Metabolic disturbances in obesity versus sleep apnoea: the importance of visceral obesity and insulin resistance

Effect of sleep apnea syndrome on the circadian profile of cortisol in obese men

It has been hypothesized that sleep apnea syndrome (SAS) increases hypothalamic-pituitary-adrenal axis activity and, through increased cortisol levels, participates in the pathophysiology of metabolic and cardiovascular complications. We compared the circadian profiles of cortisol in obese men with [obSAS+; apnea-hypopnea index (AHI) >or= 20/h] and without SAS (obSAS-; AHI <or= 5/h). 1) Salivary cortisol (5 samples: before/30 min after dinner, 2100, upon/30 min after awakening) was measured in 15 obSAS+, 19 obSAS-, and 19 normal-weight controls (NWC). 2) Plasma cortisol (every 30 min for 24 h under highly controlled conditions and portable EEG device) was measured in 9 obSAS+, 8 obSAS-, and 10 NWC men. Visceral adipose tissue surface was measured by CT scan. In both studies, obSAS+ and obSAS- men were comparable for age, BMI, waist circumference, and waist-to-hip ratio. First, no difference was found, using ANOVA for repeated measures, between obSAS+ and obSAS- subjects for any salivary cortisol measurement. No correlation was found between salivary cortisol and AHI or nocturnal SaO(2). Similarly, obSAS+ and obSAS- men showed no difference in plasma cortisol rhythmicity: 24-h minimum, maximum, and mean, ANOVA for repeated measures, mathematical modeling of cortisol rhythm (COSINOR), and morning secretory peak. Conversely, ANOVA for repeated measures showed decreased cortisol levels in obese vs. NWC men during both the trough (2200-0130) and the peak (0600-0900) independently of SAS status. We show that SAS per se is not associated with any change of the level or of the features of salivary and plasma cortisol rhythmicity and confirm that men with visceral obesity display lower plasma cortisol levels than NWC men.

Two year reduction in sleep apnea symptoms and associated diabetes incidence after weight loss in severe obesity

STUDY OBJECTIVES

To evaluate the effect of bariatric surgery on sleep apnea symptoms and obesity-associated morbidity in patients with severe obesity.

DESIGN

Prospective study.

SETTING

University hospitals and community centers in Sweden.

INTERVENTION

We investigated the influence of weight loss surgery (n=1729) on sleep apnea symptoms and obesity-related morbidity using a conservatively treated group (n=1748) as a control.

MEASUREMENTS AND RESULTS

Baseline BMI in surgical group (42.2+/-4.4 kg/m(2)) and control group (40.1+/-4.6 kg/m(2)) changed -9.7+/-5 kg/m(2) and 0+/-3 kg/m(2), respectively, at 2-year follow-up. In the surgery group, there was a marked improvement in all obstructive sleep apnea (OSA) symptoms compared with the control group (P <0.001). Persistence of snoring (21.6 vs 65.5%, adjusted OR 0.14, 95% CI 0.10-0.19) and apnea (27.9 vs 71.3%, adjusted OR 0.16, 95% I 0.10-0.23) were much less in the surgery group compared with controls. Compared with subjects with no observed apnea at follow-up (n=2453), subjects who continued to have or developed observed apnea (n=404) had a higher incidence of diabetes (adjusted OR 2.03, 95% CI 1.19-3.47) and hypertriglyceridemia (adjusted OR 1.86, 95% CI 1.07-3.25) but not hypertension (adjusted OR 1.09, 95% CI 0.65-1.83) or hypercholesterolemia (adjusted OR 0.91, 95% CI 0.53-1.58).

CONCLUSION

Bariatric surgery results in a marked improvement in sleep apnea symptoms at 2 years. Despite adjustment for weight change and baseline central obesity, subjects reporting loss of OSA symptoms had a lower 2-year incidence of diabetes and hypertriglyceridemia. Improvement in OSA in patients losing weight may provide health benefits in addition to weight loss alone.

Obesity, and not obstructive sleep apnea, is responsible for increased serum hs-CRP levels in patients with sleep-disordered breathing in Delhi

OBJECTIVE

The present study was conducted to evaluate serum levels of high-sensitivity C-reactive protein (hs-CRP) in newly diagnosed patients with obstructive sleep apnea (OSA).

SUBJECTS AND METHODS

Between April 2005 and March 2006, a total of 231 consecutive adult habitual snorers underwent polysomnography (PSG) in the sleep laboratory. Ninety-seven subjects were found suitable for hs-CRP measurement after application of the following exclusion criteria: patients with diabetes mellitus, hypertension, coronary artery disease, acromegaly, hypothyroidism, chronic renal failure, congestive cardiac failure, or smoking history, patients who were pregnant, on steroid treatment, on hormone replacement therapy, or with chronic use of drugs such as non-steroidal anti-inflammatory drugs, oral anticoagulants and lipid-lowering drugs and patients having undergone upper airway surgery. Patients were classified as apneic [apnea-hypopnea index (AHI)>5], obese non-apneic [body mass index (BMI)>25, AHI<5] and non-obese non-apneic (BMI<25, AHI<5). C-reactive protein levels were measured in stored sera by high-sensitivity enzyme immunoassay (Biocheck, Inc. Foster City, CA, USA). After checking normality with the Kolmogorov-Smirnov test and using a square-root transformation, Pearson's and partial correlation coefficients were calculated for identified risk factors and confounders. A multiple linear regression model was used to identify variables that were independently associated with hs-CRP.

RESULTS

The mean serum levels of hs-CRP were found to be 0.25+/-0.23, 0.58+/-0.55, and 0.51+/-0.37 mg/dl in non-obese non-apneics (n=23), obese non-apneics (n=45) and apneics (obese and non-obese, n=29), respectively. Pearson's correlation coefficient of hs-CRP with BMI was found to be 0.25 (p=0.01), and with AHI 0.16 (p=0.12). Partial correlation analysis showed that hs-CRP levels correlated significantly with BMI after adjustment for AHI and age (r=0.22, p=0.03), while correlation with disease severity as assessed by AHI after adjustment for BMI and age was not significant (r=0.10, p=0.33). After stepwise multiple linear regression, only BMI was found to be significantly associated with serum hs-CRP levels (beta=0.02, p=0.01).

CONCLUSIONS

In this first comprehensive cross-sectional study on Indian subjects, we found that obesity, and not obstructive sleep apnea, is associated with elevated serum levels of hs-CRP. No independent correlation was found between severity of OSA and hs-CRP in the present study.

Sleep-related disturbances and physical inactivity are independently associated with obesity in adults

OBJECTIVE

To study relationships between obesity, physical inactivity and sleep-related disturbances (obstructive sleep apnea (OSA), sleep duration, sleep disturbances concomitant with daytime tiredness) in adults (> or =30 years).

