Evaluation of pharyngeal shape and size using anatomical optical coherence tomography in individuals with and without obstructive sleep apnoea

A review on diagnostic assessments of tracheal stenosis

Tracheal stenosis (TS) is a pathological condition characterized by a reduction in the trachea diameter. It is a common complication after prolonged endotracheal intubation but may also arise from autoimmune or inflammatory processes. Clinicians can select the most appropriate treatment option based on individual patient conditions. Therefore, precise localization and evaluation of the stenosis are essential to ensure safe and effective treatment. This review summarizes current research on TS diagnosis and assessment, encompassing functional, imaging, and bronchoscopy methods. The characteristics, advantages, and disadvantages of each technique are discussed in relation to their application in the diagnosis and assessment of TS. Bronchoscopy is considered the cornerstone of TS diagnosis, and novel adjunct imaging modalities have emerged to enhance its accuracy. We explore advanced endomicroscopic methods, such as endobronchial ultrasound (EBUS), photoacoustic endoscopy (PAE), optical coherence tomography (OCT), and confocal laser endomicroscopy (CLE). Among these, EBUS is clinically approved for diagnosing lesions with high resolution and acceptable penetration depth. OCT and CLE offer real-time imaging for peripheral lesions and potentially malignant nodules, but their use is limited by cost and availability in low-resource settings. Therefore, bronchoscopy, with biopsy techniques as needed, remains the optimal approach for diagnosing tracheal stenosis.

Simulating the effect of individual upper airway anatomical features on drug deposition

This study aims to systematically isolate different anatomical features of the human pharynx with the goal to investigate their independent influence on airflow dynamics and particle deposition characteristics in a geometrically realistic human airway. Specifically, the effects of the uvula, epiglottis and soft palate on drug particle deposition are studied systematically, by carefully removing each of these anatomical features from reconstructed models based on MRI data and comparing them to a benchmark realistic airway model. Computational Fluid Dynamics using established turbulence models is employed to simulate the transport of mono-dispersed particles (3 µm) in the airway at two flow-rates. The simulations suggest three findings: 1) widening the space between the oral cavity and oropharynx and where the soft palate is situated leads to the most dramatic reduction in drug deposition in the upper airway; 2) exclusion of the uvula and epiglottis: a) affects flow dynamics in the airway; b) alters regional deposition behaviour; c) does not significantly affect the total number of particles deposited in the pharynx; and 3) the space adjacent to the soft palate is a key determinant for aerosol deposition in the extrathoracic region and is related to mechanisms of flow acceleration, diversion and recirculation.

Airway morphology and its influence on OSA severity and surgical intervention: a retrospective study

Introduction: The aim was to assess the relationship between airway morphology and surgical intervention in a cohort of patients presenting with increased body mass index (BMI) and a confirmed diagnosis of obstructive sleep apnoea (OSA). A secondary aim was to revisit the relationship between morphology and OSA severity.

Methods: A retrospective analysis was conducted of pre-operative maxillofacial 3D-CT scans of thirty-two patients with a confirmed diagnosis of OSA who received treatment from an ear nose and throat specialist (ENT). Lateral cephalograms were imported into Quick Ceph Studio (Quick Ceph Systems Inc, San Diego, CA, USA) after which linear and angular measurements of selected hard and soft tissues were obtained. 3D-CT images were loaded into the software program 3dMDVultus (3dMD) which permitted 3D visualisation of the airway. Measurements were repeated 3 times on the images of six patients after an interval of two weeks to establish the intraclass correlation coefficient (ICC) for intra-examiner accuracy and reliability. Logistic regression was applied to determine the relationships between morphology, OSA and surgical treatments.

Results: A positive correlation was found between age and the apnoea-hypopnea index (AHI). Morphological measurements of the airway did not exhibit a positive relationship with OSA severity. Posterior airway space at the level of the uvula and tongue, the length of the soft palate and position of the hyoid bone were significantly associated with BMI. No variables were found to be correlated with uvulopalatopharyngoplasty (UPPP) surgery. Notwithstanding, airway length and posterior airway space at the level of the uvula tip were significantly associated with tongue channelling.

Conclusions: Radiographic airway assessment is an invaluable and opportunistic tool for screening OSA but requires judicial use in its prescription and interpretation. There is little correlation between OSA severity and airway morphology and between surgical intervention and morphology. Additional factors need to be considered before a treatment modality is considered and is best managed in a multidisciplinary setting.

Cone beam computed tomography analysis results in patients with obstructive sleep apnoea syndrome

INTRODUCTION

The present study aimed to investigate the contribution of cone-beam computed tomography (CBCT) to the diagnosis of obstructive sleep apnoea syndrome (OSAS).

METHODS

The present study investigate the relationships among body mass index (BMI), upper airway, septum deviation, nasal cavity width, airway, and the hard and soft palate width using CBCT images of 64 patients obtained in Uşak University Faculty of Dentistry. The study included 31 (8 female and 23 male; mean age: 52.52 ± 10.01 years) and 33 patients (12 female and 21 male; mean age: 47.39 ± 10.27 years) with and without OSAS, respectively. Between-group comparisons of non-normally and normally distributed variables were performed using the Mann-Whitney U test and Student's t-test, respectively. Spearman's correlation analysis was used to determine the relationship between quantitative data. Statistical significance was evaluated at P < .01 and P < .05.

RESULTS

There were significant differences between groups in the BMI, nasal septum position, hard and soft palate width, maxillary skeletal width, and palatal alveolar angle (P < .01). In addition it was also found that BMI was higher, the nasopharyngeal airway was longer, and the soft palate was longer and wider in males. (P = .001; P < .01).

CONCLUSION

This study concluded that patients with OSAS had marked narrowing of the upper airway, nasal cavity and maxillary width, shortening and enlargement of the soft palate, and marked increase in BMI. However, to gather sufficiently reliable data for routine use in orthodontic analyses, there is a need for greater number of samples to improve the database.

