Obstructive sleep apnea

Pharmacological interventions for the treatment of obstructive sleep apnea syndrome

Obstructive Sleep Apnea Syndrome (OSAS) affects 13-33% of males and 6-9% of females globally and poses significant treatment challenges, including poor adherence to Continuous Positive Airway Pressure (CPAP) and residual excessive sleepiness (RES). This review aims to elucidate the emerging interest in pharmacological treatments for OSAS, focusing on recent advancements in this area. A thorough analysis of extensive clinical trials involving various drugs, including selective dopamine reuptake inhibitors, selective norepinephrine inhibitors, combined antimuscarinic agents, and orexin agonists, was conducted. These trials focused on ameliorating respiratory metrics and enhancing sleep quality in individuals affected by OSAS. The studied pharmacological agents showed potential in improving primary outcomes, notably the apnea-hypopnea index (AHI) and the Epworth sleepiness scale (ESS). These improvements suggest enhanced sleep quality and symptom management in OSAS patients. With a deeper understanding of OSAS, pharmacological interventions are emerging as a promising direction for its effective management. This review provides a comprehensive overview of the current state of drug research in OSAS, highlighting the potential of these treatments in addressing the disorder's complex challenges.

Mechanisms underlying the prolonged activation of the genioglossus following arousal from sleep

STUDY OBJECTIVES

Transient arousal from sleep has been shown to elicit a prolonged increase in genioglossus muscle activity that persists following the return to sleep and which may protect against subsequent airway collapse. We hypothesized that this increased genioglossal activity following return to sleep after an arousal is due to persistent firing of inspiratory-modulated motor units (MUs) that are recruited during the arousal.

METHODS

Thirty-four healthy participants were studied overnight while wearing a nasal mask with pneumotachograph to measure ventilation and with 4 intramuscular genioglossus EMG electrodes. During stable N2 and N3 sleep, auditory tones were played to induce brief (3-15s) AASM arousals. Ventilation and genioglossus MUs were quantified before the tone, during the arousal and for 10 breaths after the return to sleep.

RESULTS

A total of 1089 auditory tones were played and gave rise to 239 MUs recorded across arousal and the return to sleep in 20 participants (aged 23 ± 4.2 years and BMI 22.5 ± 2.2 kg/m2). Ventilation was elevated above baseline during arousal and the first post-arousal breath (p < .001). Genioglossal activity was elevated for five breaths following the return to sleep, due to increased firing rate and recruitment of inspiratory modulated MUs, as well as a small increase in tonic MU firing frequency.

CONCLUSIONS

The sustained increase in genioglossal activity that occurs on return to sleep after arousal is primarily a result of persistent activity of inspiratory-modulated MUs, with a slight contribution from tonic units. Harnessing genioglossal activation following arousal may potentially be useful for preventing obstructive respiratory events.

Hypoxic Burden Based on Automatically Identified Desaturations Is Associated with Adverse Health Outcomes

Rationale: Recent studies have shown that sleep apnea-specific intermittent hypoxemia quantified by the hypoxic burden (HB) predicted cardiovascular disease (CVD)-related mortality in community-based and clinical cohorts. Calculation of HB is based on manual scoring of hypopneas and apneas, which is time-consuming and prone to interscorer variability. Objective: To validate a novel method to quantify the HB that is based on automatically scored desaturations. Methods: The sample included 5,655 middle-aged or older adults from the Sleep Heart Health Study (52.8% women; age, 63.2 ± 11.3 yr). The original HB method was based on a subject-specific search window obtained from an ensemble average of oxygen saturation signals (as measured by pulse oximetry) and synchronized with respect to the termination of scored respiratory events. In this study, however, the search window was obtained from ensemble average of oxygen saturation signals that synchronized with respect to the minimum of all automatically identified desaturations (⩾2% and other thresholds, including 3% and 4%, in sensitivity analyses). The time interval between the two maxima around the minimum saturation was defined as the search window. The oximetry-derived HB (HBOxi) was defined as the total area under all desaturation curves (restricted by the search window) divided by the total sleep time. Logistic and Cox regression models assessed the adjusted odds ratio (aOR)/hazard ratio of excessive daytime sleepiness (EDS), hypertension (HTN), and CVD mortality per 1-standard deviation increase in HBOxi after adjusting for several covariates and confounders. Results: The Spearman's rank correlation between HB (median [interquartile range], 34.4 [18.4-59.8] % min/h) and HBOxi (median [interquartile range], 34.5 [21.6-53.8] % min/h) was 0.81 (P < 0.001). Similar to HB, HBOxi was significantly associated with EDS (aOR [95% confidence interval (CI)], 1.17 [1.09-1.26] per standard deviation), HTN (aOR [95% CI], 1.13 [1.05-1.21]), and CVD mortality (adjusted hazard ratio [95% CI], 1.15 [1.01-1.30]) in fully adjusted models. Conclusions: The HBOxi was highly correlated with the HB based on manually scored apneas and hypopneas and was associated with EDS, HTN, and CVD mortality with similar effect sizes as previously reported. This method could be incorporated into wearable technology that accurately records oxygen saturation signals.

Cardiovascular Disease Outcomes Associated with Obstructive Sleep Apnea in Diabetics: A Systematic Review and Meta-Analysis

BACKGROUND

There is significant pathogenic and epidemiological overlap between diabetes and obstructive sleep apnea (OSA). This systematic review aimed to ascertain the association between OSA and cardiovascular disease (CVD) in a diabetic population.

METHODS

The study protocol was registered with PROSPERO (CRD42023404126). On 15 July 2023, a comprehensive search of the literature was performed in PubMed, EBSCO, Scopus, ProQuest, and Web of Science, using keywords and synonyms of OSA, diabetes, and CVD, coupled with specific terms for different CVDs. Only observational studies that reported CVD events in diabetics (with and without OSA) were included. The quality of the studies included in the analysis was assessed using the Newcastle-Ottawa Scale.

RESULTS

In the primary literature search, 8795 studies were identified, of which 9 met the inclusion criteria and included 17,796 participants. Eight studies were eligible for meta-analysis, and a pooled risk ratio (RR) of 1.29 (95% CI = 0.91-1.83) was found for developing CVD in diabetics with OSA at a 95% prediction interval of 0.30-5.60. The included studies showed significant heterogeneity with an I2 value of 91%.

CONCLUSION

These findings show the possible association between OSA and diabetes and their impact on CVDs. Identifying and managing OSA in individuals with diabetes at an early phase could potentially reduce the risk of CVDs and its related complications.

Obstructive sleep apnoea heterogeneity and cardiovascular disease

Obstructive sleep apnoea (OSA), characterized by recurrent periods of upper airway obstruction and intermittent hypoxaemia, is prevalent in patients with cardiovascular disease (CVD), and is therefore important to consider in the prevention and management of CVD. Observational studies indicate that OSA is a risk factor for incident hypertension, poorly controlled blood pressure, stroke, myocardial infarction, heart failure, cardiac arrhythmias, sudden cardiac death and all-cause death. However, clinical trials have not provided consistent evidence that treatment with continuous positive airway pressure (CPAP) improves cardiovascular outcomes. These overall null findings might be explained by limitations in trial design and low levels of adherence to CPAP. Studies have also been limited by the failure to consider OSA as a heterogeneous disorder that consists of multiple subtypes resulting from variable contributions from anatomical, physiological, inflammatory and obesity-related risk factors, and resulting in different physiological disturbances. Novel markers of sleep apnoea-associated hypoxic burden and cardiac autonomic response have emerged as predictors of OSA-related susceptibility to adverse health outcomes and treatment response. In this Review, we summarize our understanding of the shared risk factors and causal links between OSA and CVD and emerging knowledge on the heterogeneity of OSA. We discuss the varied mechanistic pathways that result in CVD that also vary across subgroups of OSA, as well as the potential role of new biomarkers for CVD risk stratification.

