Influences of lung mechanoreceptors and carotid chemoreceptors on the response of respiratory muscle activity to tracheal occlusion.

We examined the responses of respiratory muscle electromyograms (EMGs) from internal (IIC) and external intercostal (EIC) muscles and diaphragm (DIAP) to three successive occluded breaths in anesthetized spontaneously breathing rabbits. Both inspiratory and expiratory muscle EMGs progressively increased in the course of tracheal occlusion. An increase in these muscle EMGs was still observed after release of tracheal occlusion, but those effects were short-lasting. In a separate series of experiments, for assessment of possible reflex effects involved, the responses of slowly adapting pulmonary stretch receptor (SAR), rapidly adapting pulmonary stretch receptor (RAR), and carotid chemoreceptor activities to tracheal occlusion lasting for three respiratory efforts were also examined. The inspiratory discharge of SARs decreased but the expiratory discharge of SARs increased during tracheal occlusion. Although carotid chemoreceptors increased their activity in the latency of 3-6s after the onset of tracheal occlusion, the activity of RARs was greatly reduced throughout the period of tracheal occlusion. A transient increase in both carotid chemoreceptors and RARs was still observed after release of tracheal occlusion. These results suggest that alterations of inspiratory and expiratory muscle EMGs produced by tracheal occlusion would appear to be mediated by the afferent inputs from lung mechanoreceptors and carotid chemoreceptors.