An organ systems-based review of outcomes associated with sleep apnea in hospitalized patients

The current global health crisis due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has prompted the medical community to investigate the effects of underlying medical conditions, including sleep-disordered breathing, on inpatient care. Obstructive sleep apnea (OSA) is a common form of sleep-disordered breathing that may complicate numerous acquired conditions, particularly in inpatient and critical care settings. Viral pneumonia is a major contributor to intensive care unit (ICU) admissions and often presents more severely in patients with underlying pulmonary disease, especially those with obesity and OSA. This review summarizes the most recent data regarding complications of both OSA and obesity and highlights their impact on clinical outcomes in hospitalized patients. Additionally, it will highlight pertinent evidence for the complications of OSA in an organ-systems approach. Finally, this review will also discuss impatient treatment approaches for OSA, particularly in relation to the SARS-CoV-2 pandemic.

Effect of upper airway fat on tongue dilation during inspiration in awake people with obstructive sleep apnea

STUDY OBJECTIVES

To investigate the effect of upper airway fat composition on tongue inspiratory movement and obstructive sleep apnea (OSA).

METHODS

Participants without or with untreated OSA underwent a 3T magnetic resonance imaging (MRI) scan. Anatomical measurements were obtained from T2-weighted images. Mid-sagittal inspiratory tongue movements were imaged using tagged MRI during wakefulness. Tissue volumes and percentages of fat were quantified using an mDIXON scan.

RESULTS

40 predominantly overweight participants with OSA were compared to 10 predominantly normal weight controls. After adjusting for age, BMI and gender, the percentage of fat in the tongue was not different between groups (ANCOVA, P=0.45), but apnoeic patients had a greater tongue volume (ANCOVA, P=0.025). After adjusting for age, BMI and gender, higher OSA severity was associated with larger whole tongue volume (r=0.51, P<0.001), and greater dilatory motion of the anterior horizontal tongue compartment (r=-0.33, P=0.023), but not with upper airway fat percentage. Higher tongue fat percentage was associated with higher BMI and older age (Spearman r=0.43, P=0.002, and r=0.44, P=0.001, respectively), but not with inspiratory tongue movements. Greater inspiratory tongue movement was associated with larger tongue volume (e.g. horizontal posterior compartment, r=-0.44, P=0.002) and smaller nasopharyngeal airway (e.g. oblique compartment, r=0.29, P=0.040).

CONCLUSIONS

Larger tongue volume and a smaller nasopharynx are associated with increased inspiratory tongue dilation during wakefulness in people with and without OSA. This compensatory response was not influenced by higher tongue fat content. Whether this is also true in more obese patient populations requires further investigation.

Penetration of Flurbiprofen from a Locally Applied Sore Throat Lozenge and Spray into Cadaveric Human Pharynx Tissue: A Novel ex vivo Model and Microautoradiography Method

OBJECTIVE

Flurbiprofen 8.75 mg lozenge and spray are used for symptomatic relief of sore throat, with a rapid onset of analgesia suggesting a localized mechanism of action. Building on previous studies, this investigation aimed to use microautoradiography to visualize the depth penetration of radiolabeled flurbiprofen into human pharynx tissue using an ex vivo model. Quantification of flurbiprofen in the tissue was performed to provide a quantitative representation of flurbiprofen distribution through the tissue.

METHODS

Cadaveric human pharynx tissue was mounted between the donor and receiver compartments of a Franz diffusion cell. After that 8.75 mg spray and dissolved lozenge formulations, containing radiolabeled flurbiprofen, were added to the donor compartment of a Franz diffusion cell. After incubation for one hour, the pharynx tissue was removed, processed, and sectioned both horizontally and vertically. The sections were placed within an imaging cassette to determine the penetration of radiolabeled flurbiprofen visually, before being solubilized to quantify the amount of flurbiprofen present in each section.

RESULTS

In the horizontally sectioned samples, flurbiprofen was present in the top layers of all replicates and decreased in intensity throughout the tissue. Of the applied dose, 48.0-99.9% of flurbiprofen was detected in the top one-third of the pharynx tissue, closest to the dosing site, and 0-14.8% of flurbiprofen was detected within the deepest third of pharynx tissue, furthest from the dosing site. In the vertically sectioned tissue samples, radiolabeled flurbiprofen was found at a high intensity at the dosing site and reduced in intensity throughout the thickness of the tissue. Lateral penetration of flurbiprofen was also seen in tissue dosed with the spray.

CONCLUSION

Our findings demonstrate that lozenge and spray formulations of flurbiprofen can penetrate throughout the layers of cadaveric human pharynx tissue in an ex vivo model, as visualized by microautoradiography.

Determination of the Permeation and Penetration of Flurbiprofen into Cadaveric Human Pharynx Tissue

Objective

Flurbiprofen 8.75 mg spray and lozenge have a rapid onset of action for sore throat relief, suggesting local action, although tissue penetration and the mechanism of local relief have not been determined. This investigation aimed to quantify the permeation and penetration of flurbiprofen, applied as local pharmaceutical forms, into full-thickness cadaveric human mucosal pharynx tissue, representing the clinical scenario as far as possible.

Methods

A validated high-performance liquid chromatography method quantified the permeation and penetration of flurbiprofen (spray and lozenge formulations) into human cadaveric pharynx tissue using a micro Franz cell model mimicking physiological and anatomical conditions. Full-thickness mucosal pharynx tissue, consisting of oral epithelium, basement membrane, and lamina propria, was utilized to imitate the in vivo setting. Flurbiprofen was analyzed on the surface of the pharynx tissue, within the pharynx tissue and in receiver fluid, over 60 mins.

Results

Flurbiprofen was detected in receiver fluid from 10 mins following spray application and was quantifiable from 20 mins. Flurbiprofen from lozenge was detected from 10 mins and was above the limit of quantitation in receiver fluid from 40 mins. Flurbiprofen recovered from the surface of the pharynx tissue was 24.45% and 8.48% of applied dose for spray and lozenge, respectively. Flurbiprofen recovered within pharynx tissue was 46.50% and 54.65% of applied dose for spray and lozenge, respectively. For flurbiprofen lozenge, recovery within pharynx tissue was 6-fold higher relative to recovery from the pharynx tissue surface.

