Relation of sleep-disordered breathing to cardiovascular disease risk factors: the Sleep Heart Health Study

An update on obstructive sleep apnea and the metabolic syndrome

PURPOSE OF REVIEW

Patients with obstructive sleep apnea are often overweight or obese, and they frequently exhibit metabolic aberrations, collectively known as the metabolic syndrome, an established cardiovascular risk factor. We review recent data on the relationship between obstructive sleep apnea and metabolic syndrome or its components, including abdominal obesity, insulin resistance, hypertension, and dyslipidemia.

RECENT FINDINGS

There is accumulating evidence for an independent association between obstructive sleep apnea and metabolic syndrome or its components. Recent epidemiologic and clinical data suggest a causal role of severe obstructive sleep apnea in development of hypertension, but findings for insulin resistance and dyslipidemia are controversial. Visceral obesity remains a confounding issue in analyses. Animal models and translational studies indicate that obstructive sleep apnea may promote metabolic dysfunction through cycles of intermittent hypoxia; proposed underlying pathophysiologic mechanisms include oxidative stress, sympathetic activation, and inflammation.

SUMMARY

There is suggestive evidence, but independent associations between obstructive sleep apnea and metabolic syndrome or its components are not fully established because of the confounding effect of obesity. Large randomized interventional trials are needed to identify any cause-effect relationship. Long-term follow-up studies would help to clarify the role of treatment of sleep apnea in reducing cardio-metabolic morbidity.

Usefulness of truncal obesity indices as predictive factors for obstructive sleep apnea syndrome

BACKGROUND

Optimization of the indications for nocturnal polysomnography in the diagnosis of obstructive sleep apnea syndrome (OSAS) could lead to significant reductions in health expenditure. To this end, we assessed the usefulness of truncal obesity measurements in the diagnosis of OSAS.

METHODS AND PROCEDURES

One hundred ninety-two patients (152 men and 40 women) referred to our clinic with suspected OSAS underwent a complete polysomnography study and their BMI and truncal obesity measurements were obtained.

RESULTS

Comparison of patients defined as snorers with OSAS patients, by means of the Student's t -test revealed significant differences in the truncal obesity parameters such as waist-to-hip ratio (0.94 vs. 0.98) and waist circumference (100.7 cm vs. 106.3 cm). We found no significant differences between BMI values in the two groups. Indices of truncal obesity were analyzed as predictive factors for OSAS using a multivariate logistic regression model that included variable sex, and in which waist-to-hip ratio, BMI, neck circumference, and age were analyzed as binary variables. According to this model, our patients' risk of suffering from OSAS was 2.6 times greater if the waist-to-hip ratio was >1 in men and >0.85 in women. The risk of OSAS was also increased if the patients were men or over 52 years of age.

DISCUSSION

Obtaining simple measurements such as those for truncal obesity may help prioritize the use of polysomnography in patients with a greater risk of OSAS. Our results suggest that BMI is not a good predictor of OSAS in a group of patients with a high BMI.

Intermittent hypoxia reverses the diurnal glucose rhythm and causes pancreatic beta-cell replication in mice

Obstructive sleep apnoea (OSA) and type 2 diabetes frequently co-exist and potentially interact haemodynamically and metabolically. However, the confounding effects of obesity have obscured the examination of any independent or interactive effects of the hypoxic stress of OSA and the hyperglycaemia of type 2 diabetes on haemodynamic and metabolic outcomes. We have developed a chronically catheterized, unhandled, lean murine model to examine the effects of intermittent hypoxic (IH) exposure and exogenous glucose infusion on the diurnal pattern of arterial blood pressure and blood glucose, as well as pancreatic beta-cell growth and function. Four experimental groups of adult male C57BL/J mice were exposed to 80 h of (1) either IH (nadir of inspired oxygen 5-6% at 60 cycles h(-1) for 12 h during light period) or intermittent air (IA; control) and (2) continuous infusion of either 50% dextrose or saline (control). IH exposure during saline infusion caused a sustained increase in arterial blood pressure of 10 mmHg (P < 0.0001), reversed the normal diurnal rhythm of blood glucose (P < 0.03), doubled corticosterone levels (P < 0.0001), and increased replication of pancreatic beta-cells from 1.5 +/- 0.3 to 4.0 +/- 0.8% bromodeoxyuridine (BrdU)-positive) beta-cells. The combined stimulus of IH exposure and glucose infusion attenuated the hypertension, exacerbated the reversed diurnal glucose rhythm, and produced the highest rates of apoptosis in beta-cells, without any additive effects on beta-cell replication. We conclude that, in contrast to the development of sustained hypertension, IH impaired glucose homeostasis only during periods of hypoxic exposure. IH acted as a stimulus to pancreatic beta-cell replication, but the presence of hyperglycaemia may increase the hypoxic susceptibility of beta-cells. This model will provide a basis for future mechanistic studies as well as assessing the metabolic impact of common comorbities in OSA, including obesity, insulin resistance and type 2 diabetes.

