Evidence for reflex upper airway dilator muscle activation by sudden negative airway pressure in man

Compartmental inspiratory genioglossus electromyographic activity in supine, awake individuals with and without obstructive sleep apnoea

Inspiratory-related genioglossus EMG activity is crucial to maintain upper airway patency. However, whether this activity differs between the oblique (middle) and horizontal (base) compartments or if they vary in people with obstructive sleep apnoea (OSA) is unknown. Here, intramuscular electrodes were inserted into the anterior and posterior regions of the horizontal and oblique genioglossal compartments in nine controls [apnoea-hypopnoea index (AHI) ≤ 5 events/h] and 45 OSA participants (AHI range 5-94.3 events/h). Multiunit EMG patterns were categorised as phasic (respiratory modulation) or tonic (no respiratory modulation) during nasal breathing in awake, supine participants. The effects of OSA status and genioglossus compartments were assessed through linear mixed models, controlling for nadir epiglottic pressure (Pepi) and repeated measures within participants. Phasic patterns occurred in 57.6% (n = 106/184) of compartments. Within phasic compartments, log10-transformed peak, phasic and tonic EMG (% maximum) were higher in the oblique than in the horizontal compartments. Additionally, more pronounced negative Pepi correlated with increased log10-transformed phasic EMG in the anterior oblique (beta = -0.075, P = 0.002) and posterior oblique compartments (beta = -0.080, P = 0.027), but not in the horizontal compartments. Effects of OSA severity on activity patterns or EMG measurements were not significant. To conclude, the genioglossus exhibited regional (oblique-horizontal) variation in neural drive during awake inspiration. This compartmental activity appears to be driven by reflex activation in the oblique compartments, which increase phasic EMG. People with and without OSA have similar drive during wakefulness. Understanding the mechanisms driving efficient genioglossus dilatory activity is essential to develop targeted treatments for OSA that focus on pharyngeal muscle activity. KEY POINTS: Inspiratory genioglossus multiunit EMG activity is thought to vary across different neuromuscular compartments. However, it remains unclear whether obstructive sleep apnoea (OSA) affects this compartmental variability. During quiet nasal breathing in awake supine individuals, inspiratory genioglossus EMG normalised to maximum EMG was measured in four genioglossus neuromuscular compartments in individuals with and without OSA. Both tonic (no respiratory modulation, 42%) and phasic (respiratory modulation, 58%) activity patterns were observed during breathing. When a genioglossus compartment showed phasic activity, peak, phasic and tonic EMG activities were higher in the oblique than in the horizontal compartments. Furthermore, greater phasic activity was associated with a more negative nadir epiglottic pressure only in the oblique compartments. There was no additive effect of OSA severity on top of the more negative nadir epiglottic pressure, suggesting people with and without OSA received similar drive during inspiration during wakefulness.

The activity of suprahyoid muscles during sevoflurane-induced gasping in mice

Sevoflurane-induced gasping in mice involves an enormous increase in inspiratory effort, mandibular movement, and a marked decrease in respiratory frequency (fR). We examined differences in breathing patterns and electromyogram activity (EMGSH) of the suprahyoid muscles (SHMs) during eupnea under 3.2 % (1 MAC: minimum alveolar concentration) sevoflurane inhalation and sevoflurane-induced gasping under 6.5 % (2 MAC) sevoflurane inhalation in eight spontaneously breathing, tracheally intubated, adult mice. We found that the phasic EMGSH is obtained only during inspiration in eupnea and gasping and that integrated EMGSH increases more, as a percent of baseline (% baseline) than tidal volume (VT) during gasping (median [interquartile range]; integrated EMGSH: 720 [425-1965] vs. VT: 300 [238-373], P < 0.05). We also found that the onset of EMGSH precedes the start of airflow while maintaining a bell-shaped EMGSH contour, which characterizes the EMG of upper airway dilator (UAD) muscles during eupnea and gasping. Vigorous respiratory-related mandibular movements were never observed during eupnea but were observed in seven of 8 mice during sevoflurane-induced gasping. Our observations indicate that SHMs act as a preferentially activating UAD muscle, contributing to the development of mandibular respiratory movements.

Stimulation of the internal superior laryngeal nerve as a potential therapy for obstructive sleep apnea in a porcine model

Impaired pharyngeal sensing of negative pressure (NP) can lead to a blunted response of the upper airway dilator muscles and contribute to the development of obstructive sleep apnea (OSA). This response is modulated by the nerve fibers in the internal branch of the superior laryngeal nerve (iSLN), mediating negative pressure sensation. Artificial excitation of these fibers could be a potential treatment target for OSA. To evaluate this, electrostimulation of the iSLN was performed in a porcine-isolated upper airway model. Artificial obstructions were induced by varying the levels of negative pressure, and the ability of the animal to resolve these obstructions was evaluated. The pressure at which the animal was still able to resolve the obstruction was quantified as "Resolvable Pressure." Thereby, the effects on pharyngeal patency (n = 35) and the duration of the therapeutic effect outlasting the stimulation (n = 6) were quantified. Electrostimulation before the introduction of an artificial obstruction improved the median resolvable pressure from -28.3 cmH2O [IQR: -45.9; -26.1] to -92.6 cmH2O [IQR: -105.1; -78.6]. The median therapeutic effect was found to outlast the last stimulation burst applied by 163 s when five stimulation bursts were applied in short succession [IQR: 58; 231], 58 s when two were applied [IQR: 7; 65], and 6 s when one was applied [IQR: 0; 51]. Stimulation of the iSLN increased electromyography (EMG) in the genioglossus (GG). The proposed treatment concept can improve pharyngeal patency in the model. Transfer of the results to clinical application could enable the development of a new neuromodulation therapy for OSA.NEW & NOTEWORTHY Electrostimulation before the introduction of an artificial obstruction to induce artificial sleep apnea in the pig model improves the response of the upper airway to negative pressure (NP). The electrostimulation creates a sustained therapeutic effect that outlasts the initial electrostimulation. The use of this therapy in clinical practice has the potential to treat obstructive sleep apnea (OSA).

Lack of association of impaired upper airway sensation with the presence or absence of obstructive sleep apnoea or chronic rhinosinusitis in World Trade Center responders

OBJECTIVE

Examine sensory function of the upper airway in four groups of subjects recruited from the World Trade Centre General Responder Cohort (WTCGRC), with/without obstructive sleep apnoea (OSA), and with/without chronic rhinosinusitis (CRS).

METHODS

Upper airway sensory function was determined using 2-point discrimination (2-PD) and vibration threshold (VT) in 163 WTCGRC subjects with both OSA and CRS (cases), OSA or CRS alone and without OSA or CRS (controls). Presence of OSA was determined from clinical sleep studies or home sleep testing. Presence of CRS was determined by nasal symptom questionnaire. The relationship between the presence of OSA and CRS and upper airway sensory impairment was assessed using linear regression analysis with each of 2PD and VT sensory threshold values as the dependent variable; OSA, CRS and their interaction were the independent variables. Age, gender and body mass index were covariates in the statistical model. The primary analysis was comparison of OSA+CRS versus controls (no OSA and no CRS) evaluated by linear contrasts.

