Quantitative assessment of the pharyngeal airway by dynamic magnetic resonance imaging in obstructive sleep apnea syndrome

Predicting the Outcomes of Oropharyngeal Surgery in Patients With Obstructive Sleep Apnea Using Tongue-Retaining Devices

OBJECTIVE

To determine the efficacy of a tongue-retaining device (TRD) in predicting the outcomes of oropharyngeal surgery in patients with obstructive sleep apnea (OSA) before surgery.

STUDY DESIGN

A prospective case-control study.

SETTING

A single tertiary medical center.

METHODS

Patients with moderate-severe OSA who underwent both uvulopalatopharyngoplasty and tongue base suspension between January 2022 and July 2022 were included. Each patient underwent a series of 3 overnight polysomnography. Objective outcomes include apnea-hypopnea index (AHI), minimal oxygen saturation, and reduction rate of AHI. The correlation between the reduction rate of AHI with TRD and surgery was analyzed with linear regression.

RESULTS

The reduction rates of AHI were significantly different between the group using TRD (44 ± 24%) and the postoperative group (55 ± 21%). The cross-tabulation revealed a strong association between a positive response to TRD treatment and a positive response to surgery. The use of TRD to evaluate surgical response demonstrated a positive predictive value of 90% and a negative predictive value of 70%. A strong correlation between the decrease in AHI was observed in both TRD and surgery groups, which was demonstrated by a steep slope in the scatter plot and a significant simple linear regression line.

CONCLUSION

Preoperative TRD response is an accurate tool for predicting the success of oropharyngeal surgery in managing OSA patients before surgical treatment. Furthermore, a quantifiable positive linear correlation exists between the efficacy of preoperative TRD treatment and surgery.

Upper airway imaging and function in obstructive sleep apnea in people with and without HIV

Obstructive sleep apnea (OSA) is common in people living with human immunodeficiency virus (HIV) (PLWH), but the underlying mechanisms are unclear. With improved long-term survival among PLWH, aging and obesity are increasingly prevalent in this population. These are also strong risk factors for the development of obstructive sleep apnea. We used magnetic resonance imaging (MRI) to measure upper airway (UA) anatomy and tongue fat content in PLWH with OSA (PLWH + OSA, n = 9) and in age-, sex-, and body mass index (BMI)-matched OSA controls (OSA, n = 11). We also quantified change in UA dimension during tidal breathing (during wakefulness and natural sleep) at four anatomical levels from the hard palate to the epiglottis along with synchronous MRI-compatible electroencephalogram and nasal flow measurements. All participants underwent on a separate night a baseline polysomnogram to assess OSA severity and an additional overnight physiological sleep study to measure OSA traits. We found no difference between the PLWH + OSA and the OSA control group in UA volume [PLWH + OSA: 12.8 mL (10.1-17.0), OSA: 14.0 mL (13.3-17.9), median (IQR)] or tongue volume [PLWH + OSA: 140.2 mL (125.1-156.9), OSA: 132.4 mL (126.8-154.7)] and a smaller tongue fat content in PLWH + OSA [11.2% (10.2-12.4)] than in the OSA controls [14.8% (13.2-15.5), P = 0.046]. There was no difference in the dynamic behavior of the UA between the two groups. When pooled together, both static and dynamic imaging metrics could be correlated with measures of UA mechanical properties. Our data suggest similar underlying UA physiology in OSA in subjects with and without HIV.NEW & NOTEWORTHY Obstructive sleep apnea is common in people living with human immunodeficiency virus (HIV), but the underlying mechanisms are unclear. We did not find differences in upper airway morphology using magnetic resonance imaging (MRI) during wake and natural sleep between people living with HIV (PLWH) with obstructive sleep apnea (OSA) and age, gender, and body mass index (BMI)-matched people with OSA but without HIV. Nor were there differences in tongue volume or changes in airway size during inspiration and expiration. MRI-derived anatomy was correlated with measures of airway collapse.

Dynamic sleep MRI in obstructive sleep apnea: a systematic review and meta-analysis

Purpose

The objective of this study is to systematically review the international literature for dynamic sleep magnetic resonance imaging (MRI) as a diagnostic tool in obstructive sleep apnea (OSA), to perform meta-analysis on the quantitative data from the review, and to discuss its implications in future research and potential clinical applications.

Study design

A comprehensive review of the literature was performed, followed by a detailed analysis of the relevant data that has been published on the topic.

Methods

Clinical key, Uptodate, Ovid, Ebscohost, Pubmed/MEDLINE, Scopus, Dynamed, Web of Science and The Cochrane Library were systematically searched. Once the search was completed, dynamic sleep MRI data were analyzed.

Results

Nineteen articles reported on 410 OSA patients and 79 controls that underwent dynamic sleep MRI and were included in this review. For meta-analysis of dynamic sleep MRI data, eight articles presented relevant data on 160 OSA patients. Obstruction was reported as follows: retropalatal (RP) 98%, retroglossal (RG) 41% and hypopharyngeal (HP) in 5%. Lateral pharyngeal wall (LPW) collapse was found in 35/73 (48%) patients. The combinations of RP + RG were observed in 24% and RP + RG + LPW in 16%. If sedation was used, 98% of study participants fell asleep compared to 66% of unsedated participants.

Conclusions

Dynamic sleep MRI has demonstrated that nearly all patients have retropalatal obstruction, retroglossal obstruction is common and hypopharyngeal obstruction is rare. Nearly all patients (98%) who are sedated are able to fall asleep during the MRI. There is significant heterogeneity in the literature and standardization is needed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-06942-y.

