Changes in upper airway muscle activity related to head position in awake cats.

The influence of head position on the respiratory activity of the diaphragm (DIA), posterior cricoarytenoid (PCA) and genioglossus (GG) muscles was studied in conscious cats with chronically implanted electromyographic electrodes. Tracheal pressure was also recorded through a small implanted catheter. Spontaneous or passive downward movements of the head resulted in sustained increases in the respiratory excursions of tracheal pressure and in PCA and GG activities. Conversely, these variables all decreased when the head was raised. Activity of the DIA was little affected. In animals with chronic tracheostomies, which greatly diminished tracheal pressure excursions and their changes with head movements, the postural responses of PCA and GG activities persisted, but were attenuated. The responses also persisted after bilateral superior laryngeal nerve section. These findings demonstrate responses that act to maintain the patency of the upper respiratory tract, probably by reflex mechanisms. Receptors in the upper airway contribute to the responses, but other afferents - possibly from vestibular or joint receptors - are also involved.