A New Direction for Oral Appliance and CPAP Combination Therapy

Oral appliances and apparatus have been in existence in one way or another since 1923 when a dental surgeon and physician named Pierre Robin found that babies with micrognathia and posteriorly placed tongue (glossoptosis) not only had difficulty with feeding, but also had issues with breathing in general.¹ It was from these observations, and the previous work of Lannelongue and Menard in 1891,¹ that Robin subsequently published the first case of an infant with the complete Pierre Robin Syndrome (PRS) (sequence) in 1926.² The idea of posteriorly positioned tongues and lower jaws narrowing the pharyngeal airway in general, outside of PRS, was to be further postulated for the next 30 years and a generation of dental academics.

The 1970's brought with it much research on the association of the tongue and breathing. A dental academic named Eberhart Sauerland reported that genioglossal activity occurred in "bursts" during inspiration. He teamed up with Ron Harper in 1976, who added that the stiffening of the pharyngeal walls and movement of the tongue upon inspirations was shown to be a normal activity in "normal" humans while asleep.³

The tongue has been known to be of great importance to the normal function of airway support for many years. Given the known cardiovascular issues that can threaten sufferers of obstructive sleep apnea (OSA), any therapy that is oral appliance based needs to be effective. This is especially important when one considers the known issues with the genioglossal activity in sufferers of OSA. Since at least 1993, Douglas et al.⁴ have written about the fact that those with OSA have a dulled response to intraluminal negative pressure upon inspiration during sleep. But is holding the tongue forward enough to solve the problem? This seems to be a somewhat unnatural way to alleviate an issue that is based in the unconscious patient. Is bringing the lower jaw forward with a mandibular advancement splint (MAS) going to control the tongue on its own?

Tongue retaining devices have mixed results. The action of a tongue bulb, a device that the user inserts their tongue into, and with suction that holds the tongue in place, is premised on the theory that this muscular hydrostat that is the tongue is going to be a compliant and still muscle that is held into the tongue bulb at the position of the front teeth (in between them) and therefore out of the throat. Unfortunately, for this theory, the 3D muscle fibre orientation present within this organ means that the tongue will quickly lose its place within the tongue bulb. The other factor that resists the static position of the tongue is the nature of the tongue activity at night. We all normally swallow about 500-700 times a day, and about 20-30 times at night in an average sleep period of eight hours.^5,6

This frequency is increased in patients who have sleep-disordered breathing due to arousal and increased muscle tone. In fact, Lichter and Muir, circa 1975,⁷ found that the pattern of swallowing more was associated with movement arousals from sleep and more frequent tonal activity during these times.

Interestingly, rapid eye movement (REM) sleep contained frequent swallow episodes, which points to the hypothesis that the vagal system is still quite active and influencing dilator and genioglossal muscle activity during REM when more wide-spread atonia is also present.

A more recent option for assistance in control of the tongue has been developed off the back of prior research into tongue retention during sleep, as well as myofunctional training and assistance during the day. In 2010, Wilfried Engelke et al.⁸ published a ground-breaking article, "Functional Treatment of Snoring Based on the Tongue-Repositioning Manoeuvre." The article proposed that after 4.6 months, patients with a normal body mass index (BMI) and primary snoring could be assisted in the reduction of snoring via the use of a simple shield worn in the mouth in front of the teeth and behind the lips. This simple addition to the sleeping habits promised to control the tongue and the soft palate more often to create a more stable velo and oral pharyngeal space for nasal breathing to pass through.

