Prognosis and sleep disordered breathing in heart failure

The Role of Sleep in Cardiovascular Disease

PURPOSE OF REVIEW

Sleep is an important component of cardiovascular (CV) health. This review summarizes the complex relationship between sleep and CV disease (CVD). Additionally, we describe the data supporting the treatment of sleep disturbances in preventing and treating CVD.

RECENT FINDINGS

Recent guidelines recommend screening for obstructive sleep apnea in patients with atrial fibrillation. New data continues to demonstrate the importance of sleep quality and duration for CV health. There is a complex bidirectional relationship between sleep health and CVD. Sleep disturbances have systemic effects that contribute to the development of CVD, including hypertension, coronary artery disease, heart failure, and arrhythmias. Additionally, CVD contributes to the development of sleep disturbances. However, more data are needed to support the role of screening for and treatment of sleep disorders for the prevention of CVD.

Pharmacological treatment for central sleep apnoea in adults

BACKGROUND

The term central sleep apnoea (CSA) encompasses diverse clinical situations where a dysfunctional drive to breathe leads to recurrent respiratory events, namely apnoea (complete absence of ventilation) and hypopnoea sleep (insufficient ventilation) during sleep. Studies have demonstrated that CSA responds to some extent to pharmacological agents with distinct mechanisms, such as sleep stabilisation and respiratory stimulation. Some therapies for CSA are associated with improved quality of life, although the evidence on this association is uncertain. Moreover, treatment of CSA with non-invasive positive pressure ventilation is not always effective or safe and may result in a residual apnoea-hypopnoea index.

OBJECTIVES

To evaluate the benefits and harms of pharmacological treatment compared with active or inactive controls for central sleep apnoea in adults.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 30 August 2022.

SELECTION CRITERIA

We included parallel and cross-over randomised controlled trials (RCTs) that evaluated any type of pharmacological agent compared with active controls (e.g. other medications) or passive controls (e.g. placebo, no treatment or usual care) in adults with CSA as defined by the International Classification of Sleep Disorders 3rd Edition. We did not exclude studies based on the duration of intervention or follow-up. We excluded studies focusing on CSA due to periodic breathing at high altitudes.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were central apnoea-hypopnoea index (cAHI), cardiovascular mortality and serious adverse events. Our secondary outcomes were quality of sleep, quality of life, daytime sleepiness, AHI, all-cause mortality, time to life-saving cardiovascular intervention, and non-serious adverse events. We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We included four cross-over RCTs and one parallel RCT, involving a total of 68 participants. Mean age ranged from 66 to 71.3 years and most participants were men. Four trials recruited people with CSA associated with heart failure, and one study included people with primary CSA. Types of pharmacological agents were acetazolamide (carbonic anhydrase inhibitor), buspirone (anxiolytic), theophylline (methylxanthine derivative) and triazolam (hypnotic), which were given for between three days and one week. Only the study on buspirone reported a formal evaluation of adverse events. These events were rare and mild. No studies reported serious adverse events, quality of sleep, quality of life, all-cause mortality, or time to life-saving cardiovascular intervention. Carbonic anhydrase inhibitors versus inactive control Results were from two studies of acetazolamide versus placebo (n = 12) and acetazolamide versus no acetazolamide (n = 18) for CSA associated with heart failure. One study reported short-term outcomes and the other reported intermediate-term outcomes. We are uncertain whether carbonic anhydrase inhibitors compared to inactive control reduce cAHI in the short term (mean difference (MD) -26.00 events per hour, 95% CI -43.84 to -8.16; 1 study, 12 participants; very low certainty). Similarly, we are uncertain whether carbonic anhydrase inhibitors compared to inactive control reduce AHI in the short term (MD -23.00 events per hour, 95% CI -37.70 to 8.30; 1 study, 12 participants; very low certainty) or in the intermediate term (MD -6.98 events per hour, 95% CI -10.66 to -3.30; 1 study, 18 participants; very low certainty). The effect of carbonic anhydrase inhibitors on cardiovascular mortality in the intermediate term was also uncertain (odds ratio (OR) 0.21, 95% CI 0.02 to 2.48; 1 study, 18 participants; very low certainty). Anxiolytics versus inactive control Results were based on one study of buspirone versus placebo for CSA associated with heart failure (n = 16). The median difference between groups for cAHI was -5.00 events per hour (IQR -8.00 to -0.50), the median difference for AHI was -6.00 events per hour (IQR -8.80 to -1.80), and the median difference on the Epworth Sleepiness Scale for daytime sleepiness was 0 points (IQR -1.0 to 0.00). Methylxanthine derivatives versus inactive control Results were based on one study of theophylline versus placebo for CSA associated with heart failure (n = 15). We are uncertain whether methylxanthine derivatives compared to inactive control reduce cAHI (MD -20.00 events per hour, 95% CI -32.15 to -7.85; 15 participants; very low certainty) or AHI (MD -19.00 events per hour, 95% CI -30.27 to -7.73; 15 participants; very low certainty). Hypnotics versus inactive control Results were based on one trial of triazolam versus placebo for primary CSA (n = 5). Due to very serious methodological limitations and insufficient reporting of outcome measures, we were unable to draw any conclusions regarding the effects of this intervention.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support the use of pharmacological therapy in the treatment of CSA. Although small studies have reported positive effects of certain agents for CSA associated with heart failure in reducing the number of respiratory events during sleep, we were unable to assess whether this reduction may impact the quality of life of people with CSA, owing to scarce reporting of important clinical outcomes such as sleep quality or subjective impression of daytime sleepiness. Furthermore, the trials mostly had short-term follow-up. There is a need for high-quality trials that evaluate longer-term effects of pharmacological interventions.

Prolonged Circulation Time Is Associated With Mortality Among Older Men With Sleep-Disordered Breathing

BACKGROUND

Conventional metrics to evaluate sleep-disordered breathing (SDB) have many limitations, including their inability to identify subclinical markers of cardiovascular (CV) dysfunction.

RESEARCH QUESTION

Does sleep study-derived circulation time (Ct) predict mortality, independent of CV risks and SDB severity?