Effect of sleep on upper airway dynamics in obese adolescents with obstructive sleep apnea syndrome

STUDY OBJECTIVES

The biomechanical basis of obstructive sleep apnea syndrome (OSAS) may influence upper airway dynamics. In this study, we investigate dynamic changes during respiration in wakefulness and sleep in obese adolescents with and without OSAS.

METHODS

Respiratory-gated dynamic magnetic resonance imaging (MRI) at the retropalatal and retroglossal regions was performed with simultaneous measurement of SpO2 and nasal-oral mask airflow and pressure. Airway cross-sectional area (CSA) was determined using AMIRA. Percent change in CSA was calculated from five continuous tidal breaths in states of wakefulness and sleep. Mixed effects models were used to evaluate interactions between group (OSAS/control), site (retropalatal/retroglossal), and stage (wake/sleep).

RESULTS

We studied 24 children with OSAS (mean age 15.49 ± 2.00 years, mean apnea-hypopnea index [AHI] 16.53 ± 8.72 events/h) and 19 controls (mean age 14.86 ± 1.75 years, mean AHI 2.12 ± 1.69 events/h). Groups were similar in age, sex, height, weight, and BMI Z-score. Participants with OSAS had a 48.17% greater increase in percent change of airway CSA during sleep than controls (p < 0.0001), while there was no difference between groups during wakefulness (p = 0.6589). Additionally, participants with OSAS had a 48.80% increase in percent change of airway CSA during sleep as compared with wakefulness (p < 0.0001), whereas no such relationship was observed in controls (p = 0.5513).

CONCLUSIONS

This study demonstrates significant effects of sleep on upper airway dynamics in obese children with OSAS. Dynamic MRI with physiological data can potentially provide further insight into the biomechanical basis of OSAS and assist in more effective management.

The association of OSAS and uvula: the role of MRI in this egg-chicken problem in OSAS

PURPOSE

Obstructive sleep apnea syndrome (OSAS) is a condition resulting from repetitive partial or complete upper airway obstruction, and its etiology remains uncertain. Polysomnography is the gold standard diagnostic test for OSAS. However, there are long wait times for this evaluation, so questionnaires or ancillary diagnostic methods are used to select appropriate patients. One of these is magnetic resonance imaging (MRI). The present study aimed to investigate the association between clinical features of OSAS and uvular changes on MRI.

MATERIALS AND METHODS

A total of 102 participants, 80 with OSAS and 22 controls, were included in the study. All participants underwent full-night polysomnography, MRI, and anthropometric measurements.

RESULTS

In comparisons of MRI measurements of the uvula, statistically significant differences in uvular length, thickness, and angle were observed between the OSAS and control groups. MRI measurement significantly associated with apnea-hypopnea index was uvular thickness. Evaluation of anthropometric and MRI measurements revealed statistically significant associations between waist circumference and uvular thickness, uvular width, and oropharyngeal space among the OSAS patients.

CONCLUSION

Thickened uvula on MRI is associated with the presence of OSAS, and its thickness is well correlated with the severity of the diseases. Thus, it may be a reliable indicator of OSAS and could be used as a supportive finding to identify patients suitable for referral for diagnostic polysomnography.

Upper airway dynamic imaging during tidal breathing in awake and asleep subjects with obstructive sleep apnea and healthy controls

We used magnetic resonance imaging (MRI) to quantify change in upper airway dimension during tidal breathing in subjects with obstructive sleep apnea (OSA, N = 7) and BMI-matched healthy controls (N = 7) during both wakefulness and natural sleep. Dynamic MR images of the upper airway were obtained on a 1.5 T MR scanner in contiguous 7.5 mm-thick axial slices from the hard palate to the epiglottis along with synchronous MRI-compatible electroencephalogram and nasal/oral flow measurements. The physiologic data were retrospectively scored to identify sleep state, and synchronized with dynamic MR images. For each image, the upper airway was characterized by its area, and linear dimensions (lateral and anterior-posterior). The dynamic behavior of the upper airway was assessed by the maximum change in these parameters over the tidal breath. Mean upper airway caliber was obtained by averaging data over the tidal breath. There was no major difference in the upper airway structure between OSA and controls except for a narrower airway at the low-retropalatal/high-retroglossal level in OSA than in controls. Changes in upper airway size over the tidal breath ((maximum - minimum)/mean) were significantly larger in the OSA than in the control group in the low retropalatal/high retroglossal region during both wakefulness and sleep. In the four OSA subjects who experienced obstructive apneas during MR imaging, the site of airway collapse during sleep corresponded to the region of the upper airway where changes in caliber during awake tidal breathing were the greatest. These observations suggest a potential role for dynamic OSA imaging during wakefulness.

Craniofacial, Craniocervical, and Pharyngeal Morphology in Bilateral Cleft Lip and Palate and Obstructive Sleep Apnea Patients

Objective:

The aim of this study was to analyze craniofacial, craniocervical, and pharyngeal morphology in surgically treated bilateral cleft lip and palate (BCLP) men, untreated men with obstructive sleep apnea (OSA), and a reference group of men.

Subjects and methods:

Lateral cephalograms were obtained of 27 male BCLP patients (mean age 29.0 ± 8.3 years), 27 untreated male OSA patients (mean age 38.6 ± 5.3 years), and 27 male controls serving as a reference group (mean age 30.8 ± 9.2 years). Tracings were made, and 26 variables representing craniofacial, craniocervical, and pharyngeal dimensions were obtained using Viewbox 3.1.1.6. software. The groups were compared using a one-way analysis of variance.

Results:

Craniofacial, craniocervical, and pharyngeal morphology of BCLP and OSA patients was similar except for a significantly more retrusive maxilla in the BCLP group. Compared to the reference group, the BCLP and OSA groups had significantly larger craniocervical angulations, smaller depth of the oropharynx at the tip of the velum, and a more inferiorly positioned hyoid bone. Significantly larger vertical dimensions were found in the BCLP group compared to the reference group.

