The mammalian upper airway includes the larynx, pharynx, and nose. Respiratory-related contraction of the skeletal muscles situated in and around these regions influences upper airway diameter and compliance. The pharynx is the most collapsible upper airway segment, and its diameter and compliance depend in part on tongue position and stiffness. These parameters are controlled by the genioglossus (GG) muscle, which protrudes the tongue, and the hyoglossus (HG) and styloglossus (SG) muscles, which retract the tongue. Prior work has focused almost exclusively on the GG, leaving a gap in the literature regarding the respiratory control and function of the tongue retractors. Accordingly, our overall purpose was to test the hypothesis that the tongue protrudor and retractor muscles are co-activated during inspiration and that co-activation promotes airway patency. Experiments were conducted using supine, anesthetized, tracheotomized rats. Tongue movements were quantified as either protrusive or retractive by connecting the tip of the tongue to a force transducer. The protrudor and retractor muscles were co-activated during quiet breathing and their activities increased in parallel when breathing was stimulated with high CO2 or low O 2. Co-activation of protrudor and retractor muscles was always accompanied by tongue retraction. Neural drive to both GG and HG muscles was increased in parallel when lung volume feedback was removed by single breath tracheal occlusion. The functional significance of tongue muscle co-activation was examined using an isolated upper airway preparation. Co-activation increased airflow rates and stiffened the airway, whereas selective protrudor muscle activation increased airflow but did not alter airway stiffness. A standard fatigue protocol was used to examine the influence of hypoxia on the endurance performance of tongue protrudor and retractor muscles; the results indicate that hypoxia attenuates tongue muscle endurance, possibly via impaired neuromuscular transmission. It is concluded that, in the rat, (1) the tongue protrudor and retractor muscles are co-activated during inspiration, and respond in parallel to increases in respiratory drive; (2) tongue muscle co-activation results in tongue retraction and stiffening of the pharyngeal airway, and (3) the endurance of the tongue muscles is impaired during hypoxia.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/282801 |
| Date | January 1998 |
| Creators | Fuller, David Dwight, 1970- |
| Contributors | Fregosi, Ralph F. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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