[Effect of trigeminal nerve block on respiration in vagotomized cats]

Afferent influence of the trigeminal nerves moderately inhibits activity of the respiratory center in quiet breathing both before and after bilateral vagotomy. Blockade of the trigeminal nerves entails an increase by 20-30% of lung ventilation (VI) due to cessation of the tonic influence and of the impulses induced by stimulation of the nose cavity receptors with air stream. Impulses from the trigeminal nerves increase the duration of respiratory phases by means of their direct effect upon the respiratory center as well as interacting with impulsation from the lung receptors. Stimulation of the nose cavity with air stream decreases the intensity of the inspiratory excitation which leads to deceleration of breathing frequency when the lung afferents are preserved. After vagotomy, the inhibitory effect of tonic trigeminal afferents is augmented and its influence upon the expiratory duration is weakened. At prolonged nose breathing, VI increases in comparison with the breathing through the trachea because of an enlarged dead space and adaptation.