DESIGN

Cross-sectional study with a random population sample.

PARTICIPANTS

A total of 3377 men (mean age 52.3, s.d. 14.8, years) and 4264 women (56.4, s.d. 17.2, years).

MAIN OUTCOME MEASURES

Dependent variables, measured: Waist circumference (WC) and body mass index (BMI). Independent variables, from a detailed interview/questionnaire: probable OSA, other sleep-related disturbances, sleep duration, type and frequency of leisure physical activity. Age, mental health, smoking and education were included in analyses as potential confounders.

RESULTS

In men, OSA and physical inactivity increased likelihood for abdominal obesity (WC > or =102 cm). Physical inactivity also increased, but long (> or =9 h/day) sleep decreased likelihood for abdominal overweight (WC: 94-101 cm) in men. In women, abdominal obesity (WC > or =88 cm) was associated positively with OSA, moderate sleep-related disturbances, and physical inactivity. Education modulated the influence of age on abdominal obesity in both genders. Using BMI as the dependent variable did not change the general information obtained by the model. In addition, abdominal obesity was found to be an independent risk factor also in multivariable models predicting categories of a combined sleep duration and sleep disturbances.

CONCLUSIONS

Sleep duration and sleep-related disturbances are associated with obesity, even after controlling for OSA and physical inactivity. The results support the hypothesis of vicious circle between sleep and obesity.

Measures of insulin sensitivity

Many approaches may be taken in the assessment of insulin sensitivity in humans. The euglycemic hyperinsulinemic glucose clamp and measurement of steady-state plasma glucose are direct but time- and resource-intensive approaches. Alternative approaches, including calculations based on fasting plasma insulin and glucose levels or analyses of glucose and insulin levels after intravenous or oral glucose administration, are useful but provide only modest correlation with the primary analyses. Surrogate measures of insulin sensitivity may be found in body mass index, waist circumference, or serum triglyceride or C-reactive peptide determination. New, innovative isotopic approaches now being developed offer the potential to characterize whole-body glucose metabolism in a fashion that may eventually allow routine clinical testing of insulin sensitivity.

Sleep apnea is induced by a high-fat diet and reversed and prevented by metformin in non-obese rats

OBJECTIVE

We assessed the relationship between a high-fat (HF) diet and central apnea during rapid eye movement and non-rapid eye movement sleep stages by recording ventilatory parameters in 28 non-obese rats in which insulin resistance had been induced by an HF diet. We also studied whether metformin (an anti-hyperglycemic drug frequently used to treat insulin resistance) could reverse sleep apnea or prevent its occurrence in this experimental paradigm.

RESEARCH METHODS AND PROCEDURES

Rats were fed with a standard diet (10 rats), an HF diet (8 rats), or an HF diet concomitantly with metformin treatment (10 rats). Each animal was instrumented for electroencephalographic and electromyographic recording. After 3 weeks, ventilatory parameters during sleep were recorded with a body plethysmograph. All rats were treated with metformin for 1 week, after which time the ventilatory measurements were measured again.

RESULTS

Our results showed that the three groups of animals did not differ in terms of body growth over the entire experimental period. The HF diet did not modify sleep structure or minute ventilation in the different sleep stages. A great increase (+266 +/- 48%) in central apnea frequency was observed in insulin-resistant rats. This was explained by an increase in both post-sigh (+195 +/- 35%) and spontaneous apnea (+437 +/- 65%) in the different sleep stages. These increases were suppressed by metformin treatment.

DISCUSSION

Insulin resistance induced by the HF diet could be the promoter of sleep apnea in non-obese rats. Metformin is an efficient curative and preventive treatment for sleep apnea, suggesting that insulin resistance modifies the ventilatory drive independently of obesity.

Socioeconomic status and occupation as risk factors for obstructive sleep apnea in Sweden: a population-based study

OBJECTIVES

The aim of this study was to investigate whether there is an association between socioeconomic status, occupation and obstructive sleep apnea.

METHODS

A nationwide database was constructed by linking the Swedish Census to the Hospital Discharge Register and the Cause of Death Register to obtain data on all first adult hospitalizations for obstructive sleep apnea diagnosed in Sweden during the study period from 1997 to 2001. Standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) were calculated.

RESULTS

A total of 10,336 male and 2,602 female first hospitalizations during the study period for obstructive sleep apnea were retrieved for adults aged 35 and older. The overall SIRs for hospitalizations for obstructive sleep apnea were close to unity between different socioeconomic groups and regions. Among male occupations, increased risks were noted for several occupational groups such as sales agents, seamen, drivers, engine and motor operators, and cooks and stewards. For female occupations, an increased risk was observed only among drivers. Adjustment for obesity had no effect on the risk levels.

CONCLUSIONS

Socioeconomic status and occupation have a minor effect on the population's likelihood of hospitalization for obstructive sleep apnea. Although the increased risks found for seamen, engine and motor operators, and cooks and stewards may be partly explained by their work-related exposure, residual confounding due to smoking and alcohol might be present.

SLEEP DISRUPTION IN OLDER ADULTS

Insomnia is not a normal part of aging, but nighttime sleep in older adults is often disrupted, leading to excessive daytime sleepiness and other physical, psychological, and cognitive changes that affect overall health. Even so, clinicians often pay little attention to sleep in this population. The sleep of older adults tends to be less deep than that of younger people, and coexisting conditions and treatment effects can more easily disrupt sleep. This article reviews the current literature on sleep disruption in older adults and suggests ways that nurses can apply the information in intervening to improve sleep in their older patients.

Association between inadequate sleep and insulin resistance in obese children

OBJECTIVE

To analyze the relationships between sleep duration, obstructive sleep apnea syndrome (OSAS), and markers of insulin resistance in obese children.

STUDY DESIGN

Forty obese children were evaluated for sleep-related complaints. Each child underwent a polysomnogram, an oral glucose tolerance test (OGTT), and fasting lipid panel tests. Indices of insulin resistance (HOMA-IR and WBISI) and insulin secretion (IGI) were calculated based on the results of the OGTT. Markers of insulin resistance were compared among groups categorized according to polysomnogram results.

RESULTS

Subjects with shorter sleep duration had higher fasting insulin, peak insulin, and HOMA-IR levels and lower WBISI levels, findings suggestive of insulin resistance. In contrast, differences in body mass index z scores were not observed. Subjects with OSAS (32 of 40 children) had higher triglyceride levels and HOMA-IR values than those without OSAS, but did not differ in sleep duration. Multiple linear regression analysis revealed that HOMA-IR was significantly correlated with age, sleep duration, and percentage of rapid-eye-movement sleep.

