Myofunctional training with negative airway pressure for obstructive sleep apnea: a prospective non-randomized cohort feasibility study

Abbreviations

AHI: apnea hypopnea index

BMI: body mass index

NAP: negative airway pressure

OSA: Obstructive Sleep Apnea

OMT: orofacial myofunctional therapy

PAP: positive airway pressure (could be continuous or auto-titrated)

1RM: one-repetition maximum

REM: rapid eye movement

Introduction

Obstructive sleep apnea (OSA) is caused by upper airway collapse during sleep resulting in a disruption of regular periodic breathing. The phenotypes of OSA pathology are variable and a particular patient can have the disorder because of anatomical and/or non-anatomical reasons.¹ Continuous or auto-titrated positive airway pressure (PAP) is the current standard treatment; however, other therapies have emerged as alternatives. Mandibular advancement devices (or oral appliances) are currently recommended as a second line therapy²; though the ability to properly track compliance (and thus efficacy) is a challenge. Surgical interventions have targeted anatomical or morphological problems in those unresponsive to standard therapies. However, the evidence supporting its widespread application is lacking.³

We have been studying the collapsibility of the upper airway during sedation-induced sleep by provoking its occurrence through the use of negative airway pressure (NAP).^4,5 People who are awake can breathe against this NAP (it feels like a vacuum on the back of the throat) down to negative pressures that would readily collapse the airway during sleep or sedation. Awake and healthy OSA patients have been able to tolerate breathing with the application of up to -40 cm of water.⁶ The ability to tolerate these pressures is the result of increased airway muscle tone (both tonic and reflex phasic activation of the airway dilator muscles).⁷

Subjects in our laboratory have commonly described their breathing against this vacuum as a “workout” on their airway. This idea sparked our curiosity to test the ability of NAP application as a therapeutic intervention, exercising the oropharynx, increasing muscle tone and thus decreasing upper airway collapsibility during sleep. Over the last decade, orofacial myofunctional therapy (OMT) has been applied to treat this disorder.⁸ Both as a stand-alone therapy and in conjunction with PAP, OMT has been shown to reduce the apnea hypopnea index (AHI), reduce snoring, and improve quality of sleep and life.⁹ While other OMT protocols involve methods that require specific training,^8,10,11 we considered that OSA sufferers already familiar with PAP would more easily adapt to our protocol which involves the use of a similar device. The key to our proposed therapy is the use of NAP when awake so that the increased reflex phasic drive to the muscles will result in muscle conditioning. Thus, we developed a regimen similar to OMT, with a primary hypothesis that AHI measured via attended polysomnography after treatment intervention would be %50 reduced compared to baseline AHI.

Methods

Results

Fifteen subjects completed the study and Table 1 provides their demographics, which demonstrates no significant changes in BMI, weight or neck circumference after the training session (see Figure 1 for CONSORT flow chart). The initial airway training pressures ranged from -8 to -18 cm H₂O and all airway training pressures became more negative except for one subject who stayed at -18 cm H₂O (Figure 2), which was the most extreme pressure utilized for the study.

Figure 1. CONSORT flow diagram.

Figure 2. Changes in AHI and airway pressures used for therapy by subject.

The left panel shows the change in the AHI from before and after the training for all subjects. The right panel shows the change in the initial to the final training pressure.

While the mean post study AHI was slightly improved (−4.3 ± 12.0 [−10.9, 2.3]), it was not statistically significant (Table 2). Six subjects actually increased their AHI, only one subject decreased to below 10 and this was the subject with the lowest pre-study AHI of 10.1 (Figure 2). The results were similar when the AHI was categorized by the sleep state (REM vs. non-REM). The nadir saturation was also essentially unchanged. The eight subjects with mild or moderate OSA (AHI < 30) showed similar results.

Of the 15 subjects, only 10 completed their sleep diaries. There were no differences noted in sleep quality or feeling refreshed from the intervention.

Discussion

This study demonstrates the novel use of a modified standard PAP machine to provide NAP as a form of quantifiable myofunctional therapy for OSAS. In this small cohort, the intervention did not cause significant changes in AHI. The small size of this pilot study makes it difficult to definitively exclude a clinically helpful effect, but we can exclude a clinically significant increase in the AHI, thus indicating its safety. However, we believe that sharing the methodology and results may provide clues for further study.

Though PAP therapy remains the gold standard approach for effective treatment of OSA,¹³ compliance remains a challenge.¹⁴ OMT has emerged as a promising alternative or adjunct to standard OSA therapy.⁸ In a recent review of the 11 studies published to date, de Felicio et al. provide an analysis of comparative methodology and ideas for further study.¹⁵ In most OMT studies, the intervention exercises target a variety of oral and facial muscles including the tongue, palate, pharynx, mouth, and cheeks. In our study, the NAP therapy was hypothetically the reverse of PAP and may have exercised similar structures. However, we do not know whether NAP targets specific muscles whose tone (or lack thereof) contributes to OSA. With increasing attention being paid to OSA phenotypes, it has been suggested that most would benefit from anatomic intervention.¹ In addition, standardized classification of location, directionality and severity of pharyngeal collapse as determined during drug-induced sedation endoscopy¹⁶ could be explored as a method to target appropriate candidates who might benefit from myofunctional therapy, as it has been used to evaluate success with other OSA interventions such as surgery and electrical stimulation.

We considered that prior familiarity with the PAP machine but failure to adhere to nighttime usage would be a reasonable approach for recruitment of subjects for our study, which included daytime and more limited use of the machine. In hindsight, non-use of PAP may have actually been an inappropriate criterion for inclusion as this may have predicted a phenotype á priori which would not benefit from our approach of myofunctional therapy.¹ Most PAP machines can now be interrogated to ensure patient compliance. Future investigations may benefit from recruiting PAP users and assessing devices for sleep-related pressure changes over the course of an exercise intervention during wakefulness.

As was done in our study, OMT is typically utilized during wakefulness as a method to decrease muscle hypotonia during sleep. Theoretically, the frequent repetitions at low levels of resistance may target Type 1 (slow-resistant to fatigue) muscles, such as those found in the tongue.¹⁷ These muscles and Type 2A (fast-intermediate fatigue) muscles have been stimulated electrically.^18,19 and trained^11,20 In patients with OSA there are even more type 2A fibers than in normal controls, which could contribute to the increase fatigability.²¹

Our protocol lasted for three months, a time period that is frequently used in muscle training.¹⁵ Unlike other protocols, we chose to have subjects observed in a laboratory and reasoned that visiting three times per week would not be too onerous. Many of the training protocols describe daily exercises, sometimes three^8,22 to five times²³ per day. It is possible that our training regimen was not sufficient to see an effect.

We asked our subjects to maintain a mouth closed position while performing exercises, mostly as a means to standardize their positions. It has also been shown that mouth breathing exacerbates upper airway obstruction with advocates for mouth closure training to promote airway patency maintenance during sleep.^24,25

Despite the limitations of our study, there were no reported adverse events. In contrast, participants shared that they appreciated doing this therapy, and could envision doing it at home were it to become available. We have been contacted by former subjects and a few interested citizens who have located this study on ClinicalTrials.gov to inquire about inclusion in ongoing investigations.

Conclusions

In conclusion, subjects with OSAS were able to tolerate a three-month exercise protocol using the novel application of NAP as orofacial myofunctional therapy. Though was no significant reduction in AHI in this small cohort, the methods elucidate a new daytime use for a machine with which many OSAS sufferers are familiar. Future studies utilizing this protocol may target current PAP users or those whose drug-induced sedation endoscopies indicate this approach as an alternative therapy.

Data availability