Reflex partitioning of inputs from stretch receptors of bronchi and thoracic trachea

Abstract A selective block of slowly adapting stretch receptors in anesthetized rabbits was induced by exposing to SO 2 all thoracic airways (T) or the carina and bronchi alone (B). Increment of inspiratory time (T I ) relative to control was 61% greater under B than T. The reverse would have happened if input responsible for Breuer-Hering inflation reflex originated from both bronchi and trachea. Hence, bronchial input activates inspiratory off-switch, while tracheal input delays its activation. During single inspiratory efforts with airways closed at end expiration diaphragm activity (Adi) decreased and T IO increased relative to control equally under B and T. Hence, the input facilitating central inspiratory activity at end expiratory volume does not stem from trachea. At end of inspiratory ramp Adi stopped within 43 msec at control and 57 msec under B and T. Hence, bronchial input speeds up off-switching of inspiration. Postinspiratory Adi was greater under B than T, and nearly nil at control. Hence, bronchial input inhibits postinspiratory Adi, while tracheal input facilitates it. Inspiratory and expiratory flows were more damped under B than T, and under T than at control.