CONCLUSIONS

Insulin resistance in obese children is associated with short sleep duration and OSAS.

Obstructive sleep apnea: an update on mechanisms and cardiovascular consequences

BACKGROUND AND AIM

There is growing recognition of the widespread incidence and health consequences of obstructive sleep apnea (OSA). This review examines the evidence linking sleep apnea with cardiovascular disease and discusses potential mechanisms underlying this link.

DATA SYNTHESIS

The weight of evidence provides increasing support for a causal relationship between OSA and hypertension. Furthermore, OSA may contribute to the initiation and progression of cardiac ischemia, heart failure and stroke. Chronic sympathetic activation appears to be a key mechanism linking OSA to cardiovascular disease. Other potential mechanisms include inflammation, endothelial dysfunction, increased levels of endothelin, hypercoagulability and stimulation of the renin angiotensin system. OSA, hypertension and obesity often coexist and interact, sharing multiple pathophysiological mechanisms and cardiovascular consequences. Effective treatment of OSA may attenuate neural and humoral abnormalities in circulatory control, improve blood pressure control and conceivably reduce the risk of future cardiovascular events.

CONCLUSION

Patients with OSA are at increased risk for cardiovascular disease. OSA should be considered in the differential diagnosis of hypertensive patients who are obese. In particular, OSA should be excluded in patients with hypertension resistant to conventional drug therapy.

Prediction of obstructive sleep apnea in patients presenting to a tertiary care center

The objective of this prospective observational clinical study is to derive and validate a diagnostic model for prediction of obstructive sleep apnea (OSA) in subjects presenting with non-sleep-related complaints in a tertiary care center in north India. We included 102 subjects (group I, range 31-70 years) presenting to the hospital with non-sleep-related complaints. None of the subjects had any significant comorbid illness such as respiratory or congestive cardiac failure. All subjects underwent detailed evaluation including polysomnography (PSG). Various parameters were compared between the cases (apnea-hypopnea index, AHI > or =15/h) and controls (AHI <15/h). Using multivariate logistic regression analysis, a diagnostic model for prediction of OSA was derived. Subsequently, using similar selection criteria, 104 subjects (group II, range 32-68 years) were included for validation of the newly derived diagnostic model. Body mass index [BMI; OR (95% CI), 1.14(1.1-1.2)], male gender 5.0(1.4-27.1), relative-reported snoring index (SI) 2.8(1.7-5.0), and choking index (ChI) 8.1(1.4-46.5) were significant, independent predictors of OSA. Diagnostic model was computed as score = [1.61 x (gender)] + [1.01 x (S1)] + [2.09 x (ChI)] + [0.1 x (BMI)] where, gender: 0 = female, 1 = male and SI, ChI, BMI are actual values. The diagnostic model had an area under the receiver operator characteristics curve of 89.6%. A cutoff of 4.3 for the score was associated with sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 91.3, 68.5, 70.5, and 92.3%, respectively. Misclassification rate with the application of the diagnostic model on group II subjects was 13.5% (14/104). Sensitivity, specificity, PPV, and NPV of the model for predicting OSA in this group were 82, 90.7, 89.1, and 84.5%, respectively. BMI, male gender, SI, and ChI are independent predictors of OSA. Diagnostic model derived from these parameters is useful for predicting presence of OSA and screening subjects for PSG.

Utility of the modified ATP III defined metabolic syndrome and severe obesity as predictors of insulin resistance in overweight children and adolescents: a cross-sectional study

Background

The rising prevalence of obesity and metabolic syndrome (MetS) has received increased attention since both place individuals at risk for Type II diabetes and cardiovascular disease. Insulin resistance (IR) has been implicated in the pathogenesis of obesity and MetS in both children and adults and is a known independent cardiovascular risk factor. However measures of IR are not routinely performed in children while MetS or severe obesity when present, are considered as clinical markers for IR.

Objective

The study was undertaken to assess the utility of ATPIII defined metabolic syndrome (MetS) and severe obesity as predictors of insulin resistance (IR) in a group of 576 overweight children and adolescents attending a pediatric obesity clinic in Brooklyn.

Methods

Inclusion criteria were children ages 3–19, and body mass index > 95th percentile for age. MetS was defined using ATP III criteria, modified for age. IR was defined as upper tertile of homeostasis model assessment (HOMA) within 3 age groups (3–8, n = 122; 9–11, n = 164; 12–19, n = 290). Sensitivity, specificity, positive predictive values and odds ratios (OR) with 95% confidence intervals (CI) were calculated within age groups for predicting IR using MetS and severe obesity respectively.

Results

MetS was present in 45%, 48% and 42% of the respective age groups and significantly predicted IR only in the oldest group (OR = 2.0, 95% CI 1.2, 3.4; p = .006). Sensitivities were <55%; specificities <63% and positive predictive values ≤ 42% in all groups. Severe obesity was significantly associated with IR in both the 9–11 (p = .002) and 12–18 (p = .01) groups but positive predictive values were nonetheless ≤ 51% for all groups.

Conclusion

The expression of IR in overweight children and adolescents is heterogeneous and MetS or severe obesity may not be sufficiently sensitive and specific indicators of insulin resistance. In addition to screening for MetS in overweight children markers for IR should be routinely performed. Further research is needed to establish threshold values of insulin measures in overweight children who may be at greater associated risk of adverse outcomes whether or not MetS is present.

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.

Sympathetic System Activity in Obesity and Metabolic Syndrome

Obesity is a very common disease worldwide, resulting from a disturbance in the energy balance. The metabolic syndrome is also a cluster of abnormalities with basic characteristics being insulin resistance and visceral obesity. The major concerns of obesity and metabolic syndrome are the comorbidities, such as type 2 diabetes, cardiovascular disease, stroke, and certain types of cancers. Sympathetic nervous system (SNS) activity is associated with both energy balance and metabolic syndrome. Sympathomimetic medications decrease food intake, increase resting metabolic rate (RMR), and thermogenic responses, whereas blockage of the SNS exerts opposite effects. The contribution of the SNS to the daily energy expenditure, however, is small ( approximately 5%) in normal subjects consuming a weight maintenance diet. Fasting suppresses, whereas meal ingestion induces SNS activity. Most of the data agree that obesity is characterized by SNS predominance in the basal state and reduced SNS responsiveness after various sympathetic stimuli. Weight loss reduces SNS overactivity in obesity. Metabolic syndrome is characterized by enhanced SNS activity. Most of the indices used for the assessment of its activity are better associated with visceral fat than with total fat mass. Visceral fat is prone to lipolysis: this effect is mediated by catecholamine action on the sensitive beta(3)-adrenoceptors found in the intraabdominal fat. In addition, central fat distribution is associated with disturbances in the hypothalamo-pituitary-adrenal axis, suggesting that a disturbed axis may be implicated in the development of the metabolic syndrome. Furthermore, SNS activity induces a proinflammatory state by IL-6 production, which in turn results in an acute phase response. The increased levels of inflammatory markers seen in the metabolic syndrome may be elicited, at least in part, by SNS overactivity. Intervention studies showed that the disturbances of the autonomic nervous system seen in the metabolic syndrome are reversible.