STUDY DESIGN AND METHODS

We derived average lung to finger Ct (LFCt) from sleep studies in older men enrolled in the multicenter Osteoporotic Fractures in Men (MrOS) Sleep study. LFCt was defined as the average time between end of scored respiratory events and nadir oxygen desaturations associated with those events. We calculated the hazard ratio (HRs) for the CV and all-cause mortality by LFCt quartiles, adjusting for the demographic characteristics, body habitus, baseline CV risk, and CV disease (CVD). Additional models included apnea-hypopnea index (AHI), time with oxygen saturation as measured by pulse oximetry (SpO₂) < 90% (T90), and hypoxic burden. We also repeated analyses after excluding those with CVD at baseline.

RESULTS

A total of 2,631 men (mean ± SD age, 76.4 ± 5.5 years) were included in this study. LFCt median (interquartile range) was 18 (15-22) s. During an average ± SD follow-up of 9.9 ± 3.5 years, 427 men (16%) and 1,205 men (46%) experienced CV death and all-cause death, respectively. In multivariate analysis, men in the fourth quartile of LFCt (22-52 s) had an HR of 1.36 (95% CI, 1.02-1.81) and 1.35 (95% CI, 1.14-1.60) for CV and all-cause mortality, respectively, when compared with men in the first quartile (4-15 s). The results were similar when additionally adjusting for AHI, T90, or hypoxic burden. Results were stronger among men with no history of CVD at baseline.

INTERPRETATION

LFCt is associated with both CV and all-cause mortality in older men, independent of baseline CV burden and SDB metrics. LFCt may be a novel physiologic marker for subclinical CVD and adverse outcomes in patients with SDB.

Liver and spleen elastography of dogs affected by brachycephalic obstructive airway syndrome and its correlation with clinical biomarkers

The purpose of this study is to determine whether the brachycephalic obstructive airway syndrome (BOAS) is correlated to alterations in liver and spleen elasticity. Forty-eight brachycephalic and 22 mesocephalic dogs were submitted to a BOAS functional assessment, laboratory tests, abdominal ultrasound and liver and spleen Acoustic Radiation Force Impulse (ARFI) elastography. Dogs clinically affected by BOAS had higher values of liver stiffness (p < 0.001) than healthy dogs: medial lobes (1.57 ± 0.37 m/s), left and right lateral lobes (1.54 ± 0.50 m/s, 1.23 ± 0.28 m/s, respectively) and caudate lobe (1.28 ± 0.42 m/s). Compared to the mesocephalic group, the brachycephalic group (BOAS clinically affected and unaffected dogs) had higher spleen (2.51 ± 0.45 m/s; p < 0.001) and liver stiffness (p < 0.001): medial lobes (1.53 ± 0.37 m/s), left and right lateral lobes (1.47 ± 0.47 m/s, 1.20 ± 0.30 m/s, respectively) and caudate lobe (1.23 ± 0.40 m/s). Principal component analysis explained 70% of the variances composed by liver stiffness increase, erythrocytes and alanine aminotransferase reduction. Brachycephalic dogs had higher spleen and liver stiffness and a subacute inflammatory state, which represent another BOAS systemic effect. Consequently, these dogs can be at higher risk of hepatic disorders compared with mesocephalic dogs, similarly to humans affected by sleep apnea syndrome.

Obstructive sleep apnoea-hypopnoea and arrhythmias: new updates

AIMS

Obstructive sleep apnoea-hypopnoea (OSAH) is a prevalent condition characterized by repetitive pharyngeal collapse during sleep, leading to hypoxemia, hypercapnia, and persistent inspiratory efforts against an occluded airway until arousal. Several studies demonstrated that OSAH exerts acute and chronic effects on the cardiovascular system. Thus, although being a respiratory problem, the most important consequences of OSAH are cardiovascular, among which there are arrhythmias. The purpose of this review is to systematically analyse what has been recently published about the relationship between OSAH and every cardiac arrhythmia separately.

METHODS

We searched Pubmed, Scopus, Web of Science and Cochrane Collaboration databases for 'OSAHS arrhythmias', 'OSAH arrhythmias' and 'OSA arrhythmias'. We analyse 1298 articles and meta-analyses, excluding already edited reviews.

RESULTS

Arrhythmias, especially of ventricular origin, are frequent in OSAH. Ventricular premature beats, couplets and ventricular tachycardia runs are even more frequent in patients suffering from heart failure. They may be due to left heart remodelling, overwork and ischaemia and can explain at least some sudden deaths occurring between midnight and 6 a.m. Sinus pauses and atrioventricular blocks are increased according to the severity of the disturbance and may be reduced by continuous positive airway pressure therapy, preventing pace-maker implantation. Finally, atrial fibrillation, resistance against antiarrhythmic drugs and recurrences after surgical procedures are strongly related to OSAH.

CONCLUSION

Arrhythmias are frequent in OSAH. Treatment of OSAH may reduce some of them. An implantable cardioverter-defibrillator and continuous positive airway pressure should be considered in some patients.

Treatment of Obstructive Sleep Apnea. Prospects for Personalized Combined Modality Therapy

Obstructive sleep apnea (OSA) is a common sleep disorder with serious associated morbidities. Although several treatment options are currently available, variable efficacy and adherence result in many patients either not being treated or receiving inadequate treatment long term. Personalized treatment based on relevant patient characteristics may improve adherence to treatment and long-term clinical outcomes. Four key traits of upper airway anatomy and neuromuscular control interact to varying degrees within individuals to cause OSA. These are: (1) the pharyngeal critical closing pressure, (2) the stability of ventilator chemoreflex feedback control (loop gain), (3) the negative intraesophageal pressure that triggers arousal (arousal threshold), and (4) the level of stimulus required to activated upper airway dilator muscles (upper airway recruitment threshold). Simplified diagnostic methods are being developed to assess these pathophysiological traits, potentially allowing prediction of which treatment would best suit each patient. In contrast to current practice of using various treatment modes alone, model predictions and pilot clinical trials show improved outcomes by combining several treatments targeted to each patient's pathophysiology profile. These developments could theoretically improve efficacy and adherence to treatment and in turn reduce the social and economic health burden of OSA and the associated life-threatening morbidities. This article reviews OSA pathophysiology and identifies currently available and investigational treatments that may be combined in the future to optimize therapy based on individual profiles of key patient pathophysiological traits.

