Sleep-disordered breathing, glucose intolerance, and insulin resistance

Interações entre síndrome da apnéia obstrutiva do sono e resistência à insulina

Estudos anteriores mostraram que pacientes com Apnéia Obstrutiva do Sono (AOS) apresentam maior risco para doenças cardiovasculares. Entretanto, permanece controverso se essa associação depende da obesidade ou se ocorre devido a alterações fisiológicas decorrentes da desordem do sono, como ativação do sistema nervoso simpático, da inflamação e desordens do eixo corticotrófico e somatotrófico, que predispõem a danos vasculares. Além disso, muitos fatores de risco para doenças cardiovasculares (DCV) estão fortemente associados ao distúrbio respiratório, entre eles hipertensão, obesidade, resistência à insulina e diabetes tipo 2 (DM2). Neste artigo, vamos discutir a interação entre resistência à insulina e AOS e os possíveis mecanismos fisiopatológicos que contribuem para suas co-morbidades.

Prevalence of sleep apnea in a population of adults with type 2 diabetes mellitus

OBJECTIVE

To assess the prevalence of sleep apnea (SA) in adults with type 2 diabetes mellitus (T2DM) and examine whether demographics and comorbid factors were associated with SA in this population.

METHODS

This study enrolled 330 consecutive adults with T2DM referred to a diabetes clinic, 279 of whom completed the study. Evaluation of the presence of SA was performed with use of a single-channel recording device that measures disordered breathing events from a nasal cannula airflow signal. The device was worn by the study participants in their home, after instruction in appropriate use by clinical staff at the diabetes center. The presence and severity of SA were determined by use of an apnea-hypopnea index (AHI), reflecting periods of diminished and absent breathing. Demographic and medical information data were collected to detect factors associated with SA in this study population. In addition, a time and cost analysis was conducted regarding the screening process for SA by clinical staff at the diabetes center.

RESULTS

The results show a high prevalence of SA in adults with T2DM, ranging from 48% (AHI level of >or=10 events/h) to 29% (AHI level of >or=20 events/h). At an AHI cutoff value of >or=15 events/h, the overall prevalence rate was 36% (49% in male and 21% in female participants). The following variables were associated with SA: age >or=62 years, male sex, body mass index >or=30 kg/m2, snoring, and reports of stopping breathing during sleep. The time and cost analysis showed that the screening device involved minimal setup time, was simple to use, and was a cost-effective method to screen for SA.

CONCLUSION

SA is a common disorder associated with major morbid conditions, including hypertension, obesity, cardiovascular disease, and insulin resistance. Predisposing factors for SA and T2DM are similar. This study showed that SA has a high prevalence in adults with T2DM and identified factors that may be associated with its presence in this population. Assessment for SA can be easily performed in an outpatient setting with a portable recording device such as the one used in this study. Screening for SA should be considered in the T2DM population.

Effect of CPAP on insulin resistance and HbA1c in men with obstructive sleep apnoea and type 2 diabetes

BACKGROUND

The effects of continuous positive airway pressure (CPAP) for obstructive sleep apnoea (OSA) on insulin resistance are not clear. Trials have found conflicting results and no appropriate control groups have been used.

METHODS

Forty-two men with known type 2 diabetes and newly diagnosed OSA (>10 dips/h in oxygen saturation of >4%) were randomised to receive therapeutic (n = 20) or placebo CPAP (n = 22) for 3 months. Baseline tests were performed and repeated after 3 months. The study was double blind.

RESULTS

Results are expressed as mean (SD). CPAP improved the Epworth sleepiness score significantly more in the therapeutic group than in the placebo group (-6.6 (4.5) vs -2.6 (4.9), p = 0.01). The maintenance of wakefulness test improved significantly in the therapeutic group but not in the placebo group (+10.6 (13.9) vs -4.7 (11.8) min, p = 0.001). Glycaemic control and insulin resistance did not significantly change in either the therapeutic or placebo groups: HbA1c (-0.02 (1.5) vs +0.1 (0.7), p = 0.7, 95% CI -0.6% to +0.9%), euglycaemic clamp (M/I: +1.7 (14.1) vs -5.7 (14.8), p = 0.2, 95% CI -1.8 to +0.3 l/kg/min(1000)), HOMA-%S (-1.5 (2.3) vs -1.1 (1.8), p = 0.2, 95% CI -0.3% to +0.08%) and adiponectin (-1.1 (1.2) vs -1.1 (1.3), p = 0.2, 95% CI -0.7 to +0.6 microg/ml). Body mass index, bioimpedance and anthropometric measurements were unchanged. Hours of CPAP use per night were 3.6 (2.8) in the treatment group and 3.3 (3.0) in the placebo group (p = 0.8). There was no correlation between CPAP use and the measures of glycaemic control or insulin resistance.

CONCLUSION

Therapeutic CPAP does not significantly improve measures of glycaemic control or insulin resistance in men with type 2 diabetes and OSA.