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.

Prevalence and risk factors of obstructive sleep apnea syndrome in a population of Delhi, India

OBJECTIVE

Obstructive sleep apnea (OSA) has been recognized in the Western world as a public health burden, but there has been no community-based study performed to assess the prevalence of the condition in India. The study was performed to assess the prevalence and risk factors of OSA in a semi-urban Indian population.

DESIGN

A two-stage, cross-sectional, community-based prevalence study.

SETTING

A semi-urban community in Delhi.

DURATION

Two years (2003 to 2005).

PATIENTS AND PARTICIPANTS

All citizens residing in the community who were 30 to 60 years of age. Exclusion criteria included those patients with recent myocardial infarction, upper airway surgery, class III/IV congestive heart failure, pregnancy, hypothyroidism on treatment, acromegaly, chronic renal failure, systemic steroid treatment, and hormone replacement therapy.

INTERVENTION

An OSA assessment was performed in 2,400 subjects who were screened in stage 1 of the study by means of a sleep questionnaire. Subjects were then divided into habitual and nonhabitual snorers. Eighty-three randomly selected habitual snorers and 80 nonhabitual snorers were invited to participate in stage 2 of the study, which consisted of in-hospital polysomnography studies.

OBSERVATIONS AND RESULTS

A total of 2,150 subjects returned questionnaires (response rate, 90%). Of 550 habitual snorers and 1,596 nonhabitual snorers, 77 habitual snorers and 73 nonhabitual snorers underwent polysomnography. A total of 36 habitual snorers (46.75%) and 2 nonhabitual snorers (2.73%) were found to have OSA, giving prevalence rates of 13.74% and 3.57%, respectively, for OSA and OSA syndrome (OSAS) on extrapolation. Multivariate analysis revealed that male gender, age, obesity (defined by a high body mass index), and waist/hip ratio as significant risk factors for OSAS.

CONCLUSIONS

This study demonstrated that the risk factors and prevalence for OSA in India are similar to those in the West, which is contrary to the findings of some previous reports, which had a strong inclusion bias.

Inhibition of 11beta-HSD1 as a novel treatment for the metabolic syndrome: do glucocorticoids play a role?

The metabolic syndrome (syndrome X) is a cluster of risk factors and a common cause of cardiovascular disease in humans. Although the underlying mechanism for metabolic syndrome is still poorly understood, recent clinical data and studies with transgenic animals implicate elevated intracellular glucocorticoid tone in the etiology of metabolic syndrome. Development of selective inhibitors of 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-1 and their use in rodent animal disease models encompassing several aspects of metabolic syndrome indicate the possibility of therapeutic intervention. This review will focus on recent advances in our understanding of the role of 11beta-HSD1 in metabolic disorders and other disease processes.

Plasma interleukin 6 levels are elevated in polycystic ovary syndrome independently of obesity or sleep apnea

Premenopausal women with polycystic ovary syndrome (PCOS) are at a much higher risk for excessive daytime sleepiness, fatigue, and insulin resistance than control women. Elevated levels of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) are presumably part of the pathogenesis of these clinical manifestations. Forty-two obese women with PCOS, 17 body mass index-comparable obese controls, and 15 normal-weight controls free from apnea participated in the study that included one 8-hour nighttime polysomnography, single morning cytokine plasma concentrations, and insulin resistance indices. Women with PCOS exhibited higher plasma concentrations of IL-6 than obese controls, who had intermediate values, or normal-weight controls, who had the lowest values (4.75 +/- 0.5 vs 3.65 +/- 0.4 vs 1.84 +/- 0.3 pg/mL, P < .01). Tumor necrosis factor alpha values were higher in PCOS and obese controls compared with normal-weight controls, but the difference was not statistically significant (4.05 +/- 0.3 vs 3.79 +/- 0.2 vs 3.14 +/- 0.2 pg/mL, P = .103). Based on backward regression analysis, IL-6 levels had a stronger association with the PCOS group than with the obese group, and the sleep or hypoxia variables did not make a significant contribution to either IL-6 or TNF-alpha. Both IL-6 and TNF-alpha correlated positively with body mass index (P < .01) in obese controls but not in women with PCOS. Furthermore, within the PCOS group, IL-6 and TNF-alpha correlated more strongly with indices of insulin resistance than obesity. We conclude that IL-6 levels are elevated in obese women with PCOS independently of obesity or sleep apnea and may represent a pathophysiologic link to insulin resistance.

Relationship Between the Cardiometabolic Syndrome and Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), characterized by cessation of air flow for a minimum of 10 seconds despite continuous respiratory effort, is a prevalent condition in our society. Recent studies demonstrate that OSA is an independent risk factor for insulin resistance and the cardiometabolic syndrome. Hypoxemia and sleep fragmentation from OSA appear to produce autonomic activation, alterations in neuroendocrine function, and increased amounts of inflammatory cytokines (interleukin 6 and tumor necrosis factor alpha). These variables have important roles in the pathogenesis of insulin resistance and the cardiometabolic syndrome. It can be concluded that insulin sensitivity, a key contributor to the pathogenesis of the cardiometabolic syndrome, is mainly determined by the extent of obesity and, to a lesser extent, by OSA. The authors review OSA and summarize recent discoveries and proposed mechanisms of the causal relationship that OSA has with insulin resistance and the cardiometabolic syndrome independent of many confounding comorbidities.

Treating the metabolic syndrome: acetyl-CoA carboxylase inhibition

Metabolic syndrome is defined as a clustering of cardiovascular risk factors (abdominal obesity, hyperinsulinaemia, atherogenic dislipidaemia, hypertension, hypercoagulability) that together increase the risk of developing coronary heart disease and Type-2 diabetes. Inhibition of acetyl-CoA carboxylase (ACC), with its resultant inhibition of fatty acid synthesis and stimulation of fatty acid oxidation, has the potential to favourably affect, in a concerted manner, a multitude of cardiovascular risk factors associated with metabolic syndrome. Studies in ACC2 knockout mice and in experimental animals treated with isozyme-nonselective ACC inhibitors have demonstrated the potential for treating metabolic syndrome through this modality. A variety of structurally diverse, mechanistically distinct classes of ACC inhibitors have been disclosed in the scientific and patent literature. Isozyme-nonselective ACC inhibitors may provide the optimal therapeutic potential for beneficially affecting metabolic syndrome. However, demonstration of the full potential of isozyme-selective inhibitors, once identified, should reveal advantages and liabilities associated with single isozyme inhibition. Whereas demonstrating clinical efficacy of an ACC inhibitor should be straightforward, the heterogeneity of the patient population and absence of established guidelines regarding approval end points for agents simultaneously affecting multiple aspects of metabolic syndrome will pose developmental challenges for initial market entries.