Sleep-disordered breathing, type 2 diabetes and the metabolic syndrome

Sleep-disordered breathing (SDB) encompasses a spectrum of conditions that can lead to altered sleep homeostasis. In particular, obstructive sleep apnoea (OSA) is the most common form of SDB and is associated with adverse cardiometabolic manifestations including hypertension, metabolic syndrome and type 2 diabetes, ultimately increasing the risk of cardiovascular disease. The pathophysiological basis of these associations may relate to repeated intermittent hypoxia and fragmented sleep episodes that characterize OSA which drive further mechanisms with adverse metabolic and cardiovascular consequences. The associations of OSA with type 2 diabetes and the metabolic syndrome have been described in studies ranging from epidemiological and observational studies to controlled trials investigating the effects of OSA therapy with continuous positive airway pressure (CPAP). In recent years, there have been rising prevalence rates of diabetes and obesity worldwide. Given the established links between SDB (in particular OSA) with both conditions, understanding the potential influence of OSA on the components of the metabolic syndrome and diabetes and the underlying mechanisms by which such interactions may contribute to metabolic dysregulation are important in order to effectively and holistically manage patients with SDB, type 2 diabetes or the metabolic syndrome. In this article, we review the literature describing the associations, the possible underlying pathophysiological mechanisms linking these conditions and the effects of interventions including CPAP treatment and weight loss.

Obstructive sleep apnea and atrial fibrillation: understanding the connection

There is a high incidence of atrial fibrillation (AF) in patients with obstructive sleep apnea (OSA). Whether this represents a causative relationship or is merely an association remains to be determined. This review describes the current understanding of pathophysiologic links supporting a causative relationship between OSA and AF. The management of AF with antiarrhythmics, cardioversion and ablation success depends on compliance with OSA treatment. OSA worsens every risk factor resulting in a higher stroke risk in AF patients. Strategies for early screening and compliance with OSA treatment are the need of the hour.

Spectral analysis of R wave attenuation and heart rate variability for detection of cheyne stokes breathing

Spectral analysis was carried out on the R-Wave Attenuation (RWA) trend and Heart Rate Variability (HRV) series, derived from the polysomnographic Electrocardiogram (ECG) of the subjects with and without Cheyne Stokes Breathing. Nocturnal polysomnography was performed on 16 Normal subjects and 7 subjects with Cheyne Stokes Breathing (CSB) patients. The polysomnographic ECG data was divided into fifteen minute epochs for analysis. These epochs are processed to obtain the RWA. Hilbert Transform based algorithm [4] was used for QRS detection. Power spectrum of RWA and HRV are computed for each clip by using Welch's averaged periodogram method. HRV is sensitive to REM sleep as well and hence not specific to sleep apnea [12]. Hence the parameters derived from HRV alone cannot be used as diagnostic markers. Hence a combined detection scheme which uses parameters derived from RWA and HRV power spectrum is used in the proposed method to increase detection accuracy. This method produced a sensitivity of 84.75% and specificity of 87.03% in the training set and sensitivity of 85.78% and a specificity of 87.19% in the test set.

A novel approach to the treatment of central sleep apnea in patients with heart failure

Central sleep apnea (CSA) is a common, though often unrecognized, finding in congestive heart failure (HF) patients that is associated with poor quality of life and increased morbidity and mortality. While various treatment strategies, including continuous positive airway pressure (CPAP) therapy, have been devised and tested to treat CSA in HF, none thus far have been proven effective over the long term or been shown to improve survival. Adaptive pressure support servo-ventilation (ASV) is a promising potential new therapy for CSA, but like its predecessor, CPAP, it is often not well tolerated by patients, and results from clinical trials evaluating its long-term effectiveness in reducing morbidity and mortality are still a number of years off. Recently, a new therapy utilizing unilateral transvenous phrenic nerve stimulation has been introduced to treat CSA in HF. As a totally implantable, device-based therapy, it may be better tolerated than CPAP or ASV in HF patients and, thus, improve patient compliance with treatment. Early studies using this therapy have been encouraging, with patients demonstrating significant improvement in major indices of CSA severity.

Metabolic syndrome correlates intracoronary stenosis detected by multislice computed tomography in male subjects with sleep-disordered breathing

BACKGROUND

Sleep-disordered breathing (SDB), especially obstructive sleep apnea (OSA), has frequent complications include hypertension, dyslipidemia and insulin resistance based on abdominal obesity or excess visceral fat (called Syndrome Z). OSA is a potential risk factor for cardiovascular diseases. The clinical characteristics of Japanese OSA subjects with OSA remain unclear. The present study investigated prevalence and predictive factors of intracoronary stenosis detected by multislice computed tomography (MSCT) in Japanese male subjects with SDB/OSA.

FINDINGS

The study (O-VFStudy) subjects were 39 Japanese men with SDB/OSA who underwent all-night cardiorespiratory monitoring with fully attended polysomnography, and moreover both fat computed tomography (CT) scan and 64-row MSCT coronary angiography. The prevalence of coronary stenosis in this selected population with SDB/OSA was 15%. Logistic regression analysis showed a significant relationship between age-adjusted CAD and metabolic syndrome (p < 0.05), but not serum adiponectin levels and nocturnal fall in adiponectin. Subjects with the metabolic syndrome had significantly higher prevalence of CAD (31.3 versus 4.3%, p = 0.033), and lower levels of serum adiponectin (4.5 ± 0.6 versus 6.4 ± 0.6 μg/mL, p = 0.014), compared with groups without the metabolic syndrome.

CONCLUSIONS

The present study describes that the prevalence of greater than 50% intracoronary stenotic lesions detected by MSCT was 15% and the metabolic syndrome was correlated with intracoronary stenosis detected by MSCT in Japanese SDB/OSA subjects.

TRIAL REGISTRATION

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Obstructive sleep apnea and the metabolic syndrome

Obstructive sleep apnea (OSA) and the metabolic syndrome have a strong association with each other owing to their common feature of obesity, but an association independent of obesity has been demonstrated in several studies. There is also evidence, of varying strengths, from epidemiologic and clinical studies, for the independent association between OSA and individual core components of the metabolic syndrome, including hypertension, insulin resistance and dyslipidemia. To date, the data are strongest for hypertension, while data for adverse glucose or lipid metabolism are more controversial. Obesity and other factors, such as alcohol drinking and smoking, obviously pose major confounding hurdles to the clarification of the causal or aggravational role of OSA on cardiometabolic risks. Recurrent episodes of obstructed breathing notably result in intermittent hypoxemia and sleep fragmentation, and these may in turn lead to many adverse body responses, including sympathetic activation, neurohumeral changes and inflammation, which are the seeds for cardiometabolic dysfunctions, such as atherosclerosis and diabetes mellitus. Evidence from translational studies or animal/cell work are forthcoming in the delineation of these pathogenetic mechanisms.