Conclusion

Flurbiprofen from spray and lozenge formulations penetrated human cadaveric pharynx tissue, indicating that flurbiprofen can reach all layers of the pharynx mucosal tissue, including the underlying lamina propria, which contains blood vessels and nerve fibers that contribute to pain during sore throat. This suggests that flurbiprofen may have a local mechanism of action for sore throat, although this has yet to be determined.

Bilateral hypoglossal nerve stimulation for treatment of adult obstructive sleep apnoea

BACKGROUND AND AIM

Hypoglossal nerve stimulation (HNS) decreases obstructive sleep apnoea (OSA) severity via genioglossus muscle activation and decreased upper airway collapsibility. This study assessed the safety and effectiveness at 6 months post-implantation of a novel device delivering bilateral HNS via a small implanted electrode activated by a unit worn externally, to treat OSA: the Genio™ system.

METHODS

This prospective, open-label, non-randomised, single-arm treatment study was conducted at eight centres in three countries (Australia, France and the UK). Primary outcomes were incidence of device-related serious adverse events and change in the apnoea-hypopnoea index (AHI). The secondary outcome was the change in the 4% oxygen desaturation index (ODI). Additional outcomes included measures of sleepiness, quality of life, snoring and device use. This trial was registered with ClinicalTrials.gov, number NCT03048604.

RESULTS

22 out of 27 implanted participants (63% male, aged 55.9±12.0 years, body mass index (BMI) 27.4±3.0 kg·m^-2) completed the protocol. At 6 months BMI was unchanged (p=0.85); AHI decreased from 23.7±12.2 to 12.9±10.1 events·h^-1, a mean change of 10.8 events·h^-1 (p<0.001); and ODI decreased from 19.1±11.2 to 9.8±6.9 events·h^-1, a mean change of 9.3 events·h^-1 (p<0.001). Daytime sleepiness (Epworth Sleepiness Scale; p=0.01) and sleep-related quality of life (Functional Outcomes of Sleep Questionnaire-10; p=0.02) both improved significantly. The number of bed partners reporting loud, very intense snoring, or leaving the bedroom due to participant snoring decreased from 96% to 35%. 91% of participants reported device use >5 days per week, and 77% reported use for >5 h per night. No device-related serious adverse events occurred during the 6-month post-implantation period.

CONCLUSIONS

Bilateral HNS using the Genio™ system reduces OSA severity and improves quality of life without device-related complications. The results are comparable with previously published HNS systems despite minimal implanted components and a simple stimulation algorithm.

A Device that Models Human Swallowing

The pharynx is critical for correct swallowing, facilitating the transport of both air and food transport in a highly coordinated manner, and aberrant co-ordination causes swallowing disorders (dysphagia). In this work, an in vitro model of swallowing was designed to investigate the role of rheology in swallowing and for use as a pre-clinical tool for simulation of different routes to dysphagia. The model is based on the geometry of the human pharynx. Manometry is used for pressure measurements and ultrasonic analysis is performed to analyze the flow profiles and determine shear rate in the bolus, the latter being vital information largely missing in literature. In the fully automated model, bolus injection, epiglottis/nasopharynx movement, and ultrasound transducer positioning can be controlled. Simulation of closing of the airways and nasal cavity is modulated by the software, as is a clamping valve that simulates the upper esophageal sphincter. The actions can be timed and valves opened to different degrees, resembling pathologic swallowing conditions. To validate measurements of the velocity profile and manometry, continuous and bolus flow was performed. The respective velocity profiles demonstrated the accuracy and validity of the flow characterization necessary for determining bolus flow. A maximum bolus shear rate of 80 s-1 was noted for syrup-consistency fluids. Similarly, the manometry data acquired compared very well with clinical studies.

Pharyngeal airway dimension in patients before and after treatment of myofascial pain syndrome

Objective: This study aimed: (1) to assess the localization of the anatomic landmarks of the pharyngeal airway on cone beam computed tomography (CBCT) images; and (2) to evaluate if resolution of myofascial pain syndrome (MPS) changed the airway dimensions.Methods: Twenty-nine patients with pre- and post-treatment CBCT scans were randomly selected to locate five landmarks twice, with a two-week interval. The same landmarks were used to measure the airway volume and minimal cross-sectional area (CSA_min).Results: The intra-observer reliability (ICC) was 0.99-1.00 for volumetric and CSA_min measurements, based on the five landmarks used. The paired t test showed no significant difference in the airway volume (p = 0.68) and CSA_min (p = 0.96).Discussion: The outcomes showed that the landmarks used had excellent ICCs for the volumetric and CSA_min measurements. There was no change in volume and CSA_min of the pharyngeal airway after resolution of MPS.

An Anesthesiologist's Perspective on the History of Basic Airway Management: The "Modern" Era, 1960 to Present

This fourth and last installment of my history of basic airway management discusses the current (i.e., "modern") era of anesthesia and resuscitation, from 1960 to the present. These years were notable for the implementation of intermittent positive pressure ventilation inside and outside the operating room. Basic airway management in cardiopulmonary resuscitation (i.e., expired air ventilation) was de-emphasized, as the "A-B-C" (airway-breathing-circulation) protocol was replaced with the "C-A-B" (circulation-airway-breathing) intervention sequence. Basic airway management in the operating room (i.e., face-mask ventilation) lost its predominant position to advanced airway management, as balanced anesthesia replaced inhalation anesthesia. The one-hand, generic face-mask ventilation technique was inherited from the progressive era. In the new context of providing intermittent positive pressure ventilation, the generic technique generated an underpowered grip with a less effective seal and an unspecified airway maneuver. The significant advancement that had been made in understanding the pathophysiology of upper airway obstruction was thus poorly translated into practice. In contrast to consistent progress in advanced airway management, progress in basic airway techniques and devices stagnated.