Clinical perspective of obstructive sleep apnea-induced cardiovascular complications

Obstructive sleep apnea (OSA) syndrome is a highly prevalent disorder characterized by recurrent upper airway collapse during sleep, and associated with repetitive episodes of transient oxygen desaturation during sleep. It disrupts normal ventilation and sleep architecture, and is typically associated with excessive daytime sleepiness, snoring, and witnessed apneas. Besides being associated with neurocognitive impairment, mood and behavioral effects, and increased risk for work-related and traffic accidents, OSA has also been implicated in the pathogenesis of various cardiovascular diseases, including systemic hypertension, coronary artery disease, congestive heart failure, pulmonary hypertension, stroke, and cardiac arrhythmias. The mechanisms by which OSA affects the cardiovascular system may involve mechanical effects on intrathoracic pressure, increased sympathetic activation, intermittent hypoxia, and endothelial dysfunction. Therapy with continuous positive airway pressure (CPAP) has been demonstrated to improve cardiopulmonary hemodynamics in patients with OSA and may reverse the endothelial cell dysfunction.

Sleep duration and snoring in relation to biomarkers of cardiovascular disease risk among women with type 2 diabetes

OBJECTIVE

Sleep habits have been associated with risk of cardiovascular disease (CVD) and metabolic disturbances, but the mechanisms underlying these associations have yet to be fully elucidated. We aim to determine whether sleep duration and/or snoring are associated with biomarkers of CVD in women with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We studied 935 women aged 43-69 years enrolled in the Nurses' Health Study cohort with type 2 diabetes who had no history of documented coronary heart disease or stroke in 1990. Information on sleep duration and snoring frequency was collected in 1986 from mailed questionnaires, and biomarkers of CVD were measured from blood samples taken in 1989-1990.

RESULTS

Longer sleep duration was associated with increased levels of C-reactive protein after adjusting for age, BMI, lifestyle factors, family history of diabetes, glycemic control, and medication use (P = 0.05). HDL was decreased with short and long sleep duration among normotensive (P = 0.02) but not hypertensive women. More frequent snoring was directly associated with triglycerides (P = 0.02) and inversely associated with HDL cholesterol (0.03) and adiponectin (P = 0.03) in multivariate-adjusted analyses.

CONCLUSIONS

The associations of sleep duration and snoring with lipid profile, hormone measures, and/or inflammatory markers may partially explain the previously reported relationship between sleep habits and cardiovascular and metabolic disorders.

Doença hepática não-alcoólica: evolução após derivação gastrojejunal em Y-de-Roux pela técnica de fobi-capella

RACIONAL: A doença hepática não-alcoólica apresenta alta prevalência entre pacientes com obesidade mórbida, podendo evoluir de esteatose hepática até esteatohepatite e cirrose. OBJETIVO: Determinar o efeito da derivação gástrica na incidência de doença hepática não-alcoólica e co-morbidades relacionadas em pacientes com obesidade mórbida. MÉTODOS: Os pacientes foram prospectivamente avaliados no pré-operatório e, no mínimo, após 6 meses de pós-operatório. Foram analisados: dados antropométricos, co-morbidades, medicamentos em uso, colesterol, triglicerídeos, provas hepáticas e incidência de doença hepática não-alcoólica. Todos os pacientes com alteração de provas hepáticas foram submetidos a biopsia hepática no peroperatório. RESULTADO: Vinte e oito pacientes com doença hepática não-alcoólica foram incluídos no estudo com índice de massa corpórea médio de 42 ± 4 kg/m². Vinte e cinco pacientes apresentaram 59 co-morbidades, sendo as mais freqüentes: elevação de triglicerídeos (n = 23), elevação de colesterol total (n = 13) e hipertensão arterial (n = 11). Foram submetidos a biopsia 22 pacientes: 10 apresentaram esteatose macrogoticular moderada, 5 esteatose macrogoticular discreta e 7 esteatohepatite. Os doentes foram analisados em média após 230 dias de pós-operatório. Apresentaram perda de 64% do excesso de peso, redução do índice de massa corpórea médio para 29,6 ± 3 kg/m² e 21 co-morbidades em 13 pacientes. Houve diminuição estatisticamente significante do número dos acometidos de elevação de triglicerídeos, elevação de colesterol total, hipertensão arterial e na incidência de doença hepática não-alcoólica. CONCLUSÃO: A perda de peso proporcionada pela derivação gastrojejunal em Y-de-Roux pela técnica de Fobi-Capella em pacientes com doença hepática não-alcoólica está associada à diminuição de sua incidência e de outras co-morbidades.