Conclusions:

Craniofacial, craniocervical, and pharyngeal morphology of BCLP and OSA patients demonstrate substantial similarities except for a significantly more retrusive maxilla in the BCLP group. It is suggested that airway obstruction and postural adaptation to the obstruction may possibly be related to the aberrant craniofacial, craniocervical, and pharyngeal morphology in OSA and in BCLP patients.

Computational fluid dynamics simulation of the upper airway response to large incisor retraction in adult class I bimaxillary protrusion patients

The changes of the upper airway after large retraction of the incisors in adult class I bimaxillary protrusion patients were assessed mainly focused on the anatomic variation and ignored the functional changes. This study aimed to investigate the changes of the upper airway in adult class I bimaxillary protrusion patients after extraction treatment using the functional images based on computational fluid dynamics (CFD). CFD was implemented after 3D reconstruction based on the CBCT of 30 patients who have completed extraction treatment. After treatment, pressure drop in the minimum area, oropharynx, and hypopharynx increased significantly. The minimum pressure and the maximum velocity mainly located in the hypopharynx in pre-treatment while they mostly occured in the oropharynx after treatment. Statistically significant correlation between pressure drop and anatomic parameters, pressure drop and treatment outcomes was found. No statistical significance changes in pressure drop and volume of nasopharynx was found. This study suggested that the risk of pharyngeal collapsing become higher after extraction treatment with maximum anchorage in bimaxillary protrusion adult patients. Those adverse changes should be taken into consideration especially for high-risk patients to avoid undesired weakening of the respiratory function in clinical treatment.

The Use of Remotely Controlled Mandibular Positioner as a Predictive Screening Tool for Mandibular Advancement Device Therapy in Patients with Obstructive Sleep Apnea through Single-Night Progressive Titration of the Mandible: A Systematic Review

STUDY OBJECTIVES

To perform a review of the current evidence regarding the use of a remotely controlled mandibular positioner (RCMP) and to analyze the efficacy of RCMP as a predictive selection tool in the treatment of obstructive sleep apnea (OSA) with oral appliances that protrude the mandible (OAm), exclusively relying on single-night RCMP titration.

METHODS

An extensive literature search is performed through PubMed.com, Thecochranelibrary.com (CENTRAL only), Embase.com, and recent conference meeting abstracts in the field.

RESULTS

A total of 254 OSA patients from four full-text articles and 5 conference meeting abstracts contribute data to the review. Criteria for successful RCMP test and success with OAm differed between studies. Study populations were not fully comparable due to range-difference in baseline apneahypopnea index (AHI). However, in all studies elimination of airway obstruction events during sleep by RCMP titration predicted OAm therapy success by the determination of the most effective target protrusive position (ETPP). A statistically significant association is found between mean AHI predicted outcome with RCMP and treatment outcome with OAm on polysomnographic or portable sleep monitoring evaluation (p < 0.05).

CONCLUSIONS

The existing evidence regarding the use of RCMP in patients with OSA indicates that it might be possible to protrude the mandible progressively during sleep under poly(somno)graphic observation by RCMP until respiratory events are eliminated without disturbing sleep or arousing the patient. ETPP as measured by the use of RCMP was significantly associated with success of OAm therapy in the reported studies. RCMP might be a promising instrument for predicting OAm treatment outcome and targeting the degree of mandibular advancement needed.

Dynamic upper airway collapse observed from sleep MRI: BMI-matched severe and mild OSA patients

Dynamic magnetic resonance imaging (MRI) allows real-time characterization of upper airway collapse in sleeping subjects with obstructive sleep apnea (OSA). The aim of our study was to use sleep MRI to compare differences in upper airway collapse sites between BMI-matched subjects with mild OSA and severe OSA. This is a prospective, nested case-control study using dynamic sleep MRI to compare 15 severe OSA subjects (AHI >40) and 15 mild OSA (AHI <10) subjects, who were matched for BMI. Upper airway imaging was performed on sleeping subjects in a 3.0 T MRI scanner. Sleep MRI movies were used by blinded reviewers to identify retropalatal (RP), retroglossal (RG), and lateral pharyngeal wall (LPW) airway collapse. Mean AHI in the severe OSA group was 70.3 ± 23 events/h, and in the mild group was 7.8 ± 1 events/h (p < 0.001). All mild and severe OSA subjects demonstrated retropalatal airway collapse. Eighty percent in the mild group showed single-level RP collapse (p < 0.001). All subjects in the severe group showed multi-level collapse: RP + LPW (n = 9), RP + RG + LPW (n = 6). All severe OSA subjects showed LPW collapse, as compared with three subjects in the mild group (p < 0.001). LPW collapse was positively associated with AHI in simple regression analysis (β = 51.8, p < 0.001). In conclusion, severe OSA patients present with more lateral pharyngeal wall collapse as compared to BMI-matched mild OSA patients.

Does the Pharyngeal Airway Recover After Sagittal Split Ramus Osteotomy for Mandibular Prognathism?

PURPOSE

Mandibular setback surgery can adversely affect the pharyngeal airway. The aim of this study was to investigate changes of the pharyngeal airway at specific intervals during a 12-month period after bilateral sagittal split ramus osteotomy (BSSO) for correction of mandibular prognathism.

MATERIALS AND METHODS

This retrospective cohort study included patients with mandibular prognathism who underwent BSSO. The pharyngeal airway was measured at 3 different levels on lateral cephalograms: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II), and a midanterior point on the body of the third cervical vertebra (mid-C III). The pharyngeal airway was measured preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The measurements at each level were compared. Multivariable analysis of variance was used to measure the changes in pharyngeal airway space over time.

