Sleep-related hypoventilation/hypoxemic syndromes

Pathophysiology of Chronic Hypercapnic Respiratory Failure

Chronic hypercapnic respiratory failure occurs in several conditions associated with hypoventilation. The mechanisms underlying the development of chronic hypercapnia include a combination of processes that increase metabolic CO2 production, reduce minute ventilation (V'e), or increase dead space fraction (Vd/Vt). Fundamental to the pathophysiology is a mismatch between increased load and a reduction in the capacity of the respiratory pump to compensate. Though neural respiratory drive may be decreased in a subset of central hypoventilation disorders, it is more commonly increased in attempting to maintain the load-capacity homeostatic balance.

Exploring the causal effects of sleep characteristics on TMD-related pain: a two-sample Mendelian randomization study

OBJECTIVES

The study was to explore the causal effects of sleep characteristics on temporomandibular disorder (TMD)-related pain using Mendelian randomization (MR) analysis.

MATERIALS AND METHODS

Five sleep characteristics (short sleep, insomnia, chronotype, snoring, sleep apnea) were designated as exposure factors. Data were obtained from previous publicized genome-wide association studies and single nucleotide polymorphisms (SNPs) strongly associated with them were utilized as instrumental variables (IVs). TMD-related pain was designed as outcome variable and sourced from the FinnGens database. MR analysis was employed to explore the causal effects of the five sleep characteristics on TMD-related pain. The causal effect was analyzed using the inverse variance-weighted (IVW), weighted median, and MR-Egger methods. Subsequently, sensitivity analyses were conducted using Cochran's Q tests, funnel plots, leave-one-out analyses, and MR-Egger intercept tests.

RESULTS

A causal effect of short sleep on TMD-related pain was revealed by IVW (OR: 1.60, 95% CI: 1.06-2.41, P = 0.026). No causal relationship was identified between other sleep characteristics (insomnia, chronotype, snoring, sleep apnea) and TMD-related pain.

CONCLUSIONS

Our study suggests that short sleep may increase the risk of TMD-related pain, while there was no causal relationship between other sleep characteristics and TMD-related pain. Further studies are warranted to deepen and definitively clarify their relationship.

CLINICAL RELEVANCE

These findings reveal that the short sleep may be a risk factor of TMD-related pain and highlight the potential therapeutical effect of extending sleep time on alleviating TMD-related pain.

Association between sleep-disordered breathing and periodontal diseases: A systematic review protocol

Background

Sleep-disordered breathing (SDB) is a chronic sleep-related breathing disorder, considered associated with increased risk of cardiovascular disorders, metabolic disorders, cognitive dysfunction and behavior changes. Periodontal diseases are chronic infectious diseases that are also believed to be associated with cardiovascular diseases, metabolic syndrome and cognitive dysfunction. Several studies have indicated that SDB may be associated with periodontal diseases through certain mechanisms such as inflammation response, oxidative stress and oral dryness. The aim of this systematic review is to explore the association between SDB and periodontal diseases in an integrated approach.

Materials and Methods

This systematic review will include cohort studies, cross-sectional studies and case-control studies that are identified by electronic and manual searches. Electronic searches will be conducted in the following databases: PubMed, Embase, Scopus and Web of Science. Our search will cover articles published from inception of databases to March 2022 without restrictions in language and settings. Pre-determined eligibility criteria include: participants (participants without a history of respiratory diseases, history of periodontal treatment within the past 6 months and history of medication that is known to influence SDB or periodontal diseases); exposure (participants who have been diagnosed with SDB or at high-risk for SDB); comparison (participants without SDB); and outcome (periodontal parameters, such as probing depth, clinical attachment level, bleeding on probing, radiographic bone loss). Two authors will perform study screening and data extraction independently and in duplicate. All discrepancies will be solved by discussion. The methodological quality of included studies will be assessed using the Newcastle-Ottawa Scale.

Discussion

This systematic review will summarize the existing evidence on the association between SDB and periodontal diseases, a topic of controversy and clinical significance. Its findings can provide evidence for the development of relevant prevention and treatment strategies. The results will be disseminated through peer-reviewed journals.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier: CRD42022313024. Registered on March 28th 2022.