Chronic intermittent hypoxia causes hepatitis in a mouse model of diet-induced fatty liver

Obstructive sleep apnea (OSA) causes chronic intermittent hypoxia (CIH) during sleep. OSA is associated with nonalcoholic steatohepatitis (NASH) in obese individuals and may contribute to progression of nonalcoholic fatty liver disease from steatosis to NASH. The purpose of this study was to examine whether CIH induces inflammatory changes in the liver in mice with diet-induced hepatic steatosis. C57BL/6J mice (n = 8) on a high-fat, high-cholesterol diet were exposed to CIH for 6 mo and were compared with mice on the same diet exposed to intermittent air (control; n = 8). CIH caused liver injury with an increase in serum ALT (461 +/- 58 U/l vs. 103 +/- 16 U/l in the control group; P < 0.01) and AST (637 +/- 37 U/l vs. 175 +/- 13 U/l in the control group; P < 0.001), whereas alkaline phosphatase and total bilirubin levels were unchanged. Histology revealed hepatic steatosis in both groups, with mild accentuation of fat staining in the zone 3 hepatocytes in mice exposed to CIH. Animals exposed to CIH exhibited lobular inflammation and fibrosis in the liver, which were not evident in control mice. CIH caused significant increases in lipid peroxidation in serum and liver tissue; significant increases in hepatic levels of myeloperoxidase and proinflammatory cytokines IL-1beta, IL-6, and CXC chemokine MIP-2; a trend toward an increase in TNF-alpha; and an increase in alpha1(I)-collagen mRNA. We conclude that CIH induces lipid peroxidation and inflammation in the livers of mice on a high-fat, high-cholesterol diet.

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

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Reactive oxygen species contribute to sleep apnea-induced hypertension in rats

In clinical studies, sleep apnea is associated with hypertension, oxidative stress, and increased circulating endothelin-1 (ET-1). We previously developed a model of sleep apnea by exposing rats to eucapnic intermittent hypoxia (IH-C) during sleep, which increases both blood pressure and plasma levels of ET-1. Because similar protocols in mice increase tissue and plasma markers of oxidative stress, we hypothesized that IH-C generation of reactive oxygen species (ROS) contributes to the development of ET-1-dependent hypertension in IH-C rats. To test this, male Sprague-Dawley rats were instrumented with indwelling blood pressure telemeters and drank either plain water or water containing the superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 1 mM). Mean arterial pressure (MAP) and heart rate (HR) were recorded for 3 control days and 14 treatment days with rats exposed 7 h/day to IH-C or air/air cycling (Sham). On day 14, MAP in IH-C rats treated with Tempol (107 +/- 2.29 mmHg) was significantly lower than in untreated IH-C rats (118 +/- 9 mmHg, P < 0.05). Tempol did not affect blood pressure in sham-operated rats (Tempol = 101 +/- 3, water = 101 +/- 2 mmHg). Immunoreactive ET-1 was greater in plasma from IH-C rats compared with plasma from sham-operated rats but was not different from Sham in Tempol-treated IH-C rats. Small mesenteric arteries from IH-C rats but not Tempol-treated IH-C rats had increased superoxide levels as measured by ferric cytochrome c reduction, lucigenin signaling, and dihydroethidium fluorescence. The data show that IH-C increases ET-1 production and vascular ROS levels and that scavenging superoxide prevents both. Thus oxidative stress appears to contribute to increases in ET-1 production and elevated arterial pressure in this rat model of sleep apnea-induced hypertension.