Why a polysomnogram should become part of the diagnostic evaluation of stroke and transient ischemic attack

Neurologists need to recognize, diagnose, and treat obstructive sleep apnea (OSA) in patients with stroke or transient ischemic attack (TIA). Increasing medical evidence suggests that OSA is an independent risk factor for stroke and TIA. Stroke (or TIA) is more likely a cause, rather than a consequence, of OSA because PSG studies have shown: 1) apneas in stroke are typically obstructive, not central or Cheyne-Stokes in type; 2) apneas are just as frequent and severe in patients with either TIA or stroke; 3) OSA severity is not influenced by the acuteness or location of the stroke; 4) untreated OSA patients have more strokes, stroke morbidity, and mortality than those who are treated. OSA alone can induce hypertension, especially in younger men. A causal relationship has recently been demonstrated between OSA and hypertension. A distinctive feature of OSA-induced hypertension is loss of the normal nighttime fall in blood pressure ("nondippers"). Data from the Sleep Heart Health Study showed a dose-response association between OSA severity and the presence of hypertension 4 years later. Hypertension or ischemic heart disease usually develops in untreated patients with OSA over time without particular worsening of OSA. Studies have shown sleep itself is not a risk factor for stroke because most stroke and TIAs begin between 6 am and noon, while the individual is awake. However, OSA promptly be considered in stroke beginning during sleep because 88% of strokes that develop during sleep occur in "nondippers." Premature death in OSA patients is most often cardiovascular, but occurs while the patients are awake. The risk of myocardial infarction is increased 20-fold in untreated OSA. Treating OSA patients with continuous positive airway pressure can prevent or improve hypertension, reduce abnormal elevations of inflammatory cytokines and adhesion molecules, reduce excessive sympathetic tone, avoid increased vascular oxidative stress, reverse coagulation abnormalities, and reduce leptin levels. If all this can be achieved by a polysomnogram, then this test should become part of a neurologist's armamentarium for stroke and TIA.

Waist circumference predicts the occurrence of sleep-disordered breathing in obese children and adolescents: a questionnaire-based study

BACKGROUND AND PURPOSE

To assess the presence of sleep-disordered breathing (SDB) in a population of obese children and adolescents and to investigate the role of fat distribution in predicting SDB.

PATIENTS AND METHODS

One hundred and thirty-two obese children and adolescents, aged 5.0-14.2 years, were consecutively referred to the Department of Pediatrics of the Second University of Naples for screening of obesity. The control group consisted of 453, sex- and age-matched lean subjects selected from local schools in Campania region. The sleep disturbances scale for children (SDSC) questionnaire was used to evaluate SDB prevalence. In all subjects, waist circumference, triceps and sub-scapular skin folds were measured, and Z-scores were calculated.

RESULTS

Obese subjects showed significantly higher SDB and sleep hyperhydrosis (SHY) scores than controls. The Z-score of waist circumference correlated with SDB (r=0.32; P=0.006) and SHY factor scores (r=0.37; P=0.005), while the Z-score of body mass index (BMI), triceps and sub-scapular skin folds were not correlated with any SDSC factor scores. Subjects in the higher tertile for Z-score of waist circumference had a significantly higher risk for developing SDB (OR 1.9; 95% IC 1.8-3.2) and SHY (OR 2.1; 95% IC 2.0-4.5).

CONCLUSIONS

Waist circumference is a more reliable index than total adiposity and subcutaneous fat in predicting the risk of obese children to develop SDB.

Effect of high-fat diet and metformin treatment on ventilation and sleep apnea in non-obese rats

We investigated the effect of insulin resistance on ventilation and the incidence of sleep apnea in non-obese rats and determined whether metformin could change ventilation and occurrence of sleep apneas. Five groups of rats were studied: (1) standard chow; (2) high-fat groups, with 1 with metformin; (2) had type 2 diabetes induced by streptozotocin, with 1 with metformin. Compared to standard rats, ventilatory parameters remained unchanged in the high-fat fed diet as well as in diabetic rats. However, their oxygen consumption was reduced (p<or=0.01). They had a lower ventilatory response to CO2 challenge (p<or=0.01), and their sleep apnea scores increased markedly (p<or=0.001). These results suggest that insulin resistance could impair the ventilation control. Metformin treatment, known to reduce insulin resistance, got sleep apnea scores back to their basic levels, reinforcing the idea that insulin resistance is a major factor in the occurrence of apneas in this rat model.

Overfeeding-induced ovarian dysfunction in broiler breeder hens is associated with lipotoxicity

In mammals, triacylglycerol (TAG) accumulation in nonadipose tissue, termed lipotoxicity, develops with obesity and can provoke insulin resistance, overt diabetes, and ovarian dysfunction. Leptin, an adipose tissue hormone, may mediate these effects. Feed-satiated broiler breeder hens manifest lipotoxicity-like symptoms. Changes in body and organ weights, hepatic and plasma TAG, nonesterified fatty acids (NEFA), ovarian morphology, and egg production in response to acute voluntary increases of feed intake were measured in 2 studies with Cobb 500 broiler breeder hens provided with either 145 or > or = 290 g of feed/d per hen for 10 d. In both studies, no hen fed 145 g of feed/d exhibited ovarian abnormalities, whereas approximately 50% of feed-satiated hens did. Egg production in feed-satiated hens was reduced from 73.3 to 55.8% (P = 0.001). Morphology indicated that apoptosis-induced atresia occurred in the hierarchical follicles. Fractional weight of yolk increased from 29.3 to 30.6% (P = 0.016) and no longer correlated to egg weight. Body, liver, and abdominal adipose weights were significantly greater (P < 0.05) in feed-satiated hens, as were plasma concentrations of glucose, NEFA, TAG, insulin, and leptin (P < 0.05). Feed-satiated hens with abnormal ovaries had significantly more liver and abdominal fat, greater plasma leptin and TAG concentrations, and more saturated fatty acids in plasma NEFA than did feed-satiated hens with normal ovaries. Differences in severity of lipotoxic metabolic and hormonal responses among feed-satiated hens were closely linked to the incidence of ovarian abnormalities and granulosa cell susceptibility to apoptosis and necrosis.

