Within-breath control of genioglossal muscle activation in humans: effect of sleep-wake state

Severity of tongue base collapse in various body positions in patients with obstructive sleep apnea: A trajectory analysis

BACKGROUND

Drug-induced sleep endoscopy (DISE) is used for evaluating upper airway anatomy and determining airway obstruction patterns. It is typically performed with the patient in the supine position. Airway collapse severity is influenced by body position and level of consciousness; the resultant dynamic changes may vary across patients. In this study, we evaluated the severity of upper airway collapse through awake endoscopy and DISE and identified factors affecting the pattern of airway collapse severity.

METHODS

This study included 66 patients with obstructive sleep apnea. The patients underwent type 1 polysomnography, tongue strength assessment, awake endoscopy in the sitting and supine positions, and DISE. Group-based trajectory modeling was performed to identify patients with different collapse severity patterns in different body positions and at different levels of consciousness.

RESULTS

Patient with similar severity trajectory were assigned to the same group. Two different severity trajectories (group 1 and group 2) were identified at the tongue base level. Tongue depression strength varied significantly between groups 1 and 2 (47.00 vs. 35.00 kPa; P = .047). During awake endoscopy, collapse severity was significantly higher in group 2 than in group 1. Group 1 had lower rapid eye movement/nonrapid eye movement apnea-hypopnea index ratios and higher tongue depression strength than did group 2.

CONCLUSION

In patients with obstructive sleep apnea, tongue strength may vary depending on body position. Our results should be interpreted with caution because of the limited sample size. Future studies should investigate the effect of oropharyngeal rehabilitation on tongue strength and collapse severity.

Drive versus Pressure Contributions to Genioglossus Activity in Obstructive Sleep Apnea

Rationale: Loss of pharyngeal dilator muscle activity is a key determinant of respiratory events in obstructive sleep apnea (OSA). After the withdrawal of wakefulness stimuli to the genioglossus at sleep onset, mechanoreceptor negative pressure and chemoreceptor ventilatory drive feedback govern genioglossus activation during sleep, but the relative contributions of drive and pressure stimuli to genioglossus activity across progressive obstructive events remain unclear. We recently showed that drive typically falls during events, whereas negative pressures increase, providing a means to assess their individual contributions to the time course of genioglossus activity. Objectives: For the first time, we critically test whether the loss of drive could explain the loss of genioglossus activity observed within events in OSA. Methods: We examined the time course of genioglossus activity (EMGgg; intramuscular electromyography), ventilatory drive (intraesophageal diaphragm electromyography), and esophageal pressure during spontaneous respiratory events (using the ensemble-average method) in 42 patients with OSA (apnea-hypopnea index 5-91 events/h). Results: Multivariable regression demonstrated that the falling-then-rising time course of EMGgg may be well explained by falling-then-rising drive and rising negative pressure stimuli (model R = 0.91 [0.88-0.98] [95% confidence interval]). Overall, EMGgg was 2.9-fold (0.47-∞) more closely associated with drive than pressure stimuli (ratio of standardized coefficients, βdrive:βpressure; ∞ denotes absent pressure contribution). However, individual patient results were heterogeneous: approximately one-half (n = 22 of 42) exhibited drive-dominant responses (i.e., βdrive:βpressure > 2:1), and one-quarter (n = 11 of 42) exhibited pressure-dominant EMGgg responses (i.e., βdrive:βpressure < 1:2). Patients exhibiting more drive-dominant EMGgg responses experienced greater event-related EMGgg declines (12.9 [4.8-21.0] %baseline/standard deviation of βdrive:βpressure; P = 0.004, adjusted analysis). Conclusions: Loss of genioglossus activity precipitating events in patients with OSA is strongly associated with a contemporaneous loss of drive and is greatest in those whose activity tracks drive rather than pressure stimuli. These findings were upheld for events without prior arousal. Responding to falling drive rather than rising negative pressure during events may be deleterious; future therapeutic strategies whose aim is to sustain genioglossus activity by preferentially enhancing responses to rising pressure rather than falling drive are of interest.

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.

Reboxetine and hyoscine butylbromide improve upper airway function during nonrapid eye movement and suppress rapid eye movement sleep in healthy individuals

STUDY OBJECTIVES

Recent findings indicate that noradrenergic and antimuscarinic processes are crucial for sleep-related reductions in pharyngeal muscle activity. However, there are few human studies. Accordingly, this study aimed to determine if a combined noradrenergic and antimuscarinic intervention increases pharyngeal dilator muscle activity and improves airway function in sleeping humans.

METHODS

Genioglossus (GG) and tensor palatini electromyography (EMG), pharyngeal pressure, upper airway resistance, and breathing parameters were acquired in 10 healthy adults (5 female) during two overnight sleep studies after 4 mg of reboxetine (REB) plus 20 mg of hyoscine butylbromide (HBB) or placebo using a double-blind, placebo-controlled, randomized, cross-over design.

RESULTS

Compared with placebo, peak and tonic GG EMG were lower (Mean ± SD: 83 ± 73 vs. 130 ± 75, p = 0.021 and 102 ± 102 vs. 147 ± 123 % wakefulness, p = 0.021, respectively) but the sleep-related reduction in tensor palatini was less (Median [25th, 75th centiles]: 53[45, 62] vs. 34[28, 38] % wakefulness, p = 0.008) with the drug combination during nonrapid eye movement (non-REM) sleep. These changes were accompanied by improved upper airway function including reduced pharyngeal pressure swings, airway resistance, respiratory load compensation, and increased breathing frequency during N2. REB and HBB significantly reduced rapid eye movement sleep compared with placebo (0.6 ± 1.1 vs. 14.5 ± 6.8 % total sleep time, p < 0.001).

