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Sleep therapy devices, such as Continuous Positive Airway Pressure (CPAP) devices, support and monitor patients with sleep disordered breathing. The assessment of their efficacy typically relies either on time-consuming clinical studies, whose reproducibility in real patients is challenging, or on bench testing designed to reproducibly simulate patient behavior. The purpose of this study is to address the limitations of existing approaches of simulating upper airway behavior for testing sleep therapy devices by introducing a dynamic valve system, governed by a mathematical resistance model. This approach enables real-time adjustment of upper airway obstruction levels using the parameter critical pressure. It allows for a high degree of control over the severity of airflow-limitations, ranging from no flow-limitation to complete obstruction. Additionally, by adjusting the model’s parameters it is possible to flexibly simulate various flow-limitation waveforms observed in real patients, reflecting their anatomical variations. Compared to the Starling resistor, which is the current state-of-the-art method for upper airway simulation, the proposed approach improves reproducibility by reducing dependence on material properties and eliminating aging effects associated with the resistor’s elastic segment. Bench validation against computer simulations yielded a normalized root mean square error below 4%, with recorded patterns faithfully replicating flow limitation observed in real patients. Its rigorous mathematical framework and modest hardware requirements make the system readily accessible for widespread use. In conclusion, this work provides a more robust, flexible, and comprehensive platform for evaluating sleep therapy devices.

Abstract 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 Forty 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 (analysis of covariance [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.

Hypoglossal nerve stimulation (HGNS) has evolved as a novel and effective therapy for patients with moderate-to-severe obstructive sleep apnea. Despite positive published outcomes of HGNS, there exist uncertainties regarding proper patient selection, surgical technique, and the reporting of outcomes and individual factors that impact therapy effectiveness. According to current guidelines, this therapy is indicated for select patients, and recommendations are based on the Stimulation Therapy for Apnea Reduction or STAR trial. Ongoing research and physician experiences continuously improve methods to optimize the therapy. An understanding of the way in which airway anatomy, obstructive sleep apnea phenotypes, individual health status, psychological conditions, and comorbid sleep disorders influence the effectiveness of HGNS is essential to improve outcomes and expand therapy indications. This article presents discussions on current evidence, future directions, and research gaps for HGNS therapy from the 10th International Surgical Sleep Society expert research panel. Citation: Suurna MV, Jacobowitz O, Chang J, et al. Improving outcomes of hypoglossal nerve stimulation therapy: current practice, future directions and research gaps. Proceedings of the 2019 International Sleep Surgery Society Research Forum. J Clin Sleep Med . 2021;17(12):2477–2487.

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.

Dynamic upper airway obstructions (DUAO) are common in racehorses, but their pathogenetic mechanisms have not been completely clarified yet. Multiple studies suggest that alterations of the pharyngo-laryngeal region visible at resting endoscopy may be predictive of the onset of DUAO, and the development of DUAO may be associated with pharyngeal lymphoid hyperplasia (PLH), lower airway inflammation (LAI) and exercise-induced pulmonary hemorrhage (EIPH). The present study aims to investigate the possible relationship between the findings of a complete resting evaluation of the upper and lower airways and DUAO. In this retrospective study, 360 racehorses (Standardbreds and Thoroughbreds) referred for poor performance or abnormal respiratory noises were enrolled and underwent a diagnostic protocol including resting and high-speed treadmill endoscopy, cytological examination of the bronchoalveolar lavage fluid and radiographic assessment of the epiglottis length. In this population, epiglottis flaccidity was associated with dorsal displacement of the soft palate, while no relationship was detected between DUAO and epiglottis length. No associations were detected between DUAO and PLH, LAI or EIPH. In conclusion, it is likely that epiglottis plays a role in upper airway stability, while airways inflammation does not seem to be involved in the pathogenesis of DUAO.