Pathophysiology of sleep apnea

Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anatomically compromised, collapsible airway, the sleep-induced loss of compensatory tonic input to the upper airway dilator muscle motor neurons leads to collapse of the pharyngeal airway. In turn, the ability of the sleeping subject to compensate for this airway obstruction will determine the degree of cycling of these events. Several of the classic neurotransmitters and a growing list of neuromodulators have now been identified that contribute to neurochemical regulation of pharyngeal motor neuron activity and airway patency. Limited progress has been made in developing pharmacotherapies with acceptable specificity for the treatment of sleep-induced airway obstruction. We review three types of major long-term sequelae to severe OSA that have been assessed in humans through use of continuous positive airway pressure (CPAP) treatment and in animal models via long-term intermittent hypoxemia (IH): 1) cardiovascular. The evidence is strongest to support daytime systemic hypertension as a consequence of severe OSA, with less conclusive effects on pulmonary hypertension, stroke, coronary artery disease, and cardiac arrhythmias. The underlying mechanisms mediating hypertension include enhanced chemoreceptor sensitivity causing excessive daytime sympathetic vasoconstrictor activity, combined with overproduction of superoxide ion and inflammatory effects on resistance vessels. 2) Insulin sensitivity and homeostasis of glucose regulation are negatively impacted by both intermittent hypoxemia and sleep disruption, but whether these influences of OSA are sufficient, independent of obesity, to contribute significantly to the "metabolic syndrome" remains unsettled. 3) Neurocognitive effects include daytime sleepiness and impaired memory and concentration. These effects reflect hypoxic-induced "neural injury." We discuss future research into understanding the pathophysiology of sleep apnea as a basis for uncovering newer forms of treatment of both the ventilatory disorder and its multiple sequelae.

Cheyne-stokes respiration and prognosis in modern-treated congestive heart failure

In patients with congestive heart failure (CHF), a high prevalence of sleep-disordered breathing has been described. Cheyne-Stokes respiration (CSR) is present in up to 40% of patients with CHF. During the last decade, the medical treatment has been substantially improved. This study was designed to analyze the prognosis of CSR in modern-treated patients with CHF. For this purposes, in 57 patients with CHF who received modern treatment, a 5-year follow-up after initial full night polysomnography was performed. The mean follow-up period was 38 ± 18 months. Mean age was 62 ± 13 years and the mean ejection fraction was 25 ± 7 percent. Respiratory polygraphy revealed CSR with a respiratory disturbance index >5 per hour of sleep in 39 of 57 patients. Twelve patients died. CSR was only characterized by a tendency of worsening (log-rank test, p = 0.25). However, there was a significant difference toward positive outcome for patients who received cardiac resynchronization therapy (log-rank test, p = 0.036). Using Multivariate Cox’s proportional hazard regression with the factors resynchronization and CSR, the effect of resynchronization was almost significant (p = 0.08). In conclusion, no significant change of Cheyne-Stokes prevalence can be found in our small group of modern-treated patients with CHF. Cardiac resynchronization therapy was associated with improved patient outcome.

Obstructive sleep apnea, inflammation, and the metabolic syndrome

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

Respiratory sleep disturbances in patients undergoing gastric bypass surgery and their relation to metabolic syndrome

BACKGROUND

The prevalence of obstructive sleep apnea syndrome (OSAS) is high in obese patients. Certain components of metabolic syndrome are linked to OSAS, but there is no information on their association in morbidly obese patients. Our aim was to ascertain the prevalence of respiratory disturbances during sleep in candidates for bariatric surgery and to study their association with metabolic syndrome.

METHODS

We examined the preoperative records (history, physical examination and laboratory findings, spirometry, and overnight pulse oximetry [arterial oxygen saturation by pulse oximetry, [SpO(2)]]) of patients scheduled for gastric bypass surgery for 1 year in our hospital; an overnight sleep study was performed if SpO(2) readings or symptoms suggested sleep disturbance. Metabolic syndrome was defined according to the criteria of the National Cholesterol Education Program's Adult Treatment Panel III.

RESULTS

Of the 31 patients studied, 19 (61.3%) had OSAS, including 15 newly diagnosed cases with a mean +/- standard deviation apnea-hypopnea index of 49 +/- 36. OSAS patients had higher fasting plasma glucose and triglyceride levels and a higher prevalence of diabetes. Metabolic syndrome was also more frequent in subjects with previously untreated OSAS (13/14, 92%) than in those without sleep disturbance (six of 11, 55%; p = 0.033). Conversely, the prevalence of OSAS in patients with metabolic syndrome was higher (13/19, 68%) than in subjects without metabolic syndrome (one of six, 17%; p = 0.026) even though the two groups had similar body mass index.

CONCLUSIONS

Sleep disordered breathing is very prevalent in obese patients who are candidates for bariatric surgery and its presence is related to metabolic syndrome.

Monitoring of ventilation during the early part of cardiopulmonary exercise testing: The first step to detect central sleep apnoea in chronic heart failure

BACKGROUND AND PURPOSE

To evaluate the prediction of nocturnal central sleep apnoea (CSA) syndrome from the presence of periodic breathing (PB) on diurnal monitoring of pre-exercise (cardiopulmonary exercise test [CPX]) parameters. CSA syndrome is commonly found in congestive heart failure (CHF) patients and has several prognostic and therapeutic implications but is frequently undiagnosed. Awake PB pattern is sometimes observed during the CPX cardiopulmonary monitoring period of gas exchanges in CHF patients referred to the stress test laboratory for routine peak VO2 determination.