CONCLUSIONS

Contrary to our hypothesis, GG muscle activity (% wakefulness) during non-REM sleep was lower with REB and HBB. However, sleep-related reductions in tensor palatini activity were less and upper airway function improved. These findings provide mechanistic insight into the role of noradrenergic and antimuscarinic processes on upper airway function in humans and have therapeutic potential for obstructive sleep apnea.

CLINICAL TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry, https://www.anzctr.org.au, trial ID: ACTRN12616000469415.

Sleep Apnea, Hypertension and the Sympathetic Nervous System in the Adult Population

Sleep apnea is very common in patients with cardiovascular disease, especially in patients with hypertension. Over the last few decades a number of discoveries have helped support a causal relationship between the two and even resistant hypertension. The role neurogenic mechanisms play has gathered more attention in the recent past due to their immediate bedside utility. Several innovative discoveries in pathogenesis including those exploring the role of baroreflex gain, cardiovascular variability, chemoreceptor reflex activation and the sympathetic nervous system have emerged. In this review, we discuss the epidemiology of sleep apnea and hypertension and the pathogenic mechanisms contributing to neurogenic hypertension. Furthermore, recent management strategies in addition to continuous positive airway pressure (CPAP), such as upper airway stimulation and renal denervation that target these pathogenic mechanisms, are also discussed.

Threshold of the upper airway cross-section for hypopnea onset during sleep and its identification under waking condition

Background

There is currently no method that can predict whether or under what condition hypopnea, even obstructive sleep apnea (OSA), will occur during sleep for individuals based on credible parameters measured under waking condition. We propose a threshold concept based on the narrowest cross-sectional area of the upper airway (CSA-UA) and aim to prove our hypothesis on the threshold of the area for hypopnea onset (TAHO), which can be used as an indicator of hypopnea onset during sleep and measured while awake.

Methods

We performed magnetic resonance imaging for 20 OSA patients to observe CSA-UA changes during fluid accumulation in the neck caused by elevating their legs, and identified TAHO by capturing the sudden enlargement in CSA-UA. Correlation analyses between TAHO and the body mass index (BMI), and between the reduction in CSA-UA and the increase in the neck circumference (NC) with fluid accumulation were performed. Logistic regression analysis was performed for identifying OSA patients based on the behaviors of their CSA-UA changes during leg raising. Shape changes of airway cross-section were also investigated.

Results

Four CSA-UA change patterns after fluid redistribution were identified. Six patients had similar CSA-UA variation behaviors observed in healthy subjects. From the other three change patterns involving 14 patients, a threshold value of CSA-UA 0.63 ± 0.21 cm² was identified for normal breathing. Data showed a positive correlation between TAHO and BMI (r = 0.681, p = 0.0007), and a negative correlation between the reduction in CSA-UA and the increase in NC (r = − 0.513, p = 0.051) with fluid accumulation. A sigmoid function for the probability of being a OSA patient p = 1/[1 + exp. (4.836 + 3.850 t-8.4 h)] was obtained to effectively separate OSA patients from normal subjects. The upper airway narrowing occurred in anteroposterior, lateral, or both directions, suggesting different tendencies of upper airway collapse in patients. Three types of shape changes in the cross-section of the upper airway, which had different effects on airway resistance, were measured.

Conclusions

Our findings prove TAHO hypothesis. The threshold measured while awake for normal breathing can be used clinically as the indicator of hypopnea onset during sleep, and therefore to identify OSA patients under waking condition and design effective personalized treatments for OSA patients. Both shape and size changes in the cross-section of the upper airway affect airway resistance significantly. Shape change in the cross-section of the upper airway can provide key clinical information on the collapse patterns of the upper airway for individuals.

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.

Sleep-disordered breathing in heart failure: facts and numbers

Sleep‐disordered breathing has a high prevalence in the general population, but is especially prominent in patients with heart failure (HF). HF and sleep‐disordered breathing share a bidirectional relationship, with sleep‐disordered breathing being both cause and effect of poor cardiac functioning. The high inter‐individual variability of symptom presentation can impede the clinical diagnostic process. Polysomnography is the gold‐standard method of diagnosing sleep‐disordered breathing. Therapy of sleep‐disordered breathing should always consist of optimizing the treatment of the underlying disorder of HF. Additional therapeutic measures include continuous positive airway pressure ventilation therapy. New therapeutic options using neurostimulation are yielding promising results; however, long‐term benefits still need to be confirmed.

