Phenotyping interindividual variability in obstructive sleep apnoea response to temazepam using ventilatory chemoreflexes during wakefulness

Current and Novel Treatment Options for OSA

Obstructive sleep apnoea is a challenging medical problem due to its prevalence, its impact on quality of life and performance in school and professionally, the implications for risk of accidents, and comorbidities and mortality. Current research has carved out a broad spectrum of clinical phenotypes and defined major pathophysiological components. These findings point to the concept of personalised therapy, oriented on both the distinct clinical presentation and the most relevant pathophysiology in the individual patient. This leads to questions of whether sufficient therapeutic options other than positive airway pressure (PAP) alone are available, for which patients they may be useful, if there are specific indications for single or combined treatment, and whether there is solid scientific evidence for recommendations. This review describes our knowledge on PAP and non-PAP therapies to address upper airway collapsibility, muscle responsiveness, arousability and respiratory drive. The spectrum is broad and heterogeneous, including technical and pharmaceutical options already in clinical use or at an advanced experimental stage. Although there is an obvious need for more research on single or combined therapies, the available data demonstrate the variety of effective options, which should replace the unidirectional focus on PAP therapy.

The analysis of individual pathophysiological composition opens new directions towards personalised treatment of OSA, focusing not only on pharyngeal dilation, but also on technical or pharmaceutical interventions on muscle function or breathing regulationhttps://bit.ly/3sayhkd

Obstructive sleep apnea

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

Non-REM Apnea and Hypopnea Duration Varies across Population Groups and Physiologic Traits

Rationale: Symptoms and morbidities associated with obstructive sleep apnea (OSA) vary across individuals and are not predicted by the apnea-hypopnea index (AHI). Respiratory event duration is a heritable trait associated with mortality that may further characterize OSA.Objectives: We evaluated how hypopnea and apnea durations in non-REM (NREM) sleep vary across demographic groups and quantified their associations with physiological traits (loop gain, arousal threshold, circulatory delay, and pharyngeal collapsibility).Methods: Data were analyzed from 1,546 participants from the Multi-Ethnic Study of Atherosclerosis with an AHI ≥5. Physiological traits were derived using a validated model fit to the polysomnographic airflow signal. Multiple linear regression models were used to evaluate associations of event duration with demographic and physiological factors.Measurements and Main Results: Participants had a mean age ± SD of 68.9 ± 9.2 years, mean NREM hypopnea duration of 21.73 ± 5.60, and mean NREM apnea duration of 23.87 ± 7.44 seconds. In adjusted analyses, shorter events were associated with younger age, female sex, higher body mass index (P < 0.01, all), and Black race (P < 0.05). Longer events were associated with Asian race (P < 0.01). Shorter event durations were associated with lower circulatory delay (2.53 ± 0.13 s, P < 0.01), lower arousal threshold (1.39 ± 0.15 s, P < 0.01), reduced collapsibility (-0.71 ± 0.16 s, P < 0.01), and higher loop gain (-0.27 ± 0.11 s, P < 0.05) per SD change. Adjustment for physiological traits attenuated age, sex, and obesity associations and eliminated racial differences in event duration.Conclusions: Average event duration varies across population groups and provides information on ventilatory features and airway collapsibility not captured by the AHI.

Chronic Opioid Use and Central Sleep Apnea, Where Are We Now and Where To Go? A State of the Art Review

Opioids are commonly used for pain management, perioperative procedures, and addiction treatment. There is a current opioid epidemic in North America that is paralleled by a marked increase in related deaths. Since 2000, chronic opioid users have been recognized to have significant central sleep apnea (CSA). After heart failure-related Cheyne-Stokes breathing (CSB), opioid-induced CSA is now the second most commonly seen CSA. It occurs in around 24% of chronic opioid users, typically after opioids have been used for more than 2 months, and usually corresponds in magnitude to opioid dose/plasma concentration. Opioid-induced CSA events often mix with episodes of ataxic breathing. The pathophysiology of opioid-induced CSA is based on dysfunction in respiratory rhythm generation and ventilatory chemoreflexes. Opioids have a paradoxical effect on different brain regions, which result in irregular respiratory rhythm. Regarding ventilatory chemoreflexes, chronic opioid use induces hypoxia that appears to stimulate an augmented hypoxic ventilatory response (high loop gain) and cause a narrow CO2 reserve, a combination that promotes respiratory instability. To date, no direct evidence has shown any major clinical consequence from CSA in chronic opioid users. A line of evidence suggested increased morbidity and mortality in overall chronic opioid users. CSA in chronic opioid users is likely to be a compensatory mechanism to avoid opioid injury and is potentially beneficial. The current treatments of CSA in chronic opioid users mainly focus on continuous positive airway pressure (CPAP) and adaptive servo-ventilation (ASV) or adding oxygen. ASV is more effective in reducing CSA events than CPAP. However, a recent ASV trial suggested an increased all-cause and cardiovascular mortality with the removal of CSA/CSB in cardiac failure patients. A major reason could be counteracting of a compensatory mechanism. No similar trial has been conducted for chronic opioid-related CSA. Future studies should focus on (1) investigating the phenotypes and genotypes of opioid-induced CSA that may have different clinical outcomes; (2) determining if CSA in chronic opioid users is beneficial or detrimental; and (3) assessing clinical consequences on different treatment options on opioid-induced CSA.