RESULTS

The study sample was composed of 30 patients (14 men and 16 women) who were diagnosed with mandibular prognathism. The pharyngeal airway at the uvular tip level was significantly reduced by 39% (P < .001) after surgery and was significantly improved by 26% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the low-C II level was significantly reduced by 27% (P < .001) after surgery and was significantly improved by 24% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the mid-C III level was significantly reduced by 23% (P < .001) after surgery and was improved by only 13% from baseline at 1 month postoperatively. Additional statistical changes were not noted on 3 and 6 months postoperative radiographs at all levels. The pharyngeal airway was decreased by 16, 19, and 8% from baseline at 12 months postoperatively, respectively. The upper airway length was significantly increased immediately after surgery (P < .001), but was incompletely recovered at 12 months postoperatively.

CONCLUSION

The outcomes of this study indicate that the pharyngeal airway gradually recovers over time. An immediate postoperative reduction in pharyngeal airway space can induce or exacerbate obstructive sleep apnea symptoms; thus, any pre-existing symptoms should be screened and considered for surgical treatment planning.

Evaluation of an independent linear model for acoustic noise on a conventional MRI scanner and implications for acoustic noise reduction

PURPOSE

To evaluate an independent linear model for gradient acoustic noise on a conventional MRI scanner, and to explore implications for acoustic noise reduction in routine imaging.

METHODS

Acoustic noise generated from each physical gradient axis was modeled as the prescribed gradient waveform passed through a linear time-invariant system. Homogeneity and superposition properties were experimentally determined. We also developed a new method to correct relative time shifts between the measured impulse responses for different physical gradient axes. Model accuracy was determined by comparing predicted and measured sound using normalized energy difference. Transfer functions were also measured in subjects with different body habitus and at multiple microphone locations.

RESULTS

Both superposition and homogeneity held for each physical gradient axis with errors less than 3%. When all gradients were on simultaneous sound prediction, error was reduced from 32% to 4% after time-shift correction. Transfer functions also showed high sensitivity to body habitus and microphone location.

CONCLUSION

The independent linear model predicts MRI acoustic noise with less than 4% error. Acoustic transfer functions are highly sensitive to body habitus and position within the bore, making it challenging to produce a general approach to acoustic noise reduction based on avoiding system resonance peaks.

Novel retrospective, respiratory-gating method enables 3D, high resolution, dynamic imaging of the upper airway during tidal breathing

PURPOSE

A retrospective, respiratory-gated technique for measuring dynamic changes in the upper airway over the respiratory cycle was developed, with the ultimate goal of constructing anatomically and functionally accurate upper airway models in obstructive sleep apnea patients.

METHODS

Three-dimensional cine, retrospective respiratory-gated, gradient echo imaging was performed in six adolescents being evaluated for polycystic ovary syndrome, a disorder with a high obstructive sleep apnea prevalence. A novel retrospective gating scheme, synchronized to flow from a nasal cannula, limited image acquisition to predefined physiological ranges. Images were evaluated with respect to contrast, airway signal leakage, and demonstration of dynamic airway area changes.

RESULTS

Two patients were diagnosed with obstructive sleep apnea. Motion artifacts were absent in all image sets. Scan efficiency ranged from 48 to 88%. Soft tissue-to-airway contrast-to-noise ratio varied from 6.1 to 9.6. Airway signal leakage varied between 10 and 17% of soft tissue signal. Automated segmentation allowed calculation of airway area changes over the respiratory cycle. In one severe apnea patient, the technique allowed demonstration of asynchronous airway expansion and contraction above and below a severe constriction.

CONCLUSIONS

Retrospective, respiratory gated imaging of the upper airway has been demonstrated, utilizing a gating algorithm to ensure acquisition over specified ranges of respiratory rate and tidal volume.

Tongue movements in patients with skeletal Class II malocclusion evaluated with real-time balanced turbo field echo cine magnetic resonance imaging

INTRODUCTION

The aim of this study was to evaluate the deglutitive tongue movements in patients with skeletal Class II malocclusion.

METHODS

Fifty-nine patients (26 male, 33 female) with skeletal Class II relationship were divided into 3 groups according to cephalometric analysis. Group 1 (n = 19) had mandibular retrognathism, group 2 (n = 20) had maxillary prognathism, and group 3 (n = 20) had both mandibular retrognathism and maxillary prognathism. Twenty-two skeletal Class I patients (10 male, 12 female) were also included as the controls.

RESULTS

In the mandibular retrusion group, the posterior portion of the dorsal tongue moved downward at stage 2 and upward at stage 3; the root of the dorsal tongue was in an inferior and anterior position at stage 2. In patients with both mandibular retrognathism and maxillary prognathism, the middle portion of the dorsal tongue was positioned superiorly at stage 3 relative to stage 1; the tongue tip was retruded at stage 3 relative to stages 1 and 2. In the control group, the middle portion of dorsal tongue was positioned superiorly at stage 3 relative to stages 1 and 2; the posterior portion of the tongue moved upward at stage 2 and downward at stage 3, and tongue-tip retrusion was observed at stage 2 relative to stage 1. Contact of the anterior portion of the tongue with the rugae area of the hard palate decreased in the Class II malocclusion groups relative to the control group. The middle portion of the dorsal tongue was positioned more superiorly in patients with Class II malocclusion during all stages of deglutition. The root of the tongue was more inferior and anterior, and the tongue tip was retruded in patients with Class II malocclusion compared with the control group. The posterior portion of the dorsal tongue was more inferiorly positioned in patients with mandibular retrusion than in the other Class II groups or the controls. In the third stage of deglutition, this portion of the tongue had a superior position in groups 2 and 3 relative to the control group.