Neural Control of the Upper Airway: Respiratory and State-Dependent Mechanisms

Upper airway muscles subserve many essential for survival orofacial behaviors, including their important role as accessory respiratory muscles. In the face of certain predisposition of craniofacial anatomy, both tonic and phasic inspiratory activation of upper airway muscles is necessary to protect the upper airway against collapse. This protective action is adequate during wakefulness, but fails during sleep which results in recurrent episodes of hypopneas and apneas, a condition known as the obstructive sleep apnea syndrome (OSA). Although OSA is almost exclusively a human disorder, animal models help unveil the basic principles governing the impact of sleep on breathing and upper airway muscle activity. This article discusses the neuroanatomy, neurochemistry, and neurophysiology of the different neuronal systems whose activity changes with sleep-wake states, such as the noradrenergic, serotonergic, cholinergic, orexinergic, histaminergic, GABAergic and glycinergic, and their impact on central respiratory neurons and upper airway motoneurons. Observations of the interactions between sleep-wake states and upper airway muscles in healthy humans and OSA patients are related to findings from animal models with normal upper airway, and various animal models of OSA, including the chronic-intermittent hypoxia model. Using a framework of upper airway motoneurons being under concurrent influence of central respiratory, reflex and state-dependent inputs, different neurotransmitters, and neuropeptides are considered as either causing a sleep-dependent withdrawal of excitation from motoneurons or mediating an active, sleep-related inhibition of motoneurons. Information about the neurochemistry of state-dependent control of upper airway muscles accumulated to date reveals fundamental principles and may help understand and treat OSA. © 2016 American Physiological Society. Compr Physiol 6:1801-1850, 2016.

Relationship of genioglossus muscle activation and severity of obstructive sleep apnea and hypopnea syndrome among Chinese patients

CONCLUSION

Variability of GGEMG at sleep onset is associated with apnea severity in OSA patients. At sleep onset, a lower decline in GGEMG might suggest a more severe OSA.

OBJECTIVE

The goal of this study was to evaluate genioglossus (GG) activation in the Chinese population at early sleep onset, and clarify the relationship of GG activation and the apnea severity in patients with Obstructive Sleep Apnea (OSA).

METHODS

Thirty-five OSA patients and 10 normal controls underwent overnight polysomnography with synchronous genioglossus electromyography (GGEMG) using intra-oral electrodes. The upper airway (UA) anatomy was evaluated by three-dimensional computer tomography (3D-CT) in all subjects.

RESULTS

The average GGEMG and tonic GGEMG were higher in the apnea patients than in the normal controls during wakefulness and early sleep onset period (three breaths) (p < 0.01). Eight OSA patients had increased GGEMG at sleep onset and 27 patients had decreased GGEMG values. Between the two groups, there were significant differences in the apnea-hypopnea index (AHI), minimal cross-sectional airway area (mCAS) and minimal lateral airway dimension (mLAT) at velopharynx (p < 0.05). The change in GGEMG, phasic GGEMG and tonic GGEMG from awake to sleep showed positive correlations with AHI and negative correlations with velopharynx (mLAT and mCAS) (p < 0.05).

Perioperative sleep apnea: a real problem or did we invent a new disease?

Depending on the subpopulation, obstructive sleep apnea (OSA) can affect more than 75% of surgical patients. An increasing body of evidence supports the association between OSA  and perioperative complications, but some data indicate important perioperative outcomes do not differ between patients with and without OSA. In this review we will provide an overview of the pathophysiology of sleep apnea and the risk factors for perioperative complications related to sleep apnea. We also discuss a clinical algorithm for the identification and management of OSA patients facing surgery.

Upper airway morphology in Down Syndrome patients under dexmedetomidine sedation

BACKGROUND AND OBJECTIVES

Children with Down Syndrome are vulnerable to significant upper airway obstruction due to relative macroglossia and dynamic airway collapse. The objective of this study was to compare the upper airway dimensions of children with Down Syndrome and obstructive sleep apnea with normal airway under dexmedetomidine sedation.

METHODS

IRB approval was obtained. In this retrospective study, clinically indicated dynamic sagittal midline magnetic resonance images of the upper airway were obtained under low (1mcg/kg/h) and high (3mcg/kg/h) dose dexmedetomidine. Airway anteroposterior diameters and sectional areas were measured as minimum and maximum dimensions by two independent observers at soft palate (nasopharyngeal airway) and at base of the tongue (retroglossal airway).

RESULTS AND CONCLUSIONS

Minimum anteroposterior diameter and minimum sectional area at nasopharynx and retroglossal airway were significantly reduced in Down Syndrome compared to normal airway at both low and high dose dexmedetomidine. However, there were no significant differences between low and high dose dexmedetomidine in both Down Syndrome and normal airway. The mean apnea hypopnea index in Down Syndrome was 16±11. Under dexmedetomidine sedation, children with Down Syndrome and obstructive sleep apnea when compared to normal airway children show significant reductions in airway dimensions most pronounced at the narrowest points in the nasopharyngeal and retroglossal airways.

Tongue stiffness is lower in patients with obstructive sleep apnea during wakefulness compared with matched control subjects

STUDY OBJECTIVES

This study aimed to determine whether tongue stiffness (shear modulus) in patients with obstructive sleep apnea (OSA) is different for controls matched for age, sex, and body mass index (BMI), and to investigate the effect of continuous positive airway pressure (CPAP) on stiffness.

DESIGN

Controlled experimental study.

SETTING

Medical research institute.

PARTICIPANTS

Patients with OSA and age-, sex-, and BMI-matched healthy controls.

MEASUREMENTS

Magnetic resonance elastography was performed in nine patients with OSA (apnea-hypopnea index (AHI) > 15 events/h) and seven controls (AHI < 10 events/h) matched for age, sex, and BMI. Six of these OSA subjects were also scanned while 10 cmH2O CPAP was applied. Mean isotropic shear modulus and anisotropic shear moduli parallel and perpendicular to the muscle fascicles in the tongue were calculated.

