Studies of the pulmonary vagal control of central respiratory rhythm in the absence of breathing movements

1. Breuer's hypothesis that the vagus nerves exert a tonic control of respiratory rhythm, in addition to the phasic control, was examined. 2. Closed-chest cardiopulmonary bypass was instituted in dogs weighing 20-30 kg anaesthetized with chloralose. Respiratory rhythm was recorded from a phrenic electroneurogram. 3. Complete muscular paralysis induced with gallamine triethiodide produced an increase in the duration of inspiration and an increase in the amplitude of the integrated phrenic electroneurogram. There was no consistent effect on expiratory duration. Gallamine produced no effect when given after vagotomy. 4. In the paralysed state, an increase in lung volume of 25-100 ml. for 30-60 sec produced a sustained increase in the duration of expiration and a decrease of respiratory rate: there was little effect on inspiratory duration, or the amplitude of the integrated phrenic electroneurogram. 5. A decrease in lung volume of the same order of magnitude for the same period produced a sustained decrease in the duration of expiration and an increase of respiratory rate: there was little effect on inspiratory duration or the amplitude of the integrated phrenic electroneurogram. 6. The phenomena described in (5) and (6) constitute a high gain respiratory frequency controller. They did not occur after bilateral cervical vagotomy. 7. Bilateral cervical vagotomy during complete muscular paralysis produced a further increase in the duration of inspiration and in the amplitude of the integrated phrenic electroneurogram; there was no consistent effect on expiratory duration. 8. The results confirmed Breuer's hypothesis and showed that inspiratory duration and expiratory duration are controlled independently.