Verification for Diagnosis of Sleep-Related Hypoventilation and Carbon Dioxide Partial Pressure During Sleep in Children Using End-Tidal Carbon Dioxide

Background and Objective From the past, several researchers have studied and measured the partial pressure of carbon dioxide during sleep in normal children to establish diagnostic criteria for hypoventilation in children. Here we tried to verify the existing definition of sleep-related hypoventilation in Asian by evaluating and analyzing the carbon dioxide partial pressure in pediatric subjects who underwent polysomnography.Methods We retrospectively analyzed clinical information of 196 children who underwent polysomnography at our hospital from Feb 2011 to Apr 2021. Among Asian pediatric subjects, those with serious chronic or genetic diseases, craniofacial deformities, and hypoventilation confirmed by polysomnography were excluded. We evaluated partial pressure of carbon dioxide in target group by end-tidal carbon dioxide (EtCO2) measured with a stream capnometer through nasal cannula. The target group was classified by apnea-hypopnea index and analyzed.Results The mean value of the time with EtCO₂ ≥ 45 mm Hg in total sleep time was 47.00% which is higher than previous studies. The mean value of the time with EtCO₂ ≥ 50 mm Hg in total sleep time was 2.77% which is similar to previous studies. Also, our subjects showed the highest mean EtCO₂ value in non-rapid eye movement (NREM) stage and lowest mean EtCO₂ value when wake.Conclusions In this study, the diagnostic criteria for sleep-related hypoventilation at the American Academy of Sleep Medicine (AASM) in 2017 established by measuring the EtCO₂ in western children seems appropriate to apply to Asian children to define hypoventilation.

Obesity Hypoventilation Syndrome-Related Challenges in Acute Respiratory Failure

Obesity hypoventilation syndrome (OHS) is a condition commonly found in severely obese patients in which they fail to breathe deeply or rapidly enough to offset the body's need for oxygen consumption and carbon dioxide release. This report presents a case of a 49-year-old super-super-morbid obese female with a body mass index (BMI) of 90 kilogram per meter squared (kg/m²), chronic obstructive pulmonary disease (COPD), and end-stage cor pulmonale, who was brought to the emergency department for altered mental status and requiring emergent airway due to respiratory failure secondary to OHS. The continued increase in rates of obesity worldwide, especially in those with BMI ≥ 50 kg/m², may lead to an increase in the incidence of OHS. With comorbidities secondary to obesity and associated complexity, this medically challenging case emphasizes the need for refined management strategies in caring for OHS in super-super-morbidly obese patients.

Acute Altitude Acclimatization in Young Healthy Volunteers: Nocturnal Oxygenation Increases Over Time, Whereas Periodic Breathing Persists

Ju, Jia-Der, Cristian Zhang, Francis P. Sgambati, Lidia M. Lopez, Luu V. Pham, Alan R. Schwartz, and Roberto A. Accinelli. Acute altitude acclimatization in young healthy volunteers: nocturnal oxygenation increases over time whereas periodic breathing persists. High Alt Med Biol. 22:14-23, 2021. Study Objectives: This study aimed to examine the acute effects of high altitude (HA) on sleep disordered breathing (sleep apnea and nocturnal hypoxemia) and acute mountain sickness and to characterize acclimatization over time. Methods: Ten native lowlanders residing at sea level (SL) completed the Lake Louise Score (LLS) and underwent nocturnal polygraphy (ApneaLink Plus) for nine consecutive nights (N1-N9) at HA (2,761 m) and two nights before and after HA. Nocturnal oxygen profiles were assessed by measuring the mean nocturnal oxyhemoglobin saturation (S_pO₂) during sleep, and sleep apnea severity as assessed by measuring the Apnea-Hypopnea Index (AHI). Mixed-effects linear regression was used to model responses in outcomes (mean nocturnal S_pO₂, logAHI, and LLS) between HA and SL. Changes in S_pO₂ and AHI were examined in subgroups with mild versus marked nocturnal S_pO₂ and low versus high AHI during exposure to HA and compared between subgroups. Results: Compared with SL, the mean nocturnal S_pO₂ was lower (p < 0.0001) and AHI was higher (p < 0.0001) at HA. The mean nocturnal S_pO₂ increased progressively (p < 0.001), whereas AHI remained high (p < 0.978) and relatively unchanged over nine successive nights at HA. Those with markedly reduced S_pO₂ upon arrival at HA exhibited progressive increases in the mean nocturnal S_pO₂ over time at HA compared with those with mild nocturnal desaturation. LLS rose at HA, but no differences were observed between subgroups. Conclusions: In healthy HA sojourners, the mean nocturnal S_pO₂ increased progressively over time, whereas AHI remained elevated, suggesting distinctive phenotypes and acclimatization responses to HA.