Advances in this area in terms of devices has led to the novel intermittent negative air pressure device (iNAP). This device has been shown in small studies to be very effective in the treatment of moderate to severe apnea. Reductions in the apnea hypopnea index (AHI) have been reported to reduce from 32.0 ± 11.3 events/h to 8.7 ± 9.4 events/hour.⁹

In 2017, a pilot study¹⁰ with a very small cohort of participants was conducted in Japan by Yuji Yamaguchi and Masako Kato at the Sleep Disorders Centre at the Fukuoka Urasoe Clinic in Japan. A small but significant reduction in the AHI was recorded, and more importantly, the wake after sleep onset (WASO) was reduced by approximately 20 minutes on first night use. This is promising because it suggests that the comfort of wear of the device is immediate and should be easy to get used to compared to other modes of therapy. In 2019, a larger cohort¹¹ was studied by professor Christian Guilleminault which showed an improvement in the AHI and the oxygen desaturation index (ODI) of users, with those with a greater body mass index (BMI) having more success.

Of course, no device is a panacea, and no research is free of appropriate scientific skepticism. The fact remains that oral appliances really need help when it comes to control of the tongue and the soft palate if these devices are going to rise above the reported 30% efficacy rate. This author believes that the combination of oral appliance therapy with an alternative treatment like negative air pressure could be a solution to the issue of residual snoring and positional snoring in all users of oral appliance therapy. The oral appliance makes room in the mouth for the tongue by increasing occlusal vertical dimension (OVD) and bringing the insertion point of the genioglossus at the genial tubercles forward-mandibular advancement. What the oral appliance can't do is elevate the laryngopharyngeal position to create a larger cross section for inspired air to pass through. The oral appliance can't control the spasmodic and abhorrent position and posture of the velar space, and so the soft palate is "lost in space."

The advantage of intermittent negative air pressure control in oral appliance patients is that the tongue is allowed to behave in its own way during the various stages of sleep. The posture of the tongue is controlled, especially when the patient is in the supine position or when they are in REM sleep, as well as during potential arousal events. All this assistance equates to a most important benefit, a more stable and less disrupted sleep pattern. It is the goal of all who provide therapy to sufferers of OSA to assist the medical providers in assuring a more restful and architecturally correct sleep pattern for the patient.

Given the research that has been performed on tongue position, and the known relationship that tongue encroachment has on OSA, in relation to the pharyngeal space, this author believes it is time to look harder at combination therapies that will work together to achieve better, long-term results for sufferers of OSA who do not wish to use continuous positive airway pressure (CPAP) or cannot tolerate CPAP. Also, CPAP users who struggle with tongue position may not even be aware of this issue, and because of this, they may be giving up on a therapy out of ignorance that can help them to lead more healthy lives. It is this author's hope that this article will inspire readers to investigate combination therapy and thus be able to offer the patient more therapy options for OSA.

References

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3. Sauerland EK, Harper RM. The human tongue during sleep: Electromyographic activity of the genioglossus muscle. Experimental Neurology. 1976;51(1):160-70.
4. Douglas NJ. The sleep apnoea/hypopnoea syndrome. European Journal of Clinical Investigation. 1995;25(5):285-90.
5. The frequency of deglutition in man. Archives of Oral Biology. 1965;10(1):83-IN15.
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7. Lichter I, Muir RC. The pattern of swallowing during sleep. Electroencephalogr Clin Neurophysiol. 1975;38(4):427-32.
8. Engelke W, Engelhardt W, MendozaGärtner M, Deccó O, Barrirero J, Knösel M. Functional treatment of snoring based on the tongue-repositioning manoeuvre. Eur J Orthod. 2010;32(5):490-5.
9. Cheng CY, Chen CC, Lo MT, Guilleminault C, Lin CM. Evaluation of efficacy and safety of intraoral negative air pressure device in adults with obstructive sleep apnea in Taiwan. Sleep Medicine. 2021;81.
10. Yamaguchi Y, Kato M. Pilot study of oral negative pressure therapy for obstructive sleep apnea-hypopnea syndrome. J Sleep Disord Ther. 2017;6(3):2167-0277.1000271.
11. Hung T-C, Liu T-J, Hsieh W-Y, Chen B-N, Su W-K, Sun K-H, et al. A novel intermittent negative air pressure device ameliorates obstructive sleep apnea syndrome in adults. Sleep and Breathing. 2019;23(3):849-56