Supine-dependent changes in upper airway size in awake obstructive sleep apnea patients

The relationship between specific nasopharyngoscopic features and treatment deterioration with mandibular advancement devices: a prospective study

STUDY OBJECTIVES

The variable efficacy of mandibular advancement device (MAD) treatment necessitates both accessible and accurate methods for patient selection. However, the role of awake nasopharyngoscopy for this purpose remains dubious. We introduced an assessment method based on anatomical upper airway features during tidal breathing for nasopharyngoscopy. The current study aimed to relate these features to MAD treatment outcome.

METHODS

One hundred patients diagnosed with obstructive sleep apnea were prospectively recruited for MAD treatment in a fixed 75% degree of maximal protrusion. Nasopharyngoscopic observations during Müller's maneuver and tidal breathing were recorded both with and without MAD. Treatment outcome, confirmed by 3-month follow-up polysomnography with MAD, was classified as (1) apnea-hypopnea index reduction ≥ 50%, (2) treatment apnea-hypopnea index < 5 events/h, and (3) ≥ 10% increase in apnea-hypopnea index compared with baseline (treatment deterioration).

RESULTS

A complete dataset was obtained in 65 patients. After adjusting for baseline apnea-hypopnea index, body mass index, and supine dependency, the position of the soft palate (odds ratio, 4.0; 95% confidence interval, 1.3-11.8; P = .013) and crowding of the oropharynx (odds ratio, 7.7; 95% confidence interval, 1.4-41.4; P = .017) were related to treatment deterioration. Addition of both features significantly (P = .031) improved the accuracy of baseline models based on clinical measurements alone. Moreover, with the MAD in situ, a posteriorly located soft palate (odds ratio, 9.8; 95% confidence interval, 1.7-56.3; P = .010) and a posteriorly located tongue base (odds ratio, 7.4; 95% confidence interval, 1.5-35.9; P = .013) were associated with treatment deterioration.

CONCLUSIONS

Awake nasopharyngoscopy might be a valuable office-based examination to exclude the risk of treatment deterioration and improve patient selection for MAD treatment.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Predicting Therapeutic Outcome of Mandibular Advancement Device Treatment in Obstructive Sleep Apnea (PROMAD); URL: https://clinicaltrials.gov/ct2/show/NCT01532050; Identifier: NCT01532050.

Machine learning for image-based detection of patients with obstructive sleep apnea: an exploratory study

PURPOSE

In 2-dimensional lateral cephalometric radiographs, patients with severe obstructive sleep apnea (OSA) exhibit a more crowded oropharynx in comparison with non-OSA. We tested the hypothesis that machine learning, an application of artificial intelligence (AI), could be used to detect patients with severe OSA based on 2-dimensional images.

METHODS

A deep convolutional neural network was developed (n = 1258; 90%) and tested (n = 131; 10%) using data from 1389 (100%) lateral cephalometric radiographs obtained from individuals diagnosed with severe OSA (n = 867; apnea hypopnea index > 30 events/h sleep) or non-OSA (n = 522; apnea hypopnea index < 5 events/h sleep) at a single center for sleep disorders. Three kinds of data sets were prepared by changing the area of interest using a single image: the original image without any modification (full image), an image containing a facial profile, upper airway, and craniofacial soft/hard tissues (main region), and an image containing part of the occipital region (head only). A radiologist also performed a conventional manual cephalometric analysis of the full image for comparison.

RESULTS

The sensitivity/specificity was 0.87/0.82 for full image, 0.88/0.75 for main region, 0.71/0.63 for head only, and 0.54/0.80 for the manual analysis. The area under the receiver-operating characteristic curve was the highest for main region 0.92, for full image 0.89, for head only 0.70, and for manual cephalometric analysis 0.75.

CONCLUSIONS

A deep convolutional neural network identified individuals with severe OSA with high accuracy. Future research on this concept using AI and images can be further encouraged when discussing triage of OSA.