CONCLUSIONS

Dentofacial morphology affects the position and movements of the tongue during deglutition, and adaptive changes occur in the tip, dorsum, and root of the tongue. Deglutitive tongue movements in patients with a skeletal Class II relationship are different from those with a skeletal Class I relationship.

Dynamic upper airway changes during sleep in patients with obstructive sleep apnea syndrome

CONCLUSION

The narrowing pattern of the upper airway in obstructive sleep apnea patients may be different in sleep as compared with awake. Three different types of obstruction were observed in these subjects during drug-induced sleep. The different obstruction pattern during drug-induced sleep suggests that different strategies should be selected in upper airway management.

OBJECTIVES

To identify the sites of narrowing and evaluate dynamic upper airway movement in patients with obstructive sleep apnea syndrome (OSAS) while awake and asleep.

PATIENTS AND METHODS

This study included 10 patients treated for OSAS between August 2003 and June 2004. Overnight polysomnography was performed on all patients. Parameters including gender, age, neck circumference, and body mass index were recorded. Ultra-fast MRI during awake and drug-induced sleep was arranged to evaluate the dynamic motion of the upper airway.

RESULTS

The narrowing pattern of the upper airway during awake differed from the narrowing pattern during drug-induced sleep in 3 of 10 subjects. Three different types, palatal obstruction, combined upper and lower pharyngeal obstruction, and circumferential obstruction of the upper airway, were observed in these patients during drug-induced sleep.

Role of upper airway dimensions in snore production: acoustical and perceptual findings

While considerable efforts have been expended to develop snore-driven markers for detecting obstructive sleep apnea (OSA), there is little emphasis on the relationship between the human upper airway (UA) dimensions and the attributes of snores. This paper aims to investigate the acoustical and perceptual impacts of changing the cross-sectional areas (CSA) of the pharynx and oral cavity on the production of snores. Synthetic snores were generated based on the source-filter theory, whereas natural snores were recorded from 40 snorers during nocturnal polysomnography. First formant frequency (F1), spectral peak frequency (PF), and psychoacoustic metrics (loudness, sharpness, roughness, fluctuation strength, and annoyance) of CSA perturbations were examined, completed with diagnostic appraisal of F1 and PF for single- and mixed-gender groupings using the receiver operating characteristic curve analysis. Results show that (1) narrowing the pharyngeal airway consistently increases F1, but not for PF; and (2) altering the airway dimensions yield no considerable differences in perception of snore sounds, but indirectly affect the psychoacoustics by changing the dynamics of snore source flow. Diagnostic outcomes for all groupings (p-value < 0.0001) demonstrate that F1 is more capable of distinguishing apneic and benign snorers than PF due to the close association of F1 with the UA anatomical structures. Correlation exists between the UA anatomy and the properties of snores; there is a promising future for developing snore-driven screening tools for OSA.

Respiratory gating of anatomical optical coherence tomography images of the human airway

Anatomical optical coherence tomography (aOCT) is a long-range endoscopic imaging modality capable of quantifying size and shape of the human airway. A challenge to its in vivo application is motion artifact due to respiratory-related movement of the airway walls. This paper represents the first demonstration of respiratory gating of aOCT airway data, and introduces a novel error measure to guide appropriate parameter selection. Results indicate that at least four gates per respiratory cycle should be used, with only minor improvements as the number of gates is further increased. It is shown that respiratory gating can substantially improve the quality of aOCT images and reveal events and features that are otherwise obscured by blurring.

[Update on upper airway evaluation in obstructive sleep apnea]

During the past two decades, different methods of upper airway evaluation for patients with obstructive sleep apnea (OSA) have been investigated. Although clinical assessment is the basis of any diagnostic workflow in OSA, the Mueller maneuver is apparently of no importance. Imaging techniques have increased our knowledge of the pathophysiology of OSA. Cephalometry is done only if maxillomandibular advancement is planned; dynamic investigations such as computed tomography and magnetic resonance imaging are able to picture the pharyngeal collapse and have the capacity to simulate the effect of interventions on OSA severity. So far, video endoscopy under sedation can only predict the success of oral appliances. Multichannel pressure recordings depict the distribution of obstructive events in the upper or lower pharyngeal segment during the entire night. The impact of sophisticated upper airway evaluation remains limited compared with standard clinical assessment. Further research is needed to develop valuable tools for the diagnostic workup of patients with OSA.

Cine-MRI swallowing evaluation after tongue reconstruction

OBJECTIVE

To determine the feasibility of cine-MRI for non-invasive swallowing evaluation after surgery for lingual carcinoma with reconstruction using microvascular free flaps.

METHODS

Ten patients with stage IV carcinoma of the mobile tongue and/or tongue base treated by surgical resection and reconstruction with a free flap were evaluated after an average of 4.3 years (range: 1.5-11 years), using cine-MRI in "single-shot fast spin echo" (SSFSE) mode. Fiberoptic laryngoscopy of swallowing was performed before MRI to detect aspiration. The tolerance and ability to complete the exam were noted. The mobilities of the oral and pharyngeal structures visualized were evaluated as normal, reduced or increased.

RESULTS

Cine-MRI was well tolerated in all cases; "dry" swallow was performed for the 2 patients with clinical aspiration. Tongue base-pharyngeal wall contact was observed in 5 cases. An increased anterior tongue recoil, increased mandibular recoil, increased posterior oropharyngeal wall advancement and an increased laryngeal elevation were observed in 4 cases. One case of a passive "slide" mechanism was observed.

CONCLUSIONS

Cine-MRI is a safe, non-invasive technique for the evaluation of the mobility of oral and oropharyngeal structures after free-flap reconstruction of the tongue. For selected cases, it may be complementary to clinical examination for evaluation of dysphagia after surgery and free-flap reconstruction. Further technical advances will be necessary before cine-MRI can replace videofluoroscopy, however.