Relevance of cortical arousals for risk stratification in sleep apnea: a 3 cohort analysis

STUDY OBJECTIVES

There is uncertainty on best approaches for defining apnea-hypopnea events. To clarify the contributions of desaturation vs arousal to defining hypopneas, we examined the associations of events with desaturation (≥ 3%) but not arousal (apnea-hypopnea index [AHI]≥3%Only) vs events with arousals but no desaturation (AHIArOnly) with obstructive sleep apnea-related comorbidities and incident cardiovascular disease across multiple cohorts.

METHODS

In the Sleep Heart Health Study (n = 5,473), the Multi-Ethnic Study of Atherosclerosis (n = 1,904), and the Osteoporotic Fractures in Men Study (n = 2,685), we examined the independent associations of AHI≥3%Only and AHIArOnly with hypertension, diabetes, and daytime sleepiness, and incident cardiovascular disease.

RESULTS

After adjusting for covariates and AHI based on events with electroencephalogram arousal (regardless of desaturation), AHI≥3%Only was associated with hypertension in Sleep Heart Health Study (odds ratio: 1.12; 95% confidence interval: 1.04,1.21), per 1 standard deviation increase). Similar associations were observed in the Multi-Ethnic Study of Atherosclerosis and Osteoporotic Fractures in Men Study, as well as for associations with diabetes (odds ratio: 1.30; 1.09,1.54, and 1.25; 1.07,1.47, respectively), sleepiness (odds ratio: 1.19; 1.00,1.41; and 1.17; 1.01-1.35), and incident cardiovascular disease (hazard ratio: 1.37; 1.05,1.77 and 1.14; 1.00,1.29). In contrast, after adjusting for events with desaturation (regardless of arousal), AHIArOnly was unassociated with these outcomes. In Sleep Heart Health Study, greater baseline obstructive sleep apnea severity was associated with a reduction in arousal frequency over 5 years (P < .0001).

CONCLUSIONS

In middle-aged and older individuals, addition of events with arousals does not improve the strength of associations with comorbidities or incident cardiovascular disease. Research is needed to understand generalizability to younger individuals and the mechanistic role of arousals in obstructive sleep apnea.

CITATION

Azarbarzin A, Sands SA, Han S, et al. Relevance of cortical arousals for risk stratification in sleep apnea: a 3 cohort analysis. J Clin Sleep Med. 2023;19(8):1475-1484.

Optical and pharmacological manipulation of hypoglossal motor nucleus identifies differential effects of taltirelin on sleeping tonic motor activity and responsiveness

Pharyngeal muscle activity and responsiveness are key pathophysiological traits in human obstructive sleep apnea (OSA) and strong contributors to improvements with pharmacotherapy. The thyrotropin-releasing hormone (TRH) analog taltirelin is of high pre-clinical interest given its neuronal-stimulant properties, minimal endocrine activity, tongue muscle activation following microperfusion into the hypoglossal motor nucleus (HMN) or systemic delivery, and high TRH receptor expression at the HMN compared to rest of the brain. Here we test the hypothesis that taltirelin increases HMN activity and/or responsivity to excitatory stimuli applied across sleep-wake states in-vivo. To target hypoglossal motoneurons with simultaneous pharmacological and optical stimuli we used customized "opto-dialysis" probes and chronically implanted them in mice expressing a light sensitive cation channel exclusively on cholinergic neurons (ChAT-ChR2, n = 12) and wild-type mice lacking the opsin (n = 10). Both optical stimuli applied across a range of powers (P < 0.001) and microperfusion of taltirelin into the HMN (P < 0.020) increased tongue motor activity in sleeping ChAT-ChR2 mice. Notably, taltirelin increased tonic background tongue motor activity (P < 0.001) but not responsivity to excitatory optical stimuli across sleep-wake states (P > 0.098). This differential effect on tonic motor activity versus responsivity informs human studies of the potential beneficial effects of taltirelin on pharyngeal motor control and OSA pharmacotherapy.

Chronic Intermittent Hypoxia-Induced Diaphragm Muscle Weakness Is NADPH Oxidase-2 Dependent

Chronic intermittent hypoxia (CIH)-induced redox alterations underlie diaphragm muscle dysfunction. We sought to establish if NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS) underpin CIH-induced changes in diaphragm muscle, which manifest as impaired muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) administered in the drinking water throughout exposure to CIH. In separate studies, we examined sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Apocynin co-treatment or NOX2 deletion proved efficacious in entirely preventing diaphragm muscle dysfunction following exposure to CIH. Exposure to CIH had no effect on NOX2 expression. However, NOX4 mRNA expression was increased following exposure to CIH in wild-type and NOX2 null mice. There was no evidence of overt CIH-induced oxidative stress. A NOX2-dependent increase in genes related to muscle regeneration, antioxidant capacity, and autophagy and atrophy was evident following exposure to CIH. We suggest that NOX-dependent CIH-induced diaphragm muscle weakness has the potential to affect ventilatory and non-ventilatory performance of the respiratory system. Therapeutic strategies employing NOX2 blockade may function as an adjunct therapy to improve diaphragm muscle performance and reduce disease burden in diseases characterised by exposure to CIH, such as obstructive sleep apnoea.

Contribution of obstructive sleep apnea to disrupted sleep in a large clinical cohort of patients with suspected obstructive sleep apnea

STUDY OBJECTIVES

The response of sleep depth to CPAP in patients with OSA is unpredictable. The odds-ratio-product (ORP) is a continuous index of sleep depth and wake propensity that distinguishes different sleep depths within sleep stages, and different levels of vigilance during stage wake. When expressed as fractions of time spent in different ORP deciles, nine distinctive patterns are found. Only three of these are associated with OSA. We sought to determine whether sleep depth improves on CPAP exclusively in patients with these three ORP patterns.

METHODS

ORP was measured during the diagnostic and therapeutic components of 576 split-night polysomnographic (PSG) studies. ORP architecture in the diagnostic section was classified into one of the nine possible ORP patterns and the changes in sleep architecture were determined on CPAP for each of these patterns. ORP architecture was similarly determined in the first half of 760 full-night diagnostic PSG studies and the changes in the second half were measured to control for differences in sleep architecture between the early and late portions of sleep time in the absence of CPAP.

RESULTS

Frequency of the three ORP patterns increased progressively with the apnea-hypopnea index. Sleep depth improved significantly on CPAP only in the three ORP patterns associated with OSA. Changes in CPAP in the other six patterns, or in full diagnostic PSG studies, were insignificant or paradoxical.

CONCLUSIONS

ORP architecture types can identify patients in whom OSA adversely affects sleep and whose sleep is expected to improve on CPAP therapy.

Determinants of awake oropharyngeal volume reduction between sitting and supine positions in children evaluated for snoring

Pharyngeal collapsibility is a major determinant of obstructive sleep apnea (OSA) pathophysiology, but its anatomical predictors in children are largely unknown. We hypothesised that anatomical (tonsillar hypertrophy, narrow palate, nasal obstruction, dental/skeletal malocclusion, obesity) and OSA-related (apnea-hypopnea index, AHI) parameters could be related to a measure of awake pharyngeal collapsibility. We performed acoustic pharyngometry in children evaluated for suspected OSA, allowing us to measure the reduction of oropharyngeal volume in supine versus sitting position normalised for the volume in supine position (ΔV%), a measure of pharyngeal collapsibility. In addition to polysomnography and a clinical examination (anatomical parameters), acoustic rhinometry was used to assess nasal obstruction. A total of 188 snoring children were included, 118 (63%) of whom were obese and 74 (39%) of whom had moderate to severe OSA (AHI ≥5/h). The median (25th-75th percentiles) ΔV% in the whole population was 20.1% (4.7; 43.3). ΔV% was independently and positively associated with AHI (p = 0.023), z-score of BMI (p = 0.001), tonsillar hypertrophy (p = 0.007), narrow palate (p = 0.035), and African (p < 0.001) ancestry. By contrast, ΔV% was not modified by dental or skeletal malocclusion, Friedman palate position class or nasopharyngeal obstruction. Tonsillar hypertrophy, obesity, narrow palate and African ancestry are independently associated with an increase in pharyngeal collapsibility in snoring children, thus increasing the risk of OSA. Increased pharyngeal compliance in African children may explain the increased risk of residual OSA after adenotonsillectomy observed in this population.