Sleep-related breathing disorders and pulmonary hypertension

Sleep-related breathing disorders (SBDs) include obstructive apnoea, central apnoea and sleep-related hypoventilation. These nocturnal events have the potential to increase pulmonary arterial pressure (PAP) during sleep but also in the waking state. "Pure" obstructive sleep apnoea syndrome (OSAS) is responsible for a small increase in PAP whose clinical impact has not been demonstrated. By contrast, in obesity hypoventilation syndrome (OHS) or overlap syndrome (the association of chronic obstructive pulmonary disease (COPD) with obstructive sleep apnoea (OSA)), nocturnal respiratory events contribute to the development of pulmonary hypertension (PH), which is often severe. In the latter circumstances, treatment of SBDs is essential in order to improve pulmonary haemodynamics.Patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) are at risk of developing SBDs. Obstructive and central apnoea, as well as a worsening of ventilation-perfusion mismatch, can be observed during sleep. There should be a strong suspicion of SBDs in such a patient population; however, the precise indications for sleep studies and the type of recording remain to be specified. The diagnosis of OSAS in patients with PAH or CTEPH should encourage treatment with continuous positive airway pressure (CPAP). The presence of isolated nocturnal hypoxaemia should also prompt the initiation of long-term oxygen therapy. These treatments are likely to avoid worsening of PH; however, it is prudent not to treat central apnoea and Cheyne-Stokes respiration (CSR) with adaptive servo-ventilation in patients with chronic right-heart failure because of a potential risk of serious adverse effects from such treatment.In this review we will consider the current knowledge of the consequences of SBDs on pulmonary haemodynamics in patients with and without chronic respiratory disease (group 3 of the clinical classification of PH) and the effect of treatments of respiratory events during sleep on PH. The prevalence and consequences of SBDs in PAH and CTEPH (groups 1 and 4 of the clinical classification of PH, respectively), as well as therapeutic options, will also be discussed.

Using Lempel-Ziv complexity as effective classification tool of the sleep-related breathing disorders

BACKGROUND AND OBJECTIVE

People suffer from sleep disorders caused by work-related stress, irregular lifestyle or mental health problems. Therefore, development of effective tools to diagnose sleep disorders is important. Recently, to analyze biomedical signals Information Theory is exploited. We propose efficient classification method of sleep anomalies by applying entropy estimating algorithms to encoded ECGs signals coming from patients suffering from Sleep-Related Breathing Disorders (SRBD).

METHODS

First, ECGs were discretized using the encoding method which captures the biosignals variability. It takes into account oscillations of ECG measurements around signals averages. Next, to estimate entropy of encoded signals Lempel-Ziv complexity algorithm (LZ) which measures patterns generation rate was applied. Then, optimal encoding parameters, which allow distinguishing normal versus abnormal events during sleep with high sensitivity and specificity were determined numerically. Simultaneously, subjects' states were identified using acoustic signal of breathing recorded in the same period during sleep.