Obstructive sleep apnea: what does the cardiovascular physician need to know?

Obstructive sleep apnea (OSA) is a common disorder in adults. It is becoming increasingly recognized as a risk factor for cardiovascular diseases such as hypertension, pulmonary hypertension, myocardial infarction, and stroke. Knowing the pathophysiologic effects that occur during obstructive apnea assists in understanding how chronic complications and sequelae develop. OSA is also being recognized as associated with glucose intolerance and motor vehicle accidents. Polysomnography in a sleep laboratory remains the diagnostic method of choice. Treatment options are somewhat limited in scope, but nasal continuous positive airway pressure is the first line and has been shown to clearly improve many of the symptoms and sequelae of the syndrome. Cardiovascular physicians require a working knowledge of OSA and its complications, as many of the diseases they manage have shown links to this sleep disorder.

Reference body composition in adult rhesus monkeys: glucoregulatory and anthropometric indices

Rhesus monkeys have been used as models to study obesity and disease. The aim of this study was to define body mass indices for underweight and obesity in rhesus monkeys. Longitudinal data collected over 8-14 years from 40 male and 26 female rhesus monkeys were analyzed. Body weight, insulin sensitivity index, and disposition index were regressed against percent body fat (%BF). A minimal %BF beyond which further loss of body weight resulted in loss of lean mass was determined to be 11.5% in older males, 8% in adult females, and 9% in younger adult males. Insulin sensitivity index and disposition index reached minimum values at 23% fat in older males, 18% in adult females, and 21% in younger adult males, indicating obesity. The estimated reference range for %BF was 9%-23% in male and 8%-18% in female monkeys, corresponding to body mass indices of 32-44 kg/m(2) for male and 27-35 kg/m(2) for female monkeys.

Polysomnography before and after weight loss in obese patients with severe sleep apnea

OBJECTIVE

While obstructive sleep apnea (OSA) is strongly related to obesity, few studies have examined polysomnographic (PSG) changes with major weight loss. We examined the effect of weight loss following laparoscopic adjustable gastric banding (LAGB) on the PSG changes in patients with severe OSA. In addition, we studied daytime sleepiness, the metabolic syndrome and quality of life (QOL).

METHODS

A prospective study was conducted of 25 severely obese patients (17 men, eight women) with paired diagnostic PSG, biochemical and questionnaire studies, the first prior to LAGB and the second at least 1 y later. Subjects with a baseline apnea-hypopnea index (AHI) >25/h were included.

RESULTS

Subject baseline age was 44.7 y, weight 154 kg and body mass index 52.7 kg/m(2). The second PSG study was conducted 17.7+/-10 (range 12-42) months after surgery and mean percentage of excess loss and weight loss were 50.1+/-15% (range 24-80%) and 44.9+/-22 kg (range 18-103 kg), respectively. There was a significant fall in AHI from 61.6+/-34 to 13.4+/-13, improved sleep architecture with increased REM and stage III and IV sleep, daytime sleepiness, as measured by Epworth Sleepiness Scale, of 13+/-7.0 to 3.8+/-3.0, and fewer patients requiring nasal continuous positive airways pressure (CPAP). There were also major improvements in the metabolic syndrome, QOL, body image and fewer symptoms of depression (P<0.05 for all).

CONCLUSION

Weight loss provides major improvement or resolution of OSA and CPAP requirements. It also reduces daytime sleepiness, and improves the metabolic syndrome and QOL. LAGB placement should be considered a broadly effective therapy for sleep apnea in the severely obese patient.

Functional assessment of vascular reactivity after chronic intermittent hypoxia in the rat

We recently developed a model of chronic intermittent hypoxia (CIH) (FiO2 5%, 8 h/day, 35 days) in the rat that was associated with an increased infarction in isolated heart. The aim of the present study was to characterize its functional consequences on vasoreactivity. Aorta and carotid artery were studied using organ bath technique while mesenteric vascular bed was perfused. In the three vascular beds, relaxation to acetylcholine was similar in CIH and control normoxic (NX) rats. Contractions to noradrenaline and angiotensin II were similar between CIH and NX rats. In contrast, contraction to endothelin-1 was increased by 17% (P < 0.05) in carotid artery from CIH rats. Indomethacin pre-treatment reduced by 24% (P < 0.001) contraction to endothelin-1 in carotid artery from CIH rats only. These data suggested that 35-day CIH-exposure induced no change in endothelial function of aorta, carotid artery and mesenteric bed. In contrast, CIH-exposure induced an increased contractile response to endothelin-1 in carotid artery, presumably owing to the release of constrictor cyclooxygenase-derived products.

Atrial overdrive pacing for the obstructive sleep apnea-hypopnea syndrome

BACKGROUND

The role of atrial overdrive pacing (AOP) in sleep apnea remains uncertain. We prospectively evaluated the effect of AOP after 24 hours and after one month in patients with the obstructive sleep apnea-hypopnea syndrome and compared it with the use of nasal continuous positive airway pressure (n-CPAP).

METHODS

We studied 16 patients with a moderate or severe case of the obstructive sleep apnea-hypopnea syndrome (baseline mean apnea-hypopnea index, 49) and normal left ventricular systolic function in whom a dual-chamber pacemaker had been implanted. After 48 hours, the patients were randomly assigned to AOP (pacing at 15 bpm above the spontaneous mean nocturnal heart rate) or backup atrial pacing (pacing at a heart rate below 40 bpm); the latter group began n-CPAP therapy one day later. After one month, the two groups switched therapies and were followed for an additional month. Polysomnographic studies were performed at baseline, on the first night after randomization, at crossover, and at the end of the study.

RESULTS

During AOP, no significant changes were observed in any of the respiratory variables measured. The change in the apnea-hypopnea index at one month with AOP was +0.2 (95 percent confidence interval, -2.7 to +2.3; P=0.87). In contrast, all variables improved significantly after one month of n-CPAP (change in the apnea-hypopnea index, -46.3; 95 percent confidence interval, -56.2 to -36.5; P<0.001).

CONCLUSIONS

Nasal continuous positive airway pressure therapy is highly effective for the treatment of the obstructive sleep apnea-hypopnea syndrome, whereas AOP has no significant effect.

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.