Intermittent Hypoxia and Weight Loss: Insights into the Etiology of the Sleep Apnea Phenotype

Sleep apnea (SA) is a major respiratory disorder with increased risk for hypertension and obesity; however, our understanding of the origins of this complex disorder remains limited. Because apneas lead to recurrent drops in O₂ during sleep, intermittent hypoxia (IH) is the main animal model to explore the pathophysiology of SA. Here, we assessed the impacts of IH on metabolic function and related signals. Adult male rats were exposed to 1 week of moderate IH (FiO₂ = 0.10-30 s, ten cycles/hour, 8 h/day). Using whole-body plethysmography, we measured respiratory variability and apnea index during sleep. Blood pressure and heart rate were measured by the tail-cuff method; blood samples were taken for multiplex assay. At rest, IH augmented arterial blood pressure, respiratory instability, but not apnea index. IH induced weight, fat, and fluid loss. IH also reduced food intake and plasma leptin, adrenocorticotropic hormone (ACTH), and testosterone levels but increased inflammatory cytokines. We conclude that IH does not replicate the metabolic clinical features of SA patient, thus raising our awareness of the limitations of the IH model. The fact that the risk for hypertension occurs before the appearance of apneas provides new insights into the progression of the disease.

Differential pharmacological and sex-specific effects of antimuscarinic agents at the hypoglossal motor nucleus in vivo in rats

Successful cholinergic-noradrenergic pharmacotherapy for obstructive sleep apnea (OSA) is thought to be due to effects at the hypoglossal motor nucleus (HMN). Clinical efficacy varies with muscarinic-receptor (MR) subtype affinities. We hypothesized that oxybutynin (cholinergic agent in successful OSA pharmacotherapy) is an effective MR antagonist at the HMN and characterized its efficacy with other antagonists. We recorded tongue muscle activity of isoflurane anesthetized rats (121 males and 60 females, 7–13 per group across 13 protocols) in response to HMN microperfusion with MR antagonists with and without: (i) eserine-induced increased endogenous acetylcholine at the HMN and (ii) muscarine. Eserine-induced increased acetylcholine decreased tongue motor activity (p < 0.001) with lesser cholinergic suppression in females versus males (p = 0.017). Motor suppression was significantly attenuated by the MR antagonists atropine, oxybutynin, and omadacycline (MR2 antagonist), each p < 0.001, with similar residual activity between agents (p ≥ 0.089) suggesting similar efficacy at the HMN. Sex differences remained with atropine and oxybutynin (p < 0.001 to 0.05) but not omadacycline (p = 0.722). Muscarine at the HMN also decreased motor activity (p < 0.001) but this was not sex-specific (p = 0.849). These findings have translational relevance to antimuscarinic agents in OSA pharmacotherapy and understanding potential sex differences in HMN suppression with increased endogenous acetylcholine related to sparing nicotinic excitation.

AI-based automatic segmentation of craniomaxillofacial anatomy from CBCT scans for automatic detection of pharyngeal airway evaluations in OSA patients

This study aims to generate and also validate an automatic detection algorithm for pharyngeal airway on CBCT data using an AI software (Diagnocat) which will procure a measurement method. The second aim is to validate the newly developed artificial intelligence system in comparison to commercially available software for 3D CBCT evaluation. A Convolutional Neural Network-based machine learning algorithm was used for the segmentation of the pharyngeal airways in OSA and non-OSA patients. Radiologists used semi-automatic software to manually determine the airway and their measurements were compared with the AI. OSA patients were classified as minimal, mild, moderate, and severe groups, and the mean airway volumes of the groups were compared. The narrowest points of the airway (mm), the field of the airway (mm²), and volume of the airway (cc) of both OSA and non-OSA patients were also compared. There was no statistically significant difference between the manual technique and Diagnocat measurements in all groups (p > 0.05). Inter-class correlation coefficients were 0.954 for manual and automatic segmentation, 0.956 for Diagnocat and automatic segmentation, 0.972 for Diagnocat and manual segmentation. Although there was no statistically significant difference in total airway volume measurements between the manual measurements, automatic measurements, and DC measurements in non-OSA and OSA patients, we evaluated the output images to understand why the mean value for the total airway was higher in DC measurement. It was seen that the DC algorithm also measures the epiglottis volume and the posterior nasal aperture volume due to the low soft-tissue contrast in CBCT images and that leads to higher values in airway volume measurement.

NADPH oxidase-2 is necessary for chronic intermittent hypoxia-induced sternohyoid muscle weakness in adult male mice

New Findings

What is the central question of this study?

Exposure to chronic intermittent hypoxia (CIH) evokes redox changes, culminating in impaired upper airway muscle function: what is the specific source of CIH‐induced reactive oxygen species?

What is the main finding and its importance?

Profound sternohyoid muscle dysfunction following exposure to CIH was entirely prevented by apocynin co‐treatment or NADPH oxidase 2 (NOX2) deletion. The results have implications for human obstructive sleep apnoea syndrome and point to antioxidant intervention, potentially targeting NOX2 blockade, as a therapeutic strategy.

Abstract

Exposure to chronic intermittent hypoxia (CIH) evokes redox changes, culminating in impaired upper airway muscle function. We sought to determine if NADPH oxidase 2 (NOX2)‐derived reactive oxygen species underpin CIH‐induced maladaptive changes in upper airway (sternohyoid) muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); CIH‐exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) given in the drinking water throughout exposure to CIH. In addition, we studied sham and CIH‐exposed NOX2‐null mice (B6.129S‐CybbTM^1Din/J). Profound sternohyoid muscle dysfunction following exposure to CIH was entirely prevented by apocynin co‐treatment or NOX2 deletion. Exposure to CIH increased sternohyoid muscle NOX enzyme activity, with no alteration to the gene or protein expression of NOX subunits. There was no evidence of overt oxidative stress, muscle regeneration, inflammation or atrophy following exposure to CIH. We suggest that NOX‐dependent CIH‐induced upper airway muscle weakness increases vulnerability to upper airway obstruction. Our results have implications for human obstructive sleep apnoea syndrome and point to antioxidant intervention, potentially targeting NOX2 blockade, as a therapeutic strategy.

Breathing in Duchenne muscular dystrophy: Translation to therapy

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a deficiency in dystrophin - a structural protein which stabilizes muscle during contraction. Dystrophin deficiency adversely affects the respiratory system leading to sleep-disordered breathing, hypoventilation, and weakness of the expiratory and inspiratory musculature, which culminate in severe respiratory dysfunction. Muscle degeneration associated respiratory impairment in neuromuscular disease is a result of disruptions at multiple sites of the respiratory control network, including sensory and motor pathways. As a result of this pathology, respiratory failure is a leading cause of premature death in DMD patients. Currently available treatments for DMD respiratory insufficiency attenuate respiratory symptoms without completely reversing the underlying pathophysiology. This underscores the need to develop curative therapies to improve quality of life and longevity of DMD patients. This review summarises research findings on the pathophysiology of respiratory insufficiencies in DMD disease in humans and animal models, the clinical interventions available to ameliorate symptoms, and gene-based therapeutic strategies uncovered by preclinical animal studies. Abstract figure legend: Summary of the therapeutic strategies for respiratory insufficiency in DMD (Duchenne muscular dystrophy). Treatment options currently in clinical use only attenuate respiratory symptoms without reversing the underlying pathology of DMD-associated respiratory insufficiencies. Ongoing preclinical and clinical research is aimed at developing curative therapies that both improve quality of life and longevity of DMD patients. AAV - adeno-associated virus, PPMO - Peptide-conjugated phosphorodiamidate morpholino oligomer This article is protected by copyright. All rights reserved.