Effect of deficiency in SREBP cleavage-activating protein on lipid metabolism during intermittent hypoxia

Obstructive sleep apnea (OSA), a condition leading to intermittent hypoxia (IH) during sleep, has been associated with dyslipidemia, atherosclerosis, and increased cardiovascular mortality. We previously showed in C57BL/6J mice that IH causes hypercholesterolemia and upregulation of sterol regulatory element binding protein (SREBP)-1, a transcription factor of lipid biosynthesis in the liver. The goal of the present study was to provide mechanistic evidence that IH causes hypercholesterolemia via the SREBP-1 pathway. We utilized mice with a conditional knockout of SREBP cleavage-activating protein (SCAP) in the liver (L-Scap- mice), which exhibit low levels of an active nuclear isoform of SREBP-1 (nSREBP-1). We exposed L-Scap- mice and wild-type (WT) littermates to IH or intermittent air control for 5 days. IH was induced during the 12-h light phase by decreasing Fi(O(2)) from 20.9% to 5% for a period of 30 s with rapid reoxygenation to 20.9% through the subsequent 30 s. In WT mice, IH increased fasting levels of serum total and HDL cholesterol, serum triglycerides, serum and liver phospholipids, mRNA levels of SREBP-1 and mitochondrial glycerol-3-phosphate acyltransferase (mtGPAT), and protein levels of SCAP, nSREBP-1, and mtGPAT in the liver. In L-Scap- mice, IH did not have any effect on serum and liver lipids, and expression of lipid metabolic genes was not altered. We conclude that hyperlipidemia in response to IH is mediated via the SREBP-1 pathway. Our data suggest that the SREBP-1 pathway could be used as a therapeutic target in patients with both OSA and hyperlipidemia.

Obstructive sleep apnea syndrome is associated with some components of metabolic syndrome

BACKGROUND

Obesity, hypertension, dyslipidemia, and hyperglycemia are prevalent in obstructive sleep apnea syndrome (OSAS). Metabolic syndrome, however, is defined by visceral fat obesity plus at least two of these factors. However, whether OSAS contributes to the development of metabolic syndrome has not been defined. We investigated whether the components of metabolic syndrome were associated with OSAS in nonobese patients.

METHODS

We investigated the occurrence of hypertension, dyslipidemia, and hyperglycemia in 42 men with OSAS and 52 men without OSAS matched for age, body mass index (BMI), and visceral fat accumulation.

RESULTS

Although serum levels of triglycerides, high-density lipoprotein cholesterol, and diastolic BP did not differ significantly between the two groups, fasting blood glucose (111 +/- 6 mg/dL vs 93 +/- 3 mg/dL) [mean +/- SE] and the percentage of hypertensive patients (45% vs 15%) were significantly higher in the group with OSAS. In addition, a significantly higher percentage of patients with OSAS (19% vs 4%) had at least two of the following: hypertension, hyperglycemia, and dyslipidemia. Logistic regression analysis showed that the apnea-hypopnea index value was the predictor of number of metabolic syndrome parameters such as hypertension, hyperglycemia, and dyslipidemia, while BMI and lowest arterial oxygen saturation during sleep did not.

CONCLUSION

Independent of visceral fat obesity, OSAS was associated with hypertension, dyslipidemia, and hyperglycemia. It is possible that OSAS may predispose even nonobese patients to the development of metabolic syndrome.

Effect of continuous positive airway pressure treatment on serum cardiovascular risk factors in patients with obstructive sleep apnea-hypopnea syndrome

BACKGROUND

Serum levels of circulating markers associated with cardiovascular morbidity are elevated in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). These factors are studied in patients mainly before the application of therapy with continuous positive airway pressure (CPAP), and the effects of CPAP treatment on them have not been thoroughly studied. Therefore, the aim of the study was to examine the effect of compliance to CPAP therapy on these factors.

METHODS

Patients with newly diagnosed OSAHS, nonsmokers, without comorbidities or medication use, at baseline and during the follow-up period, were included. Serum cardiovascular risk factors (ie, high-sensitivity C-reactive protein [hs-CRP], homocysteine, total cholesterol, triglycerides, high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol, apolipoprotein A-I [ApoA-I], and apolipoprotein B [ApoB]) were measured at baseline and 6 months after CPAP application. Patients were classified into the following three groups according to CPAP use: group 1 (n = 20), good compliance (>or= 4 h use per night); group 2 (n = 19), poor compliance (< 4 h use per night); and group 3 (n = 14), refusal of CPAP treatment.

