Effect of the larynx on ventilation and respiratory pattern in anesthetized rabbits.

The effects of the larynx on ventilation and pattern of breathing have been investigated in anesthetized, spontaneously breathing rabbits. Breathing was either via a tracheostomy or via a supralaryngeal tube in control condition, after laryngeal denervation and after subsequent bilateral midcervical vagotomy. Laryngeal resistance was measured in all experimental conditions when breathing was through the larynx. In control conditions the presence of the larynx in the breathing circuit, as compared to breathing through the tracheostomy, slightly but significantly lowered inspiratory and expiratory airflows, tidal volume, and minute ventilation and increased tracheal pressure. Inspiratory and expiratory durations were not significantly changed. Expiratory laryngeal resistance was higher than inspiratory. Laryngeal deafferentation did not significantly modify values of the respiratory variables. Subsequent motor denervation of the larynx enhanced the decrease in ventilatory parameters due to adding the larynx to the circuit and lengthened the respiratory cycle. Inspiratory laryngeal resistance increased sevenfold and expiratory resistance threefold. Subsequent midcervical vagotomy induced a further increase in inspiratory and expiratory durations and augmented tidal volume independent of the route of breathing, and also reduced laryngeal resistance previously increased by motor denervation. These results reveal the ventilatory effects of the larynx and show the importance of its patency in the pattern of breathing.