Genioglossus motor unit activity in supine and upright postures in obstructive sleep apnea

This study investigated whether a change in posture affected the activity of the upper-airway dilator muscle genioglossus in participants with and without obstructive sleep apnea (OSA). During wakefulness, a monopolar needle electrode was used to record single motor unit activity in genioglossus in supine and upright positions to alter the gravitational load that causes narrowing of the upper airway. Activity from 472 motor units was recorded during quiet breathing in 17 males, nine of whom had OSA. The mean number of motor units for each participant was 11.8 (SD 3.4) in the upright and 16.0 (SD 4.2) in the supine posture. For respiratory-modulated motor units, there were no significant differences in discharge frequencies between healthy controls and participants with OSA. Within each breath, genioglossus activity increased through the recruitment of phasic motor units and an increase in firing rate, with an overall increase of ~6 Hz (50%) across both postures and participant groups. However, the supine posture did not lead to compensatory increases in the peak discharge frequencies of inspiratory and expiratory motor units, despite the increase in gravitational load on the upper airway. Posture also had no significant effect on the discharge frequency of motor units that showed no respiratory modulation during quiet breathing. We postulate that, in wakefulness, any increase in genioglossus activity to compensate for the gravitational effects on the upper airway is achieved primarily through the recruitment of additional motor units in both healthy controls and participants with OSA.

Three-Dimensional Assessment of Pharyngeal Volume on Computed Tomography Scans: Applications to Anesthesiology and Endoscopy

Pharyngeal volume is important in anesthesiology for correctly assessing intubation procedures. However, most of studies are based on patients in upright position and do not assess possible relationships between pharyngeal volume and cranial size. This study aims at measuring pharyngeal volume in CT-scans and to assess possible statistically significant differences according to sex.Eighty healthy subjects (40 males and 40 females) aged between 21 and 86 years were retrospectively chosen from a hospital database of maxillofacial CT-scans; 3D segmentation was performed separately for naso-, oro- and laryngopharyngeal portion through ITK-SNAP software, and their volume was calculated. Three cranial measurements were obtained: distance between anterior and posterior nasal spine, upper facial height (nasion-prosthion) and biorbital breadth (ectoconchion-ectoconchion distance).The effect of sex on volume for each pharyngeal portion was assessed through one-way ANCOVA test using each of the 3 cranial measurements as covariate (P < 0.05).On average, the volume of nasopharynx, oropharynx and laryngopharynx was 7.2 ± 2.7 cm, 7.5 ± 4.2 cm, 3.5 ± 2.2 cm respectively in males, and 6.4 ± 2.9 cm, 5.2 ± 2.1 cm, 3.0 ± 1.8 cm in females. Statistically significant differences according to sex were found only for oropharyngeal volume, independently from cranial measurements (P < 0.05).This study provides data concerning volume of pharyngeal air space in supine subjects: these reference standards can be useful for anaesthesiologic procedures.

Volumetric upper airway changes after rapid maxillary expansion: a systematic review and meta-analysis

Background

Although Rapid Maxillary Expansion (RME) has been used for over a century, its effect on upper airways has not yet adequately been assessed in an evidence-based manner.

Objective

To investigate the volumetric changes in the upper airway spaces following RME in growing subjects by means of acoustic rhinometry, three-dimensional radiography and digital photogrammetry.

Search methods

Literature search of electronic databases and additional manual searches up to February 2016.

Selection criteria

Randomized clinical trials, prospective or retrospective controlled clinical trials and cohort clinical studies of at least eight patients, where the RME appliance was left in place for retention, and a maximum follow-up of 8 months post-expansion.

Data collection and analysis

After duplicate data extraction and assessment of the risk of bias, the mean differences and 95 per cent confidence intervals (CIs) of upper airway volume changes were calculated with random-effects meta-analyses, followed by subgroup analyses, meta-regressions, and sensitivity analyses.

Results

Twenty studies were eligible for qualitative synthesis, of which 17 (3 controlled clinical studies and 14 cohort studies) were used in quantitative analysis. As far as total airway volume is concerned patients treated with RME showed a significant increase post-expansion (5 studies; increase from baseline: 1218.3mm3; 95 per cent CI: 702.0 to 1734.6mm3), which did not seem to considerably diminish after the retention period (11 studies; increase from baseline: 1143.9mm3; 95 per cent CI: 696.9 to 1590.9mm3).

Limitations

However, the overall quality of evidence was judged as very low, due to methodological limitations of the included studies, absence of untreated control groups, and inconsistency among studies.

Conclusions

RME seems to be associated with an increase in the nasal cavity volume in the short and in the long term. However, additional well-conducted prospective controlled clinical studies are needed to confirm the present findings.

Registration

None.

Funding

Australian Society of Orthodontics Foundation for Research and Education Inc.