RESULTS

Tongue shear modulus in patients with OSA was lower than that in matched controls (2.68 ± 0.35 (mean ± standard deviation) kPa versus 2.98 ± 0.44 kPa, P < 0.001). Shear modulus decreased with increasing AHI (R = -0.496, P = 0.043), but not age, BMI, or percentage tongue fat. Anisotropic analysis revealed that reduction in stiffness was greatest parallel to the muscle fibers. CPAP had no significant effect on tongue shear modulus.

CONCLUSIONS

In awake subjects with obstructive sleep apnea, the tongue is less stiff than in similar healthy subjects and this difference occurs in the muscle fiber direction. CPAP did not significantly reduce tongue stiffness. Thus, any change in neural drive to genioglossus during wakefulness is insufficient to restore normal tongue stiffness.

Healthy humans with a narrow upper airway maintain patency during quiet breathing by dilating the airway during inspiration

A patent upper airway is essential for survival. Increased age, obesity and some upper airway anatomical features are associated with failure to maintain upper airway patency during sleep, leading to obstructive sleep apnoea. However, many healthy subjects with these risk factors do not develop this condition. The aim of this study was to determine how anatomical factors and active dilator muscle contraction contribute to upper airway patency in healthy volunteers across a broad range of age and body mass index (BMI). A 'tagged' magnetic resonance imaging technique quantified respiratory-related motion of the anterior and lateral walls of the upper airway during quiet breathing in the supine position. Fifty-two subjects aged 22-68 years with BMI from 17.5 to 40.1 kg m(-2) were studied. Higher BMI was associated with smaller airway cross-sectional area at the level of soft palate (P < 0.05). The genioglossus moved anteriorly to dilate the upper airway during inspiration. This movement increased with increasing BMI, increasing age, a smaller airway area, and steeper tongue-base angle (all P < 0.05). Motion of the lateral upper airway at the soft-palate level was variable and less strongly linked to anatomical features of the upper airway. Multiple regression indicated that anterior genioglossus motion decreased with increasing airway area (P = 0.03) and with increasing tongue-base angle (P = 0.02). These data suggest that healthy humans, including those whose anatomy places them at increased risk of airway closure, can maintain upper airway patency by dynamically dilating the airway during inspiration.

Obstructive sleep apnea and insight into mechanisms of sympathetic overactivity

Nearly two decades ago, we evaluated ten patients with obstructive sleep apnea (OSA). We determined that alarming nocturnal oscillations in arterial pressure and sympathetic nerve activity (SNA) were caused by regulatory coupling and neural interactions among SNA, apnea, and ventilation. Patients with OSA exhibited high levels of SNA when awake, during normal ventilation, and during normoxia, which contributed to hypertension and organ damage. Additionally, we achieved a beneficial and potentially lifesaving reduction in SNA through the application of continuous positive airway pressure (CPAP), which remains a primary therapeutic approach for patients with OSA. With these results in hindsight, we herein discuss three concepts with functional and therapeutic relevance to the integrative neurobiology of autonomic cardiovascular control and to the mechanisms involved in excessive sympathoexcitation in OSA.

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.

Sleep-disordered breathing in heart failure: identifying and treating an important but often unrecognized comorbidity in heart failure patients

Sleep-disordered breathing (SDB) is the most common comorbidity in patients with heart failure (HF) and has a significant impact on quality of life, morbidity, and mortality. A number of therapeutic options have become available in recent years that can improve quality of life and potentially the outcomes of HF patients with SDB. Unfortunately, SDB is not part of the routine evaluation and management of HF, so it remains untreated in most HF patients. Although recognition of the role of SDB in HF is increasing, clinical guidelines for the management of SDB in HF patients continue to be absent. This article provides an overview of SDB in HF and proposes a clinical care pathway to help clinicians to better recognize and treat SDB in their HF patients.

Respiratory Movement of Upper Airway Tissue in Obstructive Sleep Apnea

STUDY OBJECTIVES

To measure real-time movement of the tongue and lateral upper airway tissues in obstructive sleep apnea (OSA) subjects during wakefulness using tagged magnetic resonance imaging.

DESIGN

Comparison of the dynamic imaging of three groups of increasing severity OSA and a control group approximately matched for age and body mass index (BMI).

SETTING

Not-for-profit research institute.

PARTICIPANTS

24 subjects (apnea hypopnea index [AHI] range 2-84 events/h, 6 with AHI < 5 events/h).

METHODS

The upper airway was imaged awake in two planes using SPAtial Modulation of Magnetization (SPAMM). Tissue displacements were quantified with harmonic phase analysis.

MEASUREMENTS AND RESULTS

All subjects had dynamic airway opening in the sagittal plane associated with inspiration. In the nasopharynx, the increase in airway cross-sectional area during inspiration correlated with minimal cross-sectional area of the airway (R = 0.900, P < 0.001). AHI correlated negatively with movement of the nasopharyngeal lateral walls (R = - 0.542, P = 0.006). Four movement patterns were observed during inspiration: "en bloc" anterior movement of the whole posterior tongue; movement of only the oropharyngeal posterior tongue; bidirectional movement; or minimal movement. Some subjects showed different inspiratory movement patterns with different breaths. A low AHI (< 5) was associated with en bloc movement (P = 0.002).

CONCLUSIONS

Inspiratory movement of the tongue varied between and within subjects, likely as a result of local and neural factors. However, in severe OSA inspiratory movement was minimal.

CITATION

Brown EC; Cheng S; McKenzie DK; Butler JE; Gandevia SC; Bilston LE. Respiratory movement of upper airway tissue in obstructive sleep apnea. SLEEP 2013;36(7):1069-1076.

