Andrew S L Chan, Kate Sutherland,Richard J Schwab,Biao Zeng, Peter Petocz,Richard W W Lee,M Ali Darendeliler, Peter A Cistulli Thorax : The effect of mandibular advancement on upper airway structure in obstructive sleep apnea R1 김승민

Introduction Continuous positive airway pressure (CPAP) gold standard treatment of OSA gold standard treatment of OSA limited by poor patient acceptance and tolerance, and suboptimal limited by poor patient acceptance and tolerance, and suboptimal compliance compliance Mandibular advancement splint (MAS) effective alternative to CPAP effective alternative to CPAP protrude the mandible with the aim of increasing upper airway calibre prevent collapse of the upper airway protrude the mandible with the aim of increasing upper airway calibre prevent collapse of the upper airway mechanism are not understood

Introduction Mechanism of MAS not well understood not well understood Limited studies: cephalometric x-rays  two-dimensional nature. Limited studies: cephalometric x-rays  two-dimensional nature. soft tissue volumes and movements, the interaction between upper airway structural parameters and treatment response have never been systematically studied in patients soft tissue volumes and movements, the interaction between upper airway structural parameters and treatment response have never been systematically studied in patients Aim effect on upper airway structure during wakefulness using MRI effect on upper airway structure during wakefulness using MRI  evaluate the mechanism of action of MAS in patients with OSA  evaluate the mechanism of action of MAS in patients with OSA

MethodPatient recruited from a sleep disorders clinic in a university teaching hospital for treatment of OSA with a custom-made MAS recruited from a sleep disorders clinic in a university teaching hospital for treatment of OSA with a custom-made MAS Inculsion criteria two symptoms of OSA + evidence of OSA on polysomnography two symptoms of OSA + evidence of OSA on polysomnography -Sx: snoring, witnessed apneas, fragmented sleep or daytime sleepiness -Sx: snoring, witnessed apneas, fragmented sleep or daytime sleepiness -evidence of OSA on nocturnal polysomnography -evidence of OSA on nocturnal polysomnography (apnea-hypopnea index (AHI) of at least 10 events/h) (apnea-hypopnea index (AHI) of at least 10 events/h)

Method Exclusion criteria contraindications to MAS treatment contraindications to MAS treatment  periodontal disease, insufficient number of teeth,  periodontal disease, insufficient number of teeth, exaggerated gag reflex exaggerated gag reflex Patients with ferromagnetic prostheses, a contraindication to MRI Patients with ferromagnetic prostheses, a contraindication to MRIMAS A custom-made two-piece MAS A custom-made two-piece MAS (SomnoDent MAS; SomnoMed, Crows Nest, Australia) (SomnoDent MAS; SomnoMed, Crows Nest, Australia) To permit MRI of the upper airway with the MAS To permit MRI of the upper airway with the MAS not incorporate the usual adjustable screw mechanism not incorporate the usual adjustable screw mechanism

MethodApneas cessation of airflow for at least 10 s in association with oxygen desaturation of at least 3% or an arousal cessation of airflow for at least 10 s in association with oxygen desaturation of at least 3% or an arousal Hypopneas reduction in the amplitude of airflow, >50% of the baseline measurement for >10 s, in association with oxygen desaturation reduction in the amplitude of airflow, >50% of the baseline measurement for >10 s, in association with oxygen desaturation of at least 3% or an arousal of at least 3% or an arousal complete response: reduction of AHI to <5 events/h partial response: 50% reduction in AHI responders: >50% reduction in AHI. responders: >50% reduction in AHI. Non-responders: <50% reduction in AHI. Non-responders: <50% reduction in AHI.

MethodMRI wakefulness in the supine position, with and without the MAS. wakefulness in the supine position, with and without the MAS. three-dimensional volumes  airway lumen, parapharyngeal fat pads, soft palate, tongue lateral pharyngeal walls three-dimensional volumes  airway lumen, parapharyngeal fat pads, soft palate, tongue lateral pharyngeal walls Anatomical definitions velopharynx (hard palate ~~ tip of the uvula), velopharynx (hard palate ~~ tip of the uvula), oropharynx (tip of the uvula ~~ tip of the epiglottis) oropharynx (tip of the uvula ~~ tip of the epiglottis) hypopharynx (tip of the epiglottis ~~ level of the vocal cords) hypopharynx (tip of the epiglottis ~~ level of the vocal cords)

Method cephalometric measurements sella (S), nasion (Na), basion (B), anterior nasal spine (ANS), sella (S), nasion (Na), basion (B), anterior nasal spine (ANS), posterior nasal spine (PNS), A point (A), B point (B), gnathion (Gn), hyoid (H), C3 vertebra (C3). posterior nasal spine (PNS), A point (A), B point (B), gnathion (Gn), hyoid (H), C3 vertebra (C3). Sellae-nasione-A point (SNA) angle Sellae-nasione-A point (SNA) angle Sellae-nasione-B point (SNB) angle Sellae-nasione-B point (SNB) angle A pointe-nasione-B point (ANB) angle A pointe-nasione-B point (ANB) angle Basione-sellae-nasion (BaSN) angle Basione-sellae-nasion (BaSN) angle hyoid ~~ C3 vertebra (HeC3), hyoid ~~ C3 vertebra (HeC3), hyoid ~~ posterior nasal spine (HePNS) hyoid ~~ posterior nasal spine (HePNS) hyoid ~~ gnathion (HeGn). hyoid ~~ gnathion (HeGn).

Results

Characteristics of patients

Airway parameters without MAS and with MAS

Cephalometric measurements without mandibular advancement splint (MAS) and with MAS

Movement of centroid of soft tissue structure with mandibular advancement

Airway parameters without mandibular advancement splint (MAS) and with MAS according to treatment outcome

Representative axial images from a responder and non-responder

Volumetric reconstructions of the upper airway in a responder

DiscussionMAS  changes in bony and soft tissue structures  changes in bony and soft tissue structures  volume of the velopharynx in lateral dimensions↑  volume of the velopharynx in lateral dimensions↑CPAP  Upper airway dilation in the lateral dimension  Upper airway dilation in the lateral dimension  thinning of the lateral pharyngeal walls  thinning of the lateral pharyngeal walls  airway volume↑  airway volume↑

Discussion responders VS non-responders  no difference volumes of the airway & soft tissue structure at baseline  no difference volumes of the airway & soft tissue structure at baseline  no differences in cephalometric measurements at baseline  no differences in cephalometric measurements at baseline not to predict treatment response based on anatomical characteristics clinical relevance in prediction of treatment of outcomes

Limitation structural parameters  not role of upper airway functional properties (Ex: neuromuscular factors and airway collapsibility) (Ex: neuromuscular factors and airway collapsibility) during wakefulness == during sleep need to assess dynamic changes (Ex: anatomical optical coherence tomography) (Ex: anatomical optical coherence tomography) single device design changes in the morphology of individual structures  oversimplification of the changes in soft tissue anatomy  oversimplification of the changes in soft tissue anatomy

Conclusion the mechanism of action of MAS increase the volume of the upper airway, predominantly by increasing the volume of the velopharynx this increased volume is associated with changes in the surrounding bony and soft tissue structures. future studies aimed at further defining the mechanism of action of MAS, and the factors determining treatment outcome.