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

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

[Drugs affecting obstructive sleep apnea syndrome]

Sleep-disordered breathing is one of the most common sleep-associated disorders. At the same time, their prevalence tends to increase with age. One of the most common forms of respiratory failure during sleep is obstructive sleep apnea syndrome (OSA), which is characterized by repeated episodes of cessation of breathing or a significant decrease in respiratory flow while maintaining respiratory effort as a result of obstruction of the upper respiratory tract. Drugs have different effects on OSA. There are drugs that worsen OSA, drugs that do not affect OSA, and drugs that improve OSA. Benzodiazepines, opioids, muscle relaxants, and male hormones adversely affect OSA. Also of clinical interest are drugs that do not affect OSA and can even potentially improve respiratory function during sleep. These include anti-inflammatory drugs, diuretics, bronchodilators, acetylcholinesterase inhibitors, antiparkinsonian, decongestant drugs, drugs for intranasal use, topical soft tissue lubricant, female sex hormones. Finally, the effect of a number of drugs on OSA is not definitively established and requires further study (benzodiazepine receptor agonist hypnotics, angiotensin-converting enzyme inhibitors, opiate receptor antagonists, antidepressants, proton-pump inhibitors, TNF-α antagonists, glutamate receptor antagonists, drugs for the treatment of acromegaly, drugs for the treatment of narcolepsy). Raising awareness of doctors of different specialties about the impact of various drugs on OSA can not only prevent the deterioration of respiratory distress during sleep, but also, with a rational individual approach, makes it possible to even improve the quality of sleep and blood saturation, thereby contributing to a more favorable course of OSA and the underlying disease.

Targeting Endotypic Traits with Medications for the Pharmacological Treatment of Obstructive Sleep Apnea. A Review of the Current Literature

Obstructive sleep apnea (OSA) is a highly prevalent condition with few therapeutic options. To date there is no approved pharmacotherapy for this disorder, but several attempts have been made in the past and are currently ongoing to find one. The recent identification of multiple endotypes underlying this disorder has oriented the pharmacological research towards tailored therapies targeting specific pathophysiological traits that contribute differently to cause OSA in each patient. In this review we retrospectively analyze the literature on OSA pharmacotherapy dividing the medications tested on the basis of the four main endotypes: anatomy, upper airway muscle activity, arousal threshold and ventilatory instability (loop gain). We show how recently introduced drugs for weight loss that modify upper airway anatomy may play an important role in the management of OSA in the near future, and promising results have been obtained with drugs that increase upper airway muscle activity during sleep and reduce loop gain. The lack of a medication that can effectively increase the arousal threshold makes this strategy less encouraging, although recent studies have shown that the use of certain sedatives do not worsen OSA severity and could actually improve patients' sleep quality.

Association of Opioid and Benzodiazepine Use with Adverse Respiratory Events in Older Adults with Chronic Obstructive Pulmonary Disease

Rationale: Older adults with chronic obstructive pulmonary disease (COPD) are at substantially increased risk for medication-related adverse events. Two frequently prescribed classes of drugs that pose a particular risk to this patient group are opioids and benzodiazepines. Research on this topic has yielded conflicting findings.Objectives: The purpose of this study was to examine, among older adults with COPD, whether: 1) independent or concurrent use of opioid and benzodiazepine medications was associated with hospitalizations for respiratory events, and 2) this association was exacerbated by the presence of obstructive sleep apnea (OSA).Methods: We conducted a case-control study of Medicare beneficiaries aged ≥66 years, who were diagnosed with COPD in 2013, using the 5% national Medicare database. Cases (n = 3,232) were defined as patients hospitalized for a primary COPD-related respiratory diagnosis in 2014 and were matched with up to two control subjects (n = 6,247) on index date, age, sex, socioeconomic status, comorbidity, presence of OSA, COPD medication, and COPD complexity.Results: In comparison to the referent (no opioid or benzodiazepine use), opioid use alone (adjusted odds ratio [aOR], 1.73; 95% confidence interval [CI], 1.52-1.97), benzodiazepine use alone (aOR, 1.42; 95% CI, 1.21-1.66), and concurrent opioid/ benzodiazepine use (aOR, 2.32; 95% CI, 1.94-2.77) in the 30 days before the event/index date were all associated with an increased risk of hospitalization for a respiratory condition. Risk of hospitalization was higher with concurrent opioid and benzodiazepine use when compared with use of either medication alone. There was no statistically significant interaction between OSA and either of the drugs, alone or in combination. However, the adverse respiratory effects of concurrent opioid and benzodiazepine use were increased in patients with a high degree of COPD complexity. All of the above findings persisted using exposure windows that extended to 60 and 90 days before the event/index date.Conclusions: Among older adults with COPD, use of opioid and benzodiazepine medications alone or in combination were associated with increased adverse respiratory events. The adverse effects of these medications were not exacerbated in patients with COPD-OSA overlap syndrome. However, the adverse impact of dual opioid and benzodiazepine was greater in patients with high-complexity COPD.

Obstructive sleep apnoea in adults: peri-operative considerations: A narrative review

: Obstructive sleep apnoea (OSA) is a common breathing disorder of sleep with a prevalence increasing in parallel with the worldwide rise in obesity. Alterations in sleep duration and architecture, hypersomnolence, abnormal gas exchange and also associated comorbidities may all feature in affected patients.The peri-operative period poses a special challenge for surgical patients with OSA who are often undiagnosed, and are at an increased risk for complications including pulmonary and cardiovascular, during that time. In order to ensure the best peri-operative management, anaesthetists caring for these patients should have a thorough understanding of the disorder, and be aware of the individual's peri-operative risk constellation, which depends on the severity and phenotype of OSA, the invasiveness of the surgical procedure, anaesthesia and also the requirement for postoperative opioids.The objective of this review is to educate clinicians in the epidemiology, pathogenesis and diagnosis of OSA in adults and also to highlight specific tasks in the preoperative assessment, namely to select a suitable intra-operative anaesthesia regimen, and manage the extent and duration of postoperative care to facilitate the best peri-operative outcome.