EIT Imaging of Upper Airway to Estimate Its Size and Shape Changes During Obstructive Sleep Apnea

Noninvasive continuous imaging of the upper airway during natural sleep was conducted for patients with obstructive sleep apnea (OSA) using the electrical impedance tomography (EIT) technique. A safe amount of alternating current (AC) was injected into the lower head through multiple surface electrodes. Since the air is an electrical insulator, upper airway narrowing during OSA altered internal current pathways and changed the induced voltage distribution. Since the measured voltage data from the surface of the lower head were influenced not only by upper airway narrowing but respiratory motions, head motions, and blood flows, we developed a pre-processing algorithm to extract the voltage component originated from upper airway closing and opening. Using an EIT image reconstruction algorithm, time-series of EIT images of the upper airway were produced with a temporal resolution of 50 frames per second. Applying a postprocessing algorithm to the reconstructed EIT images, we could extract quantitative information about changes in the size and shape during upper airway closing and opening. Results of the clinical studies with seven normal subjects and ten OSA patients show the feasibility of the new method for OSA phenotyping and treatment planning.

Modelling mucosal surface roughness in the human velopharynx: a computational fluid dynamics study of healthy and obstructive sleep apnea airways

We previously published a unique methodology for quantifying human velopharyngeal mucosal surface topography and found increased mucosal surface roughness in obstructive sleep apnea (OSA) patients. In fluid mechanics, surface roughness is associated with increased frictional pressure losses and resistance. This study used computational fluid dynamics (CFD) to analyse the mechanistic effect of different levels of mucosal surface roughness on velopharyngeal airflow.

METHODS

Reconstructed velopharyngeal models from OSA and Control subjects were modified, giving each model three levels of roughness, quantified by the curvature based surface roughness index (CBSRI_0.6; range 24.8-68.6mm^-1). CFD using the k-ω shear stress transport (SST) turbulence model was performed (unidirectional, inspiratory, steady state, 15l/min volumetric flow rate), and the effects of roughness on flow velocity, intraluminal pressure, wall shear stress and velopharyngeal resistance (R_v) were examined.

RESULTS

Across all models, increasing roughness increased maximum flow velocity, wall shear stress and flow disruption, while decreasing intraluminal pressures. Linear mixed effects modelling demonstrated a log-linear relationship between CBSRI_0.6 and R_v, with a common slope (log(R_v)/CBSRI_0.6) of 0.0079 (95%CI 0.0015-0.0143; p=0.019) for all subjects, equating to a 1.9-fold increase in R_v when roughness increased from Control to OSA levels. At any fixed CBSRI_0.6, the estimated difference in log(R_v) between OSA and Control models was 0.9382 (95%CI 0.0032-1.8732; p=0.049), equating to an 8.7-fold increase in R_v.

CONCLUSION

This study supports the hypothesis that increasing mucosal surface roughness increases velopharyngeal airway resistance, particularly for anatomically narrower OSA airways, and may thus contribute to increased vulnerability to upper airway collapse in OSA patients.

Retropalatal and retroglossal airway compliance in patients with obstructive sleep apnea

OBJECTIVES

We hypothesized that preferential retropalatal as compared to retroglossal collapse in patients with obstructive sleep apnea was due to a narrower retropalatal area and a higher retropalatal compliance. Patients with a greater retropalatal compliance would exhibit a recognizable increase in negative effort dependence (NED).

METHODS

Fourteen patients underwent upper airway endoscopy with simultaneous recordings of airflow and pharyngeal pressure during natural sleep. Airway areas were obtained by manually outlining the lumen. Compliance was calculated by the change of airway area from end-expiration to a pressure swing of -5 cm H₂O. NED was quantified for each breath as [peak inspiratory flow minus flow at -5 cm H₂O]/[peak flow] × 100.

RESULTS

Compared to the retroglossal airway, the retropalatal airway was smaller at end-expiration (p < 0.001), and had greater absolute and relative compliances (p < 0.001). NED was positively associated with retropalatal relative area change (r = 0.47; p < 0.001).

CONCLUSIONS

Retropalatal airway is narrower and more collapsible than retroglossal airway. Retropalatal compliance is reflected in the clinically-available NED value.

Multi-modal anatomical Optical Coherence Tomography and CT for in vivo Dynamic Upper Airway Imaging

We describe a novel, multi-modal imaging protocol for validating quantitative dynamic airway imaging performed using anatomical Optical Coherence Tomography (aOCT). The aOCT system consists of a catheter-based aOCT probe that is deployed via a bronchoscope, while a programmable ventilator is used to control airway pressure. This setup is employed on the bed of a Siemens Biograph CT system capable of performing respiratory-gated acquisitions. In this arrangement the position of the aOCT catheter may be visualized with CT to aid in co-registration. Utilizing this setup we investigate multiple respiratory pressure parameters with aOCT, and respiratory-gated CT, on both ex vivo porcine trachea and live, anesthetized pigs. This acquisition protocol has enabled real-time measurement of airway deformation with simultaneous measurement of pressure under physiologically relevant static and dynamic conditions- inspiratory peak or peak positive airway pressures of 10-40 cm H₂O, and 20-30 breaths per minute for dynamic studies. We subsequently compare the airway cross sectional areas (CSA) obtained from aOCT and CT, including the change in CSA at different stages of the breathing cycle for dynamic studies, and the CSA at different peak positive airway pressures for static studies. This approach has allowed us to improve our acquisition methodology and to validate aOCT measurements of the dynamic airway for the first time. We believe that this protocol will prove invaluable for aOCT system development and greatly facilitate translation of OCT systems for airway imaging into the clinical setting.