RESULTS

Fifty-three patients (47 male patients and 6 female patients; mean [+/- SD] age, 46.09 +/- 10.87 years) were included in the study. In all groups, body mass index remained stable. In group 1, significant decreases in the levels of hs-CRP (p = 0.03), homocysteine (p = 0.005), total cholesterol (p = 0.021), total cholesterol/HDL-C ratio (p = 0.018), and ApoB/ApoA-I ratio (p = 0.021) was observed. The patients in group 2 showed a decrease in homocysteine levels (p = 0.021) only, while no significant changes were observed in the patients in group 3.

CONCLUSIONS

Good compliance to CPAP treatment lowers the serum levels of cardiovascular risk factors, indicating a beneficial effect on the overall cardiovascular risk.

Noninvasive ventilation

Noninvasive positive-pressure ventilation (NPPV) is the delivery of mechanical-assisted breathing without placement of an artificial airway such as an endotracheal tube or tracheostomy. During the first half of 20th century, negative-pressure ventilation (iron lung) provided mechanical ventilatory assistance. By the 1960s, however, invasive (ie, by means of an endotracheal tube) positive-pressure ventilation superseded negative-pressure ventilation as the primarily mode of support for ICU patients because of its superior delivery of support and better airway protection. Over the past decade, the use of NPPV has been integrated into the treatment of many medical diseases, largely because the development of nasal ventilation. Nasal ventilation has the potential benefit of providing ventilatory assistance with greater convenience, comfort, safety, and less cost than invasive ventilation. NPPV is delivered by a tightly fitted mask or helmet that covers the nares, face, or head. NPPV is used in various clinical settings and is beneficial in many acute medical situations. This article explores the trends regarding the use of noninvasive ventilation. It also provides a current perspective on applications in patients with acute and chronic respiratory failure, neuromuscular disease, congestive heart failure, and sleep apnea. Additionally, it discusses the general guidelines for application, monitoring, and avoidance of complications for NPPV.

Cardiorespiratory and cerebrovascular responses to acute poikilocapnic hypoxia following intermittent and continuous exposure to hypoxia in humans

We tested the hypothesis that intermittent hypoxia (IH) and/or continuous hypoxia (CH) would enhance the ventilatory response to acute hypoxia (HVR), thereby altering blood pressure (BP) and cerebral perfusion. Seven healthy volunteers were randomly selected to complete 10–12 days of IH (5-min hypoxia to 5-min normoxia repeated for 90 min) before ascending to mild CH (1,560 m) for 12 days. Seven other volunteers did not receive any IH before ascending to CH for the same 12 days. Before the IH and CH, following 12 days of CH and 12–13 days post-CH exposure, all subjects underwent a 20-min acute exposure to poikilocapnic hypoxia (inspired fraction of O2, 0.12) in which ventilation, end-tidal gases, arterial O2 saturation, BP, and middle cerebral artery blood flow velocity (MCAV) were measured continuously. Following the IH and CH exposures, the peak HVR was elevated and was related to the increase in BP ( r = 0.66 to r = 0.88, respectively; P < 0.05) and to a reciprocal decrease in MCAV ( r = 0.73 to r = 0.80 vs. preexposures; P < 0.05) during the hypoxic test. Following both IH and CH exposures, HVR, BP, and MCAV sensitivity to hypoxia were elevated compared with preexposure, with no between-group differences following the IH and/or CH conditions, or persistent effects following 12 days of sea level exposure. Our findings indicate that IH and/or mild CH can equally enhance the HVR, which, by either direct or indirect mechanisms, facilitates alterations in BP and MCAV.

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.

Diagnostic and therapeutic approach to nonsleepy apnea

Epidemiological and observational studies suggest that sleep-disordered breathing is associated with the subsequent development of hypertension and ultimately with cardiovascular consequences. It may therefore be assumed that continuous positive airway pressure (CPAP) not only avoids sleep-related symptoms but could also mitigate cardiovascular consequences. Short-term studies have revealed a drop in blood pressure, especially in more severe, symptomatic cases of obstructive sleep apnea. Two recent studies have reported that nonsleepy obstructive sleep apnea is associated with an absence of reduced blood pressure after CPAP treatment. This suggests that this group of patients is less susceptible to the consequences of apneas, even those with mild-moderate hypertension or other cardiovascular disorders. However, in patients with severe cardiovascular disease or a higher number of obstructive events, CPAP treatment should be seriously considered.

