VAGAL INHIBITION OF INSPIRATION, AND ACCOMPANYING CHANGES OF RESPIRATORY RHYTHM

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Abstract
In dogs under barbital-Na, one vagus (both being sectioned) was stimulated centrally. The circuit described permits stimulation to recur at the same stage in successive inspirations, the frequency, shock voltage, and number of stimuli in each series being controllable. Summation of a minimum (threshold) number of vagal volleys cuts short inspiration promptly, while a lesser number does not reduce the amplitude at all. Graded reduction of amplitude may, however, be accomplished by varying the time at which stimulation begins. Increasing the respiratory dead space does not raise the inhibitory threshold. Adequate recurring stimulation, while reducing amplitude, accelerates the rhythm. The acceleration varies in degree according to the stage at which the inspirations are cut short. It is absent if the stimuli are too weak or too few to inhibit inspiration. Both effects are simultaneously lost when a cold block of the vagus is gradually induced.