RESULTS

There were no differences in 2-PD or VT in those with OSA+CRS, OSA and CRS alone or controls. However, both 2-PD and VT were significantly higher in the WTCGRC controls compared with values seen in historical controls using the same methodology (median 2-PD 13.0; CI (11.0 to 13.5) vs 10.5; CI (8 to 11); VT: mean±SEM (9.3±0.6 vs 2.2±0.1)).

CONCLUSION

While no differences were found in upper airway sensation between cases of OSA and CRS versus controls in the WTGRC population, there was evidence of impaired upper airway sensation in the WTGRC overall.

Regional associations between inspiratory tongue dilatory movement and genioglossus activity during wakefulness in people with obstructive sleep apnoea

Inspiratory tongue dilatory movement is believed to be mediated via changes in neural drive to genioglossus. However, this has not been studied during quiet breathing in humans. Therefore, this study investigated this relationship and its potential role in obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue dilatory movement, quantified with tagged magnetic resonance imaging, and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in nine controls [apnoea-hypopnea index (AHI) ≤5 events/h] and 37 people with untreated OSA (AHI >5 events/h). Measurements were obtained for 156 neuromuscular compartments (85%). Analysis was adjusted for nadir epiglottic pressure during inspiration. Only for 106 compartments (68%) was a larger anterior (dilatory) movement associated with a higher phasic EMG [mixed linear regression, beta = 0.089, 95% CI [0.000, 0.178], t(99) = 1.995, P = 0.049, hereafter EMG↗/mvt↗]. For the remaining 50 (32%) compartments, a larger dilatory movement was associated with a lower phasic EMG [mixed linear regression, beta = -0.123, 95% CI [-0.224, -0.022], t(43) = -2.458, P = 0.018, hereafter EMG↘/mvt↗]. OSA participants had a higher odds of having at least one decoupled EMG↘/mvt↗ compartment (binary logistic regression, odds ratio [95% CI]: 7.53 [1.19, 47.47] (P = 0.032). Dilatory tongue movement was minimal (>1 mm) in nearly all participants with only EMG↗/mvt↗ compartments (86%, 18/21). These results demonstrate that upper airway dilatory mechanics cannot be predicted from genioglossus EMG, particularly in people with OSA. Tongue movement associated with minimal genioglossus activity suggests co-activation of other airway dilator muscles. KEY POINTS: Inspiratory tongue movement is thought to be mediated through changes in genioglossus activity. However, it is unknown if this relationship is altered by obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue movement, quantified with tagged magnetic resonance imaging (MRI), and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in four tongue compartments of people with and without OSA. Larger tongue anterior (dilatory) movement was associated with higher phasic genioglossus EMG for 68% of compartments. OSA participants had an ∼7-times higher odds of having at least one compartment for which a larger anterior tongue movement was not associated with a higher phasic EMG than controls. Therefore, higher genioglossus phasic EMG does not consistently translate into tongue dilatory movement, particularly in people with OSA. Large dilatory tongue movements can occur despite minimal genioglossus inspiratory activity, suggesting co-activation of other pharyngeal muscles.

Targets for obstructive sleep apnea pharmacotherapy: principles, approaches, and emerging strategies

INTRODUCTION

Obstructive sleep apnea (OSA) is a common and serious breathing disorder. Several pathophysiological factors predispose individuals to OSA. These factors are quantifiable, and modifiable pharmacologically.

AREAS COVERED

Four key pharmacotherapeutic targets are identified and mapped to the major determinants of OSA pathophysiology. PubMed and Clinicaltrials.gov were searched through April 2023.

EXPERT OPINION

Target #1: Pharyngeal Motor Effectors. Increasing pharyngeal muscle activity and responsivity with noradrenergic-antimuscarinic combination is central to recent breakthrough OSA pharmacotherapy. Assumptions, knowledge gaps, future directions, and other targets are identified. #2: Upper Airway Sensory Afferents. There is translational potential of sensitizing and amplifying reflex pharyngeal dilator muscle responses to negative airway pressure via intranasal delivery of new potassium channel blockers. Rationales, advantages, findings, and potential strategies to enhance effectiveness are identified. #3: Chemosensory Afferents and Ventilatory Control. Strategies to manipulate ventilatory control system sensitivity by carbonic anhydrase inhibitors are supported in theory and initial studies. Intranasal delivery of agents to stimulate central respiratory activity are also introduced. #4: Sleep-Wake Mechanisms. Arousability is the fourth therapeutic target rationalized. Evolving automated tools to measure key pathophysiological factors predisposing to OSA will accelerate pharmacotherapy. Although not currently ready for general clinical settings, the identified targets are of future promise.

International Consensus Statement on Obstructive Sleep Apnea

BACKGROUND

Evaluation and interpretation of the literature on obstructive sleep apnea (OSA) allows for consolidation and determination of the key factors important for clinical management of the adult OSA patient. Toward this goal, an international collaborative of multidisciplinary experts in sleep apnea evaluation and treatment have produced the International Consensus statement on Obstructive Sleep Apnea (ICS:OSA).

METHODS

Using previously defined methodology, focal topics in OSA were assigned as literature review (LR), evidence-based review (EBR), or evidence-based review with recommendations (EBR-R) formats. Each topic incorporated the available and relevant evidence which was summarized and graded on study quality. Each topic and section underwent iterative review and the ICS:OSA was created and reviewed by all authors for consensus.

RESULTS

The ICS:OSA addresses OSA syndrome definitions, pathophysiology, epidemiology, risk factors for disease, screening methods, diagnostic testing types, multiple treatment modalities, and effects of OSA treatment on multiple OSA-associated comorbidities. Specific focus on outcomes with positive airway pressure (PAP) and surgical treatments were evaluated.

CONCLUSION

This review of the literature consolidates the available knowledge and identifies the limitations of the current evidence on OSA. This effort aims to create a resource for OSA evidence-based practice and identify future research needs. Knowledge gaps and research opportunities include improving the metrics of OSA disease, determining the optimal OSA screening paradigms, developing strategies for PAP adherence and longitudinal care, enhancing selection of PAP alternatives and surgery, understanding health risk outcomes, and translating evidence into individualized approaches to therapy.

International consensus statement on allergy and rhinology: Allergic rhinitis - 2023

BACKGROUND

In the 5 years that have passed since the publication of the 2018 International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis (ICAR-Allergic Rhinitis 2018), the literature has expanded substantially. The ICAR-Allergic Rhinitis 2023 update presents 144 individual topics on allergic rhinitis (AR), expanded by over 40 topics from the 2018 document. Originally presented topics from 2018 have also been reviewed and updated. The executive summary highlights key evidence-based findings and recommendation from the full document.

METHODS

ICAR-Allergic Rhinitis 2023 employed established evidence-based review with recommendation (EBRR) methodology to individually evaluate each topic. Stepwise iterative peer review and consensus was performed for each topic. The final document was then collated and includes the results of this work.

RESULTS

ICAR-Allergic Rhinitis 2023 includes 10 major content areas and 144 individual topics related to AR. For a substantial proportion of topics included, an aggregate grade of evidence is presented, which is determined by collating the levels of evidence for each available study identified in the literature. For topics in which a diagnostic or therapeutic intervention is considered, a recommendation summary is presented, which considers the aggregate grade of evidence, benefit, harm, and cost.