RESULTS

Random sequences show normalized LZ close to 1 while for more regular sequences it is closer to 0. Our calculations show that SRBDs have normalized LZ around 0.32 (on average), while control group has complexity around 0.85. The results obtained to public database are similar, i.e. LZ for SRBDs around 0.48 and for control group 0.7. These show that signals within the control group are more random whereas for the SRBD group ECGs are more deterministic. This finding remained valid for both signals acquired during the whole duration of experiment, and when shorter time intervals were considered. Proposed classifier provided sleep disorders diagnostics with a sensitivity of 93.75 and specificity of 73.00%. To validate our method we have considered also different variants as a training and as testing sets. In all cases, the optimal encoding parameter, sensitivity and specificity values were similar to our results above.

CONCLUSIONS

Our pilot study suggests that LZ based algorithm could be used as a clinical tool to classify sleep disorders since the LZ complexities for SRBD positives versus healthy individuals show a significant difference. Moreover, normalized LZ complexity changes are related to the snoring level. This study also indicates that LZ technique is able to detect sleep abnormalities in early disorders stage.

Sleep Disordered Breathing in Duchenne Muscular Dystrophy

This review aims to explain the inevitable imbalance between respiratory load, drive, and muscular force that occurs in the natural aging of Duchenne muscular dystrophy and that predisposes these patients to sleep disordered breathing (SDB). In DMD, SDB is characterized by oxygen desaturation, apneas, hypercapnia, and hypoventilation during sleep and ultimately develops into respiratory failure during wakefulness. It can be present in all age groups. Young patients risk obstructive apneas because of weight gain, secondary to progressive physical inactivity and prolonged corticosteroid therapy; older patients hypoventilate and desaturate because of respiratory muscle weakness, in particular the diaphragm. These conditions are further exacerbated during REM sleep, the phase of maximal muscle hypotonia during which the diaphragm has to provide most of the ventilation. Evidence is given to the daytime predictors of early symptoms of SDB, important indicators for the proper time to initiate mechanical ventilation.

Effect of Antihypertensive Medications on the Severity of Obstructive Sleep Apnea: A Systematic Review and Meta-Analysis

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is an independent risk factor for hypertension (HTN). Increasing evidence from animal and human studies suggests that HTN exacerbates OSA. We performed a systematic review and meta-analysis of studies evaluating the effect of anti-hypertensive medications on the severity of OSA.

METHODS

A literature search of PubMed and Embase was done using search concepts of OSA, HTN, and drug classes used to treat HTN. Studies that reported changes in the severity of OSA objectively by using apnea-hypopnea index (AHI) or respiratory disturbance index (RDI) were included. Pooled mean difference estimates were calculated. Tests for heterogeneity, publication bias, and subgroup sensitivity analysis were conducted.

RESULTS

Of 27,376 studies screened, only 11 met inclusion criteria, including 5 randomized controlled trials and 6 single-arm prospective trials. The pooled mean difference estimate (95% confidence interval [CI]), based on a random-effects model, was -5.69 (95% CI -10.74 to -0.65), consistent with an overall decrease in AHI or RDI attributable to antihypertensive medications. The effect size was even more pronounced, -14.52 (95% CI -25.65 to -3.39), when only studies using diuretics were analyzed. There was no significant heterogeneity or publication bias among the studies. Meta-regression indicated neither age, baseline AHI, nor change in systolic/diastolic blood pressure influenced the results.

CONCLUSIONS

Collectively, findings from these relatively small, short-term studies tend to support the contention that treatment with antihypertensive agents confers a statistically significant, albeit small, reduction in the severity of OSA, which may be more pronounced with the use of diuretics.

Sleep and respiratory physiology in adults

Respiration during sleep is determined by metabolic demand; respiratory drive is determined by a central respiratory generator. Changes in pharyngeal dilator muscle tone resulting in increased upper airway resistance and collapsibility contribute to hypoventilation. Relative hypotonia of respiratory muscles, body posture changes, and altered ventilatory control result in additional physiologic changes contributing to hypoventilation. This article reviews mechanisms of central control of respiration and normal upper and lower airway physiology. Understanding sleep-related changes in respiratory physiology will help in developing new therapies to prevent hypoventilation in susceptible populations.

