Factors influencing the intensity of the breuer-hering inspiration-inhibiting reflex

The Breuer-Hering inspiration-inhibiting reflex (B-H reflex), that is the apnea due to inhibition of the respiratory centers following stimulation of some lung mechanoreceptors, was studied in three anesthetized and six awake trained dogs, by obstructing the airway at different lung volumes during spontaneous breathing or after a small inflation above the spontaneous end-inspiratory position. The B-H reflex is present in awake, intact dogs, and absent in awake, lung-vagotomized dogs. Factors which influence the duration of the B-H reflex apnea include 1) lung volume: the greater the lung volume, the longer the apnea; 2) intensity of the humoral respiratory drive: apnea is shorter in hypoxic or hypercapnic dogs than in normoxic, normocapnic dogs, and is longer in animals whose chemoreflex drive has been diminished by sinocarotid deafferentation; 3) depth of anesthesia: the duration of the reflex apnea increased the more heavily anesthetized the animal. Actual lung volume at the time of airway block, intensity of the humoral respiratory drive and depth of anesthesia must be taken into account when the strength of the inspiration-inhibiting B-H reflex is assessed.