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MADs and Positional Sleep Apnea: More than Meets the Eye!

Published Online:https://doi.org/10.5664/jcsm.6036Cited by:1

INTRODUCTION

Use of mandibular advancement devices (MAD) in the clinical setting seems to be gaining ground as we inch toward personalized treatment for obstructive sleep apnea (OSA) and especially as more and more comparative efficacy data become available.1 However, prediction of treatment outcome with MADs remains a key unresolved issue, this perhaps becoming more complicated as a plethora of devices have evolved that differ in their design, fabrication, adjustability, allowance of either vertical or lateral jaw movement, and plate connectors. Based on data from earlier studies,25 factors that predict successful MAD treatment include younger age, lower body mass index (BMI), smaller neck circumference, and supine-dependent or positional OSA (P-OSA).6 However, none of the prior studies25 compared the efficacy of MADs with continuous positive airway pressure (CPAP).

In this issue of JCSM, Takaesu et al.7 report findings of a retrospective analysis that compared the efficacy of monobloc MADs and CPAP in 96 male P-OSA patients. Patients were considered to have P-OSA if their lateral to supine apnea-hypopnea index (AHI) ratio was ≤ 0.5. Although those on CPAP had a higher baseline AHI, after matching for AHI at baseline, the authors found no significant difference in the follow up AHI between CPAP and MADs, thereby concluding that MADs are as efficacious as CPAP in P-OSA patients. However, it is important to note that this comparison represents post-treatment data and not change scores. Additionally, while both CPAP and MADs lowered the lateral AHI by the same magnitude, a similar effect was not seen in supine AHI and a significant difference remained between the CPAP and MAD treated patients in their follow up supine AHIs. Similarly, while 76% of P-OSA patients treated with CPAP achieved AHI < 5, this effect was only seen in 53% of those treated with MADs. Whereas, the results on change scores for supine AHI may not be statistically significant, post-treatment supine AHI for MADs was ≤ 10, which has clinical relevance.

Effects between CPAP and MADs also differed in patients with non-positional OSA (NP-OSA). Compared to CPAP, those treated with MADs had comparatively less improvement in their nadir SpO2 and overall AHI, which is consistent with recent data.1 However, while CPAP showed absolutely no effect on Epworth scores in either P-OSA or NP-OSA patients, MADs did show an improvement, which is intriguing. From the significant difference in supine AHIs between CPAP and MAD in the P-OSA patients and the nonsignificant effect of MADs on AHI and nadir SpO2, perhaps all that we can safely deduce from this study is that MADs may not be as efficacious as CPAP in NP-OSA patients.

P-OSA, which is seen in about 50% to 60% of OSA patients,8 has been defined differently across the literature. While an earlier MAD study4 defined this as lateral AHI of < 10, together with a supine AHI of ≥ 10, more recent studies2,3,5,6 have used the original Cartwright criteria9 with some variation, i.e., supine AHI ≥ 2 of the lateral AHI. Emerging data10,11 indicate a trend for being even more stringent on these definitions. From a definition using supine to non-supine AHI ratio of > 4:1 for supine-predominant OSA10 to further distinguishing between supine-predominant and supine-isolated OSA,11 this only gets more complicated. Not only that, earlier studies25 that associated MAD success with factors such as P-OSA not only differed in their patient population, and design but also in the type of MADs used i.e. either monobloc4,5 or duobloc.2,3 A common feature of these devices studied in earlier studies25 was their inability to allow jaw opening in sleep. The most recent study by Sutherland et al.11 used a duobloc which does allow jaw opening in sleep. Contrary to previous studies,25 they showed that both supine-predominant and supine-isolated subtypes had half the response rate of NP-OSA patients. One wonders then, if the difference in findings is from the difference in the design of MADs used, i.e., in the supine position could jaw muscle relaxation lead to mouth opening and limit the efficacy of the device? Would a similar device but with elastics as connectors prevent vertical opening?

Aside from device-related factors, this variance could also be due to certain physiological factors that determine which patients are likely to respond to MADs. Factors such as extent of airway dilatation in lateral position and caudal traction on trachea from resultant increase in lung volume play a role in P-OSA.10 How do MADs then, stabilize upper airway in supine sleep? The precise mechanism is not well understood. The predominant effect of MADs on upper airway structure has been found to be enlargement of the velopharyngeal space, mediated via an increase in lateral diameter.6 This presumably is caused by the stretching of soft tissue connections within the palatoglossal and palatopharyngeal arches that connect the mandible and tongue to the soft palate and lateral pharyngeal walls. This results in an increase in airway volume, providing a more patent airway that is less likely to collapse.12 An additional effect of MAD when worn may also be the direct stimulation of genioglossus muscle which along with indirect stimulation of pharyngeal dilator muscles also stabilizes the airway.13,14 As explained above, just as difference in the designs of the MADs may alter treatment outcome, it is possible that differences in the anatomic and neuromuscular responses to MADs in individual patients predict MAD success.

Takaesu et al.7 studied monoblocs in their study primarily because these are the most commonly used in Japan. However, practice trends elsewhere show that duoblocs are increasingly being used. Given conflicting results between earlier studies with monoblocs25 including present study by Takaesu et al.7 and recent study by Sutherland et al.11 that used a particular type of duobloc, large-scale randomized controlled trials that test different device designs on different populations with a uniform definition of P-OSA are warranted to provide more clarity. Until then, the association between MADs and P-OSA is more complex than meets the eye!

DISCLOSURE STATEMENT

Dr. Iftikhar has indicated no financial conflicts of interest.

CITATION

Iftikhar IH. MADs and positional sleep apnea: more than meets the eye! J Clin Sleep Med 2016;12(8):1079–1080.

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