A critical assessment of monitoring practices, patient deterioration, and alarm fatigue on inpatient wards: a review

Approximately forty million surgeries take place annually in the United States, many of them requiring overnight or lengthier post operative stays in the over five thousand hospitals that comprise our acute healthcare system. Leading up to this Century, it was common for most hospitalized patients and their families to believe that being surrounded by well-trained nurses and physicians assured their safety. That bubble burst with the Institute of Medicine's 1999 report: To Err Is Human, followed closely by its 2001 report: Crossing the Quality Chasm. This review article discusses unexpected, potentially lethal respiratory complications known for being difficult to detect early, especially in postoperative patients recovering on hospital general care floors (GCF). We have designed our physiologic explanations and simplified cognitive framework to give our front line clinical nurses a thorough, easy-to-recall understanding of just how these events evolve, and how to detect them early when most amenable to treatment. Our review will also discuss currently available practices in general care floor monitoring that can both improve patient safety and significantly reduce monitor associated alarm fatigue.

Sleep-induced hypoxaemia in patients with chronic obstructive pulmonary disease

Patients with moderate or severe chronic obstructive pulmonary disease run a high risk of developing sleep-induced hypoxaemia, because of alveolar hypoventilation and ventilation-perfusion mismatch. This article looks at the prevalence, significance and treatment of sleep-induced hypoxaemia in chronic obstructive pulmonary disease.

Respiratory mechanics and ventilatory control in overlap syndrome and obesity hypoventilation

The overlap syndrome of obstructive sleep apnoea (OSA) and chronic obstructive pulmonary disease (COPD), in addition to obesity hypoventilation syndrome, represents growing health concerns, owing to the worldwide COPD and obesity epidemics and related co-morbidities. These disorders constitute the end points of a spectrum with distinct yet interrelated mechanisms that lead to a considerable health burden. The coexistence OSA and COPD seems to occur by chance, but the combination can contribute to worsened symptoms and oxygen desaturation at night, leading to disrupted sleep architecture and decreased sleep quality. Alveolar hypoventilation, ventilation-perfusion mismatch and intermittent hypercapnic events resulting from apneas and hypopneas contribute to the final clinical picture, which is quite different from the “usual” COPD. Obesity hypoventilation has emerged as a relatively common cause of chronic hypercapnic respiratory failure. Its pathophysiology results from complex interactions, among which are respiratory mechanics, ventilatory control, sleep-disordered breathing and neurohormonal disturbances, such as leptin resistance, each of which contributes to varying degrees in individual patients to the development of obesity hypoventilation. This respiratory embarrassment takes place when compensatory mechanisms like increased drive cannot be maintained or become overwhelmed.

Although a unifying concept for the pathogenesis of both disorders is lacking, it seems that these patients are in a vicious cycle. This review outlines the major pathophysiological mechanisms believed to contribute to the development of these specific clinical entities. Knowledge of shared mechanisms in the overlap syndrome and obesity hypoventilation may help to identify these patients and guide therapy.

Simultaneous occurrence of chronic obstructive pulmonary disease and obstructive sleep apnea: the overlap syndrome

Obstructive sleep apnea syndrome is a common disorder in adults associated with several cardiovascular diseases and impaired quality of life. Chronic obstructive pulmonary disease is also a common clinical condition in middle-aged adults. The combination of these two conditions can eventuate a severe combined sleep-related breathing disorder. It is important to recognize coexisting sleep apnea in patients with chronic obstructive pulmonary disease in time and to treat it appropriately. Orv. Hetil., 2012, 153, 892–897.

Acute cardiopulmonary failure from sleep-disordered breathing

Sleep-disordered breathing (SDB) comprises a diverse set of disorders marked by abnormal respiration during sleep. Clinicians should realize that SDB may present as acute cardiopulmonary failure in susceptible patients. In this review, we discuss three clinical phenotypes of acute cardiopulmonary failure from SDB: acute ventilatory failure, acute congestive heart failure, and sudden death. We review the pathophysiologic mechanisms and recommend general principles for management. Timely recognition of, and therapy for, SDB in the setting of acute cardiopulmonary failure may improve short- and long-term outcomes.