New algorithm for semiautomatic segmentation of nasal cavity and pharyngeal airway in comparison with manual segmentation using cone-beam computed tomography

INTRODUCTION

Our objectives were to assess reliability, validity, and time efficiency of semiautomatic segmentation using Segura software of the nasal and pharyngeal airways, against manual segmentation with point-based analysis with color mapping.

METHODS

Pharyngeal and nasal airways from 10 cone-beam computed tomography image sets were segmented manually and semiautomatically using Segura (University of Alberta, Edmonton, Alberta, Canada). To test intraexaminer and interexaminer reliabilities, semiautomatic segmentation was repeated 3 times by 1 examiner and then by 3 examiners. In addition to volume and surface area, point-based analysis was completed to assess the reconstructed 3-dimensional models from Segura against manual segmentation. The times of both methods of segmentation were also recorded to assess time efficiency.

RESULTS

The reliability and validity of Segura were excellent (intraclass correlation coefficient, >0.9 for volume and surface area). Part analysis showed small differences between the Segura and manually segmented 3-dimensional models (greatest difference did not exceed 4.3 mm). Time of segmentation using Segura was significantly shorter than that for manual segmentation, 49 ± 11.0 vs 109 ± 9.4 minutes (P <0.001).

CONCLUSIONS

Semiautomatic segmentation of the pharyngeal and nasal airways using Segura was found to be reliable, valid, and time efficient. Part analysis with color mapping was the key to explaining differences in upper airway volume and provides meaningful and clinically relevant analysis of 3-dimensional changes.

Mandibular Advancement Device as a Comparable Treatment to Nasal Continuous Positive Airway Pressure for Positional Obstructive Sleep Apnea

STUDY OBJECTIVES

Positional obstructive sleep apnea (P-OSA) is a clinically common phenotype of OSA, which can be treated effectively with mandibular advancement devices (MADs). We hypothesized that the efficacy of an MAD is comparable to that of nasal continuous positive airway pressure (nCPAP) in P-OSA patients.

METHODS

Among patients diagnosed with OSA at a single sleep center from January 2008 to May 2014, male subjects with moderate OSA were recruited and stringently categorized as having P-OSA when the ratio of their lateral apnea-hypopnea index (AHI) to supine AHI was ≤ 0.5, their lateral sleep time was > 60 minutes, and their lateral REM sleep time was longer than 10 minutes. Treatment efficacy was compared between P-OSA subjects with an MAD (n = 34) and those with nCPAP (n = 34) after matching for age, body-mass index, and baseline AHI.

RESULTS

There were no significant differences in baseline AHI (MAD: nCPAP = 20.6 ± 3.9/h: 21.3 ± 1.7/h, p = 0.35) or in follow-up AHI (MAD: nCPAP = 4.7 ± 3.5/h: 3.4 ± 3.7/h, p = 0.12) between the 2 treatment groups, and hence MADs lowered the AHI to the same extent as nCPAP.

CONCLUSIONS

These findings suggest that an MAD is as efficacious as nCPAP for P-OSA patients. MAD treatment for this specific phenotype may be a promising patient-tailored and first-line approach to OSA.

COMMENTARY

A commentary on this article appears in this issue on page 1079.

Cone-beam CT analysis of patients with obstructive sleep apnea compared to normal controls

Purpose

To evaluate the upper airway dimensions of obstructive sleep apnea (OSA) and control subjects using a cone-beam computed tomography (CBCT) unit commonly applied in clinical practice in order to assess airway dimensions in the same fashion as that routinely employed in a clinical setting.

Materials and Methods

This was a retrospective analysis utilizing existing CBCT scans to evaluate the dimensions of the upper airway in OSA and control subjects. The CBCT data of sixteen OSA and sixteen control subjects were compared. The average area, average volume, total volume, and total length of the upper airway were computed. Width and anterior-posterior (AP) measurements were obtained on the smallest axial slice.

Results

OSA subjects had a significantly smaller average airway area, average airway volume, total airway volume, and mean airway width. OSA subjects had a significantly larger airway length measurement. The mean A-P distance was not significantly different between groups.

Conclusion

OSA subjects have a smaller upper airway compared to controls with the exception of airway length. The lack of a significant difference in the mean A-P distance may indicate that patient position during imaging (upright vs. supine) can affect this measurement. Comparison of this study with a future prospective study design will allow for validation of these results.

The effect of teeth extraction for orthodontic treatment on the upper airway: a systematic review

PURPOSE

The purpose of this study was to evaluate the effect of teeth extraction for orthodontic treatment on the upper airway.

