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

Influence of Body Posture and Apnea Severity on the Tone and Elasticity of Upper Airway Muscles in Awake Patients With Obstructive Sleep Apnea: A Cross-Sectional Study

OBJECTIVE

The purpose of this study was to compare the effect of body posture and apnea severity on the tone, stiffness, and elasticity of upper airway muscles in awake patients with obstructive sleep apnea syndrome (OSAS).

METHODS

Eighty adult patients with OSAS from the Sleep Laboratory of the Bitlis State Hospital between April and December 2021 were included in the study. The tone, stiffness, and elasticity of the genioglossus and accessory muscles (sternocleidomastoid, masseter) were measured while the patients were awake, sitting upright, and in supine posture. According to polysomnography results and the Apnea-Hypopnea Index, patients were classified as mild, moderate, or severe OSAS.

RESULTS

There were 56 male (70%) and 24 female (30%) patients (age 45.0 ± 11.0 years). Tone of genioglossus, masseter, and sternocleidomastoid muscles were higher in supine than in sitting posture (all P < .05). There was no difference in elasticity scores of the bilateral genioglossus muscle in sitting and supine posture (P > .05). The elasticity scores of the sternocleidomastoid and masseter muscles were higher in sitting (all P < .05). An interaction effect of postural change and apnea severity was observed on stiffness scores of the genioglossus muscle (P < .05).

CONCLUSION

Results showed that the genioglossus muscle and accessory muscles take on the inspiratory load that develops with postural strain, regardless of the severity of apnea, in awake patients with OSAS. For participants measured in this study, accessory muscles supported respiration by increasing their elasticity.

Comparing the characteristics of positional and nonpositional sleep apnea patients among the Jordanian population

BACKGROUND:

Obstructive sleep apnea (OSA) is a common cause of sleep-disordered breathing with a large proportion of the patients exhibiting positional OSA (POSA). In this study, we aimed to evaluate the differences in the demographics, comorbidities, and polysomnographic features between POSA and non-POSA (NPOSA) in a Jordanian sample to further discern the propulsive elements for each group.

METHODS:

In this study, we evaluated 1037 adult patients with OSA. POSA was defined as an overall apnea and hypopnea index (AHI) >5, an overall AHI severity at least 1.4 times the nonsupine severity (overall/NS-AHI), and a minimum amount of time (i.e., 20 min) in the supine and nonsupine positions. To compare the clinical characteristics between POSA and NPOSA patients, statistical analyses were performed.

RESULTS:

The prevalence of POSA was 41.7%. In comparison to NPOSA patients, POSA patients had higher female sex prevalence, milder OSA, lower body mass index, lower hypertension prevalence, and lower hemoglobin A1C levels compared to NPOSA patients. Moreover, sleep efficiency, total sleep time, and supine sleep time were significantly higher in POSA patients. Nonsupine sleep time, total AHI, rapid eye movement (REM) AHI, non-REM (NREM) AHI, supine AHI, nonsupine AHI, left and right AHI, mean oxyhemoglobin saturation (SpO₂) awake, mean REM and NREM SpO₂, SpO₂ nadir, and time SpO₂ below 90% were significantly lower among POSA patients. The multivariate regression analysis showed that only female gender and hypertension were significantly associated with POSA.

CONCLUSION:

POSA is common among OSA patients and demonstrates different clinical characteristics in comparison to NPOSA. Future prospective studies are needed to better characterize the POSA patients and investigate the benefit of positional therapy.

A consideration of factors affecting palliative oral appliance effectiveness for obstructive sleep apnea: a scoping review

STUDY OBJECTIVES

This scoping review allows physicians, researchers, and others interested in obstructive sleep apnea to consider effectiveness of oral appliances (OAs). The intent is to improve understanding of OA effectiveness by considering morphologic interaction in patients with obstructive sleep apnea.

METHODS

Morphologic and biomechanical criteria for positional alterations of the mandible assessed success rates of OA appliances. Searches of databases (Medline, PubMed, The Cochrane Library, EBSCO) using terms: OA treatment effectiveness and positive and/or negative outcome predictors. Craniofacial predictors of OAs and obstructive sleep apnea biomechanical factors of anatomical traits associated with OA effectiveness were included. Databases searched radiographic cephalometric imaging for morphology/phenotypes and apnea-hypopnea index responses. Articles were excluded if title or abstract was not relevant or a case report. If the analysis did not report mean or standard deviation for apnea-hypoxia index, it was excluded. No language, age, or sex restrictions were applied.

RESULTS

Analysis of 135 articles included in searched literature indicated alterations in musculature and pharyngeal airway structure through OA use. These alterations were individually unpredictable with wide variability 61.81% ± 12.29 (apnea-hypoxia index mean ± standard deviation). Morphologic variations as predictors were typically weak and idiosyncratic. Biomechanical factors and wide variations in the metrics of appliance application were unclear, identifying gaps in knowledge and practice of OAs.

CONCLUSIONS

An integrated basis to identify morphologic and biomechanical elements of phenotypic expressions of sleep-disordered breathing in the design and application of OAs is needed. Current knowledge is heterogeneous and shows high variability. Identification of subgroups of patients with obstructive sleep apnea responding to OAs is needed.