Patterns of unexpected in-hospital deaths: a root cause analysis

BACKGROUND

Respiratory alarm monitoring and rapid response team alerts on hospital general floors are based on detection of simple numeric threshold breaches. Although some uncontrolled observation trials in select patient populations have been encouraging, randomized controlled trials suggest that this simplistic approach may not reduce the unexpected death rate in this complex environment. The purpose of this review is to examine the history and scientific basis for threshold alarms and to compare thresholds with the actual pathophysiologic patterns of evolving death which must be timely detected.

METHODS

The Pubmed database was searched for articles relating to methods for triggering rapid response teams and respiratory alarms and these were contrasted with the fundamental timed pathophysiologic patterns of death which evolve due to sepsis, congestive heart failure, pulmonary embolism, hypoventilation, narcotic overdose, and sleep apnea.

RESULTS

In contrast to the simplicity of the numeric threshold breach method of generating alerts, the actual patterns of evolving death are complex and do not share common features until near death. On hospital general floors, unexpected clinical instability leading to death often progresses along three distinct patterns which can be designated as Types I, II and III. Type I is a pattern comprised of hyperventilation compensated respiratory failure typical of congestive heart failure and sepsis. Here, early hyperventilation and respiratory alkalosis can conceal the onset of instability. Type II is the pattern of classic CO2 narcosis. Type III occurs only during sleep and is a pattern of ventilation and SPO2 cycling caused by instability of ventilation and/or upper airway control followed by precipitous and fatal oxygen desaturation if arousal failure is induced by narcotics and/or sedation.

CONCLUSION

The traditional threshold breach method of detecting instability on hospital wards was not scientifically derived; explaining the failure of threshold based monitoring and rapid response team activation in randomized trials. Furthermore, the thresholds themselves are arbitrary and capricious. There are three common fundamental pathophysiologic patterns of unexpected hospital death. These patterns are too complex for early detection by any unifying numeric threshold. New methods and technologies which detect and identify the actual patterns of evolving death should be investigated.

The effects of sleep hypoxia on coagulant factors and hepatic inflammation in emphysematous rats

Objectives

To develop a sleep hypoxia (SH) in emphysema (SHE) rat model and to explore whether SHE results in more severe hepatic inflammation than emphysema alone and whether the inflammation changes levels of coagulant/anticoagulant factors synthesized in the liver.

Methods

Seventy-five rats were put into 5 groups: SH control (SHCtrl), treated with sham smoke exposure (16 weeks) and SH exposure (12.5% O₂, 3 h/d, latter 8 weeks); emphysema control (ECtrl), smoke exposure and sham SH exposure (21% O₂); short SHE (SHEShort), smoke exposure and short SH exposure (1.5 h/d); mild SHE (SHEMild), smoke exposure and mild SH exposure (15% O₂); standard SHE (SHEStand), smoke exposure and SH exposure. Therefore, ECtrl, SHEShort, SHEMild and SHEStand group were among emphysematous groups. Arterial blood gas (ABG) data was obtained during preliminary tests. After exposure, hepatic inflammation (interleukin -6 [IL-6] mRNA and protein, tumor necrosis factor α [TNFα] mRNA and protein) and liver coagulant/anticoagulant factors (antithrombin [AT], fibrinogen [FIB] and Factor VIII [F VIII]) were evaluated. SPSS 11.5 software was used for statistical analysis.

Results

Characteristics of emphysema were obvious in emphysematous groups and ABGs reached SH criteria on hypoxia exposure. Hepatic inflammation parameters and coagulant factors are the lowest in SHCtrl and the highest in SHEStand while AT is the highest in SHCtrl and the lowest in SHEStand. Inflammatory cytokines of liver correlate well with coagulant factors positively and with AT negatively.

Conclusions

When SH is combined with emphysema, hepatic inflammation and coagulability enhance each other synergistically and produce a more significant liver-derivative inflammatory and prothrombotic status.

