Load compensatory response of external intercostal muscles during assisted ventilation in rabbits.

Phrenic and external intercostal motor responses to inspiratory load were studied in anaesthetized rabbits and after bilateral vagotomy. Animals were ventilated with a phrenic nerve driven respirator set at different gains, i.e. volume to phrenic-signal ratio. Load was imposed by occluding the trachea at the end of expiration for the period of one breath. It was found that vagally mediated low threshold facilitation may be observed in rabbits on late-inspiratory external intercostal motor units. After vagotomy, external intercostal EMG response to load depended on the given of the servorespirator set during the period of assisted ventilation.