The effects of mouthpiece use on gas exchange parameters during steady-state exercise in college-aged men and women

BACKGROUND

The authors conducted a study to assess the effects of custom-fitted mouthpieces on gas exchange parameters, including volume of oxygen consumption over time [corrected] (VO(2)), volume of oxygen consumption over time per kilogram of body weight [corrected] (VO(2) /kg) and volume of carbon dioxide production over time [corrected] (VO(2)).

METHODS

Sixteen physically fit college students aged 18 through 21 years performed two 10-minute treadmill runs (6.5 miles per hour, 0 percent grade) for each of three treatment conditions (mouthpiece, no mouthpiece and nose breathing). The authors assigned the conditions randomly for each participant and for each session. They assessed gas exchange parameters by using a metabolic measurement system.

RESULTS

The authors used analysis of variance to compare all variables. They set the significance level at α = .05 and used a Tukey post hoc analysis of treatment means to identify differences between groups. The results showed significant improvements (P < .05) in VO(2,) VO(2) /kg and VCO(2) in the mouthpiece condition.

CONCLUSIONS

The study findings show that use of a custom-fitted mouthpiece resulted in improved specific gas exchange parameters. The authors are pursuing further studies to explain the mechanisms involved in the improved endurance performance exhibited with mouthpiece use.

CLINICAL IMPLICATIONS

Dental care professionals have an obligation to understand the increasing research evidence in support of mouthpiece use during exercise and athletic activity and to educate their patients.

Obstructive sleep apnoea syndrome: comparison between polysomnography and portable sleep monitoring based on jaw recordings

INTRODUCTION

Obstructive sleep apnoea syndrome (OSAS) constitutes a new major public health problem because of its several pathophysiologic consequences such as cognitive disorders, excessive daytime sleepiness with risks of traffic accidents, cardiovascular implications, and decrease of quality of life. The necessity of a gold-standard polysomnography to ensure an accurate diagnosis implies an expensive, technical and time-consuming examination. Thus, it seems logical to develop new systems so as to diagnose SAS and to make it possible to detect apnoeas/hypopnoeas easily during sleep even at home.

AIM OF THE STUDY

To assess a novel type-3 portable monitoring (PM) device, the Somnolter, and dedicated automatic analysis of several signals, one of which is the mandibular movement signal.

METHOD

We studied patients suffering from OSAS. For all the patients, a nocturnal diagnosis polysomnography (PSG) was recorded in hospital settings, based on six EEG channels, two EOG channels, chin EMG channel, EKG, and respiratory parameters. At the same time, the Somnolter PM device recorded the physiological parameters from its own nasal prongs, thoracic belt, pulse oxymeter, body position, and jaw movement sensors. A visual analysis of PSG recordings was made leading to the detection of apnoea/hypopnoea index (AHI-PSG) and an automatic analysis of the Somnolter traces was performed to get automatic apnoea/hypopnoea index (AHI-A). The added value of the mandible movement signals was the particular jaw movements related to arousals, to respiratory efforts and to sleep/wake state. A comparison was made between the automatic and gold AHIs standard and the correlation was calculated between them.

RESULTS

Ninety patients, aged between 47 and 70 years (mean age: 55.4±8.7) took part in the study. The linear regression and the correlation coefficient between AHI-PSG and AHI-A showed the good reliability of the automatic method. The Bland Altman analysis shows a correlation of 0.95 with a sensitivity of 83.6 and specificity of 81.8.

CONCLUSION

The dedicated automatic analysis based on mandibular movements presents a good potential for the diagnosis of OSAS. The AHI computed by the automatic method is correlated with the AHI-PSG and the Somnolter could easily be used both in hospital, and in ambulatory settings.

Control of the pharyngeal musculature during wakefulness and sleep: implications in normal controls and sleep apnea

Respiration involves the complex coordination of several pump and upper airway/pharyngeal muscles. From a respiratory perspective, the major function of the pharyngeal muscles is to keep the airway patent allowing for airflow in and out of the lung with minimal work by the respiratory pump muscles. The activity of each of the pharyngeal muscles varies depending on its function, but many reduce their activity during sleep. In healthy individuals, these muscles can respond to respiratory stimuli during sleep to prevent airway collapse. However, in individuals with an anatomically small airway, the muscles cannot always compensate for the increased mechanical load. Thus a vulnerable situation in which the airway is prone to collapse may occur with the development of obstructive sleep apnea. This article describes the current understanding regarding the control of the pharyngeal musculature during wakefulness and sleep, as well as the implications for obstructive sleep apnea.

Role of sensory stimulation in amelioration of obstructive sleep apnea

Obstructive sleep apnea (OSA), characterized by recurrent upper airway (UA) collapse during sleep, is associated with significant morbidity and disorders. Polysomnogram is employed in the evaluation of OSA and apnea-hypopnea number per hour reflects severity. For normal breathing, it is essential that the collapsible UA is patent. However, obstruction of the UA is quite common in adults and infants. Normally, important reflex mechanisms defend against the UA collapse. The muscle activity of UA dilators, including the genioglossus, tensor palatini (TP), and pharyngeal constrictors, is due to the integrated mechanism of afferent sensory input → to motor function. Snoring is harsh breathing to prevent UA obstruction. Unfortunately, snoring vibrations, pharyngeal suction collapse, negative pressure, and hypoxia cause pathological perturbations including dysfunctional UA afferent sensory activity. The current paper posits that peripheral sensory stimulation paradigm, which has been shown to be efficacious in improving several neurological conditions, could be an important therapeutic strategy in OSA also.