Upper airway lengthening caused by weight increase in obstructive sleep apnea patients

BACKGROUND

The longer upper airway is more collapsible during sleep. This study aims to reveal relationships among upper airway length, weight, and obstructive sleep apnea (OSA), particularly to answer why the upper airway of OSA patients is longer than that of healthy people and why some obese people suffer from OSA while others do not.

METHODS

We perform head and neck MRI on male patients and controls, and measure > 20 morphological parameters, including several never before investigated, to quantify the effect of weight change on upper airway length.

RESULTS

The upper airway length is longer in patients and correlates strongly to body weight. Weight increase leads to significant fat infiltration in the tongue, causing the hyoid to move downward and lengthen the airway in patients. The apnea-hypopnea index (AHI) strongly correlates to airway length and tongue size. Surprisingly, a distance parameter h and angle β near the occipital bone both show significant differences between healthy males and patients due to their different head backward tilt angle, and strongly correlates with AHI. The contributions of downward hyoid movement and head tilt on airway lengthening are 67.4-80.5% and19.5-32.6%, respectively, in patients. The parapharyngeal fat pad also correlates strongly with AHI.

CONCLUSIONS

The findings in this study reveal that the amount of body weight and distribution of deposited fat both affect airway length, and therefore OSA. Fat distribution plays a larger impact than the amount of weight, and is a better predictor of who among obese people are more prone to OSA.

Obstructive Sleep Apnea Secondary to Pharyngeal Narrowing From Horizontal Donor Site Closure During Posterior Pharyngeal Flap Surgery

The posterior pharyngeal flap is frequently the surgical intervention of choice for the correction of velopharyngeal insufficiency. Our patient initially presented for a superiorly based, posterior pharyngeal flap to correct for velopharyngeal insufficiency. However, the postoperative recovery was complicated by severe obstructive sleep apnea, which warranted division and subsequent takedown of the flap. Despite flap takedown, our patient's obstructive sleep apnea persisted. The patient's clinical course suggests that donor site closure, and not the actual pharyngeal flap, caused the persistent obstructive sleep apnea.

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.

Qualitative Phenotyping of Obstructive Sleep Apnea and Its Clinical Usefulness for the Sleep Specialist

INTRODUCTION

The anatomical collapsibility of the upper airway, neuromuscular tone and function, sleep-wake and ventilatory control instability, and the arousal threshold all interact and contribute to certain pathophysiologic features that characterize different types of obstructive sleep apnea (OSA). A model of qualitative phenotypizationallowsus to characterize the different pathophysiological traits in OSA patients.

METHODS

A narrative review was performed, to analyze the available literature evidence, with the purpose of generating a model of qualitative phenotypization to characterize pathophysiological traits in patients with OSA.

RESULTS

96 out of 3829 abstracts were selected for full-text review. Qualitative phenotyping model of OSA:Data concerning the OSA qualitative pathophysiological traits' measurement can be deducted by means of clinical PSG, grade of OSA severity, and therapeutic level of Continuous Positive Airway Pressure (CPAP) and are reported in the text. This approach would allow qualitative phenotyping with widely accessible methodology in a routine clinical scenario and is of particular interest for the sleep specialist, surgical treatment decision-making, and customized OSA multimodality treatment.

Long-term obstructive sleep apnea therapy: a 10-year follow-up of mandibular advancement device and continuous positive airway pressure

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder, commonly managed by either continuous positive airway pressure (CPAP) or a mandibular advancement device (MAD). Long-term follow-up and comparison regarding efficacy of these therapies is scarce. In this study the results of treatment, patient adherence, and satisfaction over a 10-year follow-up of these therapies are reported.

METHODS

This is a longitudinal follow-up study taken from a subset of patients initially enrolled in a randomized controlled clinical trial of 103 patients with OSA (51 and 52 patients randomized for MAD and CPAP, respectively). After a 10-year follow-up period, 14 patients using MAD and 17 patients using CPAP could be evaluated for this longitudinal follow-up study. Data were analyzed at baseline, after 3 months and at 1-, 2-, and 10-year follow-up. All 31 patients with OSA underwent polysomnography and self-reported measurements.

RESULTS

Polysomnography results showed a favorable outcome of both therapies at 10-year follow-up. At baseline, included patients in both groups did not significantly differ in apnea-hypopnea index (AHI) values. At 10-year follow-up, both the MAD and CPAP groups showed a significant reduction in AHI. At baseline the mean AHI in the MAD group was 31.7 ± 20.6 events/h whereas in the CPAP group it was 49.2 ± 26.1 events/h. At 10-year follow-up the mean AHI in the MAD group was 9.9 ± 10.3 events/h and in the CPAP group it was 3.4 ± 5.4 events/h. Both therapies resulted in a substantial improvement in self-reported neurobehavioral outcomes at 10-year follow-up.

CONCLUSIONS

Both CPAP and MAD therapy demonstrate good and stable treatment effects after a 10-year follow-up period. Therefore, when indicated, both therapies are appropriate modalities for the long-term management of OSA.