The relationship between serum cytokine levels with obesity and obstructive sleep apnea syndrome

Inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) may have a direct effect on glucose and lipid metabolism. On the other hand, it is known that IL-6 and TNF-alpha are important pro-inflammatory cytokines in the pathogenesis of atherosclerosis. The goal of present study was to test whether sleep apnea contributes to the previously reported increases of IL-6 and TNF-alpha independent of obesity. Forty-three obese (body mass index, BMI>27 kg/m2) men with newly diagnosed obstructive sleep apnea syndrome (OSAS) (apnea-hypopnea index, AHI> or =5) and age- and BMI-matched 22 obese nonapneic male controls (AHI<5) were enrolled in this study. To confirm the diagnosis, all patients underwent standard polysomnography in the sleep disorders center. Serum samples were taken at 08:00 h in the morning after overnight fasting. Serum IL-6 and TNF-alpha levels were found significantly higher in OSAS patients than in controls (p=0.002, p=0.03). Serum IL-6 and TNF-alpha levels were significantly correlated with AHI in OSAS patients (r=0.03, p=0.046 and r=0.36, p=0.016). There was no significant correlation between serum IL-6, TNF-alpha levels and AHI in controls. Serum IL-6 and TNF-alpha levels were not correlated with BMI both in OSAS patients and controls. In conclusion, circulating IL-6 and TNF-alpha levels in patients with OSAS, as independent of BMI are significantly higher than levels in controls and there is a positive relationship between previously mentioned cytokines' levels and the severity of OSAS. According to these results, the link between cardiovascular morbidity and OSAS may be explained by the coexistence of other cardiovascular risk factors such as circulating IL-6 and TNF-alpha levels.

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.

Genetic determinants of upper airway structures that predispose to obstructive sleep apnea

Genetic factors are thought to play an important role in human development. Recent data indicate that obstructive sleep apnea may have a genetic basis. Sleep apnea is a very common disorder with significant cardiovascular and neurophysiologic morbidity. The pathogenesis of sleep apnea is related to a reduction in the size of the upper airway. The reduction in airway size is secondary to increased adipose tissue (enlargement of the parapharyngeal fat pads), alterations in craniofacial structure (reduction in mandibular size) and enlargement of the surrounding soft tissue structures (tongue, lateral pharyngeal walls). Genetic factors are one of the factors that have been proposed to mediate the size of each of these anatomic risk factors for sleep apnea. Recent evidence is accumulating about the genetic loci for these structural risk factors that predispose to the development of obstructive sleep apnea.

Compensatory hyperinsulinemia and the development of an atherogenic lipoprotein profile: the price paid to maintain glucose homeostasis in insulin-resistant individuals

The ability of insulin to stimulate glucose disposal varies sixfold to eightfold among apparently healthy individuals. The only way that insulin-resistant persons can prevent the development of type 2 diabetes is by secreting the increased amount of insulin that is necessary to compensate for the resistance to insulin action. The greater the magnitude of muscle and adipose tissue insulin resistance, the more insulin must be secreted to maintain normal or near-normal glucose tolerance. Although compensatory hyperinsulinemia may prevent the development of fasting hyperglycemia in insulin-resistant individuals, the price paid is the untoward physiologic effects of increased circulating insulin concentrations on tissues that retain normal insulin sensitivity. This article focused on the interplay between insulin resistance at the level of the muscle and adipose tissue and normal hepatic insulin sensitivity; this leads to the atherogenic lipoprotein profile that is characteristic of insulin-resistant individuals. It would be inappropriate to minimize the importance of differential insulin sensitivity in the genesis of the changes in lipoprotein metabolism that increase CVD risk in insulin-resistant persons. It would be equally remiss not to emphasize that differential tissue insulin resistance also is necessary to explain why insulin-resistant/hyperinsulinemic individuals are more likely to develop the clinical syndromes (with the exception of type 2 diabetes mellitus) that are listed in Box 1.

Interactions between obstructive sleep apnea and the metabolic syndrome

The metabolic syndrome, an emerging public health problem, represents a constellation of cardiovascular risk factors. It has been suggested that the presence of obstructive sleep apnea (OSA) may increase the risk of developing some of the features of the metabolic syndrome, including hypertension, insulin resistance, and type 2 diabetes. In this article, we discuss the parallels between the metabolic syndrome and obstructive sleep apnea and describe possible OSA-related factors that may contribute to the metabolic syndrome, specifically the roles of obesity, hypertension, dyslipidemia, sex hormones, inflammation, vascular dysfunction, leptin, insulin resistance, and sleep deprivation.

Prevention and treatment of the metabolic syndrome

The prevalence of the metabolic syndrome is increasing owing to lifestyle changes leading to obesity. This syndrome is a complex association of several interrelated abnormalities that increase the risk for cardiovascular disease and progression to diabetes mellitus (DM). Insulin resistance is the key factor for the clustering of risk factors characterizing the metabolic syndrome. The National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III defined the criteria for the diagnosis of the metabolic syndrome and established the basic principles for its management. According to these guidelines, treatment involves the improvement of the underlying insulin resistance through lifestyle modification (eg, weight reduction and increased physical activity) and possibly by drugs. The coexistent risk factors (mainly dyslipidemia and hypertension) should also be addressed. Since the main goal of lipid-lowering treatment is to achieve the NCEP low-density lipoprotein cholesterol (LDL-C) target, statins are a good option. However, fibrates (as monotherapy or in combination with statins) are useful for the treatment of the metabolic syndrome that is commonly associated with hypertriglyceridemia and decreased high-density lipoprotein cholesterol (HDL-C) levels. The blood pressure target is < 140/90 mm Hg. The effect on carbohydrate homeostasis should possibly be taken into account in selecting an antihypertensive drug. Patients with the metabolic syndrome commonly have other less well-defined metabolic abnormalities (eg, hyperuricemia and raised C-reactive protein levels) that may also be associated with an increased cardiovascular risk. It seems appropriate to manage these abnormalities. Drugs that beneficially affect carbohydrate metabolism and delay or even prevent the onset of DM (eg, thiazolidinediones or acarbose) could be useful in patients with the metabolic syndrome. Furthermore, among the more speculative benefits of treatment are improved liver function in nonalcoholic fatty liver disease and a reduction in the risk of acute gout.

Sleep disturbance as a predictor of type 2 diabetes mellitus in men and women from the general population

AIMS/HYPOTHESIS

To examine gender specific associations between sleep disturbance and incident type 2 diabetes mellitus in a representative population sample in Germany.

METHODS

The study was based on 4,140 men and 4,129 women (aged 25-74 years) who participated in one of the three MONICA Augsburg surveys between 1984 and 1995, and who were free of diabetes at baseline. Incident cases of type 2 diabetes were assessed using a follow-up questionnaire in 1998. Gender specific hazard ratios were estimated from Cox proportional hazard models.