METHODS

Relevant trials assessing the effect of orthodontic extractions on the upper airway were retrieved electronically through PubMed, Embase, Medline, Web of Knowledge, and the Cochrane Library. The processes of literature search, selection, quality assessment, and data extraction were performed by two authors independently.

RESULTS

Seven articles were included in this systematic review. They were categorized into three groups according to their indications for extractions, namely anteroposterior discrepancy (group 1), crowding (group 2), and unspecified indications (group 3). In group 1, enrolled patients were diagnosed with class I bimaxillary protrusion and had four first premolars extracted, with a significant decrease in upper airway dimension. In group 2, increase in the upper airway dimension was reported in patients who were diagnosed with class I crowding and four first premolars extracted. In group 3, all patients were adolescents and no significant change in the upper airway dimension was observed.

CONCLUSIONS

Currently, it is difficult to draw evidence-based conclusions because of the exceeding heterogeneity among included studies, and more qualified trials are required to provide reliable evidence. Extractions followed by large retraction of the anterior teeth in adult bimaxillary protrusion cases could possibly lead to narrowing of the upper airway. Mesial movement of the molars appeared to increase the posterior space for the tongue and enlarge the upper airway dimensions. Although the effect of teeth extraction on upper airway dimension seems to be related to indications for extraction, accepted scientific evidence is still insufficient owing to the limited number of included studies. The relationship between the upper airway size and the respiratory function has not been demonstrated. While there may be a decrease in the upper airway volume, there is no evidence that this would turn an airway more collapsible. None of the studies assessed in this review had actual functional assessment of breathing. Additional qualified trials are necessary to verify reliability.

Influence of body position on severity of obstructive sleep apnea: a systematic review

Aim. The aim of this review is to determine the relationship between sleeping body posture and severity of obstructive sleep apnea. This relationship has been investigated in the past. However, the conclusions derived from some of these studies are conflicting with each other. This paper intends to summarize the reported relationships between sleep posture and various sleep indices in patients diagnosed with sleep apnea. Methods and Materials. A systematic review of the published English literature during a 25-year period from 1983 to 2008 was performed. Results. Published data concerning the sleep apnea severity and posture in adults are limited. Supine sleep posture is consistently associated with more severe obstructive sleep apnea indices in adults. However, relationship between sleep apnea severity indices and prone posture is inconsistent.

Change in upper airway geometry between upright and supine position during tidal nasal breathing

BACKGROUND

As the upper airway is the most important limiting factor for the deposition of inhalation medication in the lower airways, it is interesting to assess how its morphology varies between different postures. The goal of this study is to compare the upper airway morphology and functionality of healthy volunteers in the upright and supine positions during tidal nasal breathing and to search for baseline indicators for these changes. This is done by performing three-dimensional measurements on computed tomography (CT) and cone beam computed tomography (CBCT) scans.

METHODS

This prospective study was approved by all relevant institutional review boards. All patients gave their signed informed consent. In this study, 20 healthy volunteers (mean age, 62 years; age range, 37-78 years; mean body mass index, 29.26; body mass index range, 21.63-42.17; 16 men, 4 women) underwent a supine low-dose CT scan and an upright CBCT scan of the upper airway. The (local) average (Savg) and minimal (Smin) cross-sectional area, the position of the latter, the concavity, and the airway resistance were examined to determine if they changed from the upright to the supine position. If changes were found, baseline parameters were sought that were indicators for these differences.

RESULTS

There were five dropouts due to movement artifacts in the CBCT scans. Savg and Smin were 9.76% and 26.90% larger, respectively, in the CBCT scan than in the CT scan, whereas the resistance decreased by 26.15% in the upright position. The Savg of the region between the hard palate and the bottom of the uvula increased the most (49.85%). In people with a high body mass index, this value changed the least. The airway resistance in men decreased more than in women.

CONCLUSIONS

This study demonstrated that there are differences in upper airway morphology and functionality between the supine and upright positions and that there are baseline indicators for these differences.

Impact of the O-C2 angle on the oropharyngeal space in normal patients

STUDY DESIGN

Radiographic analysis using normal patients.

OBJECTIVE

To analyze the relationship between the cervical alignment and the oropharyngeal space.