PurposeTo compare the anatomical balance and shape of the upper airway in the supine position between adults with positional obstructive sleep apnea (POSA) and adults with non-positional OSA (NPOSA).MethodsAdults diagnosed with OSA (apnea-hypopnea index (AHI) > 10 events/h) were assessed for eligibility. POSA was defined as the supine AHI more than twice the AHI in non-supine positions; otherwise, patients were classified as NPOSA. Cone beam computed tomography (CBCT) imaging was performed for every participant while awake in the supine position. The anatomical balance was calculated as the ratio of the tongue size to the maxillomandibular enclosure size. The upper airway shape was calculated as the ratio of the anteroposterior dimension to the lateral dimension at the location of the minimal cross-sectional area of the upper airway (CSAmin-shape).ResultsOf 47 participants (28 males, median age [interquartile range] 56 [46 to 63] years, median AHI 27.8 [15.0 to 33.8]), 34 participants were classified as having POSA (72%). The POSA group tended to have a higher proportion of males and a lower AHI than the NPOSA group (P = 0.07 and 0.07, respectively). After controlling for both sex and AHI, the anatomical balance and CSAmin-shape were not significantly different between both groups (P = 0.18 and 0.73, respectively).ConclusionAdults with POSA and adults with NPOSA have similar anatomical balance and shape of their upper airway in the supine position.Trial registrationThis study was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR Trial ACTRN12611000409976).

Study Objectives: Hypoglossal nerve stimulation (HNS) is an effective surgical alternative for patients with obstructive sleep apnea (OSA). HNS therapy relies on the stimulation of the hypoglossal nerve to open the upper airways. This stimulation could lead to alterations in tongue strength and fatigability, which could alter treatment outcome over time. The aim of the study was to investigate whether HNS alters tongue strength and fatigability. Methods: Tongue protrusion strength (peak pressure in kPa) and fatigability (time to task failure during 50% of peak pressure contraction) were measured with a pressure transducer at least 2 months after HNS implantation (n = 30). These results were compared to a group of patients with OSA (n = 38) and a non-OSA control group (n = 35). Results: Median tongue protrusion strength was lower (54.7 [43.8, 63.0] versus 60.7 [53.7, 66.0] kPa, P =.013) and fatigue occurred more quickly (21.3 [17.4, 26.3] versus 26.0 [19.3, 31.3] seconds, P =.017) in the patients with OSA compared to the non-OSA control group. In multiple regression analysis, age was a significant factor for tongue strength and diagnosis of OSA for tongue fatigability. Tongue strength and fatigability did not differ between patients with OSA with conservative therapy or observation versus after HNS implantation (51.8 [41.3, 63.4] versus 56.3 [45.0, 62.3] kPa, P =.502; 20.8 [16.3, 26.2] versus 21.8 [18.3, 26.8] seconds, P =.418). Conclusions: Tongue strength decreases with age. Tongue fatigability is more pronounced in people with OSA. However, approximately 1.5 years of HNS therapy on average does not alter tongue strength or fatigability compared to an OSA control group. Clinical Trial Registration: Registry: ClinicalTrials.gov ; Title:Change in Tongue Strength and Fatigue After Upper Airway Stimulation Therapy; Identifier:NCT03980158 Citation: Wirth M, Unterhuber D, von Meyer F, et al. Hypoglossal nerve stimulation therapy does not alter tongue protrusion strength and fatigability in obstructive sleep apnea. J Clin Sleep Med . 2020;16(2):285–292.

PurposeThe objective was to determine if alteration in airflow induced by negative pressure (NP) applied to participants’ upper airways during wakefulness, is related to obstructive sleep apnea (OSA) severity as determined by the apnea–hypopnea index (AHI).MethodsAdults 18 years of age or greater were recruited. All participants underwent overnight polysomnography to assess their apnea–hypopnea index (AHI). While awake, participants were twice exposed, orally, to -3 cm H2O of NP for five full breaths. The ratio of the breathing volumes of the last two breaths during NP exposure to the last two breaths prior to NP exposure was deemed the NP ratio (NPR).ResultsEighteen participants were enrolled. A strong relationship between the AHI and the exponentially transformed NPR (ExpNPR) for all participants was observed (R2 = 0.55, p < 0.001). A multivariable model using the independent variable ExpNPR, age, body mass index and sex accounted for 81% of variability in AHI (p = 0.0006). A leave-one-subject-out cross-validation analysis revealed that predicted AHI using the multivariable model, and actual AHI from participants’ polysomnograms, were strongly related (R2 = 0.72, p < 0.001).ConclusionWe conclude that ExpNPR, was strongly related to the AHI, independently of demographic factors known to be related to the AHI.