Shear and extensional rheology of commercial thickeners used for dysphagia management

People who suffer from swallowing disorders, commonly referred to as dysphagia, are often restricted to a texture-modified diet. In such a diet, the texture of the fluid is modified mainly by the addition of gum or starch-based thickeners. For optimal modification of the texture, tunable rheological parameters are shear viscosity, yield stress, and elasticity. In this work, the flow properties of commercial thickeners obtained from major commercial suppliers were measured both in shear and extensional flow using a laboratory viscometer and a newly developed tube viscometry technique, termed Pulsed Ultrasound Velocimetry plus Pressure Drop (PUV + PD). The two methods gave similar results, demonstrating that the PUV + PD technique can be applied to study flow during the swallowing process in geometry similar to that of the swallowing tract. The thickeners were characterized in relation to extensional viscosity using the Hyperbolic Contraction Flow method, with microscopy used as a complementary method for visualization of the fluid structure. The gum-based thickeners had significantly higher extensional viscosities than the starch-based thickeners. The rheological behavior was manifested in the microstructure as a hydrocolloid network with dimensions in the nanometer range for the gum-based thickeners. The starch-based thickeners displayed a granular structure in the micrometer range. In addition, the commercial thickeners were compared to model fluids (Boger, Newtonian, and Shear-thinning) set to equal shear viscosity at 50/s and it was demonstrated that their rheological behavior could be tuned between highly elastic, extension-thickening to Newtonian.

PRACTICAL APPLICATIONS

Thickeners available for dysphagia management were characterized for extensional viscosity to improve the understanding of these thickeners in large scale deformation. Extensional deformation behavior was further explained by using microcopy as corresponding technique for better understanding of structure/rheology relationship. Moreover, the major challenge in capturing human swallowing process is the short transit times of the bolus flow (<1 s). Therefore, the ultrasound-based rheometry method; PUV+PD which measures the real-time flow curve in ∼50 ms was used in addition to classical shear rheometry. The two methods complimented each other indicating that the PUV+PD method can be applied to study the transient swallowing process which is part of our future research, where we are studying the flow properties of fluids in an in vitro swallowing tract.

The microbiota of the respiratory tract: gatekeeper to respiratory health

The respiratory tract is a complex organ system that is responsible for the exchange of oxygen and carbon dioxide. The human respiratory tract spans from the nostrils to the lung alveoli and is inhabited by niche-specific communities of bacteria. The microbiota of the respiratory tract probably acts as a gatekeeper that provides resistance to colonization by respiratory pathogens. The respiratory microbiota might also be involved in the maturation and maintenance of homeostasis of respiratory physiology and immunity. The ecological and environmental factors that direct the development of microbial communities in the respiratory tract and how these communities affect respiratory health are the focus of current research. Concurrently, the functions of the microbiome of the upper and lower respiratory tract in the physiology of the human host are being studied in detail. In this Review, we will discuss the epidemiological, biological and functional evidence that support the physiological role of the respiratory microbiota in the maintenance of human health.

Airway compliance measured by anatomic optical coherence tomography

Quantification of airway compliance can aid in the diagnosis and treatment of obstructive airway disorders by detecting regions vulnerable to collapse. Here we evaluate the ability of a swept-source anatomic optical coherence tomography (SSaOCT) system to quantify airway cross-sectional compliance (CC) by measuring changes in the luminal cross-sectional area (CSA) under physiologically relevant pressures of 10-40 cmH₂O. The accuracy and precision of CC measurements are determined using simulations of non-uniform rotation distortion (NURD) endemic to endoscopic scanning, and experiments performed in a simplified tube phantom and ex vivo porcine tracheas. NURD simulations show that CC measurements are typically more accurate than that of the CSAs from which they are derived. Phantom measurements of CSA versus pressure exhibit high linearity (R²>0.99), validating the dynamic range of the SSaOCT system. Tracheas also exhibited high linearity (R² = 0.98) suggestive of linear elasticity, while CC measurements were obtained with typically ± 12% standard error.

Correlation of upper airway radiographic measurements with risk status for obstructive sleep apnea syndrome in young dental patients

OBJECTIVE

The aim of the present study is to compare radiographic measurements of the upper airway (UA) in young adult patients with different levels of risk status for obstructive sleep apnea syndrome.

STUDY DESIGN

The study included 50 patients between 18 and 30 years of age who were referred for dental examination and evaluation of impacted third molars. Case record forms, including habit history, along with the Berlin Questionnaire and the Epworth Sleepiness Scale, were completed by the patients and their relatives. According to the answers, 25 low-risk patients and 25 high-risk patients were selected. Cephalometric radiographs and cone beam computed radiography images were obtained for radiographic analysis when the patients were admitted into the study.

RESULTS

There were significant differences in body mass index, neck circumference measurements, Epworth score, and smoking status between risk groups. There were significant differences for UA measurements on radiographic evaluation. Body mass index (BMI) was found to be correlated positively with neck circumference and Epworth scores and negatively with UA measurements for all patients. Velopharyngeal measurements showed the highest correlation with Epworth scores, BMI, and neck circumference.

CONCLUSIONS

The radiographic findings correlated with the survey results. Our data suggest that radiographic measurements of UA may be used as a predictor of risk for obstructive sleep apnea syndrome in a young population.

Epiglottis cross-sectional area and oropharyngeal airway length in male and female obstructive sleep apnea patients

INTRODUCTION

Obstructive sleep apnea (OSA) is a male-predominant condition, characterized by repeated upper-airway collapse with continued diaphragmatic efforts during sleep, and is accompanied by severe physiological consequences. Multiple morphological aspects, including epiglottis cross-sectional area (CSA) and oropharyngeal airway length (OPAL), can contribute to airway collapsibility in the condition. This study focused on the effects of OSA severity, sex, and race on OPA dimensions.

MATERIALS AND METHODS

Two high-resolution T1-weighted image series were collected from 40 mild-to-severe OSA subjects (age 46.9±9 years, body mass index 30.4±5.4 kg/m2, Apnea-Hypopnea Index score 32.8±22.5, 28 males) and 54 control subjects (47±9 years, 24.7±3.8 kg/m2, 32 males) using a 3 T magnetic resonance-imaging scanner. Caucasian, Asian, African-American, and "other" subjects constituted the study pool. Both image series were realigned and averaged, and reoriented to a common space. CSA and OPAL were measured, normalized for subject height, and compared between sexes and disease-severity levels in OSA and control subjects.