Metabolic consequences of intermittent hypoxia

Insulin resistance is being recognized increasingly as the basis for the constellation of metabolic abnormalities that make up the metabolic syndrome, or Syndrome X. Insulin resistance is also the primary risk factor for the development of type 2 diabetes mellitus, which is currently reaching epidemic proportions by affecting more than 170 million people worldwide. A combination of environmental and genetic factors have led to a dramatic rise in visceral adiposity, the predominant factor causing insulin resistance and type 2 diabetes. Visceral adiposity is also the major risk factor for the development of Sleep Apnea (SA)--an association that has fueled interest in the co-morbidity of SA and the metabolic syndrome, but hampered attempts to ascribe an independent causative role for Sleep Apnea in the development of insulin resistance and type 2 diabetes. Numerous population and clinic-based epidemiologic studies have shown associations, often independent of obesity, between SA (or surrogates such as snoring) and measures of glucose dysregulation or type 2 diabetes. However, treatment of SA with continuous positive airway pressure (CPAP) has not been conclusive in demonstrating improvements in insulin resistance, perhaps due to the overwhelming effects of obesity. Here we show that in lean, otherwise healthy mice that exposure to intermittent hypoxia produced whole-body insulin resistance as determined by the hyperinsulinemic euglycemic clamp and reduced glucose utilization in oxidative muscle fibers, but did not cause a change in hepatic glucose output. Furthermore, the increase in insulin resistance was not affected by blockade of the autonomic nervous system. We conclude that intermittent hypoxia can cause acute insulin resistance in otherwise lean healthy animals, and the response occurs independent of activation of the autonomic nervous system.

Sleep and the metabolic syndrome

The metabolic syndrome represents a clustering of several interrelated risk factors of metabolic origin that are thought to increase cardiovascular risk. It is still uncertain whether this clustering results from multiple underlying risk factors or whether it has a single cause. One metabolic abnormality that may underlie several clinical characteristics of the metabolic syndrome is insulin resistance. This review discusses the evidence that sleep disturbances (obstructive sleep apnoea, sleep deprivation and shift work) may independently lead to the development of both insulin resistance and individual clinical components of the metabolic syndrome. The converse may also be true, in that metabolic abnormalities associated with the metabolic syndrome and insulin resistance may potentially exacerbate sleep disorders. The notion that sleep disturbances exert detrimental metabolic effects may help explain the increasing prevalence of the metabolic syndrome and insulin resistance in the general population and may have important implications for population-based approaches to combat the increasing epidemic of metabolic and cardiovascular disease.

Sleep studies: which technologies?

The demand for sleep services for young patients has escalated due to the increased recognition of pediatric sleep disorders over the past two decades. In this overview, we will highlight the essentials of pediatric sleep monitoring and stress particular issues that require the awareness of clinicians evaluating children for sleep disorders. While many techniques used in the "adult" sleep centers may suffice for the older adolescent patient, specific tailoring of the design of the sleep center to younger children and their families, and attention to the age-sensitive components of sleep data acquisition and interpretation are increasingly important in younger children. Several promising newer technologies and their potential for future clinical utility will be also reviewed.

Metabolic risk factors for vascular disease in obstructive sleep apnea: a matched controlled study

RATIONALE

Obstructive sleep apnea (OSA) is reported to have a metabolic profile predisposing to cardiovascular disease. However, previous case-control studies have not adequately controlled for confounders.

OBJECTIVES

To determine whether OSA is associated with increased insulin resistance and related metabolic risk factors.

METHODS

We performed a matched case-control study (n = 42) examining putative metabolic risks among men with OSA attending a sleep clinic (apnea-hypopnea index [AHI] > 15] compared with no OSA (AHI < 5). Participants were matched for age +/- 5 yr, body mass index +/- 10%, and current smoking status. They were free of diabetes, clinically demonstrable cardiovascular disease, marked hypertension, and dyslipidemia.

MEASUREMENTS AND MAIN RESULTS

Mean +/- SD AHI was higher in patients with OSA (40 +/- 27) than in control subjects (3 +/- 1.3, p = 0.02), and median (interquartile range) nocturnal oxygen saturation was lower (OSA, 83 [76-88]; control, 91 [90-93]%; p < 0.001). Patients with OSA had a higher median (interquartile range) homeostasis model assessment score for insulin resistance (OSA, 1.7 [0.8-4.1]; control, 1.0 [0.7-1.8] mU.mmol/L(2); p = 0.02), total cholesterol (OSA, 5.6 [4.8-6.2]; control, 4.8 [4.3-5.4] mmol/L; p = 0.049), and low-density-lipoprotein cholesterol (OSA, 3.8 [2.9-4.2]; control, 3.1 [2.6-3.6] mmol/L; p = 0.04). Patients with OSA had higher 24-h and nocturnal (12-h) urinary norepinephrine excretion and plasma leptin levels, and lower insulin-like growth factor (IGF)-1 levels (all, p < or = 0.02). Multiple linear regression, adjusting for central obesity, age, and alcohol consumption, confirmed an independent association between OSA and metabolic risks (all, p < 0.05), with a trend for IGF-1 (p = 0.053).

CONCLUSIONS

In a sleep clinic population, men with OSA and no identifiable cardiovascular disease have increased insulin resistance and other metabolic changes that act to increase the risk of vascular disease, compared with age- and body mass index-matched attendees without OSA.

Effect of asthma on the risk of obstructive sleep apnea syndrome in atopic women

BACKGROUND

Obstructive sleep apnea syndrome is associated with significant morbidity and remains underdiagnosed in women. Identification of high-risk groups among women is important for early detection and treatment.

OBJECTIVE

To describe the prevalence of snoring in young women with atopy and to determine the risk factors for snoring in these individuals.