PurposeThe aim was to compare the outcomes of upper airway stimulation (Stim) and other upper airway surgical procedures (Surg) in the treatment of obstructive sleep apnea (OSA).MethodsData sources included PubMed, Ovid MEDLINE, Cochrane Library, Web of Science, Scopus, and reference lists. Relevant articles were identified from various databases according to the PRISMA guidelines.ResultsFive articles with a total of 990 patients were included. The mean cure rates in the Stim group and the Surg group was 63% and 22%, and the mean success rates was 86% and 51% which were higher in the Stim group (p < 0.001). The apnea–hypopnea index reduction was -23.9 events/ hour (MD, 95% CI -25.53, -22.29) in the Stim group and -15.5 events/hour (MD, 95% CI -17.50, -13.45) in the Surg group which was greater in the Stim group (P < 0.001). Epworth Sleepiness Scale decreased -4.9 (MD, 95% CI -5.45, -4.32) in the Stim group and -5.1 (MD 95% CI -5.88, -4.37) in the Surg group without significant difference between the groups (P = 0.62). Oxygen saturation nadir improvement was 8.5% (MD 95% CI 7.05%, 9.92%) in the Stim group and 2.2% (MD 95% CI—0.22%, 4.58%) in the Surg group which was higher in the Stim group (P < 0.001). Hospital stay and readmission rate were lower in the Stim group. The timing of follow-up ranged from 2 to 13 months.ConclusionUpper airway stimulation provides improved objective and similar subjective outcomes compared to other upper airway surgical procedures for selected patients with moderate to severe OSA with difficulty adhering to CPAP treatment. However, further studies are essential to confirm outcomes in the long term.

Partial neuromuscular transmission failure by acetylcholine receptor blockade (neuromuscular blockade) or antibody-mediated functional loss (myasthenia gravis), even with a magnitude of muscle weakness that does not evoke respiratory symptoms, can evoke dysphagia and decreased inspiratory airflow, and increases the risk of susceptible patients to develop severe pulmonary complications. To assess whether impaired neuromuscular transmission predisposes individuals to inspiratory upper airway collapse, we assessed supraglottic airway diameter and volume by respiratory-gated magnetic resonance imaging, upper airway dilator muscle function (genioglossus force and EMG), and changes in lung volume, respiratory timing, and peripheral muscle function before, during, and after partial neuromuscular blockade in healthy, awake volunteers. Partial neuromuscular blockade (train-of-four [TOF] ratio: 0.5 and 0.8) was associated with the following: (1) a decrease of inspiratory retropalatal and retroglossal upper airway volume to 66 +/- 22 and 82 +/- 12% of baseline, which was significantly more intense in the retropalatal area; (2) an attenuation of the normal increase in anteroposterior upper airway diameter during forced inspiration to 74 +/- 18% of baseline; (3) a decrease in genioglossus activity during maximum voluntary tongue protrusion to 39 +/- 19% (TOF, 0.5) and 73 +/- 29% (TOF, 0.8) of baseline; and (4) no effects on upper airway size during expiration, lung volume, and respiratory timing. Thus, impaired neuromuscular transmission, even to a degree insufficient to evoke respiratory symptoms, markedly impairs upper airway dimensions and function. This may be explained by an impairment of the balance between upper airway dilating forces and negative intraluminal pressure generated during inspiration by respiratory \"pump\" muscles.