Computational fluid dynamic analysis of the nasal respiratory function before and after postero-superior repositioning of the maxilla

Morphological changes in the upper airway and the resulting alteration in the nasal respiratory function after jawbone repositioning during orthognathic surgery have garnered attention recently. In particular, nasopharyngeal stenosis, because of the complex influence of both jaws, the effects of which have not yet been clarified owing to postero-superior repositioning of the maxilla, may significantly impact sleep and respiratory function, necessitating further functional evaluation. This study aimed to perform a functional evaluation of the effects of surgery involving maxillary repositioning, which may result in a larger airway resistance if the stenosis worsens the respiratory function, using CFD for treatment planning. A model was developed from CT images obtained preoperatively (PRE) and postoperatively (POST) in females (n = 3) who underwent maxillary postero-superior repositioning using Mimics and ICEM CFD. Simultaneously, a model of stenosis (STENOSIS) was developed by adjusting the severity of stenosis around the PNS to simulate greater repositioning than that in the POST. Inhalation at rest and atmospheric pressure were simulated in each model using Fluent, whereas pressure drop (ΔP) was evaluated using CFD Post. In this study, ΔP was proportional to airway resistance because the flow rate was constant. Therefore, the magnitude of ΔP was evaluated as the level of airway resistance. The ΔP in the airway was lower in the POST compared to the PRE, indicating that the analysis of the effects of repositioning on nasal ventilation showed that current surgery is appropriate with respect to functionality, as it does not compromise respiratory function. The rate of change in the cross-sectional area of the mass extending pharynx (α) was calculated as the ratio of each neighboring section. The closer the α-value is to 1, the smaller the ΔP, so ideally the airway should be constant. This study identified airway shapes that are favorable from the perspective of fluid dynamics.

Computer-Assisted Assessment of the Interaction Between Arousals, Breath-by-Breath Ventilation, and Chemical Drive During Cheyne-Stokes Respiration in Heart Failure Patients

Transient increases in ventilation induced by arousal from sleep during Cheyne-Stokes respiration in heart failure patients are thought to contribute to sustaining and exacerbating the ventilatory oscillation. The only possibility to investigate the validity of this notion is to use observational data. This entails some significant challenges: (i) accurate identification of both arousal onset and offset; (ii) detection of short arousals (<3 s); (iii) breath-by-breath analysis of the interaction between arousals and ventilation; (iv) careful control for important confounding factors. In this paper we report how we have tackled these challenges by developing innovative computer-assisted methodologies. The identification of arousal onset and offset is performed by a hybrid approach that integrates visual scoring with computer-based automated analysis. We use a statistical detector to automatically discriminate between dominant theta–delta and dominant alpha activity at each instant of time. Moreover, a statistical detector is used to validate visual scoring of K complexes, delta waves or artifacts associated with an EEG frequency shift, as well as frequency shifts to beta activity. A high-resolution (250 ms) state-transition diagram providing continuous information on the sleep-wake state of the subject is finally obtained. Based on this information, arousals are automatically identified as any state change from sleep to wakefulness lasting ≥2 s. The assessment of the interaction between arousals and ventilation is performed using a breath-by-breath, case-control approach. The arousal-associated change in ventilation is measured as the normalized difference between minute ventilation in the case breath (i.e., with arousal) and that in the control breath (i.e., without arousal), controlling for sleep stage and chemical drive. The latter is estimated by using information from pulse oximetry at the finger. In the last part of the paper, we discuss main potential sources of error inherent in the described methodologies.

Cerebral Erythropoietin Prevents Sex-Dependent Disruption of Respiratory Control Induced by Early Life Stress

Injuries that occur early in life are often at the root of adult illness. Neonatal maternal separation (NMS) is a form of early life stress that has persistent and sex-specific effects on the development of neural networks, including those that regulate breathing. The release of stress hormones during a critical period of development contributes to the deleterious consequences of NMS, but the role of increased corticosterone (CORT) in NMS-induced respiratory disturbance is unknown. Because erythropoietin (EPO) is a potent neuroprotectant that prevents conditions associated with hyperactivation of the stress neuroaxis in a sex-specific manner, we hypothesized that EPO reduces the sex-specific alteration of respiratory regulation induced by NMS in adult mice. Animals were either raised under standard conditions (controls) or exposed to NMS 3 h/day from postnatal days 3–12. We tested the efficacy of EPO in preventing the effects of NMS by comparing wild-type mice with transgenic mice that overexpress EPO only in the brain (Tg21). In 7-days-old pups, NMS augmented CORT levels ~2.5-fold by comparison with controls but only in males; this response was reduced in Tg21 mice. Respiratory function was assessed using whole-body plethysmography. Apneas were detected during sleep; the responsiveness to stimuli was measured by exposing mice to hypoxia (10% O₂; 15 min) and hypercapnia (5% CO₂; 10 min). In wild-type, NMS increased the number of apneas and the hypercapnic ventilatory response (HcVR) only in males; with no effect on Tg21. In wild-type males, the incidence of apneas was positively correlated with HcVR and inversely related to the tachypneic response to hypoxia. We conclude that neural EPO reduces early life stress-induced respiratory disturbances observed in males.

Obstructive sleep apneas naturally occur in mice during REM sleep and are highly prevalent in a mouse model of Down syndrome

STUDY OBJECTIVES

The use of mouse models in sleep apnea study is limited by the belief that central (CSA) but not obstructive sleep apneas (OSA) occur in rodents. We aimed to develop a protocol to investigate the presence of OSAs in wild-type mice and, then, to apply it to a validated model of Down syndrome (Ts65Dn), a human pathology characterized by a high incidence of OSAs.

METHODS

In a pilot study, nine C57BL/6J wild-type mice were implanted with electrodes for electroencephalography (EEG), neck electromyography (nEMG), and diaphragmatic activity (DIA), and then placed in a whole-body-plethysmographic (WBP) chamber for 8 h during the rest (light) phase to simultaneously record sleep and breathing activity. CSA and OSA were discriminated on the basis of WBP and DIA signals recorded simultaneously. The same protocol was then applied to 12 Ts65Dn mice and 14 euploid controls.

RESULTS

OSAs represented about half of the apneic events recorded during rapid-eye-movement-sleep (REMS) in each experimental group, while the majority of CSAs were found during non-rapid eye movement sleep. Compared with euploid controls, Ts65Dn mice had a similar total occurrence rate of apneic events during sleep, but a significantly higher occurrence rate of OSAs during REMS, and a significantly lower occurrence rate of CSAs during NREMS.

CONCLUSIONS

Mice physiologically exhibit both CSAs and OSAs. The latter appear almost exclusively during REMS, and are highly prevalent in Ts65Dn. Mice may, thus, represent a useful model to accelerate the understanding of the pathophysiology and genetics of sleep-disordered breathing and to help the development of new therapies.

Impact of oral appliance therapy on quality of life (QoL) in patients with obstructive sleep apnea - a systematic review and meta-analysis

PURPOSE

Treatment of patients with obstructive sleep apnea (OSA) using mandibular advancement appliances enhances the airway and may be an alternative to continuous positive airway pressure (CPAP) in individuals with reduced adherence to CPAP therapy. The effectiveness as well as improved patient compliance associated with these appliances may improve the quality of life in patients with OSA. The aim of this systematic review of studies was to determine the improvement in quality of life amongst patients with OSA who were treated with an oral appliance.

METHODS

The research study was registered on the International Prospective Register of Systematic Reviews (PROSPERO: CRD42021193386). A search was carried out using the search engines Google Scholar, PubMed, Ovid, Cochrane Trial Registry, and LILACS. Patients with OSA treated with oral appliance therapy to advance the mandible were studied. Twenty-five studies were identified through the literature search and all had varying control groups for assessment of quality of life. Seventeen studies were included for the quantitative synthesis.

RESULTS

QoL, evaluated by the Functional Outcomes of Sleep Questionnaire (FOSQ), significantly improved in patients treated with oral appliance therapy. There was a mean difference of 1.8 points between the baseline scores and the scores following treatment with an oral appliance.

CONCLUSION

Overall, a significant improvement in the QoL was observed with the Functional Outcomes of Sleep Questionnaire, following oral appliance therapy.