CONCLUSION

The ICAR-Allergic Rhinitis 2023 update provides a comprehensive evaluation of AR and the currently available evidence. It is this evidence that contributes to our current knowledge base and recommendations for patient evaluation and treatment.

Laryngopharyngeal Reflux in Sleep-Disordered Breathing Patients

INTRODUCTION

Our study aims to evaluate the distribution of laryngopharyngeal reflux (LPR) in patients with sleep-disordered breathing (SDB) via the Reflux Symptom Index (RSI) and to describe the sleep architecture in SDB patients with and without LPR.

MATERIALS AND METHODS

A cross-sectional, descriptive study was conducted. Patients with SDB were identified via the Epworth Sleepiness Scale (ESS) and STOP-BANG questionnaire; they were then screened with the RSI and physical examination for LPR. PSG was performed to evaluate obstructive sleep apnea (OSA).

RESULTS

Of 45 patients, 15 were scored as having LPR via the RSI. Utilizing the Respiratory Disturbance Index (RDI), patients were further classified into four groups: 9 non-LPR with non-OSA SDB, 21 non-LPR with OSA, 4 LPR with non-OSA SDB, and 11 LPR with OSA. The prevalence of LPR was 30.8% in the non-OSA SDB group and 34.4% in the OSA group. All SDB parameters in both groups were similar. SDB patients with high body mass index tended to have LPR and/or OSA. Average ESS scores in the four groups suggested excessive daytime sleepiness, and patients with LPR had higher ESS scores. Regardless of LPR status, SDB patients had a lower percentage of REM sleep and a higher percentage of light sleep.

CONCLUSIONS

The incidence of LPR in OSA patients was similar in non-OSA SDB patients. REM sleep percentage decreased in the four groups, with the non-OSA SDB group having the lowest percentage of REM sleep; light sleep percentage increased in the four groups, with the OSA group having the highest percentage of light sleep.

Regional genioglossus reflex responses to negative pressure pulses in people with obstructive sleep apnea

Tongue and upper airway dilator muscle movement patterns during quiet breathing vary in people with obstructive sleep apnea (OSA). Many patients have inadequate or counterproductive responses to inspiratory negative airway pressure that likely contributes to their OSA. This may be due, at least in part, to inadequate or non-homogeneous reflex drive to different regions of the largest upper airway dilator, genioglossus. To investigate potential regional heterogeneity of genioglossus reflex responses in OSA, brief suction pulses were applied via nasal breathing mask and electromyogram (EMG) was recorded in 4 regions (anterior oblique, anterior horizontal, posterior oblique, posterior horizontal) using intramuscular fine wire electrodes in 15 people with OSA. Genioglossus short-latency reflex excitation amplitude had regional heterogeneity (horizontal vs. oblique regions) when expressed in absolute units but homogeneity when normalized as a percentage of the immediate (100ms) pre-stimulus EMG. Regional variability in reflex morphology (excitation and inhibition) was present in one third of participants. Minimum cross-sectional area (CSA) of the pharyngeal airway quantified using MRI and may be related to the amplitude of the short-latency reflex response to negative pressure such that we found that people with a smaller CSA tended to have greater reflex amplitude (e.g. horizontal region r²=0.41, p=0.01). These findings highlight the complexity of genioglossus reflex control, the potential for regional heterogeneity and the functional importance of upper airway anatomy in mediating genioglossus reflex responses to rapid changes in negative pressure in OSA.

Obstructive sleep apnea

Obstructive sleep apnea (OSA) is a disease that results from loss of upper airway muscle tone leading to upper airway collapse during sleep in anatomically susceptible persons, leading to recurrent periods of hypoventilation, hypoxia, and arousals from sleep. Significant clinical consequences of the disorder cover a wide spectrum and include daytime hypersomnolence, neurocognitive dysfunction, cardiovascular disease, metabolic dysfunction, respiratory failure, and pulmonary hypertension. With escalating rates of obesity a major risk factor for OSA, the public health burden from OSA and its sequalae are expected to increase, as well. In this chapter, we review the mechanisms responsible for the development of OSA and associated neurocognitive and cardiometabolic comorbidities. Emphasis is placed on the neural control of the striated muscles that control the pharyngeal passages, especially regulation of hypoglossal motoneuron activity throughout the sleep/wake cycle, the neurocognitive complications of OSA, and the therapeutic options available to treat OSA including recent pharmacotherapeutic developments.

Exaggerated ventilatory drive estimates from epiglottic and esophageal pressure deflections in the presence of airway occlusion

Esophageal and epiglottic pressure deflections are widely used to quantify ventilatory effort during sleep in patients with obstructive sleep apnea (OSA). However, changes in upper airway patency will fundamentally alter pressure gradients across the respiratory system with different airflow and volume-dependent effects on esophageal versus epiglottic pressure. The magnitude of these obstruction effects on ventilatory effort assessed from pressure deflections has not been systematically investigated. This study sought to quantify the direct effect of airway occlusion on esophageal and epiglottic pressure deflections during sleep in patients with OSA compared with predictions based on classic respiratory mechanics. Pneumotachograph airflow and volume, and esophageal, epiglottic, mask, and gastric pressures were measured throughout a nonoccluded breath before and the first occluded breath after repeated external airway occlusions during sleep in 13 patients with OSA on constant positive airway pressure (CPAP). Inspiratory pressure deflections were approximately doubled with epiglottic pressure, and increased by around 40% with esophageal pressure on the occluded compared with the preoccluded breath. Differences in pressure between pre- and occluded breaths showed strong dependence on volume and flow, in line with theoretical models of respiratory mechanics. A relatively simple correction factor could account for these effects to provide more consistent measures of ventilatory effort from pressure, independent from measurement site and changing airflow conditions. These finding have important implications for interpreting ventilatory effort and arousal threshold measurements and for understanding the relationships between underlying ventilatory drive and pressure deflections in the presence of airway obstruction during sleep.NEW & NOTEWORTHY Esophageal and epiglottic pressure deflection measurements are widely used as gold-standard measures of ventilatory effort without consideration of differential obstruction effects between measurement sites. This study is the first to quantify the effect of airway occlusion on pressure recordings during sleep. The findings of substantial acute effects of occlusion itself on pressure deflections are important to consider in the planning, analysis, and interpretation of studies that make inferences regarding inspiratory effort.