CLINICAL TRIAL REGISTRATION

Registry: Netherlands Trial Register; Name: Management of the Obstructive Sleep Apnea-Hypopnea Syndrome: Oral Appliance versus Continuous Positive Airway Pressure Therapy; Identifier: NL75; URL: https://www.trialregister.nl/trial/75.

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.

A Screening Algorithm for Obstructive Sleep Apnea in Pregnancy

Rationale: Obstructive sleep apnea (OSA) is common in pregnancy and associated with maternal and fetal complications. Early detection of OSA may have important implications for maternal-fetal well-being. A screening tool combining several methods of assessment may better predict OSA among pregnant women compared with tools that rely solely on self-reported information.Objectives: To develop a screening tool combining subjective and objective measures to predict OSA in pregnant women.Methods: This study is a secondary analysis using data collected from a completed cohort of pregnant women (n = 121 during the first and n = 87 during the third trimester). Participants underwent full polysomnography and completed the Multivariable Apnea Prediction Questionnaire. The Obstructive Sleep Apnea/Hypopnea Syndrome Score and Facco apnea predictive model were obtained. Logistic regression analysis and area under the curve (AUC) were used to identify models predicting OSA risk.Results: Participants' mean age was 27.4 ± 7.0 years. The prevalence of OSA during the first and third trimester was 10.7% and 24.1%, respectively. The final model predicting OSA risk consisted of body mass index, age, and presence of tongue enlargement. During the first trimester, the AUC was 0.86 (95% confidence interval [CI], 0.76-0.96). During the third trimester, the AUC was 0.87 (95% CI, 0.77-0.96). When the first-trimester data were used to predict third-trimester OSA risk, the AUC was 0.87 (95% CI, 0.77-0.97). This model had high sensitivity and specificity when used during both trimesters. The negative posttest probabilities (probability of OSA given a negative test result) ranged from 0.03 to 0.07.Conclusions: A new model consisting of body mass index, age, and presence of tongue enlargement provided accurate screening of OSA in pregnant women, particularly African-Americans. This tool can be easily and rapidly administered in busy clinical practices without depending on patients' awareness of experiencing apnea symptoms.

Smartphone-based delivery of oropharyngeal exercises for treatment of snoring: a randomized controlled trial

PURPOSE

Upper airway exercises for snoring treatment can be effective but difficult to administer and monitor. We hypothesized that a brief, relatively simple daily upper airway exercise regimen, administered by a smartphone application, would reduce snoring and encourage compliance.

METHODS

Targeted vowel sounds causing tongue base movements were incorporated into a voice-controlled smartphone game application. Participants with habitual snoring, apnea hypopnea index (AHI) ≤ 14 events/h, and BMI ≤ 32 kg/m² were randomly assigned to perform 15 min of daily gameplay (intervention group) or 5 s of daily voice recording (control group) and to audio record their snoring for 2 nights/week for up to 12 weeks. Sounds above 60 dB were extracted from recordings for snore classification with machine learning support vector machine classifiers.

RESULTS

Sixteen patients (eight in each group) completed the protocol. Groups were similar at baseline in gender distribution (five males, three females), mean BMI (27.5 ± 3.8 vs 27.4 ± 3.8 kg/m²), neck circumference (15.1 ± 1.6 vs 14.7 ± 1.7 in.), Epworth Sleepiness Score (8 ± 3.5 vs 7 ± 4.0), and AHI (9.2 ± 4.0 vs 8.2 ± 3.2 events/h). At 8 weeks, the absolute change in snoring rate (> 60 dB/h) was greater for the intervention group than the control group (- 49.3 ± 55.3 vs - 6.23 ± 23.2; p = 0.037), a 22 and 5.6% reduction, respectively. All bed partners of participants in the intervention group reported reduced snoring volume and frequency, whereas no change was reported for the control group.

CONCLUSIONS

Smartphone application-administered upper airway training reduces objective and subjective snoring measures and improves sleep quality.

TRIAL REGISTRATION

ClinicalTrials.gov ; no.: NCT03264963; URL: www.clinicaltrials.gov.

Alteration in upper airway dilator muscle coactivation during sleep: comparison of patients with obstructive sleep apnea and healthy subjects

In patients with obstructive sleep apnea (OSA), substantial increases in genioglossus (GG) activity during hypopneas/apneas usually fail to restore normal airflow. We have previously suggested that sleep-induced alteration in tongue muscle coordination may explain this finding, as retractor muscle coactivation was reduced during sleep compared with wakefulness. The present study was undertaken to evaluate whether these alterations in dilator muscle activation during sleep play a role in the pathogenesis of OSA and whether coactivation of additional peripharyngeal muscles (non-GG muscles: styloglossus, geniohyoid, sternohyoid, and sternocleidomastoid) is also impaired during sleep. We compared GG and non-GG muscle electromyographic (EMG) activity in 8 patients with OSA and 12 healthy subjects during wakefulness while breathing through inspiratory resistors with the activity observed during sleep toward the end of flow limitation, before arousal, at equivalent esophageal pressures. During wakefulness, resistive breathing triggered increases in both GG and non-GG muscle activity. During sleep, flow limitation was associated with increases in GG-EMG that reached, on average, >2-fold the level observed while awake. In contrast, EMGs of the non-GG muscles, recorded simultaneously, reached, on average, only ~2/3 the wakefulness level. We conclude that during sleep GG activity may increase to levels that substantially exceed those sufficient to prevent pharyngeal collapse during wakefulness, whereas other peripharyngeal muscles do not coactivate during sleep in both patients with OSA and healthy subjects. We speculate that upper airway muscle dyssynchrony during sleep may explain why GG-EMG activation fails to alleviate flow limitation and stabilize airway patency during sleep.