The effect of acute morphine on obstructive sleep apnoea: a randomised double-blind placebo-controlled crossover trial

Objective

Anaesthesiology guidelines suggest that opioids worsen obstructive sleep apnoea (OSA) despite no randomised controlled trial evidence. We therefore conducted a randomised controlled trial to evaluate the effects of a common clinical dose of morphine on OSA, and to identify clinical phenotype and genotype vulnerability to opioid-respiratory depression.

Methods

Under a double-blind, randomised, crossover design, 60 male patients with OSA attended two visits to the hospital sleep laboratory, at least 1 week apart. Either 40 mg controlled-release oral morphine or placebo was administered. Awake ventilatory chemoreflex tests were performed post dose and prior to overnight polysomnography monitoring. Blood was sampled before sleep and the next morning for toxicology and genotype analyses. Sleep time with oxygen saturation (SpO2) <90% (T90) was the primary outcome.

Results

Despite a large inter-individual variability, 40 mg morphine did not worsen T90 and apnoea–hypopnoea index, and only decreased the SpO2 nadir by 1.3%. In patients with severe OSA, a lower baseline CO2ventilatory response threshold correlated with the worsening of T90, apnoea–hypopnoea index and oxygen desaturation index with morphine use. Patients with OSA and the A118G OPRM1 polymorphism of A/A and A/G had a significantly different morphine effect on awake ventilatory chemosensitivity and T90 during sleep.

Conclusions

40 mg oral controlled-release morphine did not worsen OSA in men, challenging traditional thinking that OSA will be worsened by opioids. Individual opioid response in patients with OSA may relate to baseline CO2 response threshold and OPRM1 genotype. Our study findings may pave the way for a precision medicine approach to avoid opioid-related risks.

Trial registration number

The Australian and New Zealand Clinical Trial Registry, ACTRN12613000858796.

Effect of 1 month of zopiclone on obstructive sleep apnoea severity and symptoms: a randomised controlled trial

Hypnotic use in obstructive sleep apnoea (OSA) is contraindicated due to safety concerns. Recent studies indicate that single-night hypnotic use worsens hypoxaemia in some and reduces OSA severity in others depending on differences in pathophysiology. However, longer clinical trial data are lacking. This study aimed to determine the effects of 1 month of zopiclone on OSA severity, sleepiness and alertness in patients with low-moderate respiratory arousal thresholds without major overnight hypoxaemia.69 participants completed a physiology screening night with an epiglottic catheter to quantify arousal threshold. 30 eligible patients (apnoea-hypopnoea index (AHI) 22±11 events·h^-1) then completed standard in-laboratory polysomnography (baseline) and returned for two additional overnight sleep studies (nights 1 and 30) after receiving either nightly zopiclone (7.5 mg) or placebo during a 1-month, double-blind, randomised, parallel trial (ANZCTR identifier ANZCTRN12613001106729).The change in AHI from baseline to night 30 was not different between zopiclone versus placebo groups (-5.9±10.2 versus -2.4±5.5 events·h^-1; p=0.24). Similarly, hypoxaemia, next-day sleepiness and driving simulator performance were not different.1 month of zopiclone does not worsen OSA severity, sleepiness or alertness in selected patients without major overnight hypoxaemia. As the first study to assess the effect of a hypnotic on OSA severity and sleepiness beyond single-night studies, these findings provide important safety data and insight into OSA pathophysiology.

Predicting response to oxygen therapy in obstructive sleep apnoea patients using a 10-minute daytime test

There is no satisfactory treatment for obstructive sleep apnoea (OSA). Supplemental low-flow oxygen therapy (LFO2) has been shown to reduce hypoxaemia and is well tolerated by patients with OSA. However, oxygen therapy may be beneficial only to certain subsets of patients with OSA. In this study, we evaluated a 10-min awake ventilatory chemoreflex test in predicting individual OSA response to 2 months of LFO2therapy.

At baseline, patients with OSA underwent ventilatory chemoreflex testing in the afternoon, prior to the overnight polysomnography. Subjects were reassessed with polysomnography after 2 months of nocturnal oxygen treatment.

20 patients with OSA completed the study. After 2 months of O2treatment, changes in the apnoea–hypopnoea index (AHI) were significantly correlated with baseline CO2ventilatory response threshold (VRT) and chemosensitivity (p<0.05). In predicting a fall in AHI, the area under the receiver operating characteristic curve (AUC) was 0.79 for VRT and 0.89 for chemosensitivity. When these two variables were combined in a logistic regression model, the prediction effect became stronger with an AUC of 0.97, sensitivity of 0.92 and specificity of 0.83.

Our awake ventilatory chemoreflex test could be considered a simple potential clinical tool to predict individual OSA response to oxygen therapy. It could provide a novel personalised medicine approach to OSA treatment.