[Continuous positive airway pressure used by adults with obstructive sleep apneas after prescription in a public referral hospital in Mexico City]

OBJECTIVE

The aim of this study was to analyze the frequency of initiation of continuous positive airway pressure (CPAP) in patients with obstructive sleep apnea syndrome (OSAS) in a referral hospital in Mexico City serving mainly patients without public health insurance coverage and to assess their level of adherence.

PATIENTS AND METHODS

Patients with OSAS diagnosed by polysomnography or by simplified respiratory polygraphy for whom nasal CPAP was prescribed were enrolled in the study. Titration of CPAP was performed during polysomnography or with an automatic CPAP device. Compliance with treatment was assessed during a medical visit or by telephone interview.

RESULTS

A total of 304 patients were enrolled upon prescription of nasal CPAP; 169 (55.5%) either purchased a device or were provided with one by the social security system. The patients most seriously ill and who had public health insurance coverage were the ones who most often acquired a device. These patients took 1.5 months to obtain the equipment and had a compliance rate of 80% at a mean 34 months of follow-up. The respiratory events index was correlated with compliance, whereas excessive daytime sleepiness (Epworth scale score) and body mass index were predictors of therapeutic CPAP pressure.

CONCLUSIONS

Nearly half the patients who were prescribed CPAP did not acquire the device. Most of those who acquired a device adhered to the treatment. In Mexico access to procedures for diagnosing OSAS is limited and access to treatment is also restricted for patients who do not have public health insurance coverage.

Relation of sleep-disordered breathing to carotid plaque and intima-media thickness

BACKGROUND

Sleep-disordered breathing (SDB) is associated with clinical cardiovascular disease (CVD), but its relation to subclinical atherosclerosis remains to be determined.

METHODS

We analyzed the cross-sectional associations of SDB, measured by the respiratory disturbance index (RDI), a hypoxemia index, and an arousal index, with carotid plaque and carotid intima-media thickness (IMT), measured by ultrasound. The sample included 985 participants in the Sleep Heart Health Study (mean age-62, median RDI-8.7) with no history of coronary heart disease and stroke, of whom 396 had evidence of a carotid plaque.

RESULTS

As compared with the first quartile of the RDI (0-1.2), the crude odds ratio for carotid plaque was 1.14, 1.27, and 1.48 for the second (1.3-4.1), third (4.2-10.7), and fourth (>10.7) quartile, respectively. After adjustment for CVD risk factors, the corresponding odds ratios were reduced (1.00, 1.04, 1.07, and 1.25). Similarly, the unadjusted mean carotid IMT increased with RDI, but adjusted means (mm) were similar (0.84, 0.85, 0.84, 0.85). Spline regression models did not show monotonicity of the dose-response functions at the right end of the RDI distribution. Neither the hypoxemia index nor the arousal index was associated with carotid plaque or carotid IMT.

CONCLUSION

The results of this study suggest that crude, positive associations between SDB and subclinical atherosclerosis can be attributed to confounding by CVD risk factors.

Chronic intermittent hypoxia predisposes to liver injury

Obstructive sleep apnea (OSA) is characterized by chronic intermittent hypoxia (CIH). OSA is associated with nonalcoholic steatohepatitis (NASH) in obese subjects. The aim of this study was to investigate the effects of CIH on the liver in the absence of obesity. Lean C57BL/6J mice (n = 15) on a regular chow diet were exposed to CIH for 12 weeks and compared with pair-fed mice exposed to intermittent air (IA, n = 15). CIH caused liver injury with an increase in serum ALT (224 +/- 39 U/l versus 118 +/- 22 U/l in the IA group, P < 0.05), whereas AST and alkaline phosphatase were unchanged. CIH also induced hyperglycemia, a decrease in fasting serum insulin levels, and mild elevation of fasting serum total cholesterol and triglycerides (TG). Liver TG content was unchanged, whereas cholesterol content was decreased. Histology showed swelling of hepatocytes, no evidence of hepatic steatosis, and marked accumulation of glycogen in hepatocytes. CIH led to lipid peroxidation of liver tissue with a malondialdehyde (MDA)/free fatty acids (FFA) ratio of 0.54 +/- 0.07 mmol/mol versus 0.30 +/- 0.01 mmol/mol in control animals (P < 0.01), and increased levels of active nuclear factor kappaB (NF-kappaB) in the nuclear fraction of hepatocytes, suggesting that CIH induced oxidative stress in the liver. Finally, CIH greatly exacerbated acetaminophen-induced liver toxicity, causing fulminant hepatocellular injury.