METHODS

The Cincinnati Childhood Allergy and Air Pollution Study is an ongoing prospective birth cohort study of infants with at least 1 atopic parent. Mothers of study participants were evaluated by questionnaire for snoring, respiratory symptoms, and smoking status. Women who snored were compared with those who did not snore. Logistic regression analysis was performed to determine risk factors for snoring.

RESULTS

Data were available on 677 women who had at least 1 live birth. Of these 677 women, 546 (81%) were white, 122 (18%) were African American, and 9 (1%) were biracial or Asian. The mean +/- SD age of the cohort at the time of evaluation for snoring was 29.6 +/- 5.6 years. Of the 677 women, 231 (34%) reported snoring at least 1 night per week, and snoring almost always (5-7 nights per week) was reported by 85 (13%). An almost 2-fold risk of snoring was associated with asthma (diagnosis and current symptoms) (odds ratio, 1.8; 95% confidence interval, 1.1-2.8) and African American race (odds ratio, 1.6; 95% confidence interval, 1.04-2.6) after controlling for income level and smoking status.

CONCLUSIONS

We found a high prevalence of snoring inyoung women with atopy and a significant association with asthma.

Non-arteritic anterior ischaemic optic neuropathy is nearly systematically associated with obstructive sleep apnoea

AIM

To evaluate newly diagnosed non-arteritic anterior ischaemic optic neuropathy (NAION) patients for the existence of an associated sleep apnoea syndrome.

METHODS

Newly identified NAION patient underwent polysomnography. The prevalence of sleep apnoea in NAION patients was compared to the prevalence previously found in the general population. Hypertension, diabetes, hyperlipidaemia, and atheromatous lesions of carotid vessels as classic risk factors associated with NAION were also identified.

RESULTS

27 consecutive newly diagnosed NAION patients (18 men and nine women, mean age 65 (SD 8) years, body mass index 27.2 (3.8) kg/m2) were included in the study. 24 of these 27 NAION patients (89%) exhibited a sleep apnoea syndrome (respiratory disturbance index: 37.2/h (SD 18.3/h). Risk ratio for a NAION patient to have sleep apnoea was 4.9 compared to the general population (p < 0.001). Sleep apnoea was 1.5-2-fold more frequent than the rate of the other identified risk factors typically associated with NAION (hypertension, diabetes).

CONCLUSIONS

Sleep apnoea is the most frequent disorder associated with NAION and should be screened in this population. At least a questionnaire related to obstructive sleep apnoea symptoms and assessment of sleepiness should be systematically proposed to patients with NAION.

CPAP treatment of a population-based sample--what are the benefits and the treatment compliance?

BACKGROUND & PURPOSE

Continuous positive airway pressure (CPAP) treatment has positive effects, including improved insulin sensitivity in sleep-laboratory cohorts with obstructive sleep apnea syndrome. There is still a lack of data on benefits obtained and possibilities to treat less symptomatic individuals. The aim of this study was to evaluate the effect of CPAP treatment on metabolic profile and quality of life (QoL) in a population-based sample of men with sleep apnea. Another purpose was to investigate the compliance to CPAP in this population.

PATIENTS AND METHODS

A population-based sample of 38 men with an AHI>or=10 were treated with CPAP regardless of symptom profile. The controls included men with AHI <10 matched for age and hypertension. The effects were evaluated after 3 weeks and 6 months. Insulin resistance was quantified using the homeostasis model assessment (HOMA). Daytime sleepiness, QoL and subjective symptom load was assessed using the Epworth Sleepiness Scale (ESS), the Medical Outcomes Study Short Form Health Survey (SF-36) and the Minor Symptoms Evaluation-Profile (MSE-P) questionnaires, respectively.

RESULTS

Complete three-week data were obtained from 28 treated men and 28 controls. Compared with controls, the CPAP group displayed a greater reduction of fasting serum insulin (P=0.02), decrease in insulin resistance (P=0.01) and an increase in IGF-1 (P=0.005). The CPAP group further showed an improvement in the SF-36 domains of mental health (P=0.03) and vitality (P=0.06) and a reduction in symptom load in the sleep dimension of the MSE-P. Only 11 (29%) of subjects starting CPAP were still on treatment after 6 months. Those who still used CPAP had a higher score on ESS at baseline (11.3 (4.4) vs. 5.9 (3.4), P<0.0001).

CONCLUSIONS

Benefits of short-term treatment included signs of reduced insulin resistance and improved QoL. However, in this population-based sample compliance with CPAP was very low. More severe sleepiness was a positive predictive factor for treatment compliance.

Relation of habitual snoring with components of metabolic syndrome in Korean adults

AIMS

To examine the association between habitual snoring and components of the metabolic syndrome in Korean adults. Whether these associations are independent of obesity was also explored.

METHODS

Four thousand five hundred and six men and 5041 women aged 40-69 years from the Korean Health and Genome Study were examined. Information of snoring frequency was obtained by a questionnaire and components of the metabolic syndrome were measured.