Obstructive sleep apnea: current perspectives

The prevalence of obstructive sleep apnea (OSA) continues to rise. So too do the health, safety, and economic consequences. On an individual level, the causes and consequences of OSA can vary substantially between patients. In recent years, four key contributors to OSA pathogenesis or "phenotypes" have been characterized. These include a narrow, crowded, or collapsible upper airway "anatomical compromise" and "non-anatomical" contributors such as ineffective pharyngeal dilator muscle function during sleep, a low threshold for arousal to airway narrowing during sleep, and unstable control of breathing (high loop gain). Each of these phenotypes is a target for therapy. This review summarizes the latest knowledge on the different contributors to OSA with a focus on measurement techniques including emerging clinical tools designed to facilitate translation of new cause-driven targeted approaches to treat OSA. The potential for some of the specific pathophysiological causes of OSA to drive some of the key symptoms and consequences of OSA is also highlighted.

Role of common hypnotics on the phenotypic causes of obstructive sleep apnoea: paradoxical effects of zolpidem

Hypnotics are contraindicated in obstructive sleep apnoea (OSA) because of concerns of pharyngeal muscle relaxation and delayed arousal worsening hypoxaemia. However, human data are lacking. This study aimed to determine the effects of three common hypnotics on the respiratory arousal threshold, genioglossus muscle responsiveness and upper airway collapsibility during sleep.21 individuals with and without OSA (18-65 years) completed 84 detailed sleep studies after receiving temazepam (10 mg), zolpidem (10 mg), zopiclone (7.5 mg) and placebo on four occasions in a randomised, double-blind, placebo-controlled, crossover trial (ACTRN12612001004853).The arousal threshold increased with zolpidem and zopiclone versus placebo (mean±sd -18.3±10 and -19.1±9 versus -14.6±7 cmH₂O; p=0.02 and p<0.001) but not with temazepam (-16.8±9 cmH₂O; p=0.17). Genioglossus muscle activity during stable non-REM sleep and responsiveness during airway narrowing was not different with temazepam and zopiclone versus placebo but, paradoxically, zolpidem increased median muscle responsiveness three-fold during airway narrowing (median -0.15 (interquartile range -1.01 to -0.04) versus -0.05 (-0.29 to -0.03)% maximum EMG per cmH₂O epiglottic pressure; p=0.03). The upper airway critical closing pressure did not change with any of the hypnotics.These doses of common hypnotics have differential effects on the respiratory arousal threshold but do not reduce upper airway muscle activity or alter airway collapsibility during sleep. Rather, muscle activity increases during airway narrowing with zolpidem.

Effects of Tiagabine on Slow Wave Sleep and Arousal Threshold in Patients With Obstructive Sleep Apnea

Introduction

Obstructive sleep apnea (OSA) severity is markedly reduced during slow-wave sleep (SWS) even in patients with a severe disease. The reason for this improvement is uncertain but likely relates to non-anatomical factors (i.e. reduced arousability, chemosensitivity, and increased dilator muscle activity). The anticonvulsant tiagabine produces a dose-dependent increase in SWS in subjects without OSA. This study aimed to test the hypothesis that tiagabine would reduce OSA severity by raising the overall arousal threshold during sleep.

Aims and Methods

After a baseline physiology night to assess patients' OSA phenotypic traits, a placebo-controlled, double-blind, crossover trial of tiagabine 12 mg administered before sleep was performed in 14 OSA patients. Under each condition, we assessed the effects on sleep and OSA severity using standard clinical polysomnography.

Results

Tiagabine increased slow-wave activity (SWA) of the electroencephalogram (1-4 Hz) compared to placebo (1.8 [0.4] vs. 2.0 [0.5] LogμV2, p = .04) but did not reduce OSA severity (apnea-hypopnea index [AHI] 41.5 [20.3] vs. 39.1 [16.5], p > .5). SWS duration (25 [20] vs. 26 [43] mins, p > .5) and arousal threshold (-26.5 [5.0] vs. -27.6 [5.1] cmH2O, p = .26) were also unchanged between nights.

Conclusions

Tiagabine modified sleep microstructure (increase in SWA) but did not change the duration of SWS, OSA severity, or arousal threshold in this group of OSA patients. Based on these findings, tiagabine should not be considered as a therapeutic option for OSA treatment.

Impact of concomitant medications on obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is characterized by repeated episodes of apnoea and hypopnoea during sleep. Little is known about the potential impact of therapy drugs on the underlying respiratory disorder. Any influence should be taken into account and appropriate action taken, including drug withdrawal if necessary. Here, we review drugs in terms of their possible impact on OSA; drugs which (1) may worsen OSA; (2) are unlikely to have an impact on OSA; (3) those for which data are scarce or contradictory; and (4) drugs with a potentially improving effect. The level of evidence is ranked according to three grades: A - randomized controlled trials (RCTs) with high statistical power; B - RCTs with lower power, non-randomized comparative studies and observational studies; C - retrospective studies and case reports. Our review enabled us to propose clinical recommendations. Briefly, agents worsening OSA or inducing weight gain, that must be avoided, are clearly identified. Drugs such as 'Z drugs' and sodium oxybate should be used with caution as the literature contains conflicting results. Finally, larger trials are needed to clarify the potential positive impact of certain drugs on OSA. In the meantime, some, such as diuretics or other antihypertensive medications, are helpful in reducing OSA-associated cardiovascular morbidity.

Zopiclone Increases the Arousal Threshold without Impairing Genioglossus Activity in Obstructive Sleep Apnea

STUDY OBJECTIVES

To determine the effects of the nonbenzodiazepine sedative zopiclone on the threshold to arousal with increasing respiratory effort and genioglossus muscle activity and to examine potential physiological factors mediating disparate effects of zopiclone on obstructive sleep apnea (OSA) severity between patients.