Inhibition of pontine noradrenergic A7 cells reduces hypoglossal nerve activity in rats

Noradrenergic (NE) excitatory drive maintains activity of hypoglossal (XII) motoneurons during wakefulness. In predisposed persons, sleep-related decrements of NE cell activity may contribute to hypotonia of upper airway muscles innervated by XII motoneurons. The goal of this study was to determine whether NE neurons of the pontine A7 group, an anatomically identified source of NE projections to the XII nucleus, provide significant, endogenous NE excitatory drive to XII motoneurons. In anesthetized rats, we microinjected clonidine (0.75 mM, 20-40 nl), an alpha(2)-adrenergic receptor agonist that inhibits pontine NE cells, aiming at the A7 region. Nine injections were placed within 0.4 mm from the A7 group identified using tyrosine hydroxylase immunohistochemistry: they reduced XII nerve activity by 31.3+/-2.8% (standard error) and decreased the central respiratory rate by 6%. Another 21 injections, including eight placed near NE cells of the sub-coeruleus region, were made at distances over 0.5 mm from the A7 group and they did not alter either XII nerve activity or respiratory rate. In control experiments, clonidine injections into the A7 group preceded by injections of an alpha(2)-receptor antagonist, RS-79948, did not change XII nerve activity. Four experiments with unilateral clonidine injections into the A7 region and with Fos immunohistochemistry used as a marker of cell activity revealed that the percentage of Fos-positive A7 cells was significantly reduced on the injected side. There was also a significant positive correlation between Fos expression in A7 cells and XII nerve activity. Thus, decrements of NE excitatory drive from the A7 group may significantly reduce XII nerve activity. In obstructive sleep apnea patients, in whom the muscles innervated by XII motoneurons act as upper airway dilators, this may contribute to sleep-related respiratory disorders.

Cervical CT derived neck fat tissue distribution differences in Japanese males and females and its effect on retroglossal and retropalatal airway volume

OBJECTIVE

The objective of this study was to investigate the difference of neck fat tissue distribution by sex and its correlation with retropalatal and retroglossal airway.

STUDY DESIGN

A total of 38 consecutive patients (male: 19; female: 19) who received a CT scan were compared in the retroglossal region and at the narrowest cross section of the airway. Retroglossal fat tissue volume (FV) was segmented with Amira software and separated into subcutaneous and internal fat volume (SFV, IFV). These volumes were normalized by retroglossal neck volume (NV).

RESULTS

Men had 51.9% more IFV/NV and 64.4% less SFV/NV compared with women. Age-adjusted BMI was negatively correlated with retroglossal airway volume (normalized by NV) and with the lateral width of the smallest cross-section airway (LW) in females. In males the IFV/NV was negatively correlated with LW, after adjusting for BMI and age.

CONCLUSION

Upper airway collapsibility analysis is needed to rule out whether increased BMI or IFV causes an increase in airway collapsibility.

Abdominal fat and sleep apnea: the chicken or the egg?

Obstructive sleep apnea (OSA) syndrome is a disorder characterized by repetitive episodes of upper airway obstruction that occur during sleep. Associated features include loud snoring, fragmented sleep, repetitive hypoxemia/hypercapnia, daytime sleepiness, and cardiovascular complications. The prevalence of OSA is 2-3% and 4-5% in middle-aged women and men, respectively. The prevalence of OSA among obese patients exceeds 30%, reaching as high as 50-98% in the morbidly obese population. Obesity is probably the most important risk factor for the development of OSA. Some 60-90% of adults with OSA are overweight, and the relative risk of OSA in obesity (BMI >29 kg/m(2)) is >or=10. Numerous studies have shown the development or worsening of OSA with increasing weight, as opposed to substantial improvement with weight reduction. There are several mechanisms responsible for the increased risk of OSA with obesity. These include reduced pharyngeal lumen size due to fatty tissue within the airway or in its lateral walls, decreased upper airway muscle protective force due to fatty deposits in the muscle, and reduced upper airway size secondary to mass effect of the large abdomen on the chest wall and tracheal traction. These mechanisms emphasize the great importance of fat accumulated in the abdomen and neck regions compared with the peripheral one. It is the abdomen much more than the thighs that affect the upper airway size and function. Hence, obesity is associated with increased upper airway collapsibility (even in nonapneic subjects), with dramatic improvement after weight reduction. Conversely, OSA may itself predispose individuals to worsening obesity because of sleep deprivation, daytime somnolence, and disrupted metabolism. OSA is associated with increased sympathetic activation, sleep fragmentation, ineffective sleep, and insulin resistance, potentially leading to diabetes and aggravation of obesity. Furthermore, OSA may be associated with changes in leptin, ghrelin, and orexin levels; increased appetite and caloric intake; and again exacerbating obesity. Thus, it appears that obesity and OSA form a vicious cycle where each results in worsening of the other.

Cine magnetic resonance imaging with single-shot fast spin echo for evaluation of dysphagia and aspiration

The aim of this study was to determine the feasibility of and interest in evaluation of swallowing using dynamic magnetic resonance imaging (cine-MRI) in patients with dysphagia and aspiration caused by an abnormal pharyngeal phase of swallow. A cohort of six patients previously treated for head and neck cancer with persistent dysphagia and/or aspiration were evaluated an average of 47 months after treatment. The morphology and mobility of the oral, oropharyngeal, and laryngeal structures were analyzed using cine-MRI using single-shot fast spin echo technology. The qualitative observations were compared with a clinical fiberoptic swallowing evaluation. Swallowing physiology was analyzable for dry (saliva) swallow in all patients. MRI was well-tolerated by all six patients and no clinical aspiration occurred during the MRI. In five of six cases, further information on the cause of dysphagia was obtained using cine-MRI compared with the clinical evaluation alone. In the remaining case, cine-MRI confirmed the clinical evaluation. Cine-MRI using the dry swallow technique is feasible and without risk in patients with clinical aspiration. Cine-MRI is complementary to clinical evaluation of swallowing in patients with an abnormal pharyngeal phase of swallowing resulting from treatment of cancer.