PATIENTS AND METHODS

Forty-five consecutive ambulatory patients (2 women/43 men; 60.2+/-11.7 years old) with clinically moderate to severe CHF (New York Heart Association [NYHA] class II/III: 22/23; mean+/-standard deviation left ventricular ejection fraction [LVEF]: 30.5+/-6.6%) underwent a classical maximal CPX test including a 2-min period (pre-test) of gas exchange monitoring and nocturnal ambulatory polygraphic monitoring. PB was defined when a cyclical pattern of VE, VO2, VCO2, was visually noted during the pre-exercise period and/or during the first 4 min of the CPX. CSA syndrome was retained as a central apnoea-plus-hypopnea index (cAHI) equal to or more than 10/h. The sleep study scoring procedure was done independently of the knowledge of the CPX results. Sensitivity, specificity and predictive values were calculated and receiver operating characteristic (ROC) curve analysis was constructed.

RESULTS

Peak VO2 reached 16.4+/-5.2 mL kg(-1)min(-1) (55% of the theoretical value adjusted for gender and age). The polygraphy was completed and validated (at least five consecutive hours of sleep) in all cases. CSA syndrome was found in 28 (62%) patients (mean cAHI: 19.3+/-8.6/h). Sensitivity for the prediction of CSA syndrome reached 92.9% (two false-negative patients with a cAHI of nine) and specificity 94.1% with a predictive accuracy of 93.3%. The only false-positive patient suffered a moderate but significant obstructive sleep apnoea syndrome. Using ROC curve analysis, the W value reached 0.99 for the prediction of CSA from the presence of PB. The presence of CSA syndrome, using logistic regression analysis, is associated with a more severe functional status (NYHA: p<0.01, peak VO2: p<0.002), a lower basal and peak end-expiratory CO2 pressure (PETCO2, all p<0.03), a worse LVEF (p<0.01) and age equal to or more than 60 years (p<0.03).

CONCLUSIONS

The observation of PB in the preliminary period of the CPX test in CHF patients appeared highly predictive of the presence of CSA syndrome during sleep and could prompt the use of polygraphic monitoring in severe CHF patients.

Association of sleep apnea severity and obesity with insulin resistance, C-reactive protein, and leptin levels in male patients with obstructive sleep apnea

Obesity is the major confounding factor in the relationship between obstructive sleep apnea and increased risk for cardiovascular disease. The aim of the study was to investigate the association of sleep apnea severity with insulin resistance, leptin, and CRP levels in a cohort of male patients. Sixty-seven men referred to our sleep laboratory for evaluation of suspected obstructive sleep apnea syndrome (OSAS) were divided into three groups according to apnea severity: non-OSAS group (n=15), mild to moderate OSAS group (n=26), and severe OSAS (n=26). Insulin resistance was estimated by the homeostasis model assessment method. HOMA values were similar in the three groups: (3.2+/-2.2 vs. 3.3+/-1.8 vs. 3.6+/-1.5, respectively, p=0.71). Leptin levels were higher in the mild to moderate OSAS group (23.1+/-21.8 ng/ml, p<0.05) and in the severe OSAS group (20.2+/-17.5 ng/ml, p<0.05) than in the non-OSAS group (9.4+/-6.4 ng/ml). CRP levels were significantly higher in severe sleep apnea (0.35+/-0.3 vs. 0.19+/-0.1 mg/dl, p<0.05). In multiple regression analyses, waist-to-hip ratio (WHR) was the most significant determinant of HOMA estimation for insulin resistance. WHR and the percentage of total sleep time spent with hypoxemia (%TST with SaO2 <90%) were significant predictors for leptin levels, while body mass index (BMI) and the %TST with SaO2 <90% were the best predicting parameters for CRP levels. Insulin resistance estimated by the HOMA method in male patients with OSAS was not associated with sleep apnea severity independent of obesity. The severity of nocturnal hypoxemia was associated with leptin and CRP levels independent of obesity.

Cardiac function after CPAP therapy in patients with chronic heart failure and sleep apnea: a multicenter study

BACKGROUND AND PURPOSE

Continuous positive airway pressure (CPAP) is an effective treatment for sleep apnea (SA), although the evidence for improving chronic heart failure (CHF) is inconclusive. Our aim was to evaluate the effect of CPAP treatment on the left ventricle ejection fraction (LVEF) among other cardiological variables in a randomized, multicenter, placebo (sham-CPAP)-controlled study.

METHODS

After the selection procedure, 60 patients with CHF with LVEF<45% and SA with an apnea-hypopnea index (AHI)>10/h were evaluated at baseline, and after 3 months of treatment with optimal CPAP or sham-CPAP. The assessment was based on the LVEF, hypertension, daytime sleepiness (Epworth sleepiness scale [ESS]), quality of life (SF-36), New York Heart Scale (NYHA score), dyspnea (by using the Borg scale) and exercise tolerance (6-min walk test).

RESULTS

The mean AHI was normalized in the optimal CPAP group but not in the sham-CPAP group. The LVEF showed a significant improvement in the group of patients treated with CPAP (2.5; 95% CI: 0.6 to 4.3), which was not observed in the sham-CPAP group (0.0; 95% CI: -2.1 to 2.1). However, the change in the LVEF from baseline to 3 months was not significantly greater in the whole group (obstructive and Cheyne-Stokes events) treated with CPAP than in the control group (p: 0.07). In patients with only obstructive sleep apnea (OSA), who account for 83% of the total population, there was a significant improvement in the LVEF in the group of patients treated with CPAP but no such improvement in the sham-CPAP group. In this OSA group, the change in the LVEF from baseline to 3 months was significantly greater in the group treated with CPAP than in the sham-CPAP group (p: 0.03). The other variables studied were not modified. When the patients were divided according to the severity of the LVEF (a LVEF cut-off of 30%), improvement was observed in those with a LVEF>30. No changes were found in the other cardiological variables.

CONCLUSIONS

CPAP therapy proved to be useful in patients with associated sleep-disordered breathing and CHF. The improvement was more marked in patients with a LVEF>30%. However, the increased LVEF in the CPAP group was not accompanied by changes in the other cardiological variables.