RESULTS

There was a clear dose-response relationship between the increasing frequency of snoring and the higher prevalence of each component of the metabolic syndrome (P<0.001). After adjustment for age, abdominal obesity, and the other metabolic components, hypertension was significantly associated with a 1.2-fold excess of habitual snoring in both men (P<0.05) and women (P<0.05). The association of habitual snoring with hypertension was unaltered by obesity. Regardless of the presence or absence of abdominal obesity, there was an increase in the prevalence of habitual snoring as the number of metabolic abnormalities increased.

CONCLUSIONS

Habitual snoring is associated with hypertension independent of obesity. While the relationship between habitual snoring and obesity is well recognized, characterization of the role of the other components of the metabolic syndrome as a cause or result of habitual snoring warrants a further study.

Sleep-disordered breathing and cardiovascular health

PURPOSE OF REVIEW

Sleep-disordered breathing is a widely prevalent condition and may have serious medical, social, and economic consequences. This review evaluates the role of sleep-disordered breathing in cardiovascular morbidity and mortality on the basis of recent literature.

RECENT FINDINGS

Epidemiologic studies, retrospective reviews, and prospective clinical trials suggest a strong association between sleep-disordered breathing and adverse cardiovascular events. Individuals with sleep-disordered breathing have a higher prevalence of hypertension, which attenuates with treatment. Furthermore, the presence of sleep-disordered breathing augurs an increased risk of coronary artery disease, cardiac arrhythmias, and heart failure.

SUMMARY

Recent research provides an emerging evidence of the role of sleep-disordered breathing as a risk factor for diverse cardiovascular disorders.

The severity of oxygen desaturation is predictive of carotid wall thickening and plaque occurrence

STUDY OBJECTIVES

To characterize carotid intima-media thickness (IMT) and plaque occurrence in patients with newly diagnosed obstructive sleep apnea (OSA) without known cardiovascular disease.

DESIGN

Prospective study.

SETTING

Sleep Laboratory and Department of Cardiology of Grenoble University Hospital.

PATIENTS AND INTERVENTION

OSA syndrome is associated with an increased cardiovascular risk. Carotid IMT is recognized as a marker of preclinic atheroma. A small number of studies have analyzed large-artery wall modifications in OSA syndrome. Eighty-three patients (74 men; mean age +/- SD, 48 +/- 11 years; mean body mass index, 27.4 +/- 4.2 kg/m(2)) were included. Mean respiratory disturbance index was 40.7 +/- 19.2/h, mean nocturnal arterial oxygen saturation (Sao(2)) was 93.1 +/- 2.0%, and mean percentage of recording time spent at Sao(2) < 90% was 8.6 +/- 16.8%. Clinical BP was measured following European Society of Hypertension/European Society of Cardiology recommendations, and 24-h ambulatory BP monitoring was assessed. Ultrasonography was used to determine the carotid IMT and atheromatous plaque occurrence.

MEASUREMENTS AND RESULTS

Twenty-five of 83 patients (30%) had carotid wall hypertrophy (IMT > 0.8 mm). In a logistic regression model, mean nocturnal Sao(2) < 92% (odds ratio [OR], 3.9; 95% confidence interval [CI], 1.1 to 12.7) was associated with carotid wall hypertrophy. ORs were even higher after adjustment for BP status (OR, 10.6; 95% CI, 1.6 to 50.9 in normotensive patients) and glucose levels (OR, 4.5; 95% CI, 1.0 to 20.9). Mean nocturnal Sao(2) < 92% and minimal nocturnal Sao(2) < 80% (ORs, 3.1 and 3.1; 95% CIs, 1.0 to 9.4 and 1.0 to 8.5, respectively) were associated with the presence of carotid plaque formation independently of the BP status (hypertensive or normotensive).

CONCLUSIONS

The severity of oxygen desaturation appears to be one of the best predictors for carotid IMT and plaque occurrence in OSA patients without known cardiovascular disease. Thus, carotid IMT and plaque formation appeared as early cardiovascular consequences in OSA patients.

Disorders of glucose metabolism in sleep apnea

Sleep is a complex behavioral state that occupies one-third of the human life span. Although viewed as a passive condition, sleep is a highly active and dynamic process. The sleep-related decrease in muscle tone is associated with an increase in resistance to airflow through the upper airway. Partial or complete collapse of the airway during sleep can lead to the occurrence of apneas and hypopneas during sleep that define the syndrome of sleep apnea. Sleep apnea has become pervasive in Western society, affecting approximately 5% of adults in industrialized countries. Given the pandemic of obesity, the prevalence of Type 2 diabetes mellitus and metabolic syndrome has also increased dramatically over the last decade. Although the role of sleep apnea in cardiovascular disease is uncertain, there is a growing body of literature that implicates sleep apnea in the pathogenesis of altered glucose metabolism. Intermittent hypoxemia and sleep fragmentation in sleep apnea can trigger a cascade of pathophysiological events, including autonomic activation, alterations in neuroendocrine function, and release of potent proinflammatory mediators such as tumor necrosis factor-alpha and interleukin-6. Epidemiologic and experimental evidence linking sleep apnea and disorders of glucose metabolism is reviewed and discussed here. Although the cause-and-effect relationship remains to be determined, the available data suggest that sleep apnea is independently associated with altered glucose metabolism and may predispose to the eventual development of Type 2 diabetes mellitus.