Clinical, anthropometric and upper airway anatomic characteristics of obese patients with obstructive sleep apnea syndrome

BACKGROUND

Obese subjects are at increased risk of developing obstructive sleep apnea syndrome (OSAS). However, the individual role of local (i.e., upper airway-related) and general (clinical and whole-body anthropometric) characteristics in determining OSAS in obese patients is still controversial.

OBJECTIVES

To contrast the clinical, anthropometric and upper airway anatomical features of obese subjects presenting or not presenting with OSAS.

METHODS

Thirty-seven obese (BMI > or =30 kg/m(2)) males with OSAS and 14 age- and gender-matched obese controls underwent clinical and anthropometric (BMI, waist-to-hip ratio and neck circumference) evaluation. In a subgroup of subjects (18 and 11 subjects, respectively), magnetic resonance imaging (MRI) during wakefulness was used to study the upper airway anatomy.

RESULTS

OSAS patients showed significantly higher BMI, waist-to-hip ratio and neck circumference as compared to controls (p < 0.05). They also referred to nonrepairing sleep, impaired attention, and previous car accidents more frequently (p < 0.05). The transversal diameter of the airways (TDAW) at the retroglossal level by MRI was found to be an independent predictor of the presence and severity of OSAS (p < 0.05). Parapharyngeal fat increase, however, was not related to OSAS. A TDAW >12 mm was especially useful to rule out severe OSAS (apnea-hypopnea index >30, negative predictive value = 88.9%, likelihood ratio for a negative test result = 0.19).

CONCLUSIONS

MRI of the upper airway can be used in association with clinical and anthropometric data to identify obese males at increased risk of OSAS.

Real time balanced turbo field echo Cine-MRI in the analysis of deglutition events and transit times

Investigation of swallowing is an important part of oral diagnosis. It usually plays a role in the aetiology of some orofacial deformities and open-bite as well as in the relapse of treated open-bite patients. In recent years, the movements of the anatomical structures that participate in deglutition have been investigated by several methods such as cineradiography, electromyography, electropalatography, electromagnetic articulography and ultrasonography. However, all these techniques have various disadvantages. Recently, dynamic magnetic resonance imaging has become available in the evaluation of swallowing function. In this study we intended to present this new technique to the dental literature and aimed to obtain dynamic images of the deglutition process. We also compared the timing of events in subjects with anterior open-bite and normal overbite during swallowing 10 mL water.

Difference of pharyngeal morphology and mechanical property between OSAHS patients and normal subjects

OBJECTIVE

The intrinsic properties such as baseline caliber and compliance of upper airway are thought to be important in the pathogenesis of obstructive sleep apnea hypopnea syndrome (OSAHS). Our study was designed to detect the difference of baseline caliber (morphological property) of pharynx during both wakefulness and sleep, and difference of pharyngeal compliance (mechanical property) between OSAHS patients and normal subjects.

METHODS

CT scan was performed on 7 normal subjects and 13 OSAHS patients when they are awake, during drug-induced sleep with minimally effective therapeutic pressure (P(eff)), 0 cmH2O, and critical pressure (P(crit)) being given via a nose mask system, respectively. 3D images of pharyngeal airway were reconstructed, and volume of each subdivision of pharynx was measured. Volume, average area and compliance of each subdivision and in total were compared between the two groups.

RESULTS

The OSAHS group was shown to have a smaller average area at upper (1.20+/-0.26 cm2 versus 1.57+/-0.17 cm2, p<0.05) and middle part of pharynx (1.89+/-0.52 cm2 versus 2.58+/-0.27 cm2, p<0.05) during wakefulness. During sleep, this difference was shown to be even more obvious at upper part (0.77+/-0.30 cm2 versus 1.45+/-0.18 cm2, p<0.01); and middle part, (1.15+/-0.47 cm2 versus 2.44+/-0.26 cm2, p<0.01). The average area during wakefulness and sleep was also shown to be highly correlated. OSAHS group had a higher compliance at middle part (0.28+/-0.15 cmH2O(-1) versus 0.13+/-0.07 cmH2O(-1), p<0.05) of pharynx.

CONCLUSION

We conclude that OSAHS patients have a narrower and more collapsible upper airway than normal subjects do, the caliber data obtained during wakefulness could reflect the baseline caliber during sleep, and our method is valid to evaluate both morphology and function of upper airway.

Changes in upper airway size during tidal breathing in children with obstructive sleep apnea syndrome

We performed respiratory-gated magnetic resonance imaging to evaluate airway dynamics during tidal breathing in 10 children with obstructive sleep apnea syndrome (OSAS; age, 4.3 +/- 2.3 years) and 10 matched control subjects (age, 5.0 +/- 2.0 years). We hypothesized that respiratory cycle fluctuations in upper airway cross-sectional area would be larger in children with OSAS.

METHODS

Studies were performed under sedation. Respiratory gating was performed automatically at 10, 30, 50, 70, and 90% of inspiratory and expiratory volume. Airway cross-sectional area was measured at four ascending oropharyngeal levels at each increment of the respiratory cycle.

RESULTS

We noted the following in subjects with OSAS compared with control subjects: (1) a smaller upper airway cross-sectional area, particularly during inspiration; (2) airway narrowing occurred during inspiration without evidence of complete airway collapse; (3) airway dilatation occurred during expiration, particularly early in the phase; and (4) magnitude of cross-sectional areas fluctuations during tidal breathing noted in OSAS at levels 1 through 4 were 317, 422, 785, and 922%, compared with 19, 15 17, and 24% in control subjects (p < 0.001, p < 0.005, p < 0.001, and p < 0.001, respectively).