Upper airway effective compliance during wakefulness and sleep in obese adolescents studied via two-dimensional dynamic MRI and semiautomated image segmentation

Novel biomarkers of upper airway biomechanics may improve diagnosis of obstructive sleep apnea syndrome (OSAS). Upper airway effective compliance (EC), the slope of cross-sectional area versus pressure estimated using computational fluid dynamics (CFD), correlates with apnea-hypopnea index (AHI) and critical closing pressure (P_crit). The study objectives are to develop a fast, simplified method for estimating EC using dynamic MRI and physiological measurements and to explore the hypothesis that OSAS severity correlates with mechanical compliance during wakefulness and sleep. Five obese children with OSAS and five control subjects with obesity aged 12-17 yr underwent anterior rhinomanometry, polysomnography, and dynamic MRI with synchronized airflow measurement during wakefulness and sleep. Airway cross section in retropalatal and retroglossal section images was segmented using a novel semiautomated method that uses optimized singular value decomposition (SVD) image filtering and k-means clustering combined with morphological operations. Pressure was estimated using rhinomanometry Rohrer's coefficients and flow rate, and EC was calculated from the area-pressure slope during five normal breaths. Correlations between apnea-hypopnea index (AHI), EC, and cross-sectional area (CSA) change were calculated using Spearman's rank correlation. The semiautomated method efficiently segmented the airway with average Dice Coefficient above 89% compared with expert manual segmentation. AHI correlated positively with EC at the retroglossal site during sleep (r_s = 0.74, P = 0.014) and with change of EC from wake to sleep at the retroglossal site (r_s = 0.77, P = 0.01). CSA change alone did not correlate significantly with AHI. EC, a mechanical biomarker which includes both CSA change and pressure variation, is a potential diagnostic biomarker for studying and managing OSAS.NEW & NOTEWORTHY This study investigated the dynamics of the upper airway at retropalatal and retroglossal sites during wakefulness and sleep by evaluating the effective compliance (EC) of each site and its correlation with apnea-hypopnea index (AHI) using novel semiautomated image processing. AHI correlated significantly with retroglossal EC during sleep and change of retroglossal EC from wake to sleep. The results suggest EC as a promising noninvasive diagnostic marker for estimating the mechanical properties of various upper airway regions in patients with OSAS.

Genioglossus muscle responses to resistive loads in severe OSA patients and healthy control subjects

This study aimed to determine whether there is impairment of genioglossus neuromuscular responses to small negative pressure respiratory stimuli, close to the conscious detection threshold, in obstructive sleep apnea (OSA). We compared genioglossus electromyogram (EMGgg) responses to midinspiratory resistive loads of varying intensity (≈1.2-6.2 cmH₂O·L^-1·s), delivered via a nasal mask, between 16 severe OSA and 17 control participants while the subjects were awake and in a seated upright position. We examined the relationship between stimulus intensity and peak EMGgg amplitude in a 200-ms poststimulus window and hypothesized that OSA patients would have an increased activation threshold and reduced sensitivity in the relationship between EMGgg activation and stimulus intensity. There was no significant difference between control and OSA participants in the threshold (P = 0.545) or the sensitivity (P = 0.482) of the EMGgg amplitude vs. stimulus intensity relationship, where change in epiglottic pressure relative to background epiglottic pressure represented stimulus intensity. These results do not support the hypothesis that deficits in neuromuscular response to negative upper airway pressure exist in OSA during wakefulness; however, the results are likely influenced by a counterintuitive and novel genioglossus muscle suppression response observed in a significant proportion of both OSA and healthy control participants. This suppression response may relate to the inhibition seen in inspiratory muscles such as the diaphragm in response to sudden-onset negative pressure, and its presence provides new insight into the upper airway neuromuscular response to the collapsing force of negative pressure.NEW & NOTEWORTHY Our study used a novel midinspiratory resistive load stimulus to study upper airway neuromuscular responses to negative pressure during wakefulness in obstructive sleep apnea (OSA). Although no differences were found between OSA and healthy groups, the study uncovered a novel and unexpected suppression of neuromuscular activity in a large proportion of both OSA and healthy participants. The unusual response provides new insight into the upper airway neuromuscular response to the collapsing force of negative pressure.

The Role of Genioglossus Activity in Predicting Uvulopalatopharyngoplasty Outcomes

OBJECTIVE

The aim of this study was to evaluate the association between genioglossus activity during sleep onset and the outcome of uvulopalatopharyngoplasty (UPPP) in patients with obstructive sleep apnea.

STUDY DESIGN

Case series with planned data collection.

SETTING

Sleep medical center.

SUBJECTS AND METHODS

Forty-four patients with obstructive sleep apnea underwent overnight polysomnography with synchronous genioglossus electromyography (GGEMG) with intraoral electrodes. In addition, all patients underwent revised UPPP with uvula preservation and were followed up with polysomnography at least 3 months after surgery.

RESULTS

Twenty-five patients (56.8%) were responders. Multiple regression analysis revealed that increasing tonsil size (odds ratio [OR], 0.086; P = .038) and higher sleep-onset GGEMG (OR, 0.664; P = .04) were significant predictors for surgical success. The area under the receiver operating characteristic curve was 0.942 (OR, 0.040; P < .001) for those predictors, 0.884 for GGEMG, and 0.848 for tonsil size. Moreover, all patients were divided into 4 groups according to tonsil size and sleep-onset GGEMG. The success rate of patients with tonsil size III or IV and sleep-onset GGEMG >11.20% (maximal GGEMG) was optimal (92.9%, 13 of 14), while the success rate of patients with tonsil size I or II and sleep-onset GGEMG ≤11.20% was 0% (0 of 10).

CONCLUSIONS

Sleep-onset GGEMG and tonsil size are both important in deciding outcomes of UPPP. Patients with tonsil size III or IV and higher sleep onset may be more suitable candidates for UPPP because of the higher probability of surgical success.

Muscarinic Inhibition of Hypoglossal Motoneurons: Possible Implications for Upper Airway Muscle Hypotonia during REM Sleep

Proper function of pharyngeal dilator muscles, including the genioglossus muscle of the tongue, is required to maintain upper airway patency. During sleep, the activity of these muscles is suppressed, and as a result individuals with obstructive sleep apnea experience repeated episodes of upper airway closure when they are asleep, in particular during rapid-eye-movement (REM) sleep. Blocking cholinergic transmission in the hypoglossal motor nucleus (MoXII) restores REM sleep genioglossus activity, highlighting the importance of cholinergic transmission in the inhibition of hypoglossal motor neurons (HMNs) during REM sleep. Glutamatergic afferent input from neurons in the parahypoglossal (PH) region to the HMNs is critical for MoXII respiratory motor output. We hypothesized that state-dependent cholinergic regulation may be mediated by this pathway. Here we studied the effects of cholinergic transmission in HMNs in adult male and female mice using patch-clamp recordings in brain slices. Using channelrhodopsin-2-assisted circuit mapping, we first demonstrated that PH glutamatergic neurons directly and robustly activate HMNs (PH^Glut → HMNs). We then show that carbachol consistently depresses this input and that this effect is presynaptic. Additionally, carbachol directly affects HMNs by a variable combination of muscarinic-mediated excitatory and inhibitory responses. Altogether, our results suggest that cholinergic signaling impairs upper airway dilator muscle activity by suppressing glutamatergic input from PH premotoneurons to HMNs and by directly inhibiting HMNs. Our findings highlight the complexity of cholinergic control of HMNs at both the presynaptic and postsynaptic levels and provide a possible mechanism for REM sleep suppression of upper airway muscle activity.SIGNIFICANCE STATEMENT Individuals with obstructive sleep apnea can breathe adequately when awake but experience repeated episodes of upper airway closure when asleep, in particular during REM sleep. Similar to skeletal postural muscles, pharyngeal dilator muscles responsible for maintaining an open upper airway become hypotonic during REM sleep. Unlike spinal motoneurons controlling postural muscles that are inhibited by glycinergic transmission during REM sleep, hypoglossal motoneurons that control the upper airway muscles are inhibited in REM sleep by the combination of monoaminergic disfacilitation and cholinergic inhibition. In this study, we demonstrated how cholinergic signaling inhibits hypoglossal motoneurons through presynaptic and postsynaptic muscarinic receptors. Our results provide a potential mechanism for upper airway hypotonia during REM sleep.

