Vagal Respiratory Responses During Chemically Induced Apnea

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Abstract
Respiratory responses to afferent vagal stimulation were examined under conditions of varying anesthesia and in the presence of interneuron depressants. Deepening anesthesia and therapeutic doses of central depressants altered the inspiratory effects of low frequency vagal stimulation to more expiratory responses, and increased the expiratory and apneic effects of higher frequency vagal excitation. Interneuron depressants in high dosage reversibly stopped spontaneous respiration. During apnea so produced rhythmic respiration was evoked by low frequency vagal excitation, high frequency vagal excitation evoked a rebound inspiration under these circumstances. In apneustic animals low doses of depressants either accelerated the rhythm or produced apnea. During this apnea medium frequency vagal stimulation lead to rhythmic respiration, and to apneusis as the depressant metabolized. It is suggested that the vagus acts on respiration not only by influencing the respiratory center at the olivary level, but also through a more rostral system.