Hyperinflation is associated with lower sleep efficiency in COPD with co-existent obstructive sleep apnea

Prior research has shown that individuals with obstructive lung disease are at risk for sleep fragmentation and poor sleep quality. We postulated that patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (known as overlap syndrome) who have more severe lung disease, as measured by lung hyperinflation (inspiratory capacity/total lung capacity), would have greater sleep disturbances independent of traditional measures of sleep apnea. We performed a retrospective chart review of consecutive patients evaluated and treated in an academic pulmonary clinic for overlap syndrome. Pulmonary function tests and polysomnogram data were collected. Thirty patients with overlap syndrome were included in the analysis. We found significant univariable associations between sleep efficiency and apnea/hypopnea index (beta = -0.285, p = 0.01) and between sleep efficiency and lung hyperinflation (beta = 0.654, p = 0.03). Using multivariable linear regression, the relationship between sleep efficiency and lung hyperinflation remained significant (beta = 1.13, p = 0.02) after adjusting for age, sex, body mass index, apnea/hypopnea index, FEV(1)% predicted, oxygen saturation nadir, medications, and cardiac disease. We conclude that increased severity of hyperinflation is associated with worse sleep efficiency, independent of apnea and nocturnal hypoxemia. The mechanisms underlying this observation are uncertain. We speculate that therapies aimed at reducing lung hyperinflation may improve sleep quality in patients with overlap syndrome.

Potential therapeutic targets in obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is a disease of ever-increasing importance due to its association with multiple impairments and rising prevalence in an increasingly susceptible demographic. The syndrome is linked with loud snoring, disrupted sleep and observed apnoeas. Serious co-morbidities associated with OSA appear to be reversed by continuous positive airway pressure (CPAP) treatment; however, CPAP is variably tolerated leaving many patients untreated and emphasising the need for alternative treatments. Virtually all OSA patients have airways that are anatomically vulnerable to collapse, but numerous pathophysiological factors underlie when and how OSA is manifested. This review describes how the complexity of OSA requires multiple treatment approaches that are individually targeted. This approach may take the form of more specific diagnoses in terms of the mechanisms underlying OSA as well as rational pharmacological treatment directed toward such disparate ends as arousal threshold and ventilatory control/chemosensitivity, and mechanical treatment in the form of surgery and augmentation of lung volumes.

Nocturnal hypoxia and arterial lactate levels in sleep-related breathing disorders

BACKGROUND

Lactate may be useful in pointing out the higher risk subgroups in sleep-related breathing disorders (SRBD) with various patterns of hypoxemia. We aimed to search whether morning and night lactate levels are related to apnea-hypopnea, hypoventilation, and hypoxemia in patients with SRBD and to compare it with patients without SRBD (No-SRBD).

METHODS

Eighty patients with suspected SRBD underwent polysomnography (PSG) testing. SRBD patients had obstructive sleep apnea syndrome with or without sleep-related hypoventilation/hypoxemic conditions. Patients without SRBD were in the control group. Measurements included pulmonary function testing, PSG, analysis of arterial blood gases, and arterial lactate before and after PSG. Arterial lactate was compared with SRBD and No-SRBD patients.

RESULTS

Morning lactate was significantly higher in the SRBD group than the No-SRBD group (1.65 +/- 0.48 and 1.35 +/- 0.57 mmol/L, respectively) (P = 0.003). Lactate levels at night and the change overnight in lactate levels were not significantly different between groups. After an adjustment for age, gender, and body mass index, lactate levels before PSG were related to the apnea-hypopnea index (beta: 0.004, 95% CI: 0.000-0.008) and the rate of sleep-time spent under 90% oxygen saturation (T90%). The following morning lactate level was correlated with the T90% (beta: 0.005, 95% CI: 0.000-0.010). After an adjustment for lactate levels before PSG, lactate in the morning was correlated with T90% (beta: 0.004, 95% CI: 0.000-0.008).

CONCLUSION

As a marker of tissue hypoxia, arterial lactate may be used to assess the severity of SRBD.

