Continuous positive airway pressure (CPAP) is the gold standard treatment for obstructive sleep apnea (OSA). In OSA, the upper airway muscle tone reduces excessively during sleep, allowing structures supported by these muscles to collapse into and block airflow partially or fully. CPAP treatment involves blowing slightly pressurized air through a mask, which fits over the nose and/or mouth, to push against airway structures so they do not collapse into the airway during sleep. Unfortunately, many patients are not compliant with CPAP treatment because of discomfort from the pressure or mask and adverse effects (e.g., aerophagia [air in the stomach]).
To counteract noncompliance, other treatment methods have been developed to maintain an open airway and prevent apnea episodes during sleep such as surgery (e.g., uvulopalatopharyngoplasty [UPPP], tonsillectomy/adenectomy; mandibular advancement surgery) and oral appliances that pull the tongue forward. In recent years, another approach - strengthening the upper airway dilator muscles, in particular the genioglossus muscle - has been studied with encouraging results.
In 1966, Gastaut and colleagues1 were the first to propose that the cessation in airflow (i.e., OSA) occurs because the tongue moves backward into the airway during sleep. In a study conducted after this proposal, Remmers and colleagues2 recorded genioglossus muscle activity during the sleep of individuals with OSA. They found that the highest activity of the muscle occurred the instant a person resumed breathing at the end of an apnea event and declined steadily thereafter as a person took breaths after the apnea. They also demonstrated that site of closure in an apnea episode was the oropharynx. Based on these findings, Remmers concluded that loss of genioglossus muscle activity during sleep was directly linked to upper airway collapsibility in patients with OSA.
The genioglossus muscle is a fan-shaped muscle that emerges from behind the chin bone and inserts on the hyoid bone (i.e., a small horseshoe-shaped bone above the thyroid) and on the bottom portion of the tongue. It forms most of the tongue mass. When it is contracted, it causes the tongue to protrude, thereby widening the oropharynx in the anterior-posterior direction.
In 1989, Miki et al.3 conducted the first studies on a device that provided external electrical stimulation of the genioglossus muscle during sleep in patients with OSA. The device consisted of a stimulator that was placed on the skin below the submental area and patients were studied overnight with and without the device. The device applied electrical pulses when it detected an apnea episode lasting less than five seconds, and the pulses immediately stopped once breathing resumed or after 10 seconds. The apnea index, apnea time/total sleep time, longest apnea duration and the number of times per hour that oxygen saturation dropped below 85% decreased significantly on the stimulation night compared to the nonstimulation night. Based on these findings, Miki suggested that an apnea demand-type stimulator could be a noninvasive and effective treatment for OSA.
Carrera et al.4 were the first scientists to report alterations in the proportions of fast-twitch and slow-twitch fibers in the genioglossal muscles of people with OSA. Fast-twitch muscle fibers quickly contract and generate short bursts of strength but fatigue easily (i.e., loss of power when contracting). Slow-twitch fibers have a slower speed of contraction, can maintain contractions for longer and can resist fatigue. The biopsy findings of genioglossus muscles from people with and without OSA revealed the percentage of fast-twitch fibers was significantly higher in people with OSA than in people without OSA. Carrera also found that genioglossus muscle fatigability was greater in patients with OSA than in patients without OSA. After a year of CPAP treatment, the patients with OSA underwent a second biopsy, which revealed that the percentage of fast-twitch to slow-twitch fibers was more like that of people without OSA.
Pae and colleagues5 similarly demonstrated that short-term external electrical stimulation of the genioglossus muscle resulted in an approximately 13% increase in slow-twitch fibers and a proportional decrease in fast-twitch fibers. Based on this finding, they suggested that exogenous electrical stimulation could be a potential therapy for OSA.
A New Daytime Treatment
An outgrowth of research into external electrical stimulation of the genioglossus muscle to treat OSA is the development of the eXciteOSA device (called "SnooZeal" outside of the United States). The eXciteOSA device consists of a somewhat Y-shaped mouthpiece that has four electrodes: one electrode sits on each side of the top of the tongue and one electrode sits on each side below the tongue, together providing electrical stimulation to the genioglossus muscle.
The components of the eXciteOSA system are the mouthpiece, a USB cable and a control unit. (The mouthpiece and control unit are connected by the USB port.) The mouthpiece is placed inside the mouth to apply the electrical stimulation and the control unit connects to a smartphone app via Bluetooth connection. Stimulation is delivered at predetermined stimulation and rest periods and migrates between three low frequencies (ranging from 0 to 20 Hz). The patient controls the intensity of therapy (to a maximum of 15 mV) to a level that does not cause discomfort. The smartphone app is used to start and stop the device, which is set to 20 minutes. After use, the control unit is disconnected from the mouthpiece, cleaned, and stored or charged (if necessary), using the USB charging cable. The stimulation is applied in 20-minute sessions once daily while a person is awake for six weeks, followed by once weekly thereafter. The eXciteOSA device (Signifer Medical Technologies, LLC, Needham, MA) was approved for clinical use in February 2021 by the US Food and Drug Administration (FDA)6 and is currently a prescription-only treatment for adults 18 years of age or older.
