Effect of co‐activation of tongue protrudor and retractor muscles on tongue movements and pharyngeal airflow mechanics in the rat

Abstract

Electromyographic recordings in animal models indicate that tongue protrudor (genioglossus, GG) and retractor muscles (styloglossus, SG; hyoglossus, HG) are co-activated during inspiration (Yasui et al. 1993, Fregosi & Fuller, 1997. Moreover, recent experiments indicate that respiratory-related co-activation of protrudor and retractor muscles results in retraction of the tongue (Fregosi & Fuller, 1997;Fuller et al. 1998). The observation that tongue muscle co-activation causes retraction of the tongue implies that respiratory-related tongue-motor activity narrows, rather than dilates, the oropharynx. However, two groups of investigators have shown that co-activation of the protrudor and retractor muscles evoked by XIIth nerve stimulation results in increased inspiratory flow rates in obstructive sleep apnoea (OSA) patients, in spite of clear tongue retraction (Eisele et al. 1997;De Backer et al. 1998). Protrusion of the tongue, evoked by either medial XIIth nerve branch stimulation (Eisele et al. 1997) or direct GG muscle stimulation (Schwartz et al. 1996) is also associated with increased inspiratory flow rates in human subjects. These observations suggest that either co-activation of tongue protrudor and retractor muscles, or independent protrudor muscle activation will improve pharyngeal flow mechanics. This is in spite of the fact that the tongue retracts 1. The purpose of these experiments was to examine the mechanisms by which either coactivation or independent activation of tongue protrudor and retractor muscles influence upper airway flow mechanics. We studied the influence of selective hypoglossal (XIIth) nerve stimulation on tongue movements and flow mechanics in anaesthetized rats that were prepared with an isolated upper airway. In this preparation, both nasal and oral flow pathways are available. 2. Inspiratory flow limitation was achieved by rapidly lowering hypopharyngeal pressure (Php) with a vacuum pump, and the maximal rate of flow (ýI,max) and the nasopharyngeal pressure associated with flow limitation (Pcrit) were measured. These experimental trials were repeated while nerve branches innervating tongue protrudor (genioglossus; medial XIIth nerve branch) and retractor (hyoglossus and styloglossus; lateral XIIth nerve branch) muscles were stimulated either simultaneously or independently at frequencies ranging from 20-100 Hz. Co-activating the protrudor and retractor muscles produced tongue retraction, whereas independently activating the genioglossus resulted in tongue protrusion. 3. Co-activation of tongue protrudor and retractor muscles increased ýI,max (peak increase 44%, P < 0·05), made Pcrit more negative (peak decrease of 44%, P < 0·05), and did not change upstream nasopharyngeal resistance (Rn). Independent protrudor muscle stimulation increased ýI,max (peak increase 61%, P < 0·05), did not change Pcrit, and decreased Rn (peak decrease of 41%, P < 0·05). Independent retractor muscle stimulation did not significantly alter flow mechanics. Changes in Pcrit and ýI,max at all stimulation fr...

Differential effects of targeted tongue exercise and treadmill running on aging tongue muscle structure and contractile properties

“…During exercise and hypercapnia, increased ventilation was associated with a progressive rise in GG EMG activity during both oral and nasal routes of breathing (21,73,88). Furthermore, activation of the GG muscle, either through hypoglossal stimulation or direct muscle stimulation, dilates the oropharynx to increase inspiratory flow rates and thus improves upper airway flow mechanics, specifically within the pharynx (16,19,23,70). Although we did not assess GG muscle activation or inspiratory flow rates during treadmill running, our results, because of alterations in muscle contractile and biochemical properties, suggest that the GG was activated and played a role to improve respiratory mechanics.…”

“…For swallowing actions, the tongue is active in bolus formation, transport, and propulsion (82). The genioglossus (GG) muscle, the primary tongue protrusor, is a major force generator during the swallow and is crucial to dilation and/or narrowing of the pharynx during breathing (19,21,23). More specifically, the GG is involved in opening the oropharynx and reducing resistance to breathing (57,70,77).…”

Adaptations of the cetacean hyolingual apparatus for aquatic feeding and thermoregulation

“…Likewise positional lingual movements, typically thought to involve mainly the protrusion-retrusion axis, likely involve simultaneous deformation of tongue shape in three dimensions, including synchronized lengthening and shortening of different regions (Hiiemae and Crompton, 1985;Fuller et al, 1999), contrary to the prevailing model of simple protrusion-retrusion. The muscular hydrostat model (Kier and Smith, 1985), in linking positional and shape changes (e.g., protrusion accompanying reduced cross-sectional area), provides a more realistic conceptual approach.…”

Acute Upper Airway Responses to Hypoglossal Nerve Stimulation during Sleep in Obstructive Sleep Apnea

“…Rather, peak flow was achieved at lower stimulation amplitudes in the non-flow-limited group, suggesting enhanced mechanical effects of lingual muscle contraction on the pharynx. This effect could reflect greater linkage between the tongue and other pharyngeal structures, because of differences in lingual muscle fiber orientation, lingual-palatine linkage, or pharyngeal site of collapse (14,28,29). Alternatively, lingual muscle recruitment patterns could differ among patients, as suggested by observed decreases in inspiratory airflow in one patient at stimulation amplitudes well above the peak flow threshold, which were also associated with tongue retraction during wakefulness and sedation.…”