CONCLUSIONS

Fluctuations in airway area during tidal breathing are significantly greater in subjects with OSAS compared with control subjects. Resistive pressure loading is a probable explanation, although increased airway compliance may be a contributing factor.

An upper airway resonator model of high-frequency inspiratory sounds in children with sleep-disordered breathing

The goal of this study was to determine how high-frequency inspiratory sounds (HFIS) are generated by sleeping children with obstructive sleep-disordered breathing (OSDB). We hypothesized that HFIS are generated when a high-velocity jet of air, generated by a narrowed upper airway, induces the upper airway to act as a resonating chamber. We tested two predictions of this hypothesis: 1) the upper airway is narrowed in children who make HFIS and 2) the length of the upper airway, calculated from HFIS harmonic intervals, is similar to that calculated from magnetic resonance imaging (MRI) scans. The study was conducted in the setting of a sleep laboratory. Participants included 29 children between 6 and 12 yr of age with adenotonsillar hypertrophy suspected of having OSDB. Minimum cross-sectional airway area and airway long dimensions (lips to larynx or soft palate) were measured in awake children with MRIs. Later that night, sound was recorded with a microphone suspended above their bed while the children underwent polysomnography. Sounds were later analyzed with fast Fourier transforms. We found that sleeping children who generated HFIS had significantly narrower upper airways compared with children who did not make HFIS [minimum airway area 20.5 +/- 4.4 vs. 70.9 +/- 22.5 mm(2) (mean +/- SE), respectively; P = 0.02]. There was a significant inverse correlation between the log(10) of the narrowest airway area and the number of HFIS recorded per hour (r(2) = 0.55, P < 0.00001). The harmonics characteristics of HFIS predicted that they were generated by sound resonating in chamber whose length was 12.0 +/- 0.9 cm, which is similar to the MRI measured distance from the lips to the larynx of 12.8 +/- 0.4 cm. In conclusion, these data suggest that children generate HFIS when 1) they have a narrowed upper airway and 2) their upper airway acts as a resonating chamber.

Morphologic parameters of normal swallowing events using single-shot fast spin echo dynamic MRI

This study was designed to determine visible and measurable morphological parameters in normal swallowing using dynamic MRI with single-shot fast spin echo (SSFSE), as a preliminary study in view of noninvasive MRI swallowing evaluation in patients with dysphagia. Seven healthy volunteers aged 24-40 underwent dynamic MRI with SSFSE, with a 1.5-T unit, using a head and neck antenna. Patients repeated dry swallow, water swallow, marshmallow swallow, cake swallow, and cookie chewing for a total of five series, with 15 acquisitions per series at a rate of 700 ms per acquisition. A checklist of swallowing events and anatomic landmarks was used to determine which anatomic landmarks are always visible, which phases or swallowing movements are always visible, and which landmarks can be used to measure oral and pharyngeal motion in swallowing. The oral preparatory, oral, and oropharyngeal phases of deglutition were visible in all cases. No aspiration, reflux, or abnormal residue was observed. Spatial resolution allowed for anatomical measurements of laryngeal elevation, oropharyngeal diameter, and tongue base and velum displacement in all cases. SSFSE dynamic MRI is pertinent for evaluation of the anatomical and physiological characteristics of swallow. The temporal parameters, however, cannot be studied using this technique. Motion artifacts preclude its use in the study of mastication. It remains complementary to videofluoroscopy and other techniques in swallow evaluation.

Sites of obstruction in obstructive sleep apnea

STUDY OBJECTIVE

The aim of this article was to identify the most common sites of obstruction in patients with obstructive sleep apnea (OSA) by a systematic review of published studies.

DESIGN

The review was conducted by a MEDLINE search of the English literature published during the years 1980 to 2002. The inclusion criteria were experiments involving five or more adult subjects, total rather than partial obstruction or narrowing of the upper airway, and techniques that were performed on the subjects while they were asleep.

CONCLUSION

Although there was considerable variability in the techniques and the results, the most common site of obstruction detected by these studies was at the level of the oropharynx, with extension to the laryngopharynx commonly observed.

Evaluating the upper airway with standardized magnetic resonance imaging

OBJECTIVES/HYPOTHESIS

Magnetic resonance imaging (MRI) potentially offers various advantages in assessing the upper airway. The aims of the presented study were 1) to evaluate which anatomical parameters of upper airway soft tissue morphology (distances, areas, volumes) could be defined using MRI scans, 2) to examine the stability or variability of these parameters over time and between different investigators, and 3) to develop a standardized protocol for MRI measurements of the upper airway.

STUDY DESIGN

Prospective clinical trial.

METHODS

Twenty-four scans were performed on six healthy subjects over a period of 4 weeks. Various parameters such as tongue dimensions, volumes and spaces, posterior airway spaces, and soft palate dimensions were established, and their variation over time between different investigators and with repeated analysis was assessed.

RESULTS

All the parameters were of high stability and reproducibility. The time of day had no significant influence on the results. An abbreviated method for the evaluation of the tongue volume was developed. Four-millimeter slices with a conventional MRI scan generate pictures of high quality in a maintainable acquisition time.

CONCLUSIONS

We were able to evaluate which anatomical parameters of upper airway could be defined using MRI scans. The variability of these parameters over time and between different investigators was assessed. We developed a standardized protocol for MRI measurements of the upper airway. Standardized protocols are mandatory, and the variability of the measurements must be taken into account if results of different clinical centers must be compared or if changes after therapeutic interventions are to be investigated.