Obstructive sleep apnoea, cigarette smoking and serum testosterone levels in a male sleep clinic cohort

This study evaluated the impact of obstructive sleep apnoea (OSA) and smoking on total serum testosterone levels in 96 men (mean age 43.3 years; range 25 - 60 years) attending a sleep clinic. Fifty-five men (57.3%) had OSA, defined as an apnoea-hypopnoea index of > or = 15 events/h, recorded during overnight polysomnography, and 42 (43.8%) were current smokers. Mean serum total testosterone levels were significantly lower in OSA subjects (3.4 ng/ml) than in non-OSA subjects (3.9 ng/ml), whereas no significant difference was observed between current smokers and nonsmokers. In a multiple linear regression analysis, serum testosterone was negatively correlated with body mass index and the apnoea-hypopnoea index, but not with age and pack-years of smoking. Our results support previous observations regarding testosterone levels in men with OSA, but, contrary to some earlier reports, there was no positive relationship between smoking and total testosterone in the present cohort.

Relationship Between β-Blocker Treatment and the Severity of Central Sleep Apnea in Chronic Heart Failure

BACKGROUND

We sought to examine the relationship between use of beta-blockers and the severity of central sleep apnea (CSA) in patients with chronic heart failure.

METHODS

We performed polysomnography in 45 patients with chronic heart failure (New York Heart Association functional class II/III and left ventricular ejection fraction < 50%) and examined the relationship between use of beta-blockers and the severity of CSA. Central apnea index (CAI) was used as an indicator of CSA.

RESULTS

Patients receiving beta-blockers (ie, carvedilol; n = 27) had lower apnea-hypopnea index (AHI) and CAI than patients not receiving beta-blockers (n = 18) [mean +/- SD, 14 +/- 11 vs 33 +/- 17, p < 0.0001; and 1.9 +/- 3.2 vs 11 +/- 12, p = 0.0004, respectively]. AHI and CAI were negatively correlated with the dose of carvedilol (Spearman rho = - 0.61, p < 0.0001; and Spearman rho = - 0.57, p = 0.0002, respectively). Multiple regression analysis selected no use of beta-blockers as an independent factor of CAI (p = 0.0006). In five patients with CAI > 5 who underwent serial sleep studies, CAI decreased significantly after 6 months of treatment with carvedilol (9.5 +/- 4.9 to 1.3 +/- 2.4, p = 0.03).

CONCLUSIONS

In patients with chronic heart failure, CAI was lower according to the dose of beta-blockers, and no use of beta-blockers was independently associated with CAI. In addition, 6 months of treatment with carvedilol decreased CAI. These results suggest that beta-blocker therapy may dose-dependently suppress CSA in patients with chronic heart failure.

Circulating ICAM-1 and VCAM-1 levels in patients with obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS)-induced hypoxic stress modulates circulating inflammatory mediators causing accelerated atherogenesis.

OBJECTIVES

We hypothesized that OSAS-induced hypoxia might result in cardiovascular disease due to increased expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the endothelial surface.

METHODS

Thirty-nine subjects with moderate-to-severe OSAS and 34 non-apneic controls matched for age, gender, body mass index (BMI), smoking history, and cardiovascular disease were included in this prospective study. Overnight polysomnography was performed. Circulating ICAM-1 and VCAM-1 levels in the serum were measured by enzyme-linked immunosorbent assay.

RESULTS

Circulating levels of both ICAM-1 (480.1 +/- 216.7 vs. 303.4 +/- 98.6 ng/ml, p < 0.0001) and VCAM-1 (1,156.6 +/- 79.8 vs. 878.8 +/- 71.1 ng/ml, p = 0.002) were significantly increased in the OSAS group compared to the control group. For an ICAM-1 cutoff level of 375 ng/ml, predictive sensitivity and specificity for OSAS were 69.2% (95% confidence interval, CI: 52.4-83.0%) and 82.4% (95% CI: 65.5-93.2%), respectively. For a VCAM-1 cutoff level of 859 ng/ml, predictive sensitivity and specificity for OSAS were 74.4% (95% CI: 57.9-86.9%) and 64.7% (95% CI: 46.5-80.2%), respectively. There was a significant positive correlation between circulating levels of ICAM-1 and ln of AHI (r = 0.276, p = 0.018). Multiple logistic regression analyses showed that OSAS was associated with high ICAM-1 and high VCAM-1 levels independent of age, gender, BMI, smoking status and cardiovascular disease.

CONCLUSION

We conclude that OSAS can independently increase circulating levels of adhesion molecules

Obesity-related cardiovascular disease: implications of obstructive sleep apnea

Obesity and obstructive sleep apnea (OSA) often coexist. OSA has been linked to cardiovascular disease. Thus, OSA may contribute to the cardiovascular consequences of obesity. In this review, we explore clinical and pathophysiological interactions between obesity, cardiovascular disease and OSA. We discuss the mechanisms whereby OSA may contribute to hypertension, atherosclerosis, insulin resistance and atrial fibrillation associated with obesity, and emphasize the potential implications for understanding why only a subgroup of obese patients develop cardiovascular disease. Identification of the OSA-dependent and OSA-independent pathways in the cardiovascular pathophysiology of obesity may hold clinical and therapeutic promise.

Obstructive sleep apnoea syndrome, plasma adiponectin levels, and insulin resistance

OBJECTIVE

To investigate whether sleep-disordered breathing and/or plasma adiponectin levels are associated with insulin resistance independent of obesity or fat distribution in obstructive sleep apnoea syndrome (OSAS).

DESIGN

Cross-sectional clinical study.

PATIENTS

Two-hundred and thirteen Japanese patients with OSAS aged 27-80 years were divided into three groups: 30 with mild OSAS [apnoea-hypopnoea index (AHI) = 10.3 +/- 0.9 episodes/h, minimum oxygen saturation (min SpO2) = 87.3 +/- 0.9%], 98 with moderate OSAS (AHI = 28.9 +/- 0.6 episodes/h, min SpO2 = 82.1 +/- 0.7%), and 85 with severe OSAS (AHI = 68.1 +/- 2.8 episodes/h, min SpO2 = 72.3 +/- 1.6%). Twenty-one patients undergoing diabetic treatments (two mild, nine moderate and 10 severe) were excluded from the assessment of insulin resistance and plasma adiponectin measurements.

MEASUREMENTS

Fat distribution [evaluated according to visceral (V) and subcutaneous (S) fat areas using computed tomography scanning at the umbilical level], blood pressure, metabolic parameters and hormones including insulin and adiponectin were measured. After full polysomnography, venous blood was collected between 0600 and 0700 h.