Stress and Loss of Ovarian Function: Novel Insights into the Origins of Sex-Based Differences in the Manifestations of Respiratory Control Disorders During Sleep

The respiratory system of women and men develops and functions in distinct neuroendocrine milieus. Despite differences in anatomy and neural control, homeostasis of arterial blood gases is ensured in healthy individuals regardless of sex. This convergence in function differs from the sex-based differences observed in many respiratory diseases. Sleep-disordered breathing (SDB) results mainly from episodes of upper airway closure. This complex and multifactorial respiratory disorder shows significant sexual dimorphism in its clinical manifestations and comorbidities. Guided by recent progress from basic research, this review discusses the hypothesis that stress is necessary to reveal the sexual dimorphism of SDB.

Effect of tube length on the buckling pressure of collapsible tubes

BACKGROUND

The higher incidence of obstructive sleep apnea (OSA) in men than in women has been attributed to the upper airway being longer in men. The Starling resistor is the paradigm biomechanical model of upper airway collapse in OSA where a collapsible tube (representing the pharynx) is located between two rigid tubes (representing the nasal cavity and trachea). While the Starling resistor has been extensively studied due to its relevance to many physiological phenomena, the effect of tube length on tube collapsibility has not been quantified yet.

METHODS

Finite element analysis of a 3-dimensional collapsible tube subjected to a transmural pressure was performed in ANSYS Workbench. The numerical methods were validated with in vitro experiments in a silicone tube whose modulus of elasticity (361 ± 28 kPa) and dimensions (length = 100 mm, diameter = 22.2 mm, and wall thickness = 1.59 mm) were selected so that tube compliance was similar to pharyngeal compliance in humans during sleep. The buckling pressure (transmural pressure at which the tube collapses) was quantified in tubes of three different diameters (10 mm, 16 mm, and 22.2 mm) and ten length-to-diameter ratios (L/D = 4 to 13), while keeping the wall-thickness-to-radius ratio constant at 0.143.

RESULTS

The absolute value of the buckling pressure decreased from 4.7 to 3.3 cmH₂O (461-324 Pa) when L/D increased from 4 to 13. The buckling pressure was nearly independent from tube length for L/D >10.

CONCLUSIONS

Our finding that longer tubes are more collapsible than shorter tubes is consistent with the higher incidence of obstructive sleep apnea in males than females.

Effect of the new dual orexin receptor antagonist daridorexant on nighttime respiratory function and sleep in patients with mild and moderate obstructive sleep apnea

In this randomized, double-blind, placebo-controlled, two-period crossover study, the effect of the dual orexin receptor antagonist daridorexant was evaluated on nighttime respiratory function and sleep in 28 patients with mild and moderate obstructive sleep apnea (OSA). In each period, 50 mg daridorexant or placebo was administered every evening for 5 days. The primary endpoint was apnea/hypopnea index (AHI) during total sleep time (TST) after the last dosing. Other endpoints included peripheral oxygen saturation (SpO2), sleep duration, latency to persistent sleep (LPS), wake after sleep onset (WASO), and sleep efficiency index (SEI). Pharmacokinetics, safety, and tolerability were also assessed. The mean treatment difference for AHI during TST (i.e. daridorexant - placebo) after the last dosing was 0.74 events/hour (90% confidence interval [CI]: -1.43, 2.92). The corresponding treatment difference for SpO2 during TST was 0.16% [90% CI: -0.21, 0.53]. Overall, there was no clinically relevant effect of daridorexant on AHI or SpO2-related data after single and repeated dosing irrespective of sleep phase (i.e. rapid eye movement [REM] vs non-REM). Moreover, after single and repeated dosing, daridorexant prolonged TST by 39.6 minutes (90% CI: 16.9, 62.3) and 38.8 minutes (19.7, 57.9), respectively, compared with placebo and favorably modulated other sleep-related endpoints (i.e. increased SEI, decreased WASO, and shortened LPS). It attained expected plasma concentrations and was well tolerated in patients with mild and moderate OSA. These results indicate that single and repeated doses of 50 mg daridorexant do not impair nighttime respiratory function and improve sleep in patients with mild and moderate OSA. Clinical Trial Registration: ClinicalTrials.gov NCT03765294. A study to investigate the effects of ACT-541468 on nighttime respiratory function in patients with mild to moderate obstructive sleep apnea. https://clinicaltrials.gov/ct2/show/ NCT03765294.

Relation between arousability and outcome of upper airway stimulation in the Stimulation for Apnea Reduction (STAR) Trial

STUDY OBJECTIVES

Upper airway stimulation (UAS) is an innovative surgical treatment for obstructive sleep apnea; however, the treatment failure rate is approximately 22%. Easy arousability may limit the tolerability of stimulation and, by extension, its effectiveness. The odds ratio product (ORP) is a continuous electroencephalographic metric of arousal propensity (range: 0 [deep sleep] to 2.5 [full wakefulness]), and its rate of decline after arousal (ORP-9) is a risk factor for susceptibility to arousal in the presence of frequent arousal stimuli. We hypothesized that individuals with deeper sleep (low average ORP and low ORP-9) are more likely to respond to UAS.

METHODS

ORP and ORP-9 were calculated from 126 baseline polysomnograms of participants in the STAR Trial. These values were compared between responders and nonresponders. Adjusted linear modeling was performed to determine the association between ORP-derived variables and treatment response.

RESULTS

No differences were found between responders and nonresponders in unadjusted comparisons of ORP-derived variables. On linear regression modeling, significant correlation was found between non-rapid eye movement ORP and reduction in apnea-hypopnea index (P = .004).

CONCLUSIONS

No significant difference in ORP was noted between responders and nonresponders to UAS therapy; however, contrary to our initial hypothesis, linear regression modeling trended toward a positive relationship between ORP and UAS response, suggesting that those who have lighter sleep are more likely to respond to therapy; however, these results are only exploratory, and future larger prospective studies are needed to confirm this relationship.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: STAR Trial; Identifier: NCT01161420.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

The role of NADPH oxidase in chronic intermittent hypoxia-induced respiratory plasticity in adult male mice

Reactive oxygen species (ROS) are proposed as mediators of chronic intermittent hypoxia (CIH)-induced respiratory plasticity. We sought to determine if NADPH oxidase 2 (NOX2)-derived ROS underpin CIH-induced maladaptive changes in respiratory control. Adult male mice (C57BL/6 J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) given in the drinking water throughout exposure to CIH. In addition, we studied sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Whole-body plethysmography was used to measure breathing and metabolic parameters. Ventilation (V̇_I/V̇CO₂) during normoxia was unaffected by CIH, but apnoea index was increased, which was prevented by apocynin, but not by NOX2 deletion. The ventilatory response to hypercapnia following exposure to CIH was potentiated in NOX2-null mice. Our results reveal ROS-dependent influences on the control of breathing and point to antioxidant intervention as a potential adjunctive therapeutic strategy in respiratory control disorders.

Effects of hypnotics on obstructive sleep apnea endotypes and severity: Novel insights into pathophysiology and treatment

Impaired upper airway anatomy is the main cause of obstructive sleep apnea (OSA). However, there are other important non-anatomical contributors or "endotypes" including ventilatory control instability, poor pharyngeal dilator muscle responsiveness and waking up too easily to minor respiratory events (low arousal threshold). Recent studies have focused on the potential to target specific OSA causes with novel treatments to reduce OSA severity and improve efficacy with existing non-CPAP therapies which are often suboptimal (e.g., mandibular advancement splints). One novel target is pharmacotherapy with hypnotics to increase the threshold for arousal and reduce OSA severity in the approximately 30% of patients who have a low arousal threshold endotype. This increasing body of work has produced varied and at times unexpected findings which have challenged previous knowledge on the effects of hypnotics on upper airway physiology and breathing during sleep in people with OSA. This review provides a concise overview of the latest research that has investigated the effects of common hypnotics/sedative agents on upper airway physiology and OSA severity and potential implications for OSA pathophysiology, treatment and safety. This includes a summary of the latest knowledge on the effects of hypnotics on OSA endotypes. Priorities for future research are also highlighted.

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.