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.

An acute exposure to intermittent negative airway pressure elicits respiratory long-term facilitation in awake humans

BACKGROUND

A sustained elevation in respiratory drive following removal of the inducing stimulus is known as respiratory long-term facilitation (rLTF). We investigated whether an acute exposure to intermittent negative airway pressure (INAP) elicits rLTF in humans.

METHOD

13 healthy males (20.9 ± 2.8 years) undertook two trials (INAP and Control). In the INAP trial participants were exposed to one hour of 30-second episodes of breathing against negative pressure (-10 cmH₂O) interspersed by 60-second intervals of breathing at atmospheric pressure. In the Control trial participants breathed at atmospheric pressure for one hour. Ventilation following INAP (recovery phase) was compared to that during baseline.

RESULTS

Ventilation increased from baseline to recovery in the INAP trial (14.9 ± 0.9 vs 19.1 ± 0.7 L/min, P = 0.002). This increase was significantly greater than the equivalent during the Control trial (P = 0.019). Data shown as mean ± SEM.

CONCLUSION

In this study INAP elicited rLTF in awake, healthy humans. Further research is required to investigate the responsible mechanisms.

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.

Genioglossus muscle activity during sniff and reverse sniff in healthy men

NEW FINDINGS

What is the central question of this study? Maximal sniff nasal inspiratory and reverse sniff nasal expiratory pressures are measured as inspiratory and expiratory muscle strength, respectively. Is the genioglossus muscle activated during short maximal inspiratory and expiratory efforts through the nose? What is the main finding and its importance? Genioglossus muscle activity occurred with inspiratory muscle activity during a maximal sniff and with expiratory muscle activity during a maximal reverse sniff. These results indicate that genioglossus muscle activity is closely related to the generation of maximal sniff nasal inspiratory and reverse sniff nasal expiratory pressures.

ABSTRACT

Maximal sniff nasal inspiratory pressure (SNIP_max ) is widely used to assess inspiratory muscle strength. The sniff nasal inspiratory pressure (SNIP) is lower in patients with neuromuscular disease with bulbar involvement compared with those without, possibly owing to impaired upper airway muscle function. However, the degree to which the genioglossus (GG) muscle, one of the upper airway muscles, is activated during inspiratory and expiratory efforts through the nose remains unclear. Therefore, we examined GG activity during short and sharp inspiratory and expiratory efforts through the nose, i.e. sniff and reverse sniff manoeuvres. In eight normal young subjects, we inserted fine wire electrodes into the GG muscle, parasternal intercostal and scalene (inspiratory) muscles and transversus abdominis (expiratory) muscle. We assessed EMG activity of each muscle and measured SNIP and reverse sniff nasal expiratory pressure (RSNEP) during sniffs and reverse sniffs from low to high intensities in the sitting position. The highest SNIP and RSNEP were analysed as SNIP_max and maximal RSNEP (RSNEP_max ), respectively. In each subject, GG EMG activity increased linearly with increasing SNIP and RSNEP. The SNIP_max and RSNEP_max were -85.1 ± 15.9 and 83.2 ± 24.2 cmH₂ O, respectively. Genioglossus EMG activity varied with EMG activity of the parasternal intercostal and scalene muscles during generation of SNIP_max and with EMG activity of the transversus abdominis muscle during RSNEP_max . Genioglossus EMG activity during generation of SNIP_max was higher than during RSNEP_max (62.9 ± 31.1% EMG of SNIP_max , P = 0.012). These results suggested that GG activity was closely related to the generation of both SNIP_max and RSNEP_max .

Genioglossus reflex responses to negative upper airway pressure are altered in people with tetraplegia and obstructive sleep apnoea

KEY POINTS

Protective reflexes in the throat area (upper airway) are crucial for breathing. Impairment of these reflexes can cause breathing problems during sleep such as obstructive sleep apnoea (OSA). OSA is very common in people with spinal cord injury for unknown reasons. This study shows major changes in protective reflexes that serve to keep the upper airway open in response to suction pressures in people with tetraplegia and OSA. These results help us understand why OSA is so common in people with tetraplegia and provide new insight into how protective upper airway reflexes work more broadly.

ABSTRACT

More than 60% of people with tetraplegia have obstructive sleep apnoea (OSA). However, the specific causes are unknown. Genioglossus, the largest upper-airway dilator muscle, is important in maintaining upper-airway patency. Impaired genioglossus muscle function following spinal cord injury may contribute to OSA. This study aimed to determine if genioglossus reflex responses to negative upper-airway pressure are altered in people with OSA and tetraplegia compared to non-neurologically impaired able-bodied individuals with OSA. Genioglossus reflex responses measured via intramuscular electrodes to ∼60 brief (250 ms) pulses of negative upper-airway pressure (∼-15 cmH₂ O at the mask) were compared between 13 participants (2 females) with tetraplegia plus OSA and 9 able-bodied controls (2 females) matched for age and OSA severity. The initial short-latency excitatory reflex response was absent in 6/13 people with tetraplegia and 1/9 controls. Genioglossus reflex inhibition in the absence of excitation was observed in three people with tetraplegia and none of the controls. When the excitatory response was present, it was significantly delayed in the tetraplegia group compared to able-bodied controls: excitation onset latency (mean ± SD) was 32 ± 16 vs. 18 ± 9 ms, P = 0.045; peak excitation latency was 48 ± 17 vs. 33 ± 8 ms, P = 0.038. However, when present, amplitude of the excitation response was not different between groups, 195 ± 26 vs. 219 ± 98% at baseline, P = 0.55. There are major differences in genioglossus reflex morphology and timing in response to rapid changes in airway pressure in people with tetraplegia and OSA. Altered genioglossus function may contribute to the increased risk of OSA in people with tetraplegia. The precise mechanisms mediating these differences are unknown.

Influence of respiratory mechanics and drive on genioglossus movement under ultrasound imaging

METHODS

Twenty healthy subjects (10 males, age 28±5 years [mean ± SD]) lay supine, awake, with the head in a neutral position. Ventilation was monitored with inductance bands. Real-time B-mode ultrasound movies were analysed. We measured genioglossus motion (i) during spontaneous breathing, voluntary targeted breathing (normal tidal volume Vt), and voluntary hyperpnoea (at 1.5Vt and 2 Vt); (ii) during inspiratory flow resistive loading; (iii) with changes in end-expiratory lung volume (EELV).

RESULTS

Average peak inspiratory displacement of the infero-posterior region of genioglossus was 0.89±0.56 mm; 1.02±0.88 mm; 1.27±0.70 mm respectively for voluntary Vt, and during voluntary hyperpnoea at 1.5Vt and 2Vt. A change in genioglossus motion was observed with increased Vt. During increasing inspiratory resistive loading, the genioglossus displaced less anteriorly (p = 0.005) but more inferiorly (p = 0.027). When lung volume was altered, no significant changes in genioglossus movement were observed (p = 0.115).

CONCLUSION

In healthy subjects, we observed non-uniform heterogeneous inspiratory motion within the inferoposterior part of genioglossus during spontaneous quiet breathing with mean peak displacement between 0.5-2 mm, with more displacement in the posterior region than the anterior. This regional heterogeneity disappeared during voluntary targeted breathing. This may be due to different neural drive to genioglossus during voluntary breathing. During inspiratory resistive loading, the observed genioglossus motion may serve to maintain upper airway patency by balancing intraluminal negative pressure with positive pressure generated by upper airway dilatory muscles. In contrast, changes in EELV were not accompanied by major changes in genioglossus motion.