NEW & NOTEWORTHY Pharyngeal obstruction during sleep may trigger genioglossus activity to levels substantially exceeding those observed during wakefulness, without ameliorating flow limitation. In contrast, other peripharyngeal muscles exhibit a much lower activity during sleep in both patients with obstructive sleep apnea and healthy subjects. Coordinated muscular synergy stabilizes the pharynx despite relatively low activity while awake, yet even higher genioglossal activity allows the pharynx to obstruct when simultaneous activity of other dilator muscles is inadequate during sleep.

Alteration in upper airway dilator muscle coactivation during sleep: comparison of patients with obstructive sleep apnea and healthy subjects

In patients with obstructive sleep apnea (OSA), substantial increases in genioglossus (GG) activity during hypopneas/apneas usually fail to restore normal airflow. We have previously suggested that sleep-induced alteration in tongue muscle coordination may explain this finding, as retractor muscle coactivation was reduced during sleep compared with wakefulness. The present study was undertaken to evaluate whether these alterations in dilator muscle activation during sleep play a role in the pathogenesis of OSA and whether coactivation of additional peripharyngeal muscles (non-GG muscles: styloglossus, geniohyoid, sternohyoid, and sternocleidomastoid) is also impaired during sleep. We compared GG and non-GG muscle electromyographic (EMG) activity in 8 patients with OSA and 12 healthy subjects during wakefulness while breathing through inspiratory resistors with the activity observed during sleep toward the end of flow limitation, before arousal, at equivalent esophageal pressures. During wakefulness, resistive breathing triggered increases in both GG and non-GG muscle activity. During sleep, flow limitation was associated with increases in GG-EMG that reached, on average, >2-fold the level observed while awake. In contrast, EMGs of the non-GG muscles, recorded simultaneously, reached, on average, only ~2/3 the wakefulness level. We conclude that during sleep GG activity may increase to levels that substantially exceed those sufficient to prevent pharyngeal collapse during wakefulness, whereas other peripharyngeal muscles do not coactivate during sleep in both patients with OSA and healthy subjects. We speculate that upper airway muscle dyssynchrony during sleep may explain why GG-EMG activation fails to alleviate flow limitation and stabilize airway patency during sleep. NEW & NOTEWORTHY Pharyngeal obstruction during sleep may trigger genioglossus activity to levels substantially exceeding those observed during wakefulness, without ameliorating flow limitation. In contrast, other peripharyngeal muscles exhibit a much lower activity during sleep in both patients with obstructive sleep apnea and healthy subjects. Coordinated muscular synergy stabilizes the pharynx despite relatively low activity while awake, yet even higher genioglossal activity allows the pharynx to obstruct when simultaneous activity of other dilator muscles is inadequate during sleep.

Personalised medicine in sleep respiratory disorders: focus on obstructive sleep apnoea diagnosis and treatment

In all fields of medicine, major efforts are currently dedicated to improve the clinical, physiological and therapeutic understanding of disease, and obstructive sleep apnoea (OSA) is no exception. The personalised medicine approach is relevant for OSA, given its complex pathophysiology and variable clinical presentation, the interactions with comorbid conditions and its possible contribution to poor outcomes. Treatment with continuous positive airway pressure (CPAP) is effective, but CPAP is poorly tolerated or not accepted in a considerable proportion of OSA patients. This review summarises the available studies on the physiological phenotypes of upper airway response to obstruction during sleep, and the clinical presentations of OSA (phenotypes and clusters) with a special focus on our changing attitudes towards approaches to treatment. Such major efforts are likely to change and expand treatment options for OSA beyond the most common current choices (i.e CPAP, mandibular advancement devices, positional treatment, lifestyle changes or upper airway surgery). More importantly, treatment for OSA may become more effective, being tailored to each patient's need.

The importance of obstructive sleep apnoea and hypopnea pathophysiology for customized therapy

The objective of this study is to highlight the importance of anatomical and not-anatomical factors' identification for customized therapy in OSAHS patients. The data sources are: MEDLINE, The Cochrane Library and EMBASE. A systematic review was performed to identify studies that analyze the role of multiple interacting factors involved in the OSAHS pathophysiology. 85 out of 1242 abstracts were selected for full-text review. A variable combinations pathophysiological factors contribute to realize differentiated OSAHS phenotypes: a small pharyngeal airway with a low resistance to collapse (increased critical closing pressure), an inadequate responses of pharyngeal dilator muscles (wakefulness drive to breathe), an unstable ventilator responsiveness to hypercapnia (high loop gain), and an increased propensity to wake related to upper airway obstruction (low arousal threshold). Identifying if the anatomical or not-anatomical factors are predominant in each OSAHS patient represents the current challenge in clinical practice, moreover for the treatment decision-making. In the future, if a reliable and accurate pathophysiological pattern for each OSAHS patient can be identified, a customized therapy will be feasible, with a significant improvement of surgical success in sleep surgery and a better understanding of surgical failure.