Impact of cold and flu medication on obstructive sleep apnoea and its underlying traits: A pilot randomized controlled trial

BACKGROUND AND OBJECTIVE

Animal studies indicate that alpha-1 adrenergic receptor agonists and antimuscarinic agents improve genioglossus muscle activity during sleep and may be candidates for the pharmacological treatment of OSA. On the other hand, noradrenergic stimulants may be wake-promoting or cause insomnia symptoms if taken before bedtime, and the addition of a medication with sedative properties, such as an antihistaminic, may reduce these side effects. In this study, we aimed to determine the effects of the combination of an alpha-1 adrenergic agonist (pseudoephedrine) and an antihistaminic-antimuscarinic (diphenhydramine) on OSA severity (AHI), genioglossus responsiveness and other endotypic traits (V_passive , muscle compensation, LG and arousal threshold).

METHODS

Ten OSA patients performed a randomized, placebo-controlled, double-blind, crossover trial comparing one night of pseudoephedrine 120 mg plus diphenhydramine 50 mg (DAW1033D) to placebo administered prior to sleep. The AHI, genioglossus muscle responsiveness to negative oesophageal pressure and the endotypic traits were measured via PSG.

RESULTS

The participants' median (interquartile range) age was 50 (46-53) years and body mass index (BMI) was 34.3 (30.6-39.2) kg/m² . The drug combination had no effect on AHI (21.6 (9.1-49.8) on placebo vs 37.9 (5.1-55.4) events/h on DAW1033D, P > 0.5) or genioglossus responsiveness (6.0 (2.6-9.2) on placebo vs 4.0 (3.5-7.3) %/cm H₂ O). Amongst the phenotypic traits, only V_passive was improved by 29 (3-55) % eupnoea, P = 0.03 (mean (95% CI)).

CONCLUSION

The combination of pseudoephedrine and diphenhydramine did not improve OSA severity or genioglossus responsiveness but induced a small improvement in upper airway collapsibility, possibly due to the decongestant effect of the medications. The results of this study do not support the use of these medications for OSA treatment.

The Sleep Apnea-Specific Hypoxic Burden Predicts Incident Heart Failure

BACKGROUND

Heart failure (HF) is a leading cause of morbidity and mortality and although it is linked to sleep apnea, which physiological stressors most strongly associate with incident disease is unclear. We tested whether sleep apnea-specific hypoxic burden (SASHB) predicts incident HF in two independent cohort studies.

RESEARCH QUESTION

In comparison with apnea-hypopnea index (AHI), how does sleep apnea-specific hypoxic burden predict incident HF?

STUDY DESIGN AND METHODS

The samples were derived from two cohort studies: The Sleep Heart Health Study (SHHS), which included 4,881 middle-aged and older adults (54.4% women), age 63.6 ± 11.1 years; and the Outcomes of Sleep Disorders in Older Men (MrOS), which included 2,653 men, age 76.2 ± 5.4 years. We computed SASHB as the sleep apnea-specific area under the desaturation curve from pre-event baseline. We used Cox models for incident HF to estimate the adjusted hazard ratios (HRs) for natural log-transformed SASHB and AHI adjusting for multiple confounders.

RESULTS

The SASHB predicted incident HF in men in both cohorts, whereas AHI did not. Men in SHHS and MrOS had adjusted HRs (per 1SD increase in SASHB) of 1.18 (95% CI, 1.02-1.37) and 1.22 (95% CI, 1.02-1.45), respectively. Associations with SASHB were observed in men with both low and high AHI levels. Associations were not significant in women.

INTERPRETATION

In men, the hypoxic burden of sleep apnea was associated with incident HF after accounting for demographic factors, smoking, and co-morbidities. The findings Suggest that quantification of an easily measured index of sleep apnea-related hypoxias may be useful for identifying individuals at risk for heart disease, while also suggesting targets for intervention.

Pathogenesis of Obstructive Sleep Apnea

The pathogenesis of obstructive sleep apnea (OSA) has undergone major revisions since it was first described in 1978. This article focuses on new advances. Although it is still necessary to have a collapsible airway to develop OSA, it is primarily the response to obstruction that determines OSA severity and clinical presentation. Identifying factors that determine whether the response is stable or unstable through phenotyping is a promising approach that may lead to pharmacologic therapy in selected patients.

Comparison of anterior mandible anatomical characteristics between obstructive sleep apnea patients and healthy individuals: a combined cone beam computed tomography and polysomnographic study

PURPOSE

This study aims to evaluate the morphology of the genial tubercle (GT) and lingual foramen (LF) between obstructive sleep apnea (OSA) and non-OSA patients for considerations of mandibular advancement surgery.

METHODS

Cone beam CT records of 198 patients were retrospectively collected and analyzed. Five variables were measured for genial tubercle; anterior mandible thickness (AMT), the distance from the lower incisors to the superior border of the genial tubercle, the distance from the inferior border of the genial tubercle to inferior border of the mandible, the height of GT, and genial tubercle width. Lingual foramen were classified according to the genial tubercle. The frequencies, distances of lingual foramen to alveolar crest, lower border of mandible (LVDL) and diameter of LF were also measured.

RESULTS

Significant differences was found for genial tubercle width, anterior mandible thickness, and the distance of lower mandibular border to the midline lingual foramina between OSA and non-OSA patients (p < 0.05). AMT gets thicker and GT gets narrower in OSA patients (p < 0.05). A linear regression analysis on the apnea hypopnea index with measured anatomical variables showed the LVDL (R = - 0.355*), body mass index (R = 0.254), and age (R = 0.33) showed a statistically significant association (p < 0.05). None of the other variables reached formal significance.

CONCLUSION

LVDL is linearly associated with sleep apnea severity. The variable dimensions and anatomy of genial tubercle as well as lingual foramen for OSA patients suggest the need of 3D preoperative radiological evaluation before genioglossus advancement surgery. Cone beam CT can be a powerful low radiation dose tool both for evaluating the anatomy of the upper airway and mandibular structures at the same time for OSA patients.

Mechanism of excessive wake time when associated with obstructive sleep apnea or periodic limb movements

STUDY OBJECTIVES

It is uncertain whether obstructive apnea (OSA) or periodic limb movements (PLMs) contribute to excessive wake time (EWT) when EWT and these disorders coexist. We hypothesized that such EWT is an independent disorder related to central regulation of sleep depth. Accordingly, we compared sleep depth in patients with EWT and OSA/PLMs (EWT+P) with patients with EWT and no OSA/PLMs (EWT-NP) and patients with a normal wake time.

METHODS

A total of 267 participants were divided into five groups: (1) EWT+P: n = 100 (wake time > 20% total recording time; TRT) with OSA (apnea-hypopnea index 5-110 events/h) and/or PLMs (PLM index 10-151 events/h); (2) EWT-NP: n = 49 (wake time > 20%TRT), no associated pathology; (3) normal wake time (NWT)+P: n = 54 (wake time < 20%TRT, with OSA/PLMs); (4) NWT-NP: n = 26; (5) Healthy participants: n = 38 (no sleep complaints, NWT and no OSA/PLMs). Sleep depth was evaluated by the odds ratio product (ORP; 0 = deep sleep, 2.5 = fully alert). We also measured ORP in the 9 seconds immediately following arousals (ORP-9) to distinguish between peripheral and central mechanisms of light sleep.

RESULTS

ORP during sleep was higher (lighter sleep) in both EWT groups than in the three NWT groups (P < 1E-11) with no difference between those with and those without OSA/PLMs. ORP-9 was also significantly higher in the EWT groups than in the NWT groups (P < 1E-19), also with no difference between those with and without OSA/PLMs, indicating that the lighter sleep was of central origin. There were highly significant correlations between wake time and ORP-9 across all groups (P < 1E-35).

CONCLUSIONS

EWT associated with OSA/PLMs is independent of OSA/PLMs and related to abnormal central regulation of sleep depth.

