The human upper airway has many important physiological functions including speech, swallowing and breathing. The human tongue forms an important part of the upper airway. It is made up of different muscles with origins both within and external to the tongue. Among these, the genioglossus (GG) is the largest dilator of the upper airway and it has been shown with ‘tagged’ MRI imaging to both depress and protrude the tongue during quiet breathing (Cheng et al 2008). Further understanding of the GG’s role in both healthy people and those with upper airway disorders can be aided by real-time imaging of the tongue’s motion.
Ultrasound does not emit radiation, is non-invasive, gives good resolution of soft tissue structures, and can display cross-sectional anatomy and tissue motion in real time. It also has been used to demonstrate dynamic upper airway motion during swallowing and speech (Shawker et al 1983; Shawker et al 1984). Given these previous studies, we hypothesised that during quiet breathing in an awake subject lying supine, ultrasonography can be used to quantify GG movement with the largest motion in an anterior direction during inspiration. We further hypothesised that the maximal displacement can be seen in the inferoposterior part of the GG and that this technique can be reproduced across different imaging sessions.
WHAT DID WE FIND?
Under ultrasound, the GG was visualized as a large fan-like muscle originating from the mandible and extending upward into the tongue body. As it contracted over the respiratory cycle, it moved the tongue forward and downward. This motion was shown to begin before inspiratory airflow, with the largest displacement observed in the infero-posterior part of the GG.
Schematic representation of subject positioning, ultrasound image, and grid used to Dr. Kwan and colleagues to measure dynamic motion of the genioglosus, the portion of the tongue muscle that attached to the mandible.
SIGNIFICANCE AND IMPLICATIONS:
This study demonstrates a novel use of ultrasound to quantify the GG movement in awake humans during quiet breathing. It is a simple, reproducible, safe technique that does not emit radiation. The observed movement is consistent with that observed during quiet breathing with tagged MRI. Given there is evidence from MRI that respiratory motion of GG is markedly impaired in disorders such as obstructive sleep apnea (Bilston & Gandevia 2014), this method, combined with physiological measures, should be broadly applicable to patients with upper airway and sleep disorders to quantify GG motion, providing a new imaging technique for anatomical ‘phenotyping’ in such patients.
PUBLICATION:
Kwan BCH, Butler JE, Hudson AL, McKenzie DK, Bilston LE, Gandevia SC (2014). A novel ultrasound technique to measure genioglossus movement in vivo. J Appl Physiol 117, 556-562.
KEY REFERENCES:
Bilston LE, Gandevia SC (2014). Biomechanical properties of the human upper airway and their effect on its behavior during breathing and in obstructive sleep apnea. J Appl Physiol 116, 314-324.
Cheng S, Butler JE, Gandevia SC, Bilston LE (2008). Movement of the tongue during normal breathing in awake healthy humans. J Physiol 586, 4283-4294.
Shawker TH, Sonies BC (1984). Tongue movement during speech: a real-time ultrasound evaluation. J Clin Ultrasound 12, 125-133.
Shawker TH, Sonies BC, Stone M (1984). Soft tissue anatomy of the tongue and floor of the mouth: an ultrasound demonstration. Brain Lang 21, 335-350.