SUMMARY OF BACKGROUND DATA

Few clinical studies stress the effect of the occipito-C2 (O-C2) alignment on the oropharyngeal space. A previous study showed dysphagia and/or dyspnea after occipitocervical fusion was caused by oropharyngeal stenosis resulting from O-C2 fixation in a flexed position. Other independent researchers showed that development or improvement of obstructive sleep apnea in rheumatoid arthritis patients was related to the O-C2 alignment. However, there are limited basic data demonstrating the relationship between the O-C2 alignment and the oropharyngeal space.

METHODS

Plain lateral cervical radiographs in five tested positions--neutral, flexion, extension, protrusion, and retraction--of 40 asymptomatic volunteers were collected. The O-C2 angle, the C2-C6 angle, and the anterior-posterior distance of the narrowest oropharyngeal airway space (nPAS) were measured, and the changes in value from the neutral to the other four positions were calculated for each patient.

RESULTS

According to the multiple regression analysis, there was an extremely strong linear correlation of the change in the O-C2 angle with the percentage change in the nPAS. Referring to the multiple regression analysis, a decrease of 10° in the O-C2 angle caused a 37% reduction in the nPAS in the neutral position. In contrast, no significant correlation was found between the change in the C2-C6 angle and the percentage change in the nPAS.

CONCLUSION

Our results show the impact of the O-C2 angle on the oropharyngeal space. This knowledge will be useful for the diagnosis and treatment of the upper cervical lesion combined with the upper airway stenosis, and for the determination of the optimal fixation angle in occipitocervical fusion.

Comparison of cone-beam CT parameters and sleep questionnaires in sleep apnea patients and control subjects

OBJECTIVE

The aim of this work was to compare the cone-beam computerized tomography (CBCT) scan measurements between patients with obstructive sleep apnea (OSA) and snorers to develop a prediction model for OSA based on CBCT imaging and the Berlin questionnaire.

STUDY DESIGN

Eighty subjects (46 OSA patients with apnea-hypoapnea index [AHI] >or= 10 and 34 snorers with AHI <10 based on ambulatory somnographic assessment) were recruited through flyers and mail at the University of Southern California School of Dentistry and at a private practice. Each patient answered the Berlin questionnaire, and was imaged with CBCT in supine position. Linear and volumetric measurements of the upper airway were performed by one blinded operator, and multivariate logistic regression analysis was used to identify risk factors for OSA.

RESULTS

The OSA patients were predominantly male and older and had a larger neck size and larger body mass index than the snorers. The minimum cross-sectional area of the upper airway and its lateral dimension were significantly smaller in the OSA patients. Airway uniformity defined as the minimum cross-sectional area divided by the average area was significantly smaller in the OSA patients.

CONCLUSIONS

Age >57 years, male gender, "high risk" on the Berlin questionnaire, and narrow upper airway lateral dimension (<17 mm) were identified as significant risk factors for OSA. The results of this study indicate that 3-dimensional CBCT airway analysis could be used as a tool to assess the presence and severity of OSA. The presence and severity (as measured by the respiratory disturbance index) of OSA is associated with a narrow lateral dimension of the airway, increasing age, male gender, and high-risk Berlin questionnaire.

Obstructive sleep apnea in older adults

The "typical" presentation of obstructive sleep apnea (OSA) is chronic loud snoring and excessive daytime sleepiness in middle-aged obese men. OSA can result in increased risk for cardiovascular morbidity and mortality. The diagnostic features of OSA in older adults are similar to those in younger adults; however, the older adult may be less likely to seek medical attention or have the sleep disorder recognized because symptoms of snoring, sleepiness, fatigue, nocturia, unintentional napping, and cognitive dysfunction may be ascribed to the aging process itself or to other disorders. This article reviews the basic terminology and pathophysiology of sleep-disordered breathing, discusses why OSA may be even more prevalent in older adults than in the middle-aged group, and reviews similarities and differences between the two groups in the manifestations, consequences, and treatments of OSA.

Smaller mandibular size in infants with a history of an apparent life-threatening event

OBJECTIVES

To examine small mandibular size and preference for a hand-to-chin posture as salient characteristics in infants with a history of an apparent life-threatening event (ALTE).

STUDY DESIGN

This was a prospective case-control study of term infants, from birth to 6 months of age, admitted post-ALTE and matched 1:2 with healthy control infants (age within 2 weeks and weight within 0.5 kg). Infants with confirmed gastroesophageal reflux and congenital anomalies, including severe micrognathia, were excluded.