Obstructive sleep apnea syndrome: natural history, diagnosis, and emerging treatment options

Sleep apnea is an entity characterized by repetitive upper airway obstruction resulting in nocturnal hypoxia and sleep fragmentation. It is estimated that 2%-4% of the middle-aged population has sleep apnea with a predilection in men relative to women. Risk factors of sleep apnea include obesity, gender, age, menopause, familial factors, craniofacial abnormalities, and alcohol. Sleep apnea has been increasingly recognized as a major health burden associated with hypertension and increased risk of cardiovascular disease and death. Increased airway collapsibility and derangement in ventilatory control responses are the major pathological features of this disorder. Polysomnography (PSG) is the gold-standard method for diagnosis of sleep apnea and assessment of sleep apnea severity; however, portable sleep monitoring has a diagnostic role in the setting of high pretest probability sleep apnea in the absence of significant comorbidity. Positive pressure therapy is the mainstay therapy of sleep apnea. Other treatment modalities, such as upper airway surgery or oral appliances, may be used for the treatment of sleep apnea in select cases. In this review, we focus on describing the sleep apnea definition, risk factor profile, underlying pathophysiologic mechanisms, associated adverse consequences, diagnostic modalities, and treatment strategies.

Obstructive sleep apnea, inflammation, and the metabolic syndrome

The combination of metabolic syndrome and obstructive sleep apnea (OSA) has been termed "syndrome Z." The prevalence of both OSA and metabolic syndrome is increasing worldwide, in part linked to the epidemic of obesity. Beyond their epidemiologic relationship, growing evidence suggests that OSA may be causally related to metabolic syndrome. We are only beginning to understand the potential mechanisms underlying the OSA-metabolic syndrome interaction. Although there is no clear consensus, there is growing evidence that alterations in the hypothalamic-pituitary axis, generation of reactive oxygen species (ROS) due to repetitive hypoxia, inflammation, and generation of adipokines may be implicated in the changes associated with both OSA and metabolic syndrome. Whether some or all of these metabolic alterations mechanistically link OSA to metabolic syndrome remains to be proven, but it is an area of intense scientific interest.

Obstructive sleep apnea: a growing problem

Obstructive sleep apnea is an underrecognized and underdiagnosed medical condition, with a myriad of negative consequences on patients' health and society as a whole. Symptoms include daytime sleepiness, loud snoring, and restless sleep. While the "gold standard" of diagnosis is by polysomnography, a detailed history and focused physical examination may help uncover previously undiagnosed cases. Undetected obstructive sleep apnea can lead to hypertension, heart disease, depression, and even death. Several modalities exist for treating obstructive sleep apnea, including continuous positive airway pressure, oral appliances, and several surgical procedures. However, conservative approaches, such as weight loss and alcohol and tobacco cessation, are also strongly encouraged in the patient with obstructive sleep apnea. With increased awareness, both the medical community and society as a whole can begin to address this disease and help relieve the negative sequelae that result from it.

Movement of the tongue during normal breathing in awake healthy humans

Electromyographic (EMG) activity of the airway muscles suggest that genioglossus is the primary upper airway dilator muscle. However, EMG data do not necessarily translate into tissue motion and most imaging modalities are limited to assessment of the surfaces of the upper airway. In this study, we hypothesized that genioglossus moves rhythmically during the respiratory cycle and that the motion within is inhomogeneous. A 'tagged' magnetic resonance imaging technique was used to characterize respiratory-related tissue motions around the human upper airway in quiet breathing. Motion of airway tissues at different segments of the eupnoeic respiratory cycle was imaged in six adult subjects by triggering the scanner at the end of inspiration. Displacements of the 'tags' were analysed using the harmonic phase method (HARP). Respiratory timing was monitored by a band around the upper abdomen. The genioglossus moved during the respiratory cycle. During expiration, the genioglossus moved posteriorly and during inspiration, it moved anteriorly. The degree of motion varied between subjects. The maximal anteroposterior movement of a point tracked on the genioglossus was 1.02 +/- 0.54 mm (mean +/- s.d.). The genioglossus moved over the geniohyoid muscle, with minimal movement in other muscles surrounding the airway at the level of the soft palate. Local deformation of the tongue was analysed using two-dimensional strain maps. Across the respiratory cycle, positive strains within genioglossus reached peaks of 17.5 +/- 9.3% and negative strains reached peaks of -16.3 +/- 9.3% relative to end inspiration. The patterns of strains were consistent with elongation and compression within a constant volume structure. Hence, these data suggest that even during respiration, the tongue behaves as a muscular hydrostat.