RESULTS

Significantly reduced epiglottis CSA appeared only in severe OSA vs controls (P=0.009). OPAL increased significantly with OSA severity vs controls (mild, P=0.027; moderate, P<0.001; severe, P<0.001). OSA males showed increased CSA and greater OPAL than OSA females, which may underlie the increased proportion of affected males with higher apnea-hypopnea index scores. However, no significant differences appeared between CSA and OPAL measures for male and female controls, suggesting that airway morphology may not be the sole contributor for airway collapse. No ethnic or racial differences appeared for CSA or OPAL measures.

CONCLUSION

Sex-based reductions in epiglottis CSA and increased OPAL in OSA subjects may enhance airway-collapse vulnerability, more so with greater disease severity, and partially underlie male vs female susceptibility to the sleep disorder.

Quantitative Evaluation of Adult Subglottic Stenosis Using Intraoperative Long-range Optical Coherence Tomography

OBJECTIVES

To determine the feasibility of long-range optical coherence tomography (LR-OCT) as a tool to intraoperatively image and measure the subglottis and trachea during suspension microlaryngoscopy before and after endoscopic treatment of subglottic stenosis (SGS).

METHODS

Long-range optical coherence tomography of the adult subglottis and trachea was performed during suspension microlaryngoscopy before and after endoscopic treatment for SGS. The anteroposterior and transverse diameters, cross-sectional area (CSA), distance from the vocal cords, and length of the SGS were measured using a MATLAB software. Pre-intervention and postintervention airway dimensions were compared. Three-dimensional volumetric airway reconstructions were generated using medical image processing software (MIMICS).

RESULTS

Intraoperative LR-OCT imaging was performed in 3 patients undergoing endoscopic management of SGS. Statistically significant differences in mean anteroposterior diameter (P < .01), transverse diameter (P < .001), and CSA (P < .001) were noted between pre-intervention and postintervention data. Three-dimensional airway models were viewed in cross-sectional format and via virtual "fly through" bronchoscopy.

CONCLUSIONS

This is the first report of intraoperative LR-OCT of the subglottic and tracheal airway before and after surgical management of SGS in humans. Long-range optical coherence tomography offers a practical means to measure the dimensions of SGS and acquire objective data on the response to endoscopic treatment of SGS.

Swept-Source Anatomic Optical Coherence Elastography of Porcine Trachea

Quantitative endoscopic imaging is at the vanguard of novel techniques in the assessment upper airway obstruction. Anatomic optical coherence tomography (aOCT) has the potential to provide the geometry of the airway lumen with high-resolution and in 4 dimensions. By coupling aOCT with measurements of pressure, optical coherence elastography (OCE) can be performed to characterize airway wall stiffness. This can aid in identifying regions of dynamic collapse as well as informing computational fluid dynamics modeling to aid in surgical decision-making. Toward this end, here we report on an anatomic optical coherence tomography (aOCT) system powered by a wavelength-swept laser source. The system employs a fiber-optic catheter with outer diameter of 0.82 mm deployed via the bore of a commercial, flexible bronchoscope. Helical scans are performed to measure the airway geometry and to quantify the cross-sectional-area (CSA) of the airway. We report on a preliminary validation of aOCT for elastography, in which aOCT-derived CSA was obtained as a function of pressure to estimate airway wall compliance. Experiments performed on a Latex rubber tube resulted in a compliance measurement of 0.68±0.02 mm2/cmH2O, with R2=0.98 over the pressure range from 10 to 40 cmH2O. Next, ex vivo porcine trachea was studied, resulting in a measured compliance from 1.06±0.12 to 3.34±0.44 mm2/cmH2O, (R2>0.81). The linearity of the data confirms the elastic nature of the airway. The compliance values are within the same order-of-magnitude as previous measurements of human upper airways, suggesting that this system is capable of assessing airway wall compliance in future human studies.

Transverse Retropalatal Collapsibility Is Associated with Obstructive Sleep Apnea Severity and Outcome of Relocation Pharyngoplasty

OBJECTIVE

The aim of this study was to investigate whether the retropalatal airway shape and collapsibility defined by awake nasopharyngoscopy with Müller's maneuver were associated with apnea-hypopnea index (AHI), positional dependency, and surgical outcome of relocation pharyngoplasty in patients with obstructive sleep apnea.

STUDY DESIGN

Case series with planned data collection.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

A total of 45 obstructive sleep apnea patients were included who underwent conservative treatment (n = 13) or relocation pharyngoplasty (n = 32), and their baseline and postoperative polysomnographies and awake nasopharyngoscopies with Müller's maneuver were reviewed. Shape ratio (transverse diameter [TD] / longitudinal diameter [LD]) in the stationary and Müller's phases and collapsibility (ColTD and ColLD) of the airway at the level of the uvular base were measured with a picture archiving and communication system. Intra- and interrater reliabilities were assessed. Associations among nasopharyngoscopic measurements, AHI, positional dependency, and surgical success (defined as a reduction of AHI ≥50% and a postoperative AHI ≤20/h) were statistically analyzed.

RESULTS

Reliability tests indicated substantial agreements of all nasopharyngoscopic measurements between raters and within raters. A higher baseline ColTD was significantly associated with an elevated AHI (r = 0.49, P = .001), whereas a lower postoperative ColTD was significantly related to surgical success (r = -0.38, P = .034). Nasopharyngoscopic findings were not statistically significantly correlated with positional dependency.

CONCLUSION

Transverse retropalatal collapsibility measured by awake nasopharyngoscopy with Müller's maneuver helps to predict individuals with moderate to severe sleep apnea and surgical outcome.