Obstructive sleep apnea and the metabolic syndrome in community-based Chinese adults in Hong Kong

OBJECTIVE

To investigate the relationship between obstructive sleep apnea (OSA) and the metabolic syndrome, an established cardiovascular risk factor, in middle-aged Chinese subjects.

DESIGN

A prospective cross-sectional study from community-dwelling volunteers.

SUBJECTS

Subjects of either sex between 30 and 60 years old were recruited from the staff in public institutions or visitors to community centers in Hong Kong.

METHODS

Demographic and anthropomentric indices, blood pressure and metabolic profile (fasting blood glucose, total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol and triglycerides) were measured. Overnight polysomnographic studies were conducted. Presence of obstructive sleep apnea (OSA) was defined as apnea-hypopnea index (AHI)5. Metabolic syndrome was defined by the criteria of the National Cholesterol Education Panel, but using Asian cut-off values for abdominal obesity.

RESULTS

A total of 255 subjects (150 men, 105 women) were studied. Subjects with OSA had five-fold risk of having metabolic syndrome. OSA was associated with the metabolic syndrome or its components, including waist circumference, diastolic blood pressure and fasting glucose, after adjusting for confounding variables. The independent determinants of OSA were age, gender, body mass index (BMI) and the metabolic syndrome.

CONCLUSION

Among community-based middle-aged Chinese subjects, the metabolic syndrome was independent predictor of OSA.

Surgically-induced weight loss significantly improves nonalcoholic fatty liver disease and the metabolic syndrome

OBJECTIVE

To evaluate the effects of surgical weight loss on fatty liver disease in severely obese patients.

SUMMARY BACKGROUND DATA

Nonalcoholic fatty liver disease (NAFLD), a spectrum that extends to liver fibrosis and cirrhosis, is rising at an alarming rate. This increase is occurring in conjunction with the rise of severe obesity and is probably mediated in part by metabolic syndrome (MS). Surgical weight loss operations, probably by reversing MS, have been shown to result in improvement in liver histology.

METHODS

Patients who underwent laparoscopic surgical weight loss operations from March 1999 through August 2004, and who agreed to have an intraoperative liver biopsy followed by at least one postoperative liver biopsy, were included.

RESULTS

There were 70 patients who were eligible. All patients underwent laparoscopic operations, the majority being laparoscopic Roux-en-Y gastric bypass. The mean excess body weight loss at time of second biopsy was 59% +/- 22% and the time interval between biopsies was 15 +/- 9 months. There was a reduction in prevalence of metabolic syndrome, from 70% to 14% (P < 0.001), and a marked improvement in liver steatosis (from 88% to 8%), inflammation (from 23% to 2%), and fibrosis (from 31% to 13%; all P < 0.001). Inflammation and fibrosis resolved in 37% and 20% of patients, respectively, corresponding to improvement of 82% (P < 0.001) in grade and 39% (P < 0.001) in stage of liver disease.

CONCLUSION

Surgical weight loss results in significant improvement of liver morphology in severely obese patients. These beneficial changes may be associated with a significant reduction in the prevalence of the metabolic syndrome.

Pathophysiology of obstructive sleep apnea

This article explores the physiologic basis and symptoms of obstructive sleep apnea--a general term encompassing central sleep apnea and obstructive sleep apnea. The former is relatively uncommon while the latter is much more common. Episodic collapse and blockage of the upper airway occur during sleep despite continuous respiratory effort. Three types of sleep obstructive breathing--apnea, hypopnea, and airway resistance--are associated with respiratory-related arousals from sleep.

Sleep apnea is a manifestation of the metabolic syndrome

Obstructive sleep apnea (OSA) is a prevalent disorder particularly among middle-aged, obese men, although its existence in women as well as in lean individuals is increasingly recognized. Despite the early recognition of the strong association between OSA and obesity, and OSA and cardiovascular problems, sleep apnea has been treated as a 'local abnormality' of the respiratory track rather than as a 'systemic illness.' In 1997, we first reported that the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFalpha) were elevated in patients with disorders of excessive daytime sleepiness (EDS) and proposed that these cytokines were mediators of daytime sleepiness. Also, we reported a positive correlation between IL-6 or TNFalpha plasma levels and the body-mass-index (BMI). In subsequent studies, we showed that IL-6, TNFalpha, and insulin levels were elevated in sleep apnea independently of obesity and that visceral fat, was the primary parameter linked with sleep apnea. Furthermore, our findings that women with the polycystic ovary syndrome (PCOS) (a condition associated with hyperandrogenism and insulin resistance) were much more likely than controls to have sleep disordered breathing (SDB) and daytime sleepiness, suggests a pathogenetic role of insulin resistance in OSA. Other findings that support the view that sleep apnea and sleepiness in obese patients may be manifestations of the Metabolic Syndrome, include: obesity without sleep apnea is associated with daytime sleepiness; PCOS and diabetes type 2 are independently associated with EDS after controlling for SDB, obesity, and age; increased prevalence of sleep apnea in post-menopausal women, with hormonal replacement therapy associated with a significantly reduced risk for OSA; lack of effect of continuous positive airway pressure (CPAP) in obese patients with apnea on hypercytokinemia and insulin resistance indices; and that the prevalence of the metabolic syndrome in the US population from the Third National Health and Nutrition Examination Survey (1988-1994) parallels the prevalence of symptomatic sleep apnea in general random samples. Finally, the beneficial effect of a cytokine antagonist on EDS in obese, male apneics and that of exercise on SDB in a general random sample, supports the hypothesis that cytokines and insulin resistance are mediators of EDS and sleep apnea in humans. In conclusion, accumulating evidence provides support to our model of the bi-directional, feed forward, pernicious association between sleep apnea, sleepiness, inflammation, and insulin resistance, all promoting atherosclerosis and cardiovascular disease.