Upper airway mechanics

This review discusses the pathophysiological aspects of sleep-disordered breathing, with focus on upper airway mechanics in obstructive and central sleep apnoea, Cheyne-Stokes respiration and obesity hypoventilation syndrome. These disorders constitute the end points of a spectrum with distinct yet interrelated mechanisms that lead to substantial pathology, i.e. increased upper airway collapsibility, control of breathing instability, increased work of breathing, disturbed ventilatory system mechanics and neurohormonal changes. Concepts are changing. Although sleep apnoea is considered more and more to be an increased loop gain disorder, the central type of apnoea is now considered as an obstructive event, because it causes pharyngeal narrowing, associated with prolonged expiration. Although a unifying concept for the pathogenesis is lacking, it seems that these patients are in a vicious circle. Knowledge of common patterns of sleep-disordered breathing may help to identify these patients and guide therapy.

Mechanisms of apnea

This paper focuses on the underlying mechanisms contributing to sleep-disordered breathing. Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder and is characterized by repetitive narrowing or collapse of the pharyngeal airway during sleep. Conversely, central sleep apnea (CSA), highly prevalent in congestive heart failure, is distinguished by a lack of drive to breathe during sleep, resulting in repetitive periods of insufficient ventilation. Both lead to compromised gas exchange, impaired sleep continuity, and catecholamine surges and are associated with major comorbidities including excessive daytime sleepiness and increased risk of cardiovascular disease. Although OSA and CSA exist on a spectrum of sleep-disordered breathing, the 2 entities may overlap in their underlying pathophysiologies. This brief review summarizes the etiology and current understanding of OSA and CSA pathophysiology and the role that the cardiovascular system may play in contributing to disease pathology and highlights the likely substantial overlap that exists between the various forms of sleep-disordered breathing.

Central alveolar hypoventilation syndrome due to surgical resection for bulbar hemangioblastoma

A 29-year-old man with a history of resected bulbar hemangioblastoma was admitted to hospital with nighttime breathing disturbance, but with apparently normal breathing while awake. After diagnostic work-up, including polysomnographic testing, he was diagnosed as having central alveolar hypoventilation syndrome due to surgical resection for bulbar hemangioblastoma. Non-invasive positive pressure ventilation (NIPPV) via oronasal facemask was given for nocturnal ventilatory support. Two months after leaving our hospital, he was readmitted because of aspiration pneumonia. The pneumonia was successfully treated with antibiotics, but the desaturation during sleep worsened despite non-invasive ventilatory support. Higher bi-level positive pressure using a full facemask successfully alleviated sleep hypoventilation and apnea. To the best of our knowledge, this is the first case report of central alveolar hypoventilation syndrome due to surgical resection for bulbar hemangioblastoma.

Spontaneous mode non-invasive ventilation fails to treat respiratory failure in a patient with Multi-mincore disease: a case report

The increased morbidity and mortality resulting from respiratory failure in patients with neuromuscular disorders and/or kyphoscoliosis can be reversed with non-invasive ventilation. Spontaneous mode bilevel pressure ventilation is preferred to other modes of ventilation, due to relative ease of use, but may not be suitable for all patients. We report a 27-year old woman with Multi-minicore disease whose respiratory failure was refractory to spontaneous mode bilevel pressure ventilation. When we altered settings and provided mandatory inspiratory rise time and respiratory rate, it augmented her respiratory efforts and improved ventilation. Our case report describes the benefit of individualising non-invasive ventilation in the management of respiratory failure due to neuromuscular weakness and kyphoscoliosis.

Sleep-predominant lowering of ambulatory blood pressure by bedtime inhalation of a novel muscarinic M3 receptor antagonist: a new "bronchoantihypertensive" strategy targeting the lung in hypertension with chronic obstructive pulmonary disease

Bedtime inhalation of a novel muscarinic M3 receptor antagonist markedly lowered ambulatory blood pressure (ABP), predominantly during sleep, in a chronic obstructive pulmonary disease (COPD) patient with masked nocturnal hypertension. This is the first case demonstrating that a bronchodilator significantly lowered ABP in a COPD patient with hypertension. This case suggests that bronchodilator therapy may have potential as a new antihypertensive strategy targeting the lung in hypertensive patients with impaired lung function. This "bronchoantihypertensive" therapy seems to be more effective for reducing sleep blood pressure in hypertensive patients with COPD and sleep hypoventilatory/hypoxemic syndromes.