METHODS

Twelve patients with OSA (apnea-hypopnea index = 41 ± 8 events/h) were studied during 2 single night sleep studies conducted approximately 1 w apart after receiving 7.5 mg of zopiclone or placebo according to a double-blind, placebo-controlled, randomized, crossover design. The respiratory arousal threshold (epiglottic pressure immediately prior to arousal during naturally occurring respiratory events), genioglossus activity and its responsiveness to pharyngeal pressure during respiratory events, and markers of OSA severity were compared between conditions. Genioglossus movement patterns and upper airway anatomy were also assessed via magnetic resonance imaging in a subset of participants (n = 7) during wakefulness.

RESULTS

Zopiclone increased the respiratory arousal threshold versus placebo (-31.8 ± 5.6 versus -26.4 ± 4.6 cmH2O, P = 0.02) without impairing genioglossus muscle activity or its responsiveness to negative pharyngeal pressure during respiratory events (-0.56 ± 0.2 versus -0.44 ± 0.1 %max/-cmH2O, P = 0.48). There was substantial interindividual variability in the changes in OSA severity with zopiclone explained, at least in part, by differences in pathophysiological characteristics including body mass index, arousal threshold, and genioglossus movement patterns.

CONCLUSIONS

In a group of patients with predominantly severe OSA, zopiclone increased the arousal threshold without reducing genioglossus muscle activity or its responsiveness to negative pharyngeal pressure. These properties may be beneficial in some patients with OSA with certain pathophysiological characteristics but may worsen hypoxemia in others.

CLINICAL TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry, http://www.anzctr.org.au, trial ID: ACTRN12614000364673.

Obstructive sleep apnea, pain, and opioids: is the riddle solved?

PURPOSE OF REVIEW

Perioperative opioid-based pain management of patients suffering from obstructive sleep apnea (OSA) may present challenges because of concerns over severe ventilatory compromise. The interaction between intermittent hypoxia, sleep fragmentation, pain, and opioid responses in OSA, is complex and warrants a special focus of perioperative outcomes research.

RECENT FINDINGS

Life-threatening opioid-related respiratory events are rare. Epidemiologic evidence suggests that OSA together with other serious renal and heart disease, is among those conditions predisposing patients for opioid-induced ventilatory impairment (OIVI) in the postoperative period. Both intermittent hypoxia and sleep fragmentation, two distinct components of OSA, enhance pain. Intermittent hypoxia may also potentiate opioid analgesic effects. Activation of major inflammatory pathways may be responsible for the effects of sleep disruption and intermittent hypoxia on pain and opioid analgesia. Recent experimental evidence supports that these, seemingly contrasting, phenotypes of pain-increasing and opioid-enhancing effects of intermittent hypoxia, are not mutually exclusive. Although the effect of intermittent hypoxia on OIVI has not been elucidated, opioids worsen postoperative sleep-disordered breathing in OSA patients. A subset of these patients, characterized by decreased chemoreflex responsiveness and high arousal thresholds, might be at higher risk for OIVI.

SUMMARY

OSA may complicate opioid-based perioperative management of pain by altering both pain processing and sensitivity to opioid effect.

Effects of opioid, hypnotic and sedating medications on sleep-disordered breathing in adults with obstructive sleep apnoea

BACKGROUND

Obstructive sleep apnoea (OSA) is a common sleep disorder characterised by partial or complete upper airway occlusion during sleep, leading to intermittent cessation (apnoea) or reduction (hypopnoea) of airflow and dips in arterial oxygen saturation during sleep. Many patients with recognised and unrecognised OSA receive hypnotics, sedatives and opiates/opioids to treat conditions including pain, anxiety and difficulty sleeping. Concerns have been expressed that administration of these drugs to people with co-existing OSA may worsen OSA.

OBJECTIVES

To investigate whether administration of sedative and hypnotic drugs exacerbates the severity of OSA (as measured by the apnoea-hypopnoea index (AHI) or the 4% oxygen desaturation index (ODI)) in people with known OSA.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register (CAGR) of trials. The search was current as of March 2015.

SELECTION CRITERIA

Randomised, placebo-controlled trials including adult participants with confirmed OSA, where participants were randomly assigned to use opiates or opioids, sedatives, hypnotics or placebo. We included participants already using continuous positive airway pressure (CPAP) or a mandibular advancement device.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as recommended by The Cochrane Collaboration.

