MODIFICATION OF RESPIRATORY MOVEMENTS BY VAGAL STIMULATION

Abstract

Under urethane anesthesia, low frequency central vagal stimulation in dogs caused respiratory acceleration. High frequency stimulation continuously or during expiration slowed the breathing by prolonging the expiratory phase, unless the duration of the stimulus was limited so that only a small number of shocks was applied when respiratory acceleration occurred. Acceleration was also caused by high frequency afferent vagal stimulation during inspiration, i.e., by intermittent inspiratory inhibition analogous to the lung stretch reflexes. Under barbiturate anesthesia, respiratory acceleration with low frequencies of vagal stimulation usually failed to occur, and these stimuli usually inhibited the breathing. Vagal stimulation during the inspiratory phase alone did cause respiratory acceleration in most instances, even under barbitone. In explanation of the results, a theory was presented in which it was suggested that each afferent vagal impulse serves as a unitary contributor to the development of a central state affecting the respiratory center or its connections. Under urethane, a low frequency stimulus or a limited number of impulses at high frequency was considered to result only in a slight build-up of this central state. A rapid and sufficiently prolonged stimulus was considered to result in development of the central state to a greater degree. Comparisons were made with the actions of various drugs in weak and strong conens. It was suggested that when the central state was of slight extent or degree, its effect on the respiratory center was augmentor; when of greater extent or degree, its effect was inhibitor. With barbitone, the failure of respiratory acceleration to occur with low frequency stimuli was attributed to the effect of this drug in accentuating the development of an inhibitory level of the central state. The results of the expts. reported upon were interpreted to indicate that whether acceleration or inhibition resulted from different forms of vagal stimulation, the type of response was due to a central selective action to impulses conveyed in a single type of afferent path rather than to stimulation of specific augmentor and inhibitor types of fibers in the vagi.