RESULTS

Severe OSAS patients were more hypertensive than mild and moderate OSAS. Fasting plasma glucose (FPG) and fasting plasma insulin and homeostasis model assessment of insulin resistance (HOMA-IR) levels were all higher in severe OSAS than mild and moderate OSAS patients. HOMA-IR was correlated not only with obesity [body mass index (BMI), V and S areas] but also with apnoea (AHI, min SpO2 and desaturation time). Additionally, HOMA-IR was correlated positively with haemoglobin (Hb)A1c, systolic (SBP) and diastolic blood pressure (DBP), triglycerides and free fatty acids (FFA), and negatively with high density lipoprotein (HDL)-cholesterol, suggesting that insulin resistance is a key component of the metabolic syndrome in OSAS. Plasma adiponectin levels were not different between mild, moderate and severe OSAS groups. Plasma adiponectin levels were correlated with HOMA-IR and V area, but not AHI or min SpO2. Stepwise multiple regression analysis, however, revealed that BMI, AHI and plasma adiponectin were independently associated with HOMA-IR.

CONCLUSION

Sleep-disordered breathing was associated with insulin resistance independent of obesity. Although plasma adiponectin was also an independent determinant of HOMA-IR in OSAS patients, plasma adiponectin was more closely related to obesity than to sleep apnoea. Although treatment of sleep-disordered breathing with nasal continuous positive airway pressure reportedly improves insulin sensitivity, our findings suggest that treatment of obesity is also essential in ameliorating insulin resistance at least through increased plasma adiponectin levels in OSAS.

Classification of Cheyne-Stokes breathing and obstructive sleep apnea using ECG

High cost of diagnostic studies to detect sleep disordered breathing and lack of availability of certified sleep laboratories in all inhabited areas make investigation of alternative methods of detecting sleep disordered breathing attractive. This study aimed to explore the possibility of discerning obstructive sleep apnea (OSA) from Cheyne-Stokes respiration (CSR) using overnight electrocardiography (ECG). Polysomnographic and ECG signals were acquired from the 13 OSA and 7 CSR volunteer subjects. Two signals: R-Wave Attenuation (RWA) and Heart Rate Variability (HRV) series were derived from the ECG. Using frequency domain analysis, various frequency bands in the power spectrum of RWA and HRV signals were identified that showed sensitivity to OSA and CSR events. A three-stage algorithm was developed to detect and differentiate OSA events from CSR events using RWA and HRV analysis. To test the algorithm, the ECG data was divided into fifteen minute epochs for analysis. Seventy two epochs containing OSA and 72 with CSR events were selected. 48 OSA clips and 48 CSR clips were randomly selected to form the training set. The remaining 24 clips in each category formed the test set. This method produced an average sensitivity of 95.83% and specificity of 79.16% in the training set and sensitivity of 87.5% and a specificity of 75% in the test set.

Heart failure and sleep apnoea: to sleep perchance to dream

Heart failure and sleep apnoea are major health problems with an increasingly recognized association; evidence suggests that sleep apnoea may play a role in the progression of heart failure. However, confounding factors such as obesity, hypertension and coronary heart disease make this relationship uncertain and an independent correlation remains unproven. Diagnosis of sleep apnoea is suboptimal, as it is often asymptomatic and polysomnography is expensive and time-consuming. A simple and reliable screening protocol is required. All heart failure patients should be considered to be at high risk of sleep apnoea, as this association might be linked to adverse outcome. Continuous positive airway pressure has shown some beneficial effects, but long-term outcome and improvement in survival remains to be demonstrated. Despite recent advances in the understanding of the complex relationship between heart failure and sleep apnoea, there are a number of areas requiring further investigation, which may have important implications for the management and prognosis of a significant number of patients.

Chronic liver injury during obstructive sleep apnea

Patients with obstructive sleep apnea (OSA) are at risk for the development of fatty liver as a result of being overweight. Several data suggest that OSA per se could be a risk factor of liver injury; ischemic hepatitis during OSA has been reported, and OSA is an independent risk factor for insulin resistance. Therefore, we investigated liver damage and potential mechanisms in 163 consecutive nondrinking patients with nocturnal polysomnographic recording for clinical suspicion of OSA. Serum levels of liver enzymes were measured in all patients. Liver biopsy was offered to patients with elevated liver enzymes. Intrahepatic hypoxia was assessed by the expression of vascular endothelial growth factor (VEGF) on liver biopsy specimens. Severe OSA (apnea-hypopnea index [AHI] > 50/hr) was seen in 27% of patients; 52% had moderate OSA (AHI 10-50/hr), and 21% had no OSA. Overall, 20% had elevated liver enzymes. Independent parameters associated with elevated liver enzymes were body mass index (BMI) (OR: 1.13; CI: 1.03-1.2) and severe OSA (OR: 5.9; CI: 1.2-29). Liver biopsy was performed in 18 of 32 patients with elevated liver enzymes and showed steatohepatitis in 12 cases, associated with fibrosis in 7 cases. Patients with severe OSA were more insulin-resistant according to homeostasis model assessment, had higher percentage of steatosis as well as scores of necrosis and fibrosis, despite similar BMI. Hepatic immunostaining used as an indirect marker of hypoxia was not different between patients with or without severe OSA. In conclusion, severe OSA is a risk factor for elevated liver enzymes and steatohepatitis independent of body weight. Promotion of insulin resistance is probably involved. Further studies are needed to determine whether hypoxia contributes directly to liver injury.

Impact of heart failure on quality of sleep

Chronic heart failure is an important health problem associated with a high mortality and morbidity. Appropriate treatment reduces mortality and leads to improved exercise tolerance but many patients report poor quality of sleep. Sleep studies of patients with heart failure suggest that sleep disordered breathing is experienced in 50% of patients and is a powerful predictor of poor prognosis. Sleep disordered breathing broadly comprises obstructive sleep apnoea, when upper airway instability causes mechanical obstruction to breathing; and central sleep apnoea, characterised by an absence of ventilatory effort. Sleep disordered breathing occurring in patients with heart failure is in most part attributable to central sleep apnoea and reflects uncompensated instability of the ventilatory feedback mechanism.