RESULTS

A total of 119 cases of incident type 2 diabetes among men and 69 among women were registered during the mean follow-up period of 7.5 years. In both sexes, difficulty maintaining sleep was associated with a higher risk of type 2 diabetes. After adjustment for age, survey, hypertension, dyslipidemia, parental history of diabetes, history of angina pectoris, regular smoking, physical activity, alcohol intake, body mass index and education, the hazard ratio in men was 1.60 (95% CI: 1.05-2.45) and the hazard ratio in women was 1.98 (95% CI: 1.20-3.29). In contrast, difficulty initiating sleep was not associated with a significantly increased risk of developing type 2 diabetes mellitus after multivariable adjustment in both sexes in the present study.

CONCLUSIONS/INTERPRETATION

Difficulty maintaining sleep was associated with an increased risk of type 2 diabetes in men and women from the general population. Although, the causal pathway is not entirely clear, it seems that both insulin resistance and chronic low-grade systemic inflammation may be involved.

Difficult cases in heart failure: polycystic ovary syndrome and heart failure

This is a case of a 21-year-old female with a history of polycystic ovary syndrome who was subsequently diagnosed with heart failure. The patient did not have a family history of heart failure, nor did the patient herself have evidence of ischemic or valvular heart disease or prior viral infection. The patient was found, upon further evaluation, to have significant obstructive sleep apnea, a condition that has been linked to the development and/or worsening of heart failure. Interestingly enough, recent evidence has revealed that patients with polycystic ovary syndrome have been found to have a predilection for developing obstructive sleep apnea, irrespective of body weight or habitus.

Sleep, appetite, and obesity--what is the link?

There is a well known relationship between short sleep duration and high body mass index. A new study suggests that the missing link could be the appetite regulating hormones leptin and ghrelin.

Developmental and metabolic implications of the hypoxic ventilatory response

This review explores the evidence to support the leading hypothesis that the metabolic response to hypoxia early in life provides the pathophysiological basis for the metabolic syndrome. Hypoxia is a frequent occurrence during early development and induces a state of energy depletion that triggers a wide range of 'metabolic' responses to preserve homeostasis. Recent interest in the sequelae of energy depletion through hypoxic mechanisms has grown, particularly because of demonstrated links with ensuing metabolic abnormalities and increased risk for future cardiovascular disease. The 'metabolic syndrome' refers to the combination of obesity, hyperinsulinaemia, dyslipidaemia and hypertension in adults. The metabolic responses to energy depletion during early development provide explanations for some of the mechanisms that ultimately lead to serological features of metabolic dysfunction in children with sleep-disordered breathing. Thus, the acute compensatory response of energy conservation to hypoxia during early development at the cellular, serological and whole organism levels suggests that the metabolic abnormalities that develop later in life may in fact originate very early in life; in other words, constitute early life antecedents of adult disease. Evidence regarding the circumstances under which responses to hypoxia become maladaptive will be discussed, with a focus on chronic conditions and those associated with intermittent respiratory dysfunction such as sleep-disordered breathing.

Cholesterol (and cardiovascular risk) in adolescence

PURPOSE OF REVIEW

Atherosclerosis is a significant cause of adult morbidity and mortality. New evidence confirms that it begins in childhood and accelerates at adolescence. Many new studies have solidified the understanding of its risk factors and changed the approach to their clinical management.

RECENT FINDINGS

The important descriptions of known risk factors and their clear relation to the pathophysiologic process of atherosclerosis are reviewed here. Some emerging risk factors are discussed. Furthermore, the many new studies on treatment options are reviewed.

SUMMARY

These new findings make it imperative that adolescents be screened for traditional risk factors and that they be treated with therapeutic lifestyle change. With the weight of new evidence on the safety and efficacy of statins in this age group, clinicians can feel more confident in their use when indicated. Research into emerging risk factors like obesity, metabolic syndrome, diabetes. and homocysteine will be important in the future management.

The metabolic syndrome or the insulin resistance syndrome? Different names, different concepts, and different goals

The goal of this article is to differentiate the insulin resistance syndrome from the metabolic syndrome. In the case of the insulin resistance syndrome, the abnormalities and clinical syndromes that are increased in prevalence in insulin-resistant individuals have been summarized, with a brief discussion of the causal relationship between insulin resistance, compensatory hyperinsulinemia, and associated consequences. Discussion of the metabolic syndrome has focused on the five criteria chosen by the adult treatment panel III to diagnose the syndrome, evaluating them in terms of their relationship to insulin resistance and their role as cardiovascular disease risk factors.

Autonomic dysregulation as a basis of cardiovascular, endocrine, and inflammatory disturbances associated with obstructive sleep apnea and other conditions of chronic hypoxia, hypercapnia, and acidosis

Obstructive sleep apnea has traditionally been viewed as a structural disease. A multitude of systemic endocrine and cardiovascular abnormalities have been previously attributed to the prevalence of obesity in these patients. A growing body of clinical evidence, however, points to a relationship between sleep apnea and its systemic abnormalities independent of obesity. We hypothesize that this association is based on a maladaptive autonomic response of chemoreceptors, reacting to the hypoxia, hypercapnia, and acidosis of sleep apnea. The elevated sympathetic response triggers an inflammatory cascade that results in a myriad of downstream consequences including insulin resistance, hypertension, diabetes, atherosclerosis and metabolic syndrome. The sympathetic bias and endocrine disturbances may further exacerbate sleep disturbance in a potentially pernicious cycle. Our proposal may extend to any chronic respiratory or metabolic conditions that manifest hypoxia, hypercapnia, and acidosis and elicit a maladaptive autonomic and inflammatory response.

Relationship to insulin resistance of the adult treatment panel III diagnostic criteria for identification of the metabolic syndrome

The Adult Treatment Panel III (ATP III) has published criteria for diagnosing the metabolic syndrome, a cluster of closely related abnormalities related to insulin resistance that increase cardiovascular disease risk. The present analysis was performed to evaluate the ability of these criteria to identify insulin-resistant individuals. The population consisted of 443 healthy volunteers, with measurements of BMI, blood pressure, fasting plasma glucose, triglycerides, HDL cholesterol concentrations, and steady-state plasma glucose (SSPG) concentration. Insulin resistance was defined as being in the top tertile of SSPG concentrations. Of the population, 20% satisfied ATP III criteria for the metabolic syndrome. Although insulin resistance and the presence of the metabolic syndrome were significantly associated (P < 0.001), the sensitivity and positive predictive value equaled 46% (69 of 149) and 76% (69 of 91), respectively. Being overweight, with high triglycerides, low HDL cholesterol, or elevated blood pressure, most often resulted in a diagnosis of the metabolic syndrome. Thus, the ATP III criteria do not provide a sensitive approach to identifying insulin-resistant individuals. The individual components vary both in terms of their utility in making a diagnosis of the metabolic syndrome and their relationship to insulin resistance, with the obesity and lipid criteria being most useful.