MAIN RESULTS

Fourteen studies examining the effects of 10 drugs and including a total of 293 participants contributed to this review. Trials were small, with only two trials, which used sodium oxybate, recruiting more than 40 participants, and all but three trials were of only one to three nights in duration. Most participants had mild to moderate OSA with a mean AHI of 11 to 25 events/h, and only two trials recruited patients with severe OSA. Two trials investigating the effects of ramelteon, a treatment option for insomnia, recruited adults over 60 years of age with OSA and concomitant insomnia.The drugs studied in this review included remifentanil (infusion) 0.75 mcg/kg/h, eszopiclone 3 mg, zolpidem 10 and 20 mg, brotizolam 0.25 mg, flurazepam 30 mg, nitrazepam 10 mg to 15 mg, temazepam 10 mg, triazolam 0.25 mg, ramelteon 8 mg and 16 mg and sodium oxybate 4.5 g and 9 g. We were unable to pool most of the data, with the exception of data for eszopiclone and ramelteon.None of the drugs in this review produced a significant increase in AHI or ODI. Two trials have shown a beneficial effect on OSA. One study showed that a single administration of eszopiclone 3 mg significantly decreased AHI compared with placebo (24 ± 4 vs 31 ± 5; P value < 0.05), and a second study of sodium oxybate 4.5 g showed a significant decrease in AHI compared with placebo (mean difference (MD) -7.41, 95% confidence interval (CI) -14.17 to -0.65; N = 48).Only four trials reported outcome data on ODI. No significant increase, in comparison with placebo, was shown with eszopiclone (21 (22 to 37) vs 28.0 (15 to 36); P value = NS), zolpidem (0.81 ± 0.29 vs 1.46 ± 0.53; P value = NS), flurazepam (18.6 ± 19 vs 19.6 ± 15.9; P value = NS) and temazepam (6.53 ± 9.4 vs 6.56 ± 8.3; P value = 0.98).A significant decrease in minimum nocturnal peripheral capillary oxygen saturation (SpO2) was observed with zolpidem 20 mg (76.8 vs 85.2; P value = 0.002), flurazepam 30 mg (81.7 vs 85.2; P value = 0.002), remifentanil infusion (MD -7.00, 95% CI -11.95 to -2.05) and triazolam 0.25 mg in both rapid eye movement (REM) and non-REM (NREM) sleep (MD -14.00, 95% CI -21.84 to -6.16; MD -10.20, 95% CI -16.08 to -4.32, respectively.One study investigated the effect of an opiate (remifentanil) on patients with moderate OSA. Remifentanil infusion did not significantly change AHI (MD 10.00, 95% CI -9.83 to 29.83); however it did significantly decrease the number of obstructive apnoeas (MD -9.00, 95% CI -17.40 to -0.60) and significantly increased the number of central apnoeas (MD 16.00, 95% CI -2.21 to 34.21). Similarly, although without significant effect on obstructive apnoeas, central apnoeas were increased in the sodium oxybate 9 g treatment group (MD 7.3 (18); P value = 0.005) in a cross-over trial.Drugs studied in this review were generally well tolerated, apart from adverse events reported in 19 study participants prescribed remifentanil (n = 1), eszopiclone (n = 6), sodium oxybate (n = 9) or ramelteon (n = 3).

AUTHORS' CONCLUSIONS

The findings of this review show that currently no evidence suggests that the pharmacological compounds assessed have a deleterious effect on the severity of OSA as measured by change in AHI or ODI. Significant clinical and statistical decreases in minimum overnight SpO2 were observed with remifentanil, zolpidem 20 mg and triazolam 0.25 mg. Eszopiclone 3 mg and sodium oxybate 4.5 g showed a beneficial effect on the severity of OSA with a reduction in AHI and may merit further assessment as a potential therapeutic option for a subgroup of patients with OSA. Only one trial assessed the effect of an opioid (remifentanil); some studies included CPAP treatment, whilst in a significant number of participants, previous treatment with CPAP was not stated and thus a residual treatment effect of CPAP could not be excluded. Most studies were small and of short duration, with indiscernible methodological quality.Caution is therefore required when such agents are prescribed for patients with OSA, especially outside the severity of the OSA cohorts and the corresponding dose of compounds given in the particular studies. Larger, longer trials involving patients across a broader spectrum of OSA severity are needed to clarify these results.

Clinical predictors of the respiratory arousal threshold in patients with obstructive sleep apnea

RATIONALE

A low respiratory arousal threshold (ArTH) is one of several traits involved in obstructive sleep apnea pathogenesis and may be a therapeutic target; however, there is no simple way to identify patients without invasive measurements.

OBJECTIVES

To determine the physiologic determinates of the ArTH and develop a clinical tool that can identify patients with low ArTH.

METHODS

Anthropometric data were collected in 146 participants who underwent overnight polysomnography with an epiglottic catheter to measure the ArTH (nadir epiglottic pressure before arousal). The ArTH was measured from up to 20 non-REM and REM respiratory events selected randomly. Multiple linear regression was used to determine the independent predictors of the ArTH. Logistic regression was used to develop a clinical scoring system.

MEASUREMENTS AND MAIN RESULTS

Nadir oxygen saturation as measured by pulse oximetry, apnea-hypopnea index, and the fraction of events that were hypopneas (Fhypopneas) were independent predictors of the ArTH (r(2) = 0.59; P < 0.001). Using this information, we used receiver operating characteristic analysis and logistic regression to develop a clinical score to predict a low ArTH, which allocated a score of 1 to each criterion that was satisfied: (apnea-hypopnea index, <30 events per hour) + (nadir oxygen saturation as measured by pulse oximetry >82.5%) + (Fhypopneas >58.3%). A score of 2 or above correctly predicted a low arousal threshold in 84.1% of participants with a sensitivity of 80.4% and a specificity of 88.0%, a finding that was confirmed using leave-one-out cross-validation analysis.

CONCLUSIONS

Our results demonstrate that individuals with a low ArTH can be identified from standard, clinically available variables. This finding could facilitate larger interventional studies targeting the ArTH.

Arousal from sleep does not lead to reduced dilator muscle activity or elevated upper airway resistance on return to sleep in healthy individuals

STUDY OBJECTIVES

To compare changes in end-tidal CO2, genioglossus muscle activity and upper airway resistance following tone-induced arousal and the return to sleep in healthy individuals with small and large ventilatory responses to arousal.

DESIGN

Observational study.

SETTING

Two sleep physiology laboratories.

PATIENTS OR PARTICIPANTS

35 men and 25 women with no medical or sleep disorders.

