa) increased significantly and TEa was shortened. On the other hand, after vagotomy, the rate of rise remained unchanged and TEa was prolonged. An expiratory off-switch model is postulated according to the quantitative relationship between the time and amplitude of the tidal expiratory activity. The expiratory activity pattern in vagotomized rabbits was similar to that in humans.