Recent eXciteOSA Studies and Research
Wessoleck and colleagues7 were the first scientists to examine the effects of using the eXciteOSA device on nocturnal snoring. After having participants use the device twice daily for 20 minutes for six weeks, the researchers found that the mean snoring score was reduced by approximately 43% and that the reduction in snoring remained when re-evaluated two weeks after treatment stopped. However, snoring was more greatly reduced in patients with an apnea-hypopnea index (AHI) less than 10 than in patients with an AHI greater than 10, where the treatment had no effect on reducing the AHI. They suggested that the device could be beneficial for snorers and for people with an AHI of less than 10.
Baptista et al.8 demonstrated similar findings. In their study, individuals who snored only and had mild OSA used the device for 20 minutes once daily for six weeks. The change in the percentage of time spent snoring was measured objectively with a two night sleep study before and after therapy. Ninety percent of the participants objectively experienced, on average, a 41% reduction in snoring time (based on sleep study findings). The bedpartners subjectively reported that the snoring of the participants had reduced significantly. The treatment also improved sleep quality, latency, efficiency and daytime dysfunction in the participants and their bedpartners.
Daytime oral stimulation of the genioglossus muscle is a novel, effective, noninvasive treatment for people with mild OSA or who snore only. However, this information is based on findings of participants who had used daytime oral stimulation of the genioglossus muscle for six weeks. Therefore, scientists currently do not know whether a longer period would be necessary to induce changes in fast-twitch and slow-twitch fibers of the genioglossus muscle in people with moderate to severe OSA. Future research may clarify this issue and determine whether other types of patients with OSA can benefit from this novel therapy, such as patients who have undergone unsuccessful OSA surgery. Future research may also determine whether combining daytime oral stimulation with CPAP treatment could help reduce the pressure required for CPAP treatment (and potentially increase CPAP treatment compliance). For now, research continues to focus on the efficacy and safety of daytime genioglossus muscle stimulation to treat OSA.
References
- Gastaut H, Tassinari CA, Duron B. Polygraphic study of the episodic diurnal and nocturnal (hypnic and respiratory) manifestations of the Pickwick syndrome. Brain Research. 1966;1:167-186. doi:10.1016/0006-8993(66)90117-x
- Remmers JE, deGroot WJ, Sauerland EK, et al. Pathogenesis of upper airway occlusion during sleep. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology. 1978;44:931-938. doi:10.1152/jappl.1978.44.6.931
- Miki H, Hida W, Chonan T, et al. Effects of submental electrical stimulation during sleep on upper airway patency in patients with obstructive sleep apnea. American Review of Respiratory Disease. 1989;140:1285-1289. doi:10.1164/ajrccm/140.5.1285
- Carrera M, Barbe F, Sauleda J, et al. Patients with obstructive sleep apnea exhibit genioglossus dysfunction that is normalized after treatment with continuous positive airway pressure. American Journal of Respiratory and Critical Care Medicine. 1999;159:1960-1966. doi:10.1164/ajrccm.159.6.9809052
- Pae EK, Hyatt JP, Wu J, et al. Short-term electrical stimulation alters tongue muscle fibre type composition. Archives of Oral Biology. 2007;52:544-551. doi:10.1016/j.archoralbio.2006.12.002
- S. Food and Drug Administration (FDA). FDA authorizes marketing of novel device to reduce snoring and mild obstructive sleep apnea in patients 18 years and older [press release]. FDA; February 5, 2021. Accessed on May 15, 2022. Available at https://www.fda.gov/news-events/press-announcements/fda-authorizes-marketing-novel-device-reduce-snoring-and-mildobstructive-sleep-apnea-patients-18
- Wessolleck E, Bernd E, Dockter S, et al. Intraoral electrical muscle stimulation in the treatment of snoring. Somnologie (Berl). 2018;22(Suppl 2):47-52. doi:10.1007/s11818-018-0179-z
- Baptista PM, Martinez Ruiz de Apodaca P, Carrasco M, et al. Daytime neuromuscular electrical therapy of tongue muscles in improving snoring in individuals with primary snoring and mild obstructive sleep apnea. Journal of Clinical Medicine. 2021;10:1883-1893. doi:10.3390/jcm10091883
Regina Patrick, RPSGT, RST