Drive to the human respiratory muscles

The motor control of the respiratory muscles differs in some ways from that of the limb muscles. Effectively, the respiratory muscles are controlled by at least two descending pathways: from the medulla during normal quiet breathing and from the motor cortex during behavioural or voluntary breathing. Neurophysiological studies of single motor unit activity in human subjects during normal and voluntary breathing indicate that the neural drive is not uniform to all muscles. The distribution of neural drive depends on a principle of neuromechanical matching. Those motoneurones that innervate intercostal muscles with greater mechanical advantage are active earlier in the breath and to a greater extent. Inspiratory drive is also distributed differently across different inspiratory muscles, possibly also according to their mechanical effectiveness in developing airway negative pressure. Genioglossus, a muscle of the upper airway, receives various types of neural drive (inspiratory, expiratory and tonic) distributed differentially across the hypoglossal motoneurone pool. The integration of the different inputs results in the overall activity in the muscle to keep the upper airway patent throughout respiration. Integration of respiratory and non-respiratory postural drive can be demonstrated in respiratory muscles, and respiratory drive can even be observed in limb muscles under certain circumstances. Recordings of motor unit activity from the human diaphragm during voluntary respiratory tasks have shown that depending on the task there can be large changes in recruitment threshold and recruitment order of motor units. This suggests that descending drive across the phrenic motoneurone pool is not necessarily consistent. Understanding the integration and distribution of drive to respiratory muscles in automatic breathing and voluntary tasks may have implications for limb motor control.

Safety of sildenafil in the treatment of erectile dysfunction in patients with obstructive sleep apnoea

Obstructive sleep apnoea, characterised by repetitive occlusion of the upper airway during sleep, is recognised as a risk or even an aetiological factor for erectile dysfunction. On the other hand, sleep-disordered breathing has been reported by many patients with erectile dysfunction. Sildenafil, a very commonly used erectile dysfunction treatment, could, at least theoretically, exacerbate sleep apnoea by interfering with pharyngeal muscle tone, nasal patency and gas exchange in the lung. A recent safety study suggested a detrimental effect of oral sildenafil on respiratory events in patients with obstructive sleep apnoea. Given the inconclusiveness of evidence on pathophysiological mechanisms and the paucity of relevant clinical data the safety risk of sildenafil administration in patients with obstructive sleep apnoea should be questioned. More clinical trials are needed to clarify this issue.

Upper airway collapsibility, dilator muscle activation and resistance in sleep apnoea

The calibre of the upper airway is thought to be dependant upon its passive anatomy/collapsibility and the activation of pharyngeal dilator muscles. During awake periods, the more collapsible upper airway in obstructive sleep apnoea (OSA) increases the dilator muscle activity through a negative-pressure reflex. A direct correlation between the critical closing pressure (P(crit)), as a measure of anatomy/collapsability and electromyogram (EMG) activity of genioglossus EMG (GG-EMG) and tensor palatini EMG (TP-EMG), was hypothesised. The relationship between these indices and pharyngeal resistance (R(phar)) was also examined. The study involved eight males with a mean age of 48 (interquartile range 46-52) yrs with OSA, and an apnoea/hypopnoea index of 75 (65-101).hr(-1) on two nights breathing normally and on nasal continuous positive airway pressure (nCPAP). The P(crit )was measured during nonrapid eye movement sleep on nCPAP using brief, incremental reductions in mask pressure. GG-EMG and TP-EMG were measured breath-by-breath, awake, during sleep onset and on nCPAP. R(phar) was measured using airway pressures and flow. Wakeful GG-EMG, early sleep TP-EMG and the sleep decrement in TP-EMG were directly related to P(crit). Muscle activation was negatively correlated with R(phar) for TP-EMG awake and GG-EMG early in sleep. In conclusion these results confirm that dilator muscle activation is directly related to airway narrowing and reduces resistance across patients with obstructive sleep apnoea.

Influence of wakefulness on pharyngeal airway muscle activity

BACKGROUND

Whether loss of wakefulness itself can influence pharyngeal dilator muscle activity and responsiveness is currently unknown. A study was therefore undertaken to assess the isolated impact of sleep on upper airway muscle activity after minimising respiratory/mechanical inputs.

METHODS

Ten healthy subjects were studied. Genioglossus (GG), tensor palatini (TP) and diaphragm (DIA) electromyography (EMG), ventilation and sleep-wake status were recorded. Non-invasive positive pressure ventilation was applied. Expiratory pressure was adjusted to yield the lowest GGEMG, thereby minimising airway negative pressure (mechanoreceptor) effects. Inspiratory pressure, respiratory rate and inspiratory time were adjusted until the subjects ceased spontaneous ventilation, thereby minimising central respiratory input. Muscle activity during wakefulness, wake-sleep transitions, stable non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep were evaluated in the supine position.

RESULTS

In transitions from wakefulness to sleep, significant decrements were observed in both mean GGEMG and TPEMG (1.6 (0.5)% to 1.3 (0.4)% of maximal GGEMG; 4.3 (2.3)% to 3.7 (2.1)% of maximal TPEMG). Compared with sleep onset, the activity of TP during stable NREM sleep and REM sleep was further decreased (3.7 (2.1)% vs 3.0 (2.0)% vs 3.0 (2.0)% of maximal EMG). However, GGEMG was only further reduced during REM sleep (1.3 (0.4)% vs 1.0 (0.3)% vs 1.1 (0.4)% of maximal EMG).

CONCLUSION

This study suggests that wakefulness per se, independent of respiratory/mechanical stimuli, can influence pharyngeal dilator muscle activity.

Obstructive sleep apnea - management update

Obstructive sleep apnea (OSA) is a highly significant condition based both on the high prevalence in community and significant consequences. Obstructive sleep apnea syndrome (OSAS), OSA together with hypersomnolence, is seen in 4% of middle-aged men and 2% of middle-aged women. OSA is associated with impaired quality of life and increased risks of motor vehicle accidents, cardiovascular disease (including hypertension and coronary artery disease), and metabolic syndrome. There is some evidence for the use of conservative interventions such as weight loss and position modification. CPAP remains the mainstay of treatment in this condition with high-level evidence supporting its efficacy. Continuous positive airway pressure (CPAP) is an intrusive therapy, with long-term adherence rates of less than 70%. Dental appliances have been shown to be effective therapy in some subjects but are limited by the inability to predict treatment responders. Alternative treatments are discussed but there is little role for upper airway surgery (except in a select few experienced institutions) or pharmacological treatment. The current levels of evidence for the different treatment regimens are reviewed.