Sleep apnea-induced hypertension: mechanisms of vascular changes

Obstructive sleep apnea-induced hypertension appears to constitute a distinct pathophysiologic entity. Various neurohormonal and inflammatory mediators and hypoxia-induced injury link the two conditions. Obstructive sleep apnea-induced hypertension appears to be reversible in its early phases, but becomes a permanent condition with irreparable vascular changes in later stages. Hence, defining obstructive sleep apnea-induced hypertension and elucidating its role in cardiovascular disease will facilitate appropriate prevention and intervention. This review will clarify the unique set of features of hypertension associated with obstructive sleep apnea and examine the mechanisms that contribute to its cardiovascular consequences.

Intermittent hypoxia induces hyperlipidemia in lean mice

Obstructive sleep apnea, a syndrome leading to recurrent intermittent hypoxia (IH), has been associated previously with hypercholesterolemia, independent of underlying obesity. We examined the effects of experimentally induced IH on serum lipid levels and pathways of lipid metabolism in the absence and presence of obesity. Lean C57BL/6J mice and leptin-deficient obese C57BL/6J-Lep(ob) mice were exposed to IH for five days to determine changes in serum lipid profile, liver lipid content, and expression of key hepatic genes of lipid metabolism. In lean mice, exposure to IH increased fasting serum levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, phospholipids (PLs), and triglycerides (TGs), as well as liver TG content. These changes were not observed in obese mice, which had hyperlipidemia and fatty liver at baseline. In lean mice, IH increased sterol regulatory element binding protein 1 (SREBP-1) levels in the liver, increased mRNA and protein levels of stearoyl-coenzyme A desaturase 1 (SCD-1), an important gene of TG and PL biosynthesis controlled by SREBP-1, and increased monounsaturated fatty acid content in serum, which indicated augmented SCD-1 activity. In addition, in lean mice, IH decreased protein levels of scavenger receptor B1, regulating uptake of cholesterol esters and HDL by the liver. We conclude that exposure to IH for five days increases serum cholesterol and PL levels, upregulates pathways of TG and PL biosynthesis, and inhibits pathways of cholesterol uptake in the liver in the lean state but does not exacerbate the pre-existing hyperlipidemia and metabolic disturbances in leptin-deficient obesity.

Oxidative stress in obstructive sleep apnoea

AIMS

Any sustained elevation of oxidative stress in patients with obstructive sleep apnoea (OSA) might help explain their increased risk for cardiovascular diseases. We tested the hypothesis that measures of oxidative stress are increased in otherwise healthy subjects with OSA when compared to closely matched OSA-free control subjects.

METHODS AND RESULTS

Plasma indices of oxidative stress and lipid peroxidation [thiobarbituric acid-reactive substances (TBARS), oxidized LDL (oxLDL), isoprostanes] were measured in 41 moderate-severe OSA males without other diseases and in 35 matched controls first before sleep, then after 4 h of untreated OSA, and again in the morning after 4 h of effective treatment with continuous positive airway pressure (CPAP). Plasma levels of oxLDL, TBARS, and isoprostanes in OSA patients (n=34, 26, 17, respectively) were comparable to the controls (n=28, 27, 15 for the three markers, respectively). Neither untreated OSA nor CPAP treatment nor normal sleep affected levels of any of the three measures of oxidative stress. There was no association between the severity of sleep apnoea and any measure of oxidative stress.

CONCLUSION

Otherwise healthy OSA patients, without any other co-morbidities, do not manifest evidence for higher oxidative stress and lipid peroxidation. Thus, oxidative stress and lipid peroxidation do not appear to be key mediators of increased cardiovascular disease in OSA patients.