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.

Cortical Drive to Breathe during Wakefulness in Patients with Obstructive Sleep Apnea Syndrome

STUDY OBJECTIVES

The obstructive sleep apnea syndrome (OSAS) involves recurrent sleep-related upper airways (UA) collapse. UA mechanical properties and neural control are altered, imposing a mechanical load on inspiration. UA collapse does not occur during wakefulness, hence arousal-dependent compensation. Experimental inspiratory loading in normal subjects elicits respiratory-related cortical activity. The objective of this study was to test whether awake OSAS patients would exhibit a similar cortical activity.

DESIGN

Descriptive physiology study.

SETTING

Sleep laboratory in a large university affiliated tertiary hospital.

PATIENTS

26 patients with moderate OSAS according to polysomnography (5 < apnea-hypopnea index [AHI] ≤ 30, n = 14) or severe OSAS (AHI > 30, n = 12); 13 non-OSAS patients for comparison.

INTERVENTIONS

None.

MEASUREMENTS

Respiratory time-locked electroencephalographic segments ensemble averaged and analyzed for slow premotor potentials preceding inspiration ("pre-inspiratory potentials" [PIPs]).

RESULTS

PIPs were present in 1/13 controls and 11/26 patients (P = 0.0336; 4/14 "moderate" and 7/12 "severe" patients). Awake OSAS patients therefore exhibit respiratory-related cortical activity during quiet breathing significantly more frequently than non-OSAS individuals. The corresponding PIPs resemble those observed during prepared voluntary inspirations and in response to experimental inspiratory loads in normal subjects, which involve a cortical network comprising the supplementary motor area.

CONCLUSIONS

A respiratory-related cortical activity could contribute to the increased neural drive to upper airway and to inspiratory muscles that has previously been described in obstructive sleep apnea, and could therefore contribute to the arousal-dependent compensation of upper airway abnormalities. Whether or not such cortical compensatory mechanisms have cognitive consequences remains to be determined.

Obstructive sleep apnea in the perioperative setting: complications and management strategies

Obstructive sleep apnea (OSA) is frequently encountered in an undiagnosed, untreated state in perioperative patients. It increases the risk of respiratory, cardiac, and infectious complications following surgical procedures. Patients with OSA may require additional monitoring, unplanned escalations in care, and prolonged hospitalization. It is important to identify patients at risk for OSA during the preoperative assessment so that appropriate anesthesia, postsurgical monitoring, and pain control can be planned. Herein, we discuss data regarding perioperative outcomes in patients with OSA, methods to quickly identify patients at high risk for OSA, and implementation of clinical safeguards to minimize OSA-associated complications. An algorithm is provided to guide the perioperative management of patients with OSA.

The relationship of vertical skeletofacial morphology to oropharyngeal airway shape using cone beam computed tomography: possible implications for airway restriction

OBJECTIVE

To determine if the shape of the oropharyngeal airway is related to the vertical morphology of the skeletofacial complex, including the hyoid bone.

MATERIALS AND METHODS

Cone beam computed tomography scans from 50 pretreatment adult orthodontic records were used to obtain skeletal and airway measurements. Linear regression statistics were used to compare soft tissue variables to hard tissue predictor variables.

RESULTS

Transverse airway widening was significantly increased when the distance between the hyoid and vertebrae was reduced; when the three-dimensional (3D) facial axis angle decreased (became more vertical); when the 3D mandibular plane angle increased; when the width of the hyoid increased, or when the calculated length of the geniohyoid decreased.

CONCLUSIONS

A laterally elliptical airway-found when the face is more vertical and when the hyoid is closer to the cervical vertebrae-is hypothetically more resistant to collapse. Patients with a retrognathic, skeletal deep bite and a rounded oropharynx should be identified and corrected early to prevent potential airway problems.

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.

Development of a computational biomechanical model of the human upper-airway soft-tissues toward simulating obstructive sleep apnea

Numerous challenges are faced in investigations aimed at developing a better understanding of the pathophysiology of obstructive sleep apnea (OSA). The anatomy of the tongue and other upper-airway tissues, and the ability to model their behavior, are central to such investigations. We present details of the construction and development of a soft-tissue model of the human upper airway, with the ultimate goal of simulating obstructive sleep apnea. The steps taken to produce a representative anatomical geometry, of which the associated muscle histology is also captured, are documented. An overview of the mathematical models used to describe tissue behavior, both at a macro- and microscopic level, is given. A neurological model, which mimics the proprioceptive capabilities of the body, is described as it is applies to control of the active dynamics of the tongue. A simplified scenario, which allows for the manipulation of several environmental influences, is presented. It is demonstrated that the response of the genioglossus is qualitatively similar to that determined through experimental techniques. Furthermore, insights into the stress distribution developed within the tongue are discussed. It is shown that changes in almost any aspect of the breathing or physiological conditions invoke a significant change in the response of the airway dilators. The results of this study provide further evidence of the importance of modeling and simulation techniques as an aid in understanding the complex behavior of the human body.

