A comprehensive assessment of genioglossus electromyographic activity in healthy adults

Abstract

Vranish JR, Bailey EF. A comprehensive assessment of genioglossus electromyographic activity in healthy adults. J Neurophysiol 113: 2692-2699, 2015. First published February 18, 2015 doi:10.1152/jn.00975.2014 is an extrinsic muscle of the human tongue that plays a critical role in preserving airway patency. In the last quarter century, Ͼ50 studies have reported on respiratory-related GG electromyographic (EMG) activity in human subjects. Remarkably, of the studies performed, none have duplicated subject body position, electrode recording locations, and/or breathing task(s), making interpretation and integration of the results across studies extremely challenging. In addition, more recent research assessing lingual anatomy and muscle contractile properties has identified regional differences in muscle fiber type and myosin heavy chain expression, giving rise to the possibility that the anterior and posterior regions of the muscle fulfill distinct functions. Here, we assessed EMG activity in anterior and posterior regions of the GG, across upright and supine, in rest breathing and in volitionally modulated breathing tasks. We tested the hypotheses that GG EMG is greater in the posterior region and in supine, except when breathing is subject to volitional modulation. Our results show differences in the magnitude of EMG (%regional maximum) between anterior and posterior muscle regions (7.95 Ϯ 0.57 vs. 11.10 Ϯ 0.99, respectively; P Ͻ 0.001), and between upright and supine (8.63 Ϯ 0.73 vs. 10.42 Ϯ 0.90, respectively; P ϭ 0.008). Although the nature of a task affects the magnitude of EMG (P Ͻ 0.001), the effect is similar for anterior and posterior muscle regions and across upright and supine (P Ͼ 0.2). electromyography; respiration; electrode THE GENIOGLOSSUS (GG) muscle of the human tongue is involved in functions critical to survival, including swallowing, speech, and breathing. In view of the muscle's role as an airway dilator, the preponderance of research has focused on electromyographic (EMG) activity during sleep and wakefulness when subjects are in the supine or side-lying position (Eastwood et al.

Phonation-related rate coding and recruitment in the genioglossus muscle

“…We show here that the magnitude of GG EMG in the loudness ramp approximated that for FDI during finger abduction (Figure 1). Second, the magnitude of whole muscle EMG attained in the maximum loudness task is comparable to the magnitude of EMG attained in the maximum force task (range 0.6-1.0mV), and falls within the range of forces reported for GG during tongue protrusion (range 0.5-1.5mV) (Vranish and Bailey 2015). On this basis, the ramp loudness task appears to offer a suitable framework within which to assess tongue muscle activation and against which to compare muscle and motor unit activities in FDI.…”

Neural Control of the Upper Airway: Respiratory and State‐Dependent Mechanisms

“…This has been recently confirmed in healthy humans (576), but was not observed in rats (315). The magnitude of the total, or only the respiratory-modulated component, of lingual muscle activity in awake healthy humans, rats, and cats depends on the head position, being increased with ventral flexion or when the animal assumes a curled position (52, 341, 370, 475).…”

“…In studies in humans, it is common to scale the integrated EMG activity recorded during sleep and wakefulness relative to the amount of activity generated by the same subject during maximal voluntary activation (e.g., 345). This approach reveals that the total magnitude of combined tonic and respiratory-phasic baseline activity in upper airway muscles recorded during quiet wakefulness from healthy human subjects is very low (e.g., 67,246,278,280,455,541,576,601). In different studies and subjects, it ranged between 1% and 11% of the peak voluntarily generated activity (e.g., 247,346,510,541,576).…”

“…In different muscles the tonic and phasic components are expressed to variable degrees and with a pattern characteristic of that muscle. For example, during eupneic breathing in wakefulness, tensor veli palatini, and digastricus show only low level tonic, or no, activity but respiratory modulation appears in response to hypercapnia or airway occlusion (346, 374, 541, 576). In healthy humans, the combined phasic inspiratory and tonic components represent less than 2% of maximal spontaneous GG activity (247).…”

“…This positional influence is only partially dependent on reflex stimulation of upper airway muscle tone by upper airway mechanoreceptors sensitive to negative upper airway pressure (52). In healthy humans, GG activity is higher in the supine than in the upright position which is, at least in part, due to gravitational effects on the tongue (112, 475, 576). …”