INTERVENTIONS

Auditory tones to induce 3-s to 15-s cortical arousals from sleep.

MEASUREMENTS AND RESULTS

During arousal from sleep, subjects with large ventilatory responses to arousal had higher ventilation (by analytical design) and tidal volume, and more marked reductions in the partial pressure of end-tidal CO2 compared to subjects with small ventilatory responses to arousal. However, following the return to sleep, ventilation, genioglossus muscle activity, and upper airway resistance did not differ between high and low ventilatory response groups (Breath 1 on return to sleep: ventilation 6.7±0.4 and 5.5±0.3 L/min, peak genioglossus activity 3.4%±1.0% and 4.8%±1.0% maximum, upper airway resistance 4.7±0.7 and 5.5±1.0 cm H2O/L/s, respectively). Furthermore, dilator muscle activity did not fall below the pre-arousal sleeping level and upper airway resistance did not rise above the pre-arousal sleeping level in either group for 10 breaths following the return to sleep.

CONCLUSIONS

Regardless of the magnitude of the ventilatory response to arousal from sleep and subsequent reduction in PETCO2, healthy individuals did not develop reduced dilator muscle activity nor increased upper airway resistance, indicative of partial airway collapse, on the return to sleep. These findings challenge the commonly stated notion that arousals predispose to upper airway obstruction.

Hidden in plain view: degeneracy in complex systems

Degeneracy is a word with two meanings. The popular usage of the word denotes deviance and decay. In scientific discourse, degeneracy refers to the idea that different pathways can lead to the same output. In the biological sciences, the concept of degeneracy has been ignored for a few key reasons. Firstly, the word "degenerate" in popular culture has negative, emotionally powerful associations that do not inspire scientists to consider its technical meaning. Secondly, the tendency of searching for single causes of natural and social phenomena means that scientists can overlook the multi-stranded relationships between cause and effect. Thirdly, degeneracy and redundancy are often confused with each other. Degeneracy refers to dissimilar structures that are functionally similar while redundancy refers to identical structures. Degeneracy can give rise to novelty in ways that redundancy cannot. From genetic codes to immunology, vaccinology and brain development, degeneracy is a crucial part of how complex systems maintain their functional integrity. This review article discusses how the scientific concept of degeneracy was imported into genetics from physics and was later introduced to immunology and neuroscience. Using examples of degeneracy in immunology, neuroscience and linguistics, we demonstrate that degeneracy is a useful way of understanding how complex systems function. Reviewing the history and theoretical scope of degeneracy allows its usefulness to be better appreciated, its coherency to be further developed, and its application to be more quickly realized.

Medication effects on sleep and breathing

Sleep respiration is regulated by circadian, endocrine, mechanical and chemical factors, and characterized by diminished ventilatory drive and changes in Pao2 and Paco2 thresholds. Hypoxemia and hypercapnia are more pronounced during rapid eye movement. Breathing is influenced by sleep stage and airway muscle tone. Patient factors include medical comorbidities and body habitus. Medications partially improve obstructive sleep apnea and stabilize periodic breathing at altitude. Potential adverse consequences of medications include precipitation or worsening of disorders. Risk factors for adverse medication effects include aging, medical disorders, and use of multiple medications that affect respiration.

Trazodone increases the respiratory arousal threshold in patients with obstructive sleep apnea and a low arousal threshold

STUDY OBJECTIVES

The effect of common sedatives on upper airway physiology and breathing during sleep in obstructive sleep apnea (OSA) has been minimally studied. Conceptually, certain sedatives may worsen OSA in some patients. However, sleep and breathing could improve with certain sedatives in patients with OSA with a low respiratory arousal threshold. This study aimed to test the hypothesis that trazodone increases the respiratory arousal threshold in patients with OSA and a low arousal threshold. Secondary aims were to examine the effects of trazodone on upper airway dilator muscle activity, upper airway collapsibility, and breathing during sleep.

DESIGN

Patients were studied on 4 separate nights according to a within-subjects cross-over design.

SETTING

Sleep physiology laboratory.

PATIENTS

Seven patients with OSA and a low respiratory arousal threshold.

INTERVENTIONS

In-laboratory polysomnograms were obtained at baseline and after 100 mg of trazodone was administered, followed by detailed overnight physiology experiments under the same conditions. During physiology studies, continuous positive airway pressure was transiently lowered to measure arousal threshold (negative epiglottic pressure prior to arousal), dilator muscle activity (genioglossus and tensor palatini), and upper airway collapsibility (Pcrit).

MEASUREMENTS AND RESULTS

Trazodone increased the respiratory arousal threshold by 32 ± 6% (-11.5 ± 1.4 versus -15.3 ± 2.2 cmH2O, P < 0.01) but did not alter the apnea-hypopnea index (39 ± 12 versus 39 ± 11 events/h sleep, P = 0.94). Dilator muscle activity and Pcrit also did not systematically change with trazodone.

CONCLUSIONS

Trazodone increases the respiratory arousal threshold in patients with obstructive sleep apnea and a low arousal threshold without major impairment in dilator muscle activity or upper airway collapsibility. However, the magnitude of change in arousal threshold was insufficient to overcome the compromised upper airway anatomy in these patients.

Physiology in medicine: obstructive sleep apnea pathogenesis and treatment--considerations beyond airway anatomy

We review evidence in support of significant contributions to the pathogenesis of obstructive sleep apnea (OSA) from pathophysiological factors beyond the well-accepted importance of airway anatomy. Emphasis is placed on contributions from neurochemical control of central respiratory motor output through its effects on output stability, upper airway dilator muscle activation, and arousability. In turn, we consider the evidence demonstrating effective treatment of OSA via approaches that address each of these pathophysiologic risk factors. Finally, a case is made for combining treatments aimed at both anatomical and ventilatory control system deficiencies and for individualizing treatment to address a patient's own specific risk factors.