Sleeping tongue: current perspectives of genioglossus control in healthy individuals and patients with obstructive sleep apnea

The focus of this review was on the genioglossus (GG) muscle and its role in maintaining upper airway patency in both healthy individuals and obstructive sleep apnea (OSA) patients. This review provided an overview of GG anatomy and GG control and function during both wakefulness and sleep in healthy individuals and in those with OSA. We reviewed evidence for the role of the GG in OSA pathogenesis and also highlighted abnormalities in GG morphology, responsiveness, tissue movement patterns and neurogenic control that may contribute to or result from OSA. We summarized the different methods for improving GG function and/or activity in OSA and their efficacy. In addition, we discussed the possibility that assessing the synergistic activation of multiple upper airway dilator muscles may provide greater insight into upper airway function and OSA pathogenesis, rather than assessing the GG in isolation.

A Genetically Defined Circuit for Arousal from Sleep during Hypercapnia

The precise neural circuitry that mediates arousal during sleep apnea is not known. We previously found that glutamatergic neurons in the external lateral parabrachial nucleus (PBel) play a critical role in arousal to elevated CO2 or hypoxia. Because many of the PBel neurons that respond to CO2 express calcitonin gene-related peptide (CGRP), we hypothesized that CGRP may provide a molecular identifier of the CO2 arousal circuit. Here, we report that selective chemogenetic and optogenetic activation of PBel^CGRP neurons caused wakefulness, whereas optogenetic inhibition of PBel^CGRP neurons prevented arousal to CO2, but not to an acoustic tone or shaking. Optogenetic inhibition of PBel^CGRP terminals identified a network of forebrain sites under the control of a PBel^CGRP switch that is necessary to arouse animals from hypercapnia. Our findings define a novel cellular target for interventions that may prevent sleep fragmentation and the attendant cardiovascular and cognitive consequences seen in obstructive sleep apnea. VIDEO ABSTRACT.

Modest Improvement of Untreated Severe Sleep-Disordered Breathing in the Middle-Aged and Elderly

OBJECTIVE

It has been reported that untreated sleep-disordered breathing (SDB) deteriorates over time, however this remains contentious. The aim of the present study is to evaluate the clinical course of SDB in middle-aged and older SDB patients, and to identify how relevant factors contribute to the change in SDB severity.

METHODS

Baseline and follow-up polysomnographic data of 56 untreated SDB patients (mean age, 61.2±5.71) were obtained retrospectively and the mean interval was 62.4±22.0 months. Subgroup analysis was performed based on the baseline severity, and the factors associated with the course of SDB were analyzed.

RESULTS

At the baseline, 13 subjects were simple snorers, 15 had mild to moderate SDB, and 28 were severe SDB patients. While there was no significant change in apnea-hypopnea index (AHI) as a whole, subgroup analysis showed decrease of AHI in severe SDB patients (43.9±10.6 to 35.6±20.0, p=0.009). The change in supine time percent and baseline AHI were associated with the change in AHI (β=0.387, p=0.003; β=-0.272, p=0.037).

CONCLUSION

Untreated SDB did not deteriorate over time with modest improvement in severe SDB. A proportion of severe SDB patients might expect decrease in SDB severity irrespective of changes in sleep position or body weight.

Obstructive sleep apnoea pathogenesis from mild to severe: Is it all the same?

Obstructive sleep apnoea (OSA) is a common disorder caused by not only an impaired upper airway anatomy (i.e. anatomically narrow/collapsible airway), but also by several non-anatomical factors. In this review, we summarise what is known about how each of the pathological factors that cause OSA vary according to disease severity as measured by the apnoea-hypopnoea index. Our synthesis of the available literature indicates that most of the key factors that cause OSA vary with disease severity. However, there is substantial heterogeneity such that the relative contribution of each of these traits varies both between patients and within different severities of disease. These differences likely contribute to variable efficacy of many non-continuous positive airway pressure treatments and inconsistencies in responses with regard to different OSA severities at baseline.

Computational fluid dynamics upper airway effective compliance, critical closing pressure, and obstructive sleep apnea severity in obese adolescent girls

Obstructive sleep apnea syndrome (OSAS) is associated with anatomical abnormalities restricting upper airway size and functional factors decreasing pharyngeal dilator activity in sleep. In this study we hypothesized that OSAS is also associated with altered pharyngeal mechanical compliance during wakefulness. Five OSAS and six control obese girls between 14 and 18 years of age were studied. All underwent polysomnography, critical closing pressure (P_crit) studies, and dynamic MRI of the upper airway during awake tidal breathing. Effective airway compliance was defined as the slope of cross-sectional area vs. average pressure between maximum inspiration and maximum expiration along the pharyngeal airway. Pharyngeal pressure fields were calculated by using image-based computational fluid dynamics and nasal resistance. Spearman correlations were calculated to test associations between apnea-hypopnea index (AHI), P_crit, and airway compliance. Effective compliances in the nasopharynx (C_NP) and velopharynx (C_VP) were lower and negative in OSAS compared with controls: -4.4 vs. 1.9 (mm²/cmH₂O, P = 0.012) and -2.1 vs. 3.9 (mm²/cmH₂O, P = 0.021), respectively, suggesting a strong phasic pharyngeal dilator activity during inspiration in OSAS compared with controls. For all subjects, C_NP and AHI correlated negatively (r_S = -0.69, P = 0.02), and passive P_crit correlated with C_NP (r_S = -0.76, P = 0.006) and with AHI (r_S = 0.86, P = 0.0006). Pharyngeal mechanics obtained during wakefulness could be used to characterize subjects with OSAS. Moreover, negative effective compliance during wakefulness and its correlation to AHI and P_crit suggest that phasic dilator activity of the upper pharynx compensates for negative pressure loads in these subjects.

Effect of head and jaw position on respiratory-related motion of the genioglossus

Head and jaw position influence upper airway patency and electromyographic (EMG) activity of the main upper airway dilator muscle, the genioglossus. However, it is not known whether changes in genioglossus EMG activity translate into altered muscle movement during respiration. The aim of this study was to determine the influence of head and jaw position on dilatory motion of the genioglossus in healthy adult men during quiet breathing by measuring the displacement of the posterior tongue in six positions—neutral, head extension, head rotation, head flexion, mouth opening, and mandibular advancement. Respiratory-related motion of the genioglossus was imaged with spatial modulation of magnetization (SPAMM) in 12 awake male participants. Tissue displacement was quantified with harmonic phase (HARP) analysis. The genioglossus moved anteriorly beginning immediately before or during inspiration, and there was greater movement in the oropharynx than in the velopharynx in all positions. Anterior displacements of the oropharyngeal tongue varied between neutral head position (0.81 ± 0.41 mm), head flexion (0.62 ± 0.45 mm), extension (0.39 ± 0.19 mm), axial rotation (0.39 ± 0.2 mm), mouth open (1.24 ± 0.72 mm), and mandibular advancement (1.08 ± 0.65 mm). Anteroposterior displacement increased in the mouth-open position and decreased in the rotated position relative to cross-sectional area (CSA) ( P = 0.002 and 0.02, respectively), but CSA did not independently predict anteroposterior movement overall ( P = 0.057). The findings of this study suggest that head position influences airway dilation during inspiration and may contribute to variation in airway patency in different head positions.