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.

Postoperative Respiratory Muscle Dysfunction

Postoperative pulmonary complications are responsible for significant increases in hospital cost as well as patient morbidity and mortality; respiratory muscle dysfunction represents a contributing factor. Upper airway dilator muscles functionally resist the upper airway collapsing forces created by the respiratory pump muscles. Standard perioperative medications (anesthetics, sedatives, opioids, and neuromuscular blocking agents), interventions (patient positioning, mechanical ventilation, and surgical trauma), and diseases (lung hyperinflation, obesity, and obstructive sleep apnea) have differential effects on the respiratory muscle subgroups. These effects on the upper airway dilators and respiratory pump muscles impair their coordination and function and can result in respiratory failure. Perioperative management strategies can help decrease the incidence of postoperative respiratory muscle dysfunction. Such strategies include minimally invasive procedures rather than open surgery, early and optimal mobilizing of respiratory muscles while on mechanical ventilation, judicious use of respiratory depressant anesthetics and neuromuscular blocking agents, and noninvasive ventilation when possible.

Upper airway collapsibility and patterns of flow limitation at constant end-expiratory lung volume

The passive pharyngeal critical closing pressure (Pcrit) is measured using a series of pressure drops. However, pressure drops also lower end-expiratory lung volume (EELV), which independently affects Pcrit. We describe a technique to measure Pcrit at a constant EELV. Continuous positive airway pressure (CPAP)-treated obstructive sleep apnea (OSA) patients and controls were instrumented with an epiglottic catheter, magnetometers (to measure change in EELV), and nasal mask/pneumotachograph and slept supine on nasal CPAP. Pcrit was measured in standard fashion and using our novel "biphasic technique" in which expiratory pressure only was lowered for 1 min before the inspiratory pressure was dropped; this allowed EELV to decrease to the drop level before performing the pressure drop. Seven OSA and three controls were studied. The biphasic technique successfully lowered EELV before the inspiratory pressure drop. Pcrit was similar between the standard and biphasic techniques (-0.4 ± 2.6 vs. -0.6 ± 2.3 cmH(2)O, respectively, P = 0.84). Interestingly, we noted three different patterns of flow limitation: 1) classic Starling resistor type: flow fixed and independent of downstream pressure; 2) negative effort dependence within breaths: substantial decrease in flow, sometimes with complete collapse, as downstream pressure decreased; and 3) and negative effort dependence across breaths: progressive reductions in peak flow as respiratory effort on successive breaths increased. Overall, EELV changes do not influence standard passive Pcrit measurements if breaths 3-5 of pressure drops are used. These results also highlight the importance of inspiratory collapse in OSA pathogenesis. The cause of negative effort dependence within and across breaths is not known and requires further study.

Computational model of soft tissues in the human upper airway

This paper presents a three-dimensional finite element model of the tongue and surrounding soft tissues with potential application to the study of sleep apnoea and of linguistics and speech therapy. The anatomical data was obtained from the Visible Human Project, and the underlying histological data was also extracted and incorporated into the model. Hyperelastic constitutive models were used to describe the material behaviour, and material incompressibility was accounted for. An active Hill three-element muscle model was used to represent the muscular tissue of the tongue. The neural stimulus for each muscle group was determined through the use of a genetic algorithm-based neural control model. The fundamental behaviour of the tongue under gravitational and breathing-induced loading is investigated. It is demonstrated that, when a time-dependent loading is applied to the tongue, the neural model is able to control the position of the tongue and produce a physiologically realistic response for the genioglossus.

The effect of exercise training on obstructive sleep apnea and sleep quality: a randomized controlled trial

STUDY OBJECTIVES

To evaluate the efficacy of a 12-week exercise training program for reducing obstructive sleep apnea (OSA) severity and improving sleep quality, and to explore possible mechanisms by which exercise may reduce OSA severity.

DESIGN

Randomized controlled trial.

SETTING

Clinical exercise physiology center, sleep laboratory.

PARTICIPANTS

Forty-three sedentary and overweight/obese adults aged 18-55 years with at least moderate-severity untreated OSA (screening apnea-hypopnea index [AHI] ≥ 15).

INTERVENTIONS

Participants randomized to exercise training (n = 27) met 4 times/week for 12 weeks and performed 150 min/week of moderate-intensity aerobic activity, followed by resistance training twice/week. Participants randomized to a stretching control (n = 16) met twice weekly for 12 weeks to perform low-intensity exercises designed to increase whole-body flexibility.