Blockade of Na+/H+ exchanger type 3 causes intracellular acidification and hyperexcitability via inhibition of pH-sensitive K+ channels in chemosensitive respiratory neurons of the dorsal vagal nucleus in rats

Extracellular pH (pHe) and intracellular pH (pHi) are important factors for the excitability of chemosensitive central respiratory neurons that play an important role in respiration and obstructive sleep apnea. It has been proposed that inhibition of central Na(+)/H(+) exchanger 3 (NHE-3), a key pHi regulator in the brainstem, decreases the pHi, leading to membrane depolarization for the maintenance of respiration. However, how intracellular pH affects the neuronal excitability of respiratory neurons remains largely unknown. In this study, we showed that NHE-3 mRNA is widely distributed in respiration-related neurons of the rat brainstem, including the dorsal vagal nucleus (DVN). Whole-cell patch clamp recordings from DVN neurons in brain slices revealed that the standing outward current (Iso) through pH-sensitive K(+) channels was inhibited in the presence of the specific NHE-3 inhibitor AVE0657 that decreased the pHi. Exposure of DVN neurons to an acidified pHe and AVE0657 (5 μmol/L) resulted in a stronger effect on firing rate and Iso than acidified pHe alone. Taken together, our results showed that intracellular acidification by blocking NHE-3 results in inhibition of a pH-sensitive K(+) current, leading to synergistic excitation of chemosensitive DVN neurons for the regulation of respiration.

Arousal from sleep: implications for obstructive sleep apnea pathogenesis and treatment

Historically, brief awakenings from sleep (cortical arousals) have been assumed to be vitally important in restoring airflow and blood-gas disturbances at the end of obstructive sleep apnea (OSA) breathing events. Indeed, in patients with blunted chemical drive (e.g., obesity hypoventilation syndrome) and in instances when other defensive mechanisms fail, cortical arousal likely serves an important protective role. However, recent insight into the pathogenesis of OSA indicates that a substantial proportion of respiratory events do not terminate with a cortical arousal from sleep. In many cases, cortical arousals may actually perpetuate blood-gas disturbances, breathing instability, and subsequent upper airway closure during sleep. This brief review summarizes the current understanding of the mechanisms mediating respiratory-induced cortical arousal, the physiological factors that influence the propensity for cortical arousal, and the potential dual roles that cortical arousal may play in OSA pathogenesis. Finally, the extent to which existing sedative agents decrease the propensity for cortical arousal and their potential to be therapeutically beneficial for certain OSA patients are highlighted.

Drug effects on ventilatory control and upper airway physiology related to sleep apnea

Understanding the inter-relationship between pharmacological agents, ventilatory control, upper airway physiology and their consequent effects on sleep-disordered breathing may provide new directions for targeted drug therapy. Where available, this review focuses on human studies that contain both drug effects on sleep-disordered breathing and measures of ventilatory control or upper airway physiology. Many of the existing studies are limited in sample size or comprehensive methodology. At times, the presence of paradoxical findings highlights the complexity of drug therapy for OSA. The existing studies also highlight the importance of considering inter-individual pharmacokinetics and underlying causes of sleep apnea in interpreting drug effects on sleep-disordered breathing. Practical ways to assess an individual's ventilatory control and how it interacts with upper airway physiology is required for future targeted pharmacotherapy in sleep apnea.

The effects of testosterone on ventilatory responses in men with obstructive sleep apnea: a randomised, placebo-controlled trial

We recently showed that testosterone therapy worsens sleep-disordered breathing at 6-7 weeks, but not after 18 weeks, in men with obstructive sleep apnea. Changes in ventilatory chemoreflexes may be responsible. The effect of testosterone on ventilatory chemoreflexes in men with obstructive sleep apnea has not been systematically studied before. Twenty-one obese men with obstructive sleep apnea, a subgroup of our recent report, were randomised in an 18-week, randomised, double-blind, placebo-controlled, parallel group trial to three intramuscular injections (0, 6, 12 weeks) of either 1000 mg testosterone undecanoate (n = 10) or placebo (n = 11). Awake ventilatory chemoreflex testing was performed before (week 0), during (week 6) and at the end of treatment (week 18) to determine the ventilatory carbon dioxide recruitment threshold and chemosensitivity. Sleep and breathing was assessed by overnight polysomnography at 0, 7 and 18 weeks. Serum hormones levels were measured at every visit. A significant increase in blood testosterone levels (5.65 nmol L(-1) , 0.51-10.8 nmol L(-1) , P = 0.03) and lean muscle mass (2.36 kg, 0.8-3.9 kg, P = 0.007) between the two groups was observed as expected. No significant differences were seen in ventilatory chemoreflexes between the two groups at 6 weeks or at 18 weeks. However, positive correlations were observed between changes in serum testosterone and hyperoxic ventilatory recruitment threshold (r = 0.55, P = 0.03), and between changes in hyperoxic ventilatory recruitment threshold and time spent with oxygen saturations during sleep <90% (r = 0.57, P = 0.03) at 6-7 weeks, but not at 18 weeks. Time-dependent alterations in ventilatory recruitment threshold may therefore mediate the time-dependent changes in sleep breathing observed with testosterone.