Optical coherence tomography in respiratory science and medicine: from airways to alveoli

Optical coherence tomography is a rapidly maturing optical imaging technology, enabling study of the in vivo structure of lung tissue at a scale of tens of micrometers. It has been used to assess the layered structure of airway walls, quantify both airway lumen caliber and compliance, and image individual alveoli. This article provides an overview of the technology and reviews its capability to provide new insights into respiratory disease.

Pharyngeal mucosal wall folds in subjects with obstructive sleep apnea

Mechanical processes underlying pharyngeal closure have not been examined. We hypothesized that the pharyngeal mucosal surface would fold during closure, and lowering the upper airway lining liquid surface tension would unfold areas of mucosal apposition, i.e., folds. We compared baseline pharyngeal fold numbers and response to reduction in upper airway liquid surface tension in healthy and obstructive sleep apnea (OSA) subjects. Awake, gated magnetic resonance pharyngeal airway images of 10 healthy and 11 OSA subjects were acquired before and after exogenous surfactant administration (beractant). Upper airway liquid surface tension was measured at the beginning and end of image acquisition and averaged. Velopharyngeal and oropharyngeal images were segmented and analyzed separately for average cross-sectional area, circumference, and fold number. Compared with healthy subjects, at baseline, velopharynx for OSA subjects had a smaller cross-sectional area (98.3 ± 32.5 mm(2) healthy, 52.3 ± 23.6 mm(2) OSA) and circumference (46.5 ± 8.1 mm healthy, 30.8 ± 6.1 mm OSA; both P < 0.05, unpaired t-test), and fewer folds (4.9 ± 1.6 healthy, 3.1 ± 1.8 OSA, P < 0.03). There were no differences in oropharynx for cross-sectional area, circumference, or folds. Reduction in upper airway liquid surface tension from 61.3 ± 1.2 to 55.3 ± 1.5 mN/m (P < 0.0001) did not change cross-sectional area or circumference for velopharynx or oropharynx in either group; however, in OSA subjects, oropharyngeal folds fell from 6.8 ± 3.1 to 4.7 ± 1.2 (n = 8, P < 0.05), and velopharyngeal folds from 3.3 ± 1.9 to 2.3 ± 1.2 (P = 0.08), and were unchanged in healthy subjects. Subjects with OSA have fewer velopharyngeal wall folds, which decrease further when surface tension falls. We speculate that reduced pharyngeal wall folds contribute to an increase in pharyngeal collapsibility.

Biomechanical properties of the human upper airway and their effect on its behavior during breathing and in obstructive sleep apnea

The upper airway is a complex, multifunctional, dynamic neuromechanical system. Its patency during breathing requires moment-to-moment coordination of neural and mechanical behavior and varies with posture. Failure to continuously recruit and coordinate dilator muscles to counterbalance the forces that act to close the airway results in hypopneas or apneas. Repeated failures lead to obstructive sleep apnea (OSA). Obesity and anatomical variations, such as retrognathia, increase the likelihood of upper airway collapse by altering the passive mechanical behavior of the upper airway. This behavior depends on the mechanical properties of each upper airway tissue in isolation, their geometrical arrangements, and their physiological interactions. Recent measurements of respiratory-related deformation of the airway wall have shown that there are different patterns of airway soft tissue movement during the respiratory cycle. In OSA patients, airway dilation appears less coordinated compared with that in healthy subjects (matched for body mass index). Intrinsic mechanical properties of airway tissues are altered in OSA patients, but the factors underlying these changes have yet to be elucidated. How neural drive to the airway dilators relates to the biomechanical behavior of the upper airway (movement and stiffness) is still poorly understood. Recent studies have highlighted that the biomechanical behavior of the upper airway cannot be simply predicted from electromyographic activity (electromyogram) of its muscles.

Recent advances in optical coherence tomography for the diagnoses of lung disorders

There have been many advances in the field of diagnostic and therapeutic pulmonary medicine in the past several years, with major progress in the field of imaging. Optical coherence tomography (OCT) is a high-resolution (micron level) imaging modality currently being advanced with the potential to image airway wall structures in real time and at higher resolution than previously possible. OCT has the potential to increase the sensitivity and specificity of biopsies, create 3D images of the airway to guide diagnostics, and may have a future role in diverse areas such as the evaluation and treatment of patients with obstructive sleep apnea, tracheal stenosis, airway remodeling and inhalation injury. OCT has recently been investigated to monitor airway compliance in chronic obstructive pulmonary disease and asthma patients as well as differentiate causes of pulmonary hypertension. In future clinical and research applications, OCT will likely be combined with other endoscopic based modalities such as ultrasound, spectroscopy, confocal, and/or photoacoustic tomography to determine functional and biomolecular properties. This article discusses the current uses of OCT, its potential applications, as it relates to specific pulmonary diseases, and the future directions for OCT.

Phenotyping airway disease with optical coherence tomography

Airway diseases are a major concern around the world. However, the pace of new drug and biomarker discovery has lagged behind those of other common disorders such as cardiovascular diseases and diabetes. One major barrier in airway research has been the inability to accurately visualize large or small airway remodelling or dysplastic/neoplastic (either pre or early cancerous) changes using non- or minimally invasive instruments. The advent of optical coherence tomography (OCT) has the potential to revolutionize airway research and management by allowing investigators and clinicians to visualize the airway with resolution approaching histology and without exposing patients to harmful effects of ionizing radiation. Thus, with the aid of OCT, we may be able to accurately determine and quantify the extent of airway remodelling in asthma and chronic obstructive pulmonary disease, detect early pre-cancerous lesions in smokers for chemoprevention, study the upper airway anatomy of patients with obstructive sleep apnea in real time while they are asleep and facilitate optimal selection of stents for those with tracheal obstruction. In this paper, we review the current state of knowledge of OCT and its possible application in airway diseases.