MEASUREMENTS AND RESULTS

OSA severity was assessed with one night of laboratory polysomnography (PSG) before and following the 12-week intervention. Measures of sleep quality included PSG, actigraphy (7-10 days), and the Pittsburgh Sleep Quality Index. Compared with stretching, exercise resulted in a significant AHI reduction (exercise: 32.2 ± 5.6 to 24.6 ± 4.4, stretching: 24.4 ± 5.6 to 28.9 ± 6.4; P < 0.01) as well as significant changes in oxygen desaturation index (ODI; P = 0.03) and stage N3 sleep (P = 0.03). Reductions in AHI and ODI were achieved without a significant decrease in body weight. Improvements in actigraphic sleep and subjective sleep quality were also noted following exercise compared with stretching.

CONCLUSIONS

Exercise training had moderate treatment efficacy for the reduction of AHI in sedentary overweight/obese adults, which suggests that exercise may be beneficial for the management of OSA beyond simply facilitating weight loss.

TRIAL REGISTRATION

Clinicaltrials.gov identification number NCT00956423.

Respiratory-inductive-plethysmography-derived flow can be a useful clinical tool to detect patients with obstructive sleep apnea syndrome

BACKGROUND/PURPOSE

Obstructive sleep apnea (OSA) is a common disorder characterized by recurrent episodes of a complete or partial collapse of the upper airway during sleep. The disease is traditionally diagnosed by overnight polysomnography with detection flow limitation by nasal pressure cannulas. The aim of this study was to evaluate the accuracy of flow (X flow) from calibrated respiratory inductive plethysmography.

METHODS

We studied 60 male and 26 female patients who came to our sleep center in 2007. All the participants received overnight polysomnography and data were graded blindly and randomly by two experienced technicians.

RESULTS

Patients with OSA were predominantly male, with higher body mass index, higher percentage of snorers, and more events of oxygen desaturation and arousal than those without OSA. There was a good correlation of X flow and flow from nasal pressure cannulas, regardless of total apnea-hypopnea, apnea or hypopnea events. The correlation was especially strong in severe OSA patients. The sensitivity and specificity to find OSA (apnea-hypopnea index ≥5) from X flow versus standard polysomnography was 98% and 100%, respectively. Positive predictive value was 100% and negative predictive value was 97%.

CONCLUSION

X flow could be a good clinical tool to be used instead of flow from nasal pressure cannulas in OSA patients.

Anatomy and physiology of the upper airway

The nose is the major portal of air exchange between the internal and external environment. The nose participates in the vital functions of conditioning inspired air toward a temperature of 37°C and 100% relative humidity, providing local defense and filtering inhaled particulate matter and gases. It also functions in olfaction, which provides both a defense and pleasure for the individual. Understanding normal physiology provides the basis for recognizing abnormalities.

Effects of pentobarbital on upper airway patency during sleep

We hypothesised that pentobarbital would improve upper airway mechanics based on an increase in latency to arousal and amplitude of the phasic genioglossus electromyogram (EMG), and a decrease in the active upper airway critical closing pressure (P(crit)). 12 healthy subjects received pentobarbital (100 mg) or placebo in a double-blind, crossover protocol. During wakefulness, we measured the genioglossus reflex response to negative pressure pulses. During sleep, carbon dioxide was insufflated into the inspired air. Airway pressure was then decreased in a stepwise fashion until arousal from sleep. With basal breathing during sleep: flow rate was lower in volunteers given pentobarbital; end-tidal CO(2) concentration and upper airway resistance were greater; and P(crit) was unaffected (pentobarbital mean ± SD -11.7 ± 4.5 versus placebo -10.25 ± 3.6 cmH(2)O; p = 0.11). Pentobarbital increased the time to arousal (297 ± 63s versus 232 ± 67 s; p<0.05), at which time phasic genioglossus EMG was higher (6.2 ± 4.8% maximal versus 3.1 ± 3%; p<0.05) as were CO(2) levels. The increase in genioglossus EMG after CO(2) administration was greater after pentobarbital versus placebo. Pentobarbital did not affect the genioglossus negative-pressure reflex. Pentobarbital increases the time to arousal and stimulates genioglossus muscle activity, but it also increases upper airway resistance during sleep.

Determinants of ventilatory instability in obstructive sleep apnea: inherent or acquired?

STUDY OBJECTIVES

Certain respiratory control characteristics determine whether patients with collapsible upper airway develop stable or unstable breathing during sleep, thereby influencing the severity of obstructive apnea (OSA). These include arousal threshold (T(A)), response to transient hypoxia and hypercapnia (Dynamic Response) and the increase in respiratory drive required for arousal-free airway opening (T(ER)). We wished to determine whether these characteristics are inherent or are acquired during untreated OSA.

DESIGN

T(A), Dynamic Response, and T(ER) were measured in patients with severe OSA before and after treatment with continuous positive airway pressure (CPAP). Changes observed after treatment were deemed to have been acquired during untreated OSA.

SETTING

University-based sleep laboratory.

PATIENTS

15 patients with severe OSA.

INTERVENTIONS

(1) 30-sec alterations in inspired gases during sleep on CPAP. (2) Brief dial-downs of CPAP (dial-downs) both during air breathing and when ventilation was increased to different levels.