RESULTS

Infants with a history of an ALTE (n = 25) were matched to 47 healthy controls. Infants with a history of an ALTE had mandibular indices (larger index indicates a smaller mandible) that were 3.8 mm greater on the left side (95% CI: 2.0-5.6, P < .001) and 4.2 mm greater on the right side (95% CI: 2.7-5.6, P < .001) adjusting for length and non-white race. Controlling for matching and length, a 1-mm increase in the average mandibular index increased the odds of an ALTE by 62% (OR = 1.62, 95% CI: 1.22-2.44, P < .001).

CONCLUSIONS

Smaller mandibular size was associated with ALTE, suggesting airway obstruction as a potential cause of ALTE. The association of this characteristic with ALTE also offers the potential for prospective quantification of ALTE risk.

The interaction between changes in upright mandibular position and supine airway size in patients with obstructive sleep apnea

INTRODUCTION

The purpose of this study was to investigate the interaction between upright mandibular position change and supine upper airway size in men with obstructive sleep apnea fitted with titratable oral appliances.

METHODS

Baseline supine cephalometry before placement of the oral appliance and after titration with the oral appliance in place were undertaken in 14 patients, and upright mandibular position change was evaluated with and without the titrated oral appliance in place with a DigiGraph workstation (Dolphin Imaging Systems, Valencia, Calif).

RESULTS

The apnea-hypopnea index was significantly reduced after titration of the oral appliance (P < .01). Upright mandibular position change was associated with significant vertical (P < .01) and horizontal (P < .01) mandibular repositioning. The size of the supine velopharynx (P < .05), but not the supine oropharynx, was significantly enlarged at the titrated mandibular position. The supine oropharyngeal size change was correlated with the upright horizontal repositioning of the mandible (r = 0.69, P < .01).

CONCLUSIONS

Evaluation of upright mandibular position changes with the DigiGraph workstation enables one to predict supine oropharyngeal enlargement with oral appliance therapy. Dose-dependent effects of the horizontal component of upright mandibular protrusion on supine oropharyngeal size in addition to velopharyngeal enlargement might contribute to oral appliance effectiveness in obstructive sleep apnea patients.

Elevated posture for the management of obstructive sleep apnea

This study aimed to evaluate the effectiveness of elevated posture in the management of obstructive sleep apnea (OSA). Fourteen subjects presenting with mild-moderate OSA, (apnea-hypopnea index [AHI] 10 to 60/h), were included in a randomized crossover investigation. A shoulder-head elevation pillow (SHEP) was compared with nasal continuous positive airway pressure (nCPAP) therapy. Treatment success was defined as AHI<or=10/h and partial success as AHI>10<16/h. Four subjects achieved treatment success with the SHEP and three achieved partial success. The remaining seven subjects were treatment failures. In contrast, success was achieved with nCPAP in 12 subjects. One subject achieved partial success and one was a treatment failure. With the SHEP, the mean AHI decreased from 27+/-12/h to 21+/-17/h. With nCPAP, the mean AHI was 5+/-3/h; (p=0.008 for the difference between treatments). Although somewhat variable, these data provide evidence that elevated posture during sleep is helpful in the management of OSA in some individuals. Results support the use of elevated posture as second-line therapy in the management of OSA. However, no relationships could be identified between baseline data, including the identification of positional OSA, and objective outcomes that might predict patients who are likely to benefit from treatment in an elevated position.

Effects of an anteriorly titrated mandibular position on awake airway and obstructive sleep apnea severity

The objective of this study was to investigate whether a reduction of obstructive sleep apnea (OSA) severity was associated with significant upper airway (UA) changes after an anterior titration of the mandibular position. Eighteen OSA patients with a mean (SD) apnea hypopnea index (AHI) of 32.5 (12.3) were recruited. Baseline supine cephalometry was obtained before the initial insertion, and follow-up supine cephalometry was undertaken after titration with a titratable oral appliance in place. The mean AHI before treatment was significantly reduced to 9.7 (7.4) (P <.001) after titration. In 13 responders with AHI reduced to < or =15/h, a significant forward displacement of the anterior wall of the velopharynx (P <.05) was observed. In addition, there was a significant forward displacement of the posterior wall of the oropharynx and the hypopharynx (P <.05). In the 5 nonresponders, no significant changes in the position of the anterior and posterior wall were observed. There was no significant difference in the total amount of mandibular advancement between responders and nonresponders. We conclude that treatment success with oral appliance therapy appears to depend not only on anterior titration of the mandibular position to enlarge the UA, but also on the amount of change in the size of the UA in response to mandibular advancement.