Sleep disordered breathing at the extremes of age: the elderly

KEY POINTS

Sleep disordered breathing (SDB) is common and its prevalence increases with age. Despite this high prevalence, SDB is frequently unrecognised and undiagnosed in older people.There is accumulating evidence that SDB in older people is associated with worsening cardio- cerebrovascular, cognitive and functional outcomes.There is now good evidence to support the use of continuous positive airway pressure therapy in older patients with symptomatic SDB.

EDUCATIONAL AIMS

To highlight the prevalence and presentation of sleep disordered breathing (SDB) in older people.To inform readers about the risk factors for SDB in older people.To explore the impact of SDB in older people.To introduce current evidence based treatment options for SDB in older people. Sleep disordered breathing (SBD) increases in prevalence as we age, most likely due to physiological and physical changes that occur with ageing. Additionally, SDB is associated with comorbidity and its subsequent polypharmacy, which may increase with increasing age. Finally, the increased prevalence of SDB is intrinsically linked to the obesity epidemic. SDB is associated with serious outcomes in younger people and, likewise, older people. Thus, identification, diagnosis and treatment of SDB is important irrelevant of age. This article reviews the age-related changes contributing to SDB, the epidemiology and the risk factors for SDB in older people, the association of SDB with adverse outcomes, and diagnostic and treatment options for this population.

Tailored treatment strategies for obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by repetitive collapse of the upper airway (UA) during sleep and is associated with chronic intermittent hypoxemia, catecholamine surges, and sleep disrupt. Multiple pathophysiological risk factors have been identified and contribute to OSA, including anatomical abnormalities (elevated UA mechanical load), compromised UA dilators, increased loop gain (unstable respiratory control), and decreased arousal threshold. These factors may contribute to the pathophysiology of sleep apnea in different individuals and recent evidence suggests that treatment may be targeted towards underlying pathophysiological mechanism. In some cases, combination therapy may be required to treat the condition.

Time of day affects the frequency and duration of breathing events and the critical closing pressure during NREM sleep in participants with sleep apnea

We investigated if the number and duration of breathing events coupled to upper airway collapsibility were affected by the time of day. Male participants with obstructive sleep apnea completed a constant routine protocol that consisted of sleep sessions in the evening (10 PM to 1 AM), morning (6 AM to 9 AM), and afternoon (2 PM to 5 PM). On one occasion the number and duration of breathing events was ascertained for each sleep session. On a second occasion the critical closing pressure that demarcated upper airway collapsibility was determined. The duration of breathing events was consistently greater in the morning compared with the evening and afternoon during N1 and N2, while an increase in event frequency was evident during N1. The critical closing pressure was increased in the morning (2.68 ± 0.98 cmH2O) compared with the evening (1.29 ± 0.91 cmH2O; P ≤ 0.02) and afternoon (1.25 ± 0.79; P ≤ 0.01). The increase in the critical closing pressure was correlated to the decrease in the baseline partial pressure of carbon dioxide in the morning compared with the afternoon and evening (r = -0.73, P ≤ 0.005). Our findings indicate that time of day affects the duration and frequency of events, coupled with alterations in upper airway collapsibility. We propose that increases in airway collapsibility in the morning may be linked to an endogenous modulation of baseline carbon dioxide levels and chemoreflex sensitivity (12), which are independent of the consequences of sleep apnea.

Mechanisms contributing to the response of upper-airway muscles to changes in airway pressure

This study assessed the effects of inhaled lignocaine to reduce upper airway surface mechanoreceptor activity on 1) basal genioglossus and tensor palatini EMG, 2) genioglossus reflex responses to large pulses (∼10 cmH2O) of negative airway pressure, and 3) upper airway collapsibility in 15 awake individuals. Genioglossus and tensor palatini muscle EMG and airway pressures were recorded during quiet nasal breathing and during brief pulses (250 ms) of negative upper-airway pressure. Lignocaine reduced peak inspiratory (5.6 ± 1.5 vs. 3.8 ± 1.1% maximum; mean ± SE, P < 0.01) and tonic (2.8 ± 0.8 vs. 2.1 ± 0.7% maximum; P < 0.05) genioglossus EMG during quiet breathing but had no effect on tensor palatini EMG (5.0 ± 0.8 vs. 5.0 ± 0.5% maximum; P = 0.97). Genioglossus reflex excitation to negative pressure pulses decreased after anesthesia (60.9 ± 20.7 vs. 23.6 ± 5.2 μV; P < 0.05), but not when expressed as a percentage of the immediate prestimulus baseline. Reflex excitation was closely related to the change in baseline EMG following lignocaine ( r2 = 0.98). A short-latency genioglossus reflex to rapid increases from negative to atmospheric pressure was also observed. The upper airway collapsibility index (%difference) between nadir choanal and epiglottic pressure increased after lignocaine (17.8 ± 3.7 vs. 28.8 ± 7.5%; P < 0.05). These findings indicate that surface receptors modulate genioglossus but not tensor palatini activity during quiet breathing. However, removal of input from surface mechanoreceptors has minimal effect on genioglossus reflex responses to large (∼10 cmH2O), sudden changes in airway pressure. Changes in pressure rather than negative pressure per se can elicit genioglossus reflex responses. These findings challenge previous views and have important implications for upper airway muscle control.

A comprehensive assessment of genioglossus electromyographic activity in healthy adults

The genioglossus (GG) is an extrinsic muscle of the human tongue that plays a critical role in preserving airway patency. In the last quarter century, >50 studies have reported on respiratory-related GG electromyographic (EMG) activity in human subjects. Remarkably, of the studies performed, none have duplicated subject body position, electrode recording locations, and/or breathing task(s), making interpretation and integration of the results across studies extremely challenging. In addition, more recent research assessing lingual anatomy and muscle contractile properties has identified regional differences in muscle fiber type and myosin heavy chain expression, giving rise to the possibility that the anterior and posterior regions of the muscle fulfill distinct functions. Here, we assessed EMG activity in anterior and posterior regions of the GG, across upright and supine, in rest breathing and in volitionally modulated breathing tasks. We tested the hypotheses that GG EMG is greater in the posterior region and in supine, except when breathing is subject to volitional modulation. Our results show differences in the magnitude of EMG (%regional maximum) between anterior and posterior muscle regions (7.95 ± 0.57 vs. 11.10 ± 0.99, respectively; P < 0.001), and between upright and supine (8.63 ± 0.73 vs. 10.42 ± 0.90, respectively; P = 0.008). Although the nature of a task affects the magnitude of EMG (P < 0.001), the effect is similar for anterior and posterior muscle regions and across upright and supine (P > 0.2).

Role of preoperative screening for adult patients for obstructive sleep apnea

Obstructive sleep apnea (OSA) is a chronic disease with increasing prevalence. Underdiagnosed in the surgical population, OSA can reach a prevalence of up to 70% in bariatric surgery, and be associated with difficult airways and postoperative cardiopulmonary adverse events. Despite its association with escalation of care, increased health care resource utilization, and length of hospital stay, < 25% of health care institutions in the United States have OSA perioperative protocols to improve patient safety. This is explained in part by a lack of studies that support a widely accepted systematic approach to preoperative screening and risk stratification. This review evaluates the role of preoperative screening tools for adult patients with suspected OSA.