CONCLUSION

In the absence of obesity, CIH leads to mild liver injury via oxidative stress and excessive glycogen accumulation in hepatocytes and sensitizes the liver to a second insult, whereas NASH does not develop.

Sleep disturbances in caregivers of persons with dementia: contributing factors and treatment implications

Estimates suggest that there are more than 10 million adult caregivers of persons with dementia, two-thirds of who experience some form of sleep disturbance during the course of their caregiving career. Health care professionals are in the best position to detect and address this significant public health problem. Three major contributors to caregiver sleep disturbance are discussed in this paper: (1) the presence of caregiver disrupted sleep routines; (2) caregiver burden and depression; and, (3) the caregiver's physical health status. Successful treatment of a caregiver's sleep disturbance requires careful consideration of each of these contributors. We review and analyze the scientific literature concerning the multiple complex factors associated with the development and maintenance of sleep disturbances in caregivers. We provide a clinical vignette that illustrates the interplay of these contributing factors, and close by providing recommendations for clinicians and researchers treating and investigating the development and maintenance of sleep problems in family caregivers.

Sleep‐Disordered Breathing and the Association With Cardiovascular Risk

Breathing-related sleep disorders, particularly obstructive sleep apnea, have been largely undiagnosed in people with cardiovascular disease, probably due to limited health care provider awareness of the association between the two conditions. Solid evidence is emerging that the apneic events that occur during sleep lead to acute and chronic hemodynamic changes during wake time, including elevated sympathetic tone, decreased stroke volume and cardiac output, increased heart rate, and changes in circulating hormones that regulate blood pressure, fluid volume, vasoconstriction, and vasodilation. Obstructive sleep apnea is associated with known cardiovascular risk factors such as obesity and hyperlipidemia, and is considered by many sleep clinicians to be an independent risk factor for hypertension. Additionally, sleep apnea has been implicated in the pathogenesis of heart failure and stroke. Treatment with positive airway pressure during sleep eliminates the apneic events and the ensuing acute hemodynamic changes. Improvements in daytime blood pressure and left ventricular function also have been noted in persons with hypertension and heart failure. Because effective treatment is available for sleep apnea, this condition needs to be diagnosed and treated in persons with cardiovascular disease.

The effect of an increased intake of vegetables and fruit on weight loss, blood pressure and antioxidant defense in subjects with sleep related breathing disorders

OBJECTIVE

To assess the effect of an increased consumption of vegetables and fruit on body weight, risk factors for cardiovascular disease (CVD) and antioxidant defense in obese patients with sleep-related breathing disorders (SRBD).

DESIGN

Randomized, controlled trial of an intervention to increase the intake of vegetables to 400 g/day and fruit to 300 g/day. Dietary intake was calculated from a food frequency questionnaire. Antioxidant status was assessed with the ferric-reducing/antioxidant power (FRAP) assay. Plasma carotenoids were biomarkers for the intake of vegetables and fruit.

SETTING

A hospital clinic preventing risk factors for CVD.

SUBJECTS

Subjects were 103 men and 35 women with a body mass index of 36.7+/-5.8 kg/m(2) of which 57 (86%) in the control and 68 (94%) in the intervention group completed the study.

INTERVENTION

Group-based behavioral program during 3 months.

RESULTS

The mean between group differences in body weight was -2.0% (95% CI -3.6, -0.5), P<0.0001. The mean between group difference in systolic and diastolic blood pressure (BP) was -7.1 mm Hg (95% CI: -11.6, -2.6), P=0.0022 and -3.9 mm Hg (95% CI: -7.0, -0.9), P=0.0120, respectively. The mean change in daily intake of vegetables and fruit was 12 g (95% CI: -33, 57) and -4 g (95% CI: -79, 71) versus 245 g (95% CI: 194, 296) and 248 g (95% CI: 176, 320) in the control and intervention groups, respectively. This was reflected in higher concentrations of alpha-carotene and beta-carotene. No change in FRAP was seen. In a multiple regression analysis the change in intake of vegetables was a significant contributor (R(adj)(2)=0.073 (95% CI: 0.019, 0.214)) to the change in weight.

CONCLUSION

Targeted dietary advice to increase the intake of vegetables and fruit among subjects with SRBD contributed to weight reduction and reduced systolic and diastolic BP, but had no effect on antioxidant defense measured with FRAP.