Muscles of Breathing: Development, Function, and Patterns of Activation

This review is a comprehensive description of all muscles that assist lung inflation or deflation in any way. The developmental origin, anatomical orientation, mechanical action, innervation, and pattern of activation are described for each respiratory muscle fulfilling this broad definition. In addition, the circumstances in which each muscle is called upon to assist ventilation are discussed. The number of "respiratory" muscles is large, and the coordination of respiratory muscles with "nonrespiratory" muscles and in nonrespiratory activities is complex-commensurate with the diversity of activities that humans pursue, including sleep (8.27). The capacity for speech and adoption of the bipedal posture in human evolution has resulted in patterns of respiratory muscle activation that differ significantly from most other animals. A disproportionate number of respiratory muscles affect the nose, mouth, pharynx, and larynx, reflecting the vital importance of coordinated muscle activity to control upper airway patency during both wakefulness and sleep. The upright posture has freed the hands from locomotor functions, but the evolutionary history and ontogeny of forelimb muscles pervades the patterns of activation and the forces generated by these muscles during breathing. The distinction between respiratory and nonrespiratory muscles is artificial, as many "nonrespiratory" muscles can augment breathing under conditions of high ventilator demand. Understanding the ontogeny, innervation, activation patterns, and functions of respiratory muscles is clinically useful, particularly in sleep medicine. Detailed explorations of how the nervous system controls the multiple muscles required for successful completion of respiratory behaviors will continue to be a fruitful area of investigation. © 2019 American Physiological Society. Compr Physiol 9:1025-1080, 2019.

Noradrenergic terminal density varies among different groups of hypoglossal premotor neurons

In obstructive sleep apnea (OSA) patients, contraction of the muscles of the tongue is needed to protect the upper airway from collapse. During wakefulness, norepinephrine directly excites motoneurons that innervate the tongue and other upper airway muscles but its excitatory effects decline during sleep, thus contributing to OSA. In addition to motoneurons, NE may regulate activity in premotor pathways but little is known about these upstream effects. To start filling this void, we injected a retrograde tracer (beta-subunit of cholera toxin-CTb; 5-10 nl, 1%) into the hypoglossal (XII) motor nucleus in 7 rats. We then used dual immunohistochemistry and brightfield microscopy to count dopamine beta-hydroxylase (DBH)-positive axon terminals closely apposed to CTb cells located in five anatomically distinct XII premotor regions. In different premotor groups, we found on the average 2.2-4.3 closely apposed DBH terminals per cell, with ˜60% more terminals on XII premotor neurons located in the ventrolateral pontine parabrachial region and ventral medullary gigantocellular region than on XII premotor cells of the rostral or caudal intermediate medullary reticular regions. This difference suggests stronger control by norepinephrine of the interneurons that mediate complex behavioral effects than of those mediating reflexes or respiratory drive to XII motoneurons.

Airflow limitation in a collapsible model of the human pharynx: physical mechanisms studied with fluid-structure interaction simulations and experiments

The classical Starling Resistor model has been the paradigm of airway collapse in obstructive sleep apnea (OSA) for the last 30 years. Its theoretical framework is grounded on the wave-speed flow limitation (WSFL) theory. Recent observations of negative effort dependence in OSA patients violate the predictions of the WSFL theory. Fluid-structure interaction (FSI) simulations are emerging as a technique to quantify how the biomechanical properties of the upper airway determine the shape of the pressure-flow curve. This study aimed to test two predictions of the WSFL theory, namely (1) the pressure profile upstream from the choke point becomes independent of downstream pressure during flow limitation and (2) the maximum flowrate in a collapsible tube is V I max = A 3 / 2 ( ρ d A / d P ) - 1 / 2 , where ρ is air density and A and P are the cross-sectional area and pressure at the choke point respectively. FSI simulations were performed in a model of the human upper airway with a collapsible pharynx whose wall thickness varied from 2 to 8 mm and modulus of elasticity ranged from 2 to 30 kPa. Experimental measurements in an airway replica with a silicone pharynx validated the numerical methods. Good agreement was found between our FSI simulations and the WSFL theory. Other key findings include: (1) the pressure-flow curve is independent of breathing effort (downstream pressure vs. time profile); (2) the shape of the pressure-flow curve reflects the airway biomechanical properties, so that V I max is a surrogate measure of pharyngeal compliance.

Neural Circuitry Underlying Waking Up to Hypercapnia

Obstructive sleep apnea is a sleep and breathing disorder, in which, patients suffer from cycles of atonia of airway dilator muscles during sleep, resulting in airway collapse, followed by brief arousals that help re-establish the airway patency. These repetitive arousals which can occur hundreds of times during the course of a night are the cause of the sleep-disruption, which in turn causes cognitive impairment as well as cardiovascular and metabolic morbidities. To prevent this potential outcome, it is important to target preventing the arousal from sleep while preserving or augmenting the increase in respiratory drive that reinitiates breathing, but will require understanding of the neural circuits that regulate the cortical and respiratory responses to apnea. The parabrachial nucleus (PB) is located in rostral pons. It receives chemosensory information from medullary nuclei that sense increase in CO2 (hypercapnia), decrease in O2 (hypoxia) and mechanosensory inputs from airway negative pressure during apneas. The PB area also exerts powerful control over cortical arousal and respiration, and therefore, is an excellent candidate for mediating the EEG arousal and restoration of the airway during sleep apneas. Using various genetic tools, we dissected the neuronal sub-types responsible for relaying the stimulus for cortical arousal to forebrain arousal circuits. The present review will focus on the circuitries that regulate waking-up from sleep in response to hypercapnia.

Brain Circuitry for Arousal from Apnea

We wanted to understand the brain circuitry that awakens the individual when there is elevated CO₂ or low O₂ (e.g., during sleep apnea or asphyxia). The sensory signals for high CO₂ and low O₂ all converge on the parabrachial nucleus (PB) of the pons, which contains neurons that project to the forebrain. So, we first deleted the vesicular glutamate transporter 2, necessary to load glutamate into synaptic vesicles, from neurons in the PB, and showed that this prevents awakening to high CO₂ or low O₂ We then showed that PB neurons that express calcitonin gene-related peptide (CGRP) show cFos staining during high CO₂ Using CGRP-Cre-ER mice, we expressed the inhibitory opsin archaerhodopsin just in the PB^CGRP neurons. Photoinhibition of the PB^CGRP neurons effectively prevented awakening to high CO₂, as did photoinhibition of their terminals in the basal forebrain, amygdala, and lateral hypothalamus. The PB^CGRP neurons are a key mediator of the wakening response to apnea.

The hypoxic burden of sleep apnoea predicts cardiovascular disease-related mortality: the Osteoporotic Fractures in Men Study and the Sleep Heart Health Study

AIMS

Apnoea-hypopnoea index (AHI), the universal clinical metric of sleep apnoea severity, poorly predicts the adverse outcomes of sleep apnoea, potentially because the AHI, a frequency measure, does not adequately capture disease burden. Therefore, we sought to evaluate whether quantifying the severity of sleep apnoea by the 'hypoxic burden' would predict mortality among adults aged 40 and older.

METHODS AND RESULTS

The samples were derived from two cohort studies: The Outcomes of Sleep Disorders in Older Men (MrOS), which included 2743 men, age 76.3 ± 5.5 years; and the Sleep Heart Health Study (SHHS), which included 5111 middle-aged and older adults (52.8% women), age: 63.7 ± 10.9 years. The outcomes were all-cause and Cardiovascular disease (CVD)-related mortality. The hypoxic burden was determined by measuring the respiratory event-associated area under the desaturation curve from pre-event baseline. Cox models were used to calculate the adjusted hazard ratios for hypoxic burden. Unlike the AHI, the hypoxic burden strongly predicted CVD mortality and all-cause mortality (only in MrOS). Individuals in the MrOS study with hypoxic burden in the highest two quintiles had hazard ratios of 1.81 [95% confidence interval (CI) 1.25-2.62] and 2.73 (95% CI 1.71-4.36), respectively. Similarly, the group in the SHHS with hypoxic burden in the highest quintile had a hazard ratio of 1.96 (95% CI 1.11-3.43).