Prevalence of sleep-disordered breathing and sleep apnea in middle-aged urban Indian men

No data are available on the prevalence of sleep-disordered breathing (SDB) and obstructive sleep apnea-hypopnea syndrome (OSAHS) in Indians. We conducted a two-phase cross-sectional prevalence study for the same in healthy urban Indian males (35-65 years) coming to our hospital in Bombay for a routine health check. We also investigated its risk factors and evaluated the significance of the most commonly asked questions that best correlated with the presence of OSAHS. In the first phase, 658 subjects (94%) returned completed questionnaires regarding their sleep habits and associated medical conditions. In the second phase, 250 of these underwent an overnight home sleep study. The estimated prevalence of SDB (apnea-hypopnea index of 5 or more) was 19.5%, and that of OSAHS (SDB with daytime hypersomnolence) was 7.5%. Multiple stepwise logistic regression determined body mass index, neck girth, and history of diabetes mellitus as the principal covariates of SDB. The presence of snoring, nocturnal choking, unrefreshing sleep, recurrent awakening from sleep, daytime hypersomnolence, and daytime fatigue was each statistically significant for identifying patients with OSAHS. The higher prevalence of OSAHS in urban Indian men is striking and may have major public health implications in a developing country.

Sleep-Disordered Breathing in Patients With Heart Failure: Pathophysiology, Assessment, and Management

PURPOSE

To provide clinicians in primary care settings information on the effects of sleep-disordered breathing in patients with heart failure (HF). Assessment and screening tools, as well as management considerations, are presented.

DATA SOURCES

Review of the scientific literature of the past 10 years, along with classic studies and Internet sources.

CONCLUSIONS

HF is an increasingly prevalent problem with a high degree of associated sleep-disordered breathing. There are two broad categories of sleep-disordered breathing: obstructive sleep apnea and central sleep apnea/Cheyne-Stokes breathing. Both of these occur on a continuum of mild hypopnea to severe apnea with hypoxia. Sleep apneas are particularly harmful to patients with HF and, if left untreated, may adversely affect their prognosis. Yet sleep apnea is not routinely screened for in this population.

IMPLICATIONS FOR PRACTICE

Given the serious consequences of untreated sleep-disordered breathing, there is sound justification to screen for sleep apnea in all patients with HF. Subsequent treatment of those patients with sleep apnea can significantly improve their quality of life and can decrease their mortality.

Obstructive sleep apnea and cardiovascular disease

Obstructive sleep apnea (OSA) is a common disorder associated with an increased risk of cardiovascular disease and stroke. As it is strongly associated with known cardiovascular risk factors, including obesity, insulin resistance, and dyslipidemia, OSA is an independent risk factor for hypertension and has also been implicated in the pathogenesis of congestive cardiac failure, pulmonary hypertension, arrhythmias, and atherosclerosis. Obesity is strongly linked to an increased risk of OSA, and weight loss can reduce the severity of OSA. The current standard treatment for OSA-nasal continuous positive airway pressure (CPAP)-eliminates apnea and the ensuing acute hemodynamic changes during sleep. Long-term CPAP treatment studies have shown a reduction in nocturnal cardiac ischemic episodes and improvements in daytime blood pressure levels and left ventricular function. Despite the availability of effective therapy, OSA remains an underdiagnosed and undertreated condition. A lack of physician awareness is one of the primary reasons for this deficit in diagnosis and treatment.

Sleep and the endocrine system: new associations to old diseases

Sleep and sleep disorders play a prominent role in hormone regulation. Given that sleep disordered breathing (SDB) and diabetes mellitus (DM) are thought to result from obesity, it has been assumed that when the two coexist, the diabetes was caused by the obesity. However, new data has shed light on the effects that SDB, sleep deprivation, and snoring have on glucose regulation. It now appears that in addition to causing daytime drowsiness, cardiovascular disease, mood and memory disturbances, impotence, and car wrecks, obstructive sleep apnea (OSA) also promotes insulin resistance. Though data is still sketchy on the optimum management of coexisting DM and OSA, large-scale studies will most likely prove that homeostatic glucose control in patients with sleep apnea will require aggressive treatment of their SDB.

Increased incidence of cardiovascular disease in middle-aged men with obstructive sleep apnea: a 7-year follow-up

The incidence of a cardiovascular disease (CVD) was explored in a consecutive sleep clinic cohort of 182 middle-aged men (mean age, 46.8 +/- 9.3; range, 30-69 years in 1991) with or without obstructive sleep apnea (OSA). All subjects were free of hypertension or other CVD, pulmonary disease, diabetes mellitus, psychiatric disorder, alcohol dependency, as well as malignancy at baseline. Data were collected via the Swedish Hospital Discharge Register covering a 7-year period before December 31, 1998, as well as questionnaires. Effectiveness of OSA treatment initiated during the period as well as age, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP) at baseline, and smoking habits were controlled. The incidence of at least one CVD was observed in 22 of 60 (36.7%) cases with OSA (overnight oxygen desaturations of 30 or more) compared with in 8 of 122 (6.6%) subjects without OSA (p < 0.001). In a multiple logistic regression model, significant predictors of CVD incidence were OSA at baseline (odds ratio [OR] 4.9; 95% confidence interval [CI], 1.8-13.6) and age (OR 23.4; 95% CI, 2.7-197.5) after adjustment for BMI, SBP, and DBP at baseline. In the OSA group, CVD incidence was observed in 21 of 37 (56.8%) incompletely treated cases compared with in 1 of 15 (6.7%) efficiently treated subjects (p < 0.001). In a multiple regression analysis, efficient treatment was associated with a significant risk reduction for CVD incidence (OR 0.1; 95% CI, 0.0-0.7) after adjustment for age and SBP at baseline in the OSA subjects. We conclude that the risk of developing CVD is increased in middle-aged OSA subjects independently of age, BMI, SBP, DBP, and smoking. Furthermore, efficient treatment of OSA reduces the excess CVD risk and may be considered also in relatively mild OSA without regard to daytime sleepiness.

Central sleep apnoea syndrome in patients with chronic heart disease: a critical review of the current literature

The prevalence, prognosis, clinical presentation, pathophysiology, diagnosis, and treatment of the central sleep apnoea syndrome (CSAS) are reviewed and its relationship with congestive heart failure (CHF) is discussed. Adequately powered trials are needed with survival and health status as end points to establish whether correction of sleep related breathing abnormalities improves the outcome in patients with CHF.