Metabolic syndrome in obstructive sleep apnea and related cardiovascular risk

BACKGROUND

There is little evidence available about the relationship between metabolic syndrome as a comprehensive clinical entity and obstructive sleep apnea (OSA) with respect to the cardiovascular risk of patients with coexisting metabolic syndrome and OSA.

METHODS

Eighty-nine consecutive patients (males 85%, aged 62 +/- 11 years) with newly-diagnosed OSA were evaluated for the presence of metabolic syndrome and the incidence of cardiovascular events after implementation of continuous positive airway pressure (CPAP) therapy was registered during medium-term follow-up. The diagnosis of OSA and metabolic syndrome was obtained by overnight polygraphy [with a presence of an apnea-hypopnea index (AHI) >or= 15] and following NCEP ATP III recommendations, respectively.

RESULTS

Forty-seven (53%) OSA patients had coexisting metabolic syndrome, with increased waist circumference (98%), high blood pressure (89%) and decreased high-density lipoprotein-cholesterol (83%) as the most frequent features. OSA patients with metabolic syndrome were also younger (58 +/- 11 years versus 65 +/- 4 years, P < 0.001) and presented an higher AHI (43.5 +/- 20.2 versus 34.8 +/- 17.3, P < 0.05) as compared to those without metabolic syndrome. Follow-up lasted 22 +/- 10 months. OSA patients who also presented metabolic syndrome suffered events less frequently compared to those who did not (6% versus 24%, P < 0.05), whereas the single end-points for follow-up (i.e. death, acute coronary syndrome, cerebrovascular event, peripheral vascular event, venous thromboembolism) did not significantly differ between the two groups.

CONCLUSIONS

Metabolic syndrome was a frequent comorbidity in OSA patients, reflecting higher degrees of sleep-disordered breathing, and did not increase the risk of cardiovascular events after adoption of CPAP therapy.

Risk factors and myocardial infarction in patients with obstructive sleep apnea: impact of beta2-adrenergic receptor polymorphisms

BACKGROUND

The increased sympathetic nervous activity in patients with obstructive sleep apnea (OSA) is largely responsible for the high prevalence of arterial hypertension, and it is suggested to adversely affect triglyceride and high-density lipoprotein (HDL) cholesterol levels in these patients. The functionally relevant polymorphisms of the beta2-adrenergic receptor (Arg-47Cys/Arg16Gly and Gln27Glu) have been shown to exert modifying effects on these risk factors in previous studies, but results are inconsistent.

METHODS

We investigated a group of 429 patients (55 +/- 10.7 years; 361 men, 68 women) with moderate to severe obstructive sleep apnea (apnea/hypopnea index (AHI) 29.1 +/- 23.1/h) and, on average, a high cardiovascular risk profile (body mass index 31.1 +/- 5.6, with hypertension in 60.1%, dyslipidemia in 49.2%, and diabetes in 17.2% of patients). We typed the beta2-adrenergic receptor polymorphisms and investigated the five most frequent haplotypes for their modifying effects on OSA-induced changes in blood pressure, heart rate, and lipid levels. The prevalence of cardiovascular risk factors and coronary heart disease (n = 55, 12.8%) and survived myocardial infarction (n = 27, 6.3%) were compared between the genotypes and haplotypes.

RESULTS

Multivariate linear/logistic regressions revealed a significant and independent (from BMI, age, sex, presence of diabetes, use of antidiabetic, lipid-lowering, and antihypertensive medication) influence of AHI on daytime systolic and diastolic blood pressure, heart rate, prevalence of hypertension, and triglyceride and HDL levels. The beta2-adrenergic receptor genotypes and haplotypes showed no modifying effects on these relationships or on the prevalence of dyslipidemia, diabetes, and coronary heart disease, yet, for all three polymorphisms, heterozygous carriers had a significantly lower relative risk for myocardial infarction (Arg-47Cys: n = 195, odds ratio (OR) = 0.32, P = 0.012; Arg16Gly: n = 197, OR = 0.39, P = 0.031; Gln27Glu: OR = 0.37, P = 0.023). Carriers of the most frequent haplotype (n = 113) (haplotype 1; heterozygous for all three polymorphisms) showed a five-fold lower prevalence of survived myocardial infarction (OR = 0.21, P = 0.023).

CONCLUSION