Chronic intermittent hypoxia upregulates genes of lipid biosynthesis in obese mice

Obstructive sleep apnea (OSA), a condition tightly linked to obesity, leads to chronic intermittent hypoxia (CIH) during sleep. There is emerging evidence that OSA is independently associated with insulin resistance and fatty liver disease, suggesting that OSA may affect hepatic lipid metabolism. To test this hypothesis, leptin-deficient obese (ob/ob) mice were exposed to CIH during the light phase (9 AM-9 PM) for 12 wk. Liver lipid content and gene expression profile in the liver (Affymetrix 430 GeneChip with real-time PCR validation) were determined on completion of the exposure. CIH caused a 30% increase in triglyceride and phospholipid liver content (P < 0.05), whereas liver cholesterol content was unchanged. Gene expression analysis showed that CIH upregulated multiple genes controlling 1) cholesterol and fatty acid biosynthesis [malic enzyme and acetyl coenzyme A (CoA) synthetase], 2) predominantly fatty acid biosynthesis (acetyl-CoA carboxylase and stearoyl-CoA desaturases 1 and 2), and 3) triglyceride and phospholipid biosynthesis (mitochondrial glycerol-3-phosphate acyltransferase). A majority of overexpressed genes were transcriptionally regulated by sterol regulatory element-binding protein (SREBP) 1, a master regulator of lipogenesis. A 2.8-fold increase in SREBP-1 gene expression in CIH was confirmed by real-time PCR (P = 0.001). Expression of major genes of cholesterol biosynthesis, SREBP-2 and 3-hydroxy-3-methylglutaryl-CoA reductase, was unchanged. In conclusion, we have shown that CIH may exacerbate preexisting fatty liver of obesity via upregulation of the pathways of lipid biosynthesis in the liver.

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.

Obstructive Sleep Apnea-Hypopnea Syndrome

OSAHS should be an expected condition in many patients encountered by primary care providers. The diagnosis may arise because of patient daytime dysfunction, partner prompting, or in the course of managing comorbidities adversely influenced by the hemodynamic, neural, humoral,and inflammatory consequences of repetitive desaturations and arousals.OSAHS should be suspected in patients who exhibit habitually loud snoring, witnessed apneas/choking/gasping during sleep, hypertension, neck circumferences of 17 inches or greater, obesity, and laterally narrowed oropharynxes. Diagnosis is established by polysomnography. CPAP is the treatment of choice for most patients. Education, follow-up, and heated humidification may help bolster compliance. Lifestyle modifications, oral appliances, and upper surgeries are additional treatment options.

Neuroendocrine changes in sleep apnea

PURPOSE OF REVIEW

To review recent investigations examining the effects of neuroendocrine changes in obstructive sleep apnea.

RECENT FINDINGS

Gonadal hormones have long been implicated in the pathogenesis of obstructive sleep apnea. Recently, exogenous testosterone has been shown to exacerbate obstructive sleep apnea, whereas hormone replacement therapy in menopausal women may be protective in obstructive sleep apnea. Effective treatment of obstructive sleep apnea with nasal continuous positive airway pressure has been associated with improved insulin sensitivity and testicular function in individuals with obstructive sleep apnea.

SUMMARY

It is important to consider the potential development of sleep apnea in any patient who has an endocrine disorder or is receiving certain hormonal therapies. Effective assessment and management of obstructive sleep apnea with nasal continuous positive airway pressure may lead to a reduction in insulin resistance and hypertension as well as other markers of vascular risk in patients with metabolic syndrome.

Linkage of serum leptin levels in families with sleep apnea

OBJECTIVE

To identify regions on the genome linked to plasma leptin levels.

DESIGN

Full genome scan with 402 microsatellite markers, spaced approximately 10 cM apart. Data were analyzed using the Haseman-Elston regression linkage analysis.

SUBJECTS

A total of 160 sibling pairs from 59 predominantly African American, obese families recruited to participate in a genetic-epidemiological study of obstructive sleep apnea.

MEASUREMENTS

Serum leptin levels adjusted for age, sex, race and body mass index (BMI).

RESULTS

Suggestive linkage peaks were observed on chromosomes 2 (P=0.00170; marker D2S1384), 3 (P=0.00007; marker D3S3034), 4 (P=0.00020; marker D4S1652) and 21 (P=0.00053; marker D21s1411).

CONCLUSION

The peak on chromosome 3 is near the gene for glycogensynthase kinase 2 beta, an important factor in glucose homeostasis. Linkage was generally stronger after BMI adjustment, suggesting the potential influence of a number of metabolic pathways on leptin levels other than those that directly determine obesity levels. The evidence of linkage for leptin levels is consistent with prior linkage analyses for cholesterol, hypertension and other metabolic phenotypes.

Nonalcoholic fatty liver disease in individuals with severe obesity

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disorder occurring in individuals without significant alcohol consumption. It consists of a spectrum of liver disease, ranging from simple steatosis to steatohepatitis, cirrhosis, liver failure, and hepatocellular carcinoma. Although a number of conditions have been identified as risk factors, obesity is by far the most dominant risk factor for developing NAFLD. Over the past decade, it became apparent that NAFLD in some patients is a progressive disorder,leading to cirrhosis and liver failure. Despite lack of direct evidence,due to the ongoing epidemic of obesity in western countries, it is believed that the incidence of NAFLD is increasing, and patients with complicated and uncomplicated NAFLD will present in increasing numbers to primary care physicians as well as specialists. This article discusses the prevalence, histologic spectrum, and natural history of NAFLD in subjects with severe obesity as well as the hepatic effects of drastic weight loss induced by bariatric surgery or severe calorie restriction.