Pathogenesis of obstructive sleep apnea

The pathogenesis of obstructive sleep apnea (OSA) has been under investigation for over 25 years, during which a number of factors that contribute to upper airway (UA) collapse during sleep have been identified. Structural/anatomic factors that constrict space for the soft tissues surrounding the pharynx and its lumen are crucial to the development of OSA in many patients. Enlargement of soft tissues enveloping the pharynx, including hypertrophied tonsils, adenoids, and tongue, is also an important factor predisposing to UA collapse, inasmuch as this can impinge on the pharyngeal lumen and narrow it during sleep. Other factors, including impairment of UA mechanoreceptor sensitivity and reflexes that maintain pharyngeal patency and respiratory control system instability, have also been identified as possible mechanisms facilitating UA instability. This suggests that OSA may be a heterogeneous disorder, rather than a single disease entity. Therefore, the extent to which various pathogenic factors contribute to the phenomenon of repetitive collapse of the UA during sleep probably varies from patient to patient. Further elucidation of specific pathogenic mechanisms in individuals with OSA may facilitate the development of new therapies that can be tailored to individual patient needs according to the underlying mechanism(s) of their disease.

Pathogenesis of Obstructive and Central Sleep Apnea

Considerable progress has been made over the last several decades in our understanding of the pathophysiology of both central and obstructive sleep apnea. Central sleep apnea, in its various forms, is generally the product of an unstable ventilatory control system (high loop gain) with increased controller gain (high hypercapnic responsiveness) generally being the cause. High plant gain can contribute under certain circumstances (hypercapnic patients). On the other hand, obstructive sleep apnea can develop as the result of a variety of physiologic characteristics. The combinations of these may vary considerably between patients. Most obstructive apnea patients have an anatomically small upper airway with augmented pharyngeal dilator muscle activation maintaining airway patency awake, but not asleep. However, individual variability in several phenotypic characteristics may ultimately determine who develops apnea and how severe the apnea will be. These include: (1) upper airway anatomy, (2) the ability of upper airway dilator muscles to respond to rising intrapharyngeal negative pressure and increasing Co(2) during sleep, (3) arousal threshold in response to respiratory stimulation, and (4) loop gain (ventilatory control instability). As a result, patients may respond to different therapeutic approaches based on the predominant abnormality leading to the sleep-disordered breathing.

Tonic and phasic respiratory drives to human genioglossus motoneurons during breathing

A tongue muscle, the genioglossus (GG), is important in maintaining pharyngeal airway patency. Previous recordings of multiunit electromyogram (EMG) suggest it is activated during inspiration in humans with some tonic activity in expiration. We recorded from populations of single motor units in GG in seven subjects during quiet breathing when awake. Ultrasonography assisted electrode placement. The activity of single units was separated into six classes based on a step-wise analysis of the discharge pattern. Phasic and tonic activities were analyzed statistically with the coefficient of determination (r2) between discharge frequency and lung volume. Of the 110 motor units, 29% discharged tonically without phasic respiratory modulation (firing rate approximately 19 Hz). Further, 16% of units increased their discharge during expiration (expiratory phasic and expiratory tonic units). Only half the units increased their discharge during inspiration (inspiratory phasic and inspiratory tonic units). Units firing tonically with an inspiratory increase had significantly higher discharge rates than those units that only fired phasically (peak rates 25 vs. 16 Hz, respectively). Simultaneous recordings of two or three motor units showed neighboring units with differing respiratory and tonic drives. Our results provide a classification and the first quantitative measures of human GG motor-unit behavior and suggest this activity results from a complex interaction of inspiratory, expiratory, and tonic drives at the hypoglossal motor nucleus. The presence of different drives to GG implies that complex premotor networks can differentially engage human hypoglossal motoneurons during respiration. This is unlike the ordered recruitment of motor units in limb and axial muscles.

The impact of anatomic manipulations on pharyngeal collapse: results from a computational model of the normal human upper airway

Obstructive sleep apnea (OSA) is a common disease with important neurocognitive and cardiovascular sequelae. Existing therapies are unsatisfactory, leading investigators to seek alternative forms of anatomic manipulation to influence pharyngeal mechanics. We have developed a two-dimensional computational model of the normal human upper airway based on signal averaging of MRI. Using the finite element method, we can perform various anatomic perturbations on the structure in order to assess the impact of these manipulations on pharyngeal mechanics and collapse. By design, the normal sleeping upper airway model collapses at -13 cm H2O. This closing pressure becomes more negative (ie, less collapsible) when we perform mandibular advancement (-21 cm H2O), palatal resection (-18 cm H2O), or palatal stiffening (-17 cm H2O). Where clinical data are available in the literature, the results of our model correspond reasonably well. Furthermore, our model provides information regarding the site of obstruction and provides hypotheses for clinical studies that can be undertaken in the future (eg, combination therapies). We believe that, in the future, finite element modeling will provide a useful tool to help advance our understanding of OSA and its response to various therapies.