CONCLUSION

The 'hypoxic burden', an easily derived signal from overnight sleep study, predicts CVD mortality across populations. The findings suggest that not only the frequency but the depth and duration of sleep related upper airway obstructions, are important disease characterizing features.

Knowledge Gaps in the Perioperative Management of Adults with Obstructive Sleep Apnea and Obesity Hypoventilation Syndrome. An Official American Thoracic Society Workshop Report

The purpose of this workshop was to identify knowledge gaps in the perioperative management of obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS). A single-day meeting was held at the American Thoracic Society Conference in May, 2016, with representation from many specialties, including anesthesiology, perioperative medicine, sleep, and respiratory medicine. Further research is urgently needed as we look to improve health outcomes for these patients and reduce health care costs. There is currently insufficient evidence to guide screening and optimization of OSA and OHS in the perioperative setting to achieve these objectives. Patients who are at greatest risk of respiratory or cardiac complications related to OSA and OHS are not well defined, and the effectiveness of monitoring and other interventions remains to be determined. Centers involved in sleep research need to develop collaborative networks to allow multicenter studies to address the knowledge gaps identified below.

Comparison of methods of chemical loop gain measurement during tidal ventilation in awake healthy subjects

The loop gain (LG) is defined as the ratio of a ventilatory response over the perturbation in ventilation, and it is used to analyze ventilatory control stability. The LG can be derived from minute ventilation (V̇e), end-tidal Pco2 ([Formula: see text]), and end-tidal Po2 ([Formula: see text]) values. Several methods of LG assessment have been developed, which have never been compared. We evaluated the computability, the short-term repeatability, and the agreement of six published (or slightly modified) models for LG determination. These models included three unconstrained autoregressive models, univariate (V̇e), bivariate (V̇e, [Formula: see text]), and trivariate (V̇e, [Formula: see text], and [Formula: see text]), and three analytical transfer function constrained models based on V̇e, V̇e and CO2-sensitivity, and V̇e and central and peripheral CO2 sensitivities, respectively. The models were tested with tidal breathing data in 37 awake healthy subjects (median age 35 yr; 23 women, 14 men). Modeling failed in 11, 0, and 0 subjects for the three unconstrained models, respectively, and 4, 1, and 9 subjects for the three constrained models, respectively. Bland and Altman analyses of the LG values in the medium frequency range of two separate recordings demonstrated good repeatability for four models, excluding univariate and trivariate unconstrained models. The four repeatable models gave LG values that were in agreement (medium frequency LG, median 0.100–0.210), although the constrained model based on V̇e systematically overestimated LG values. The variances explained by these models were ∼20%. In conclusion, model-based analyses of tidal breathing were performed with different approaches that gave comparable results for chemical LG and explained variance.

NEW & NOTEWORTHY Several methods of chemical loop gain measurement have been published but never compared. We show that a better repeatability is obtained with analytical constrained models compared with autoregressive unconstrained models and that the repeatable models gave comparable results of loop gain, even if the calculation based on ventilation-only recording gave higher values than those obtained with both ventilation and end-tidal Pco2 recording. The explained variance of ventilation was similar whatever the model.

Increased tongue use enhances 5-HT2C receptor immunostaining in hypoglossal motor nucleus

Hypoglossal (XII) motoneurons are activated by type 2 receptors for serotonin (5-HT). This activation is especially strong during wakefulness which facilitates diverse motor functions of the tongue, including the maintenance of upper airway patency in obstructive sleep apnea (OSA) patients. We tested whether 5-HT₂ receptor levels in the XII nucleus vary with intensity of tongue use. Three groups of rats were housed overnight under conditions of increasing oromotor activity: W-water available ad lib; S-sweetened water to stimulate drinking; S + O-sweetened water + oil applied on fur to increase grooming. After the exposures, immunostaining for 5-HT_2C, but not 5-HT_2A, receptors was higher in the XII nucleus in S + O than in W rats (65 ± 1.8 (SE) vs. 60 ± 2.0 arbitrary units; p = 0.008). In the medullary raphé obscurus region, the percentage of c-Fos-positive 5-HT cells was 13% higher (p = 0.03) in S + O than in W rats. The positive feedback between tongue use and 5-HT_2C receptor immunostaining reveals a novel mechanism potentially relevant for OSA and neuromuscular disorders.

Modulation of Motoneuronal Activity With Sleep-Wake States and Motoneuronal Gene Expression Vary With Circadian Rest-Activity Cycle

In both nocturnal and diurnal mammals, sleep and wake states differentially aggregate during the rest and active phases of circadian cycle. Closely associated with this rhythm are prominent changes in motor activity. Here, we quantified the magnitudes of electromyographic activity (EMG) measured separately during different sleep-wake states across the rest-activity cycle, thereby separating amplitude measurements from the known dependance of the timing of wake and sleep on the phase of circadian rest-activity cycle. In seven rats chronically instrumented for electroencephalogram and EMG monitoring, nuchal and lingual muscle EMGs were measured as a commonly used postural output in behavioral sleep studies and as a cranial motor output with potential clinical relevance in obstructive sleep apnea (OSA) syndrome, respectively. We found that, for both motor outputs, EMG measured during wake episodes was significantly higher during the active phase, than during the rest phase, of circadian cycle. The corresponding patterns observed during slow-wave sleep (SWS) and rapid eye movement sleep (REMS) were different. During SWS, lingual EMG was very low and did not differ between the rest and active phase, whereas nuchal EMG had pattern similar to that during wakefulness. During REMS, lingual EMG was, paradoxically, higher during the rest phase due to increased twitching activity, whereas nuchal EMG was very low throughout the rest and active periods (postural atonia). In the follow-up comparison of differences in transcript levels in tissue samples obtained from the medullary hypoglossal motor nucleus and inferior olive (IO) at rest onset and active period onset conducted using microarrays, we identified significant differences for multiple transcripts representing the core members of the molecular circadian clock and other genes important for the regulation of cell metabolism and activity (up to n = 130 at p < 0.001). Collectively, our data indicate that activity of motoneurons is regulated to optimally align it with the rest-activity cycle, with the process possibly involving transcriptional mechanisms at the motoneuronal level. Our data also suggest that OSA patients may be relatively better protected against sleep-related upper airway obstructions during REMS episodes generated during the rest phase, than during active phase, of the circadian cycle.

Sleep quality in survivors of critical illness

PURPOSE

There is limited data regarding the sleep quality in survivors of critical illness, while the time course of the sleep abnormalities observed after ICU discharge is not known. The aim of this study was to assess sleep quality and the time course of sleep abnormalities in survivors of critical illness.

METHODS

Eligible survivors of critical illness without hypercapnia and hypoxemia were evaluated within 10 days (1st evaluation, n = 36) and at 6 months after hospital discharge (2nd evaluation, n = 29). At each visit, all patients underwent an overnight full polysomnography and completed health-related quality of life questionnaires (HRQL). Lung function and electro-diagnostic tests (ED) were performed in 24 and 11 patients, respectively.

RESULTS

At 1st evaluation, sleep quality and HRQL were poor. Sleep was characterised by high percentages of N1, low of N3 and REM stages, and high apnea-hypopnea index (AHI, events/h). Twenty-two out of 36 patients (61%) exhibited AHI ≥ 15 (21 obstructive, 1 central). None of the patients' characteristics, including HRQL and lung function, predicted the occurrence of AHI ≥ 15. At 6 months, although sleep quality remained poor (high percentages of N1 and low of REM), sleep architecture had improved as indicated by the significant increase in N3 [4.2% (0-12.5) vs. 9.8% (3.0-20.4)] and decrease in AHI [21.5 (6.5-29.4) vs. 12.8 (4.7-20.4)]. HRQL improved slightly but significantly at 6 months. Neither the changes in HRQL nor in lung function tests were related to these of sleep architecture. Six out of eight patients with abnormal ED at 1st evaluation continued to exhibit abnormal results at 6 months.

CONCLUSIONS

Survivors of critical illness exhibited a high prevalence of obstructive sleep-disordered breathing and poor sleep architecture at hospital discharge, which slightly improved 6 months later, indicating that reversible factors are partly responsible for these abnormalities.