Influence of tongue muscle contraction and transmural pressure on nasopharyngeal geometry in the rat

The mammalian pharynx is a hollow muscular tube that participates in ingestion and respiration, and its size, shape, and stiffness can be altered by contraction of skeletal muscles that lie inside or outside of its walls. MRI was used to determine the interaction between pharyngeal pressure and selective stimulation of extrinsic tongue muscles on the shape of the rat nasopharynx. Pressure (-9, -6, -3, 3, 6, and 9 cmH₂O) was applied randomly to the isolated pharyngeal airway of anesthetized rats that were positioned in a 4.7-T MRI scanner. The anterior-posterior (AP) and lateral diameters of the nasopharynx were measured in eight axial slices at each level of pressure, with and without bilateral hypoglossal nerve stimulation (0.1-ms pulse, 1/3 maximal force, 80 Hz). The rat nasopharynx is nearly circular, and positive pharyngeal pressure caused similar expansion of AP and lateral diameters; as a result, airway shape (ratio of lateral to AP diameter) remained constant. Negative pressure did not change AP or lateral diameter significantly, suggesting that a negative pressure reflex activated the tongue or other pharyngeal muscles. Stimulation of tongue protrudor muscles alone or coactivation of protrudor and retractor muscles caused greater AP than lateral expansion, making the nasopharynx slightly more elliptical, with the long axis in the AP direction. These effects tended to be more pronounced at negative pharyngeal pressures and greater in the caudal than rostral nasopharynx. These data show that stimulation of rodent tongue muscles can adjust pharyngeal shape, extending previous work showing that tongue muscle contraction alters pharyngeal compliance and volume, and provide physiological insight that can be applied to the treatment of obstructive sleep apnea.

Variability of human upper airway collapsibility during sleep and the influence of body posture and sleep stage

The critical pressure at which the pharynx collapses (Pcrit) is an objective measurement of upper airway collapsibility, an important pathogenetic factor in obstructive sleep apnoea. This study examined the inherent variability of passive Pcrit measurement during sleep and evaluated the effects of sleep stage and body posture on Pcrit. Repeated measurements of Pcrit were assessed in 23 individuals (15 male) with diagnosed obstructive sleep apnoea throughout a single overnight sleep study. Body posture and sleep stage were unrestricted. Applied upper airway pressure was repetitively reduced to obtain multiple measurements of Pcrit. In 20 subjects multiple measurements of Pcrit were obtained. The overall coefficient of repeatability for Pcrit measurement was 4.1 cm H₂O. Considering only the lateral posture, the coefficient was 4.8 cm H₂O. It was 3.3 cm H₂O in the supine posture. Pcrit decreased from the supine to lateral posture [supine mean 2.5 cm H₂O, 95% confidence interval (CI) 1.4-3.6; lateral mean 0.3 cm H₂O, 95% CI -0.8-1.4, P = 0.007] but did not vary with sleep stage (P = 0.91). This study has shown that the overall coefficient of repeatability was 4.1 cm H₂O, implying that the minimum detectable difference, with 95% probability, between two repeated Pcrit measurements in an individual is 4.1 cm H₂O. Such variability in overnight measures of Pcrit indicates that a single unqualified value of Pcrit cannot be used to characterize an individual's overall collapsibility during sleep. When within-subject variability is accounted for, change in body posture from supine to lateral significantly decreases passive pharyngeal collapsibility.

Comparative effects of two oral appliances on upper airway structure in obstructive sleep apnea

STUDY OBJECTIVES

Oral appliances are increasingly being used for treatment of obstructive sleep apnea (OSA). Mandibular advancement splint (MAS) mechanically protrudes the mandible, while the tongue stabilizing device (TSD) protrudes and holds the tongue using suction. Although both appliances can significantly improve or ameliorate OSA, their comparative effects on upper airway structure have not been investigated.

DESIGN

Cohort study.

SETTING

Sleep Investigation Unit.

PATIENTS

39 patients undergoing oral appliance treatment for OSA.

INTERVENTIONS

OSA patients underwent magnetic resonance imaging (MRI) of the upper airway during wakefulness at baseline and with MAS and TSD in randomized order. Treatment efficacy was determined by polysomnography in a subset of 18 patients.

MEASUREMENTS AND RESULTS

Upper airway lumen and surrounding soft tissue structures were segmented using image analysis software. Upper airway dimensions and soft tissue centroid movements were determined. Both appliances altered upper airway geometry, associated with movement of the parapharyngeal fat pads away from the airway. TSD increased velopharyngeal lateral diameter to a greater extent (+0.35 ± 0.07 vs. +0.18 ± 0.05 cm; P<0.001) and also increased antero-posterior diameter with anterior displacement of the tongue (0.68 ± 0.04 cm; P<0.001) and soft palate (0.12 ± 0.03 cm; P<0.001). MAS resulted in significant anterior displacement of the tongue base muscles (0.35 ± 0.04 cm). TSD responders (AHI reduction ≥50%) increased velopharyngeal volume more than non-responders (+2.65 ± 0.9 vs. -0.44 ± 0.8 cm(3); P < 0.05). Airway structures did not differ between MAS responders and non-responders.

CONCLUSIONS

These results indicate that the patterns and magnitude of changes in upper airway structure differ between appliances. Further studies are warranted to evaluate the clinical relevance of these changes, and whether they can be used to predict treatment outcome.

Imaging true 3D endoscopic anatomy by incorporating magnetic tracking with optical coherence tomography: proof-of-principle for airways

Endoscopic imaging using optical coherence tomography (OCT) has been demonstrated as clinically useful in the assessment of human airways. These airways have a complex 3D structure, bending, tapering and bifurcating. Previously published 3D OCT reconstructions have not accounted for changes in the orientation and trajectory of the endoscopic probe as it moves through the airway during imaging. We propose a novel endoscopic setup incorporating a magnetic tracking system that accounts for these changes, yielding reconstructions that reveal the true 3D nature of the imaged anatomy. We characterize the accuracy of the system, and present the first published magnetic tracker-assisted endoscopic OCT reconstructions using a phantom airway.