[A clinical investigation of pediatric patients with sleep-disordered breathing who suffered perioperative respiratory complications of adenotonsillectomy]

The aim of this study was to investigate the clinical background and identify the risk factors for perioperative respiratory complication in pediatric patients with sleep-disordered breathing (SDB) who underwent adenotonsillectomy (AT). Of the 186 pediatric subjects (male: 131, female: 55) undergoing AT as the first surgical treatment for SDB, 14 patients (male: 9, female: 5) fulfilled the following criteria: 1) disturbed ventilation, 2) cyanosis with an oxygen saturation of less than 90% on pulse oximetry during the perioperative period and 3) the subsequent need for medical intervention, including immediate intubation, continuous positive airway pressure (CPAP) or airway insertion. Among these 14 patients, nine were less than 3 years of age. In addition, 5 and 3 patients had hypotonia due to cerebral paralysis and metabolic disturbances, respectively. Seven had a short stature with an SD of worse than - 1.5. A statistical analysis showed that cases with either an age of less than 3 years, hypotonia or a short stature had a high risk for suffering from respiratory complications, and suggested that low body weight and a high value for preoperative apnea-hypopnea index were additional risk factors. However, a chart review exhibited that, of the 14 cases with respiratory complications, the 8 cases whose age was under 3 years had either of hypotonia or a short stature. In thirteen of the 14 cases, respiratory complications were associated with the process of general anesthesia, and ten patients exhibited pharyngeal collapse. After surgery, 7 and 3 patients required intensive care in the ICU and the pediatric recovery unit, respectively. Based on these results, it is suggested that pediatric SDB cases under 3 years of age and either with hypotonia or a short stature have a high risk for respiratory complications associated with AT, and therefore AT for such patients should only be performed in medical facilities with an ICU or an equivalent department.

Respiratory and auditory cortical processing in children with obstructive sleep apnea syndrome

RATIONALE

Children with obstructive sleep apnea syndrome (OSAS) have impaired cortical processing of respiratory afferent stimuli, manifested by blunted sleep respiratory-related evoked potentials (RREP). However, whether this impairment is limited to respiratory stimuli, or reversible after successful treatment, is unknown. We hypothesized that, during sleep, children with OSAS have (1) abnormal RREP, (2) normal cortical processing of nonrespiratory stimuli, and (3) persistence of abnormal RREP after treatment.

OBJECTIVES

To measure sleep RREP and auditory evoked potentials in normal control subjects and children with OSAS before and after treatment.

METHODS

Twenty-four children with OSAS and 24 control subjects were tested during N3 sleep. Thirteen children with OSAS repeated testing 4-6 months after adenotonsillectomy.

MEASUREMENTS AND MAIN RESULTS

RREP were blunted in OSAS compared with control subjects (N350 at Cz -27 ± 15.5 vs. -47.4 ± 28.5 μV; P = 0.019), and did not improve after OSAS treatment (N350 at Cz pretreatment -25.1 ± 7.4 vs. -29.8 ± 8.1 post-treatment). Auditory evoked potentials were similar in OSAS and control subjects at baseline (N350 at Cz -58 ± 33.1 vs. -66 ± 31.1 μV), and did not change after treatment (N350 at Cz -67.5 ± 36.8 vs. -65.5 ± 20.3).

CONCLUSIONS

Children with OSAS have persistent primary or irreversible respiratory afferent cortical processing deficits during sleep that could put them at risk of OSAS recurrence. OSAS does not seem to affect the cortical processing of nonrespiratory (auditory) afferent stimuli during sleep.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive collapse of the pharyngeal airway during sleep. Control of pharyngeal patency is a complex process relating primarily to basic anatomy and the activity of many pharyngeal dilator muscles. The control of these muscles is regulated by a number of processes including respiratory drive, negative pressure reflexes, and state (sleep) effects. In general, patients with OSA have an anatomically small airway the patency of which is maintained during wakefulness by reflex-driven augmented dilator muscle activation. At sleep onset, muscle activity falls, thereby compromising the upper airway. However, recent data suggest that the mechanism of OSA differs substantially among patients, with variable contributions from several physiologic characteristics including, among others: level of upper airway dilator muscle activation required to open the airway, increase in chemical drive required to recruit the pharyngeal muscles, chemical control loop gain, and arousal threshold. Thus, the cause of sleep apnea likely varies substantially between patients. Other physiologic mechanisms likely contributing to OSA pathogenesis include falling lung volume during sleep, shifts in blood volume from peripheral tissues to the neck, and airway edema. Apnea severity may progress over time, likely due to weight gain, muscle/nerve injury, aging effects on airway anatomy/collapsibility, and changes in ventilatory control stability.

Neural control of the upper airway: integrative physiological mechanisms and relevance for sleep disordered breathing

The various neural mechanisms affecting the control of the upper airway muscles are discussed in this review, with particular emphasis on structure-function relationships and integrative physiological motor-control processes. Particular foci of attention include the respiratory function of the upper airway muscles, and the various reflex mechanisms underlying their control, specifically the reflex responses to changes in airway pressure, reflexes from pulmonary receptors, chemoreceptor and baroreceptor reflexes, and postural effects on upper airway motor control. This article also addresses the determinants of upper airway collapsibility and the influence of neural drive to the upper airway muscles, and the influence of common drugs such as ethanol, sedative hypnotics, and opioids on upper airway motor control. In addition to an examination of these basic physiological mechanisms, consideration is given throughout this review as to how these mechanisms relate to integrative function in the intact normal upper airway in wakefulness and sleep, and how they may be involved in the pathogenesis of clinical problems such obstructive sleep apnea hypopnea.

State-dependent and reflex drives to the upper airway: basic physiology with clinical implications

The root cause of the most common and serious of the sleep disorders is impairment of breathing, and a number of factors predispose a particular individual to hypoventilation during sleep. In turn, obstructive hypopneas and apneas are the most common of the sleep-related respiratory problems and are caused by dysfunction of the upper airway as a conduit for airflow. The overarching principle that underpins the full spectrum of clinical sleep-related breathing disorders is that the sleeping brain modifies respiratory muscle activity and control mechanisms and diminishes the ability to respond to respiratory distress. Depression of upper airway muscle activity and reflex responses, and suppression of arousal (i.e., "waking-up") responses to respiratory disturbance, can also occur with commonly used sedating agents (e.g., hypnotics and anesthetics). Growing evidence indicates that the sometimes critical problems of sleep and sedation-induced depression of breathing and arousal responses may be working through common brain pathways acting on common cellular mechanisms. To identify these state-dependent pathways and reflex mechanisms, as they affect the upper airway, is the focus of this paper. Major emphasis is on the synthesis of established and recent findings. In particular, we specifically focus on 1) the recently defined mechanism of genioglossus muscle inhibition in rapid-eye-movement sleep; 2) convergence of diverse neurotransmitters and signaling pathways onto one root mechanism that may explain pharyngeal motor suppression in sleep and drug-induced brain sedation; 3) the lateral reticular formation as a key hub of respiratory and reflex drives to the upper airway.