MEASUREMENTS AND RESULTS

T(A): the increase in ventilation associated with a 50% probability of arousal (T(A)50). Dynamic Response: the increase in ventilation on the 5th breath following breathing 3% CO2 in 11% to 15% O2. T(ER): the increase in ventilation prior to dial-downs that was associated with an arousal-free airway opening during dial-down. CPAP therapy (10.5 +/- 4.3 months) resulted in marked reduction in Dynamic Response (131% +/- 95% to 52% +/- 34% baseline ventilation, P < 0.005), a decrease in T(A)50 (134% +/- 78% to 86% +/- 47% baseline ventilation, P < 0.05), and no change in T(ER).

CONCLUSIONS

T(ER) may be an inherent characteristic. Untreated OSA results in an increase in dynamic response to asphyxia and an increase in arousal threshold.

Upper airway function in the pathogenesis of obstructive sleep apnea: a review of the current literature

PURPOSE OF REVIEW

Obstructive sleep apnea is an increasingly prevalent disease, with a considerable societal burden. The disease is defined by recurrent intermittent collapse of the upper airway. Understanding of and treatment for the disease is largely confined to relief of the mechanical obstruction of the upper airway by application of continuous positive airway pressure, and less commonly weight loss or surgery. However, recent work has focused on the function, rather than structure alone, of the upper airway.

RECENT FINDINGS

The following contributors to upper airway structure and function have been studied: traditional fixed anatomical abnormalities, dynamic anatomical changes, upper airway dilator muscle dysfunction, lung volumes, and instability in control of breathing. In each patient with obstructive sleep apnea, the relative contribution of each of these components may be quite variable. The studies reviewed here describe methods to evaluate these factors, and some attempts at treatment.

SUMMARY

Ongoing studies are attempting to classify patients on the basis of the underlying pathophysiology. This work suggests that obstructive sleep apnea is a heterogeneous disease with multiple root causes. Ultimately, such a classification may allow more individualized treatment, not only relying on mechanical relief of the upper airway obstruction.

Role of respiratory control mechanisms in the pathogenesis of obstructive sleep disorders

Obstructive sleep disorders develop when the normal reduction in pharyngeal dilator activity at sleep onset occurs in an individual whose pharynx requires a relatively high level of dilator activity to remain sufficiently open. They range from steady snoring, to slowly evolving hypopneas, to fast-recurring obstructive hypopneas and apneas. A fundamental observation is that the polysomnographic picture differs substantially among subjects with the same pharyngeal collapsibility, and even in the same subject at different times, indicating that the type and severity of the disorder is determined to a large extent by the individual's response to the obstruction. The present report reviews the various mechanisms involved in the response to sleep-induced obstructive events. When the obstructive event takes the form of mild-moderate flow limitation, compensation can take place through an increase in the fraction of time spent in inspiration (Ti/Ttot) without any increase in maximum flow (V(MAX)). With more severe obstructions, V(MAX) must increase. Recent data indicate that the obstructed upper airway can reopen reflexly, without arousal, if chemical drive is allowed to reach a threshold (T(ER)) but that this is often preempted by a low arousal threshold. The relation between T(ER) and arousal threshold, as well as the lung-to-carotid circulation time and the rate of rise of chemical drive during the obstructive event, determine the magnitude of ventilatory overshoot at the end of an event and, by extension, whether initial obstructive events will be followed by stable breathing, slow evolving hypopneas with occasional arousals, or repetitive events.

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.

Differential effects of isoflurane and propofol on upper airway dilator muscle activity and breathing

BACKGROUND

Anesthesia impairs upper airway integrity, but recent data suggest that low doses of some anesthetics increase upper airway dilator muscle activity, an apparent paradox. The authors sought to understand which anesthetics increase or decrease upper airway dilator muscle activity and to study the mechanisms mediating the effect.

METHODS

The authors recorded genioglossus electromyogram, breathing, arterial blood pressure, and expiratory carbon dioxide in 58 spontaneously breathing rats at an estimated ED50 (median effective dose) of isoflurane or propofol. The authors further evaluated the dose-response relations of isoflurane under different study conditions: (1) normalization of mean arterial pressure, or end-expiratory carbon dioxide; (2) bilateral lesion of the Kölliker-Fuse nucleus; and (3) vagotomy. To evaluate whether the markedly lower inspiratory genioglossus activity during propofol could be recovered by increasing flow rate, a measure of respiratory drive, the authors performed an additional set of experiments during hypoxia or hypercapnia.

RESULTS

In vagally intact rats, tonic and phasic genioglossus activity were markedly higher with isoflurane compared with propofol. Both anesthetics abolished the genioglossus negative pressure reflex. Inspiratory flow rate and anesthetic agent predicted independently phasic genioglossus activity. Isoflurane dose-dependently decreased tonic and increased phasic genioglossus activity, and increased flow rate, and its increasing effects were abolished after vagotomy. Impairment of phasic genioglossus activity during propofol anesthesia was reversed during evoked increase in respiratory drive.

CONCLUSION

Isoflurane compared with propofol anesthesia yields higher tonic and phasic genioglossus muscle activity. The level of respiratory depression rather than the level of effective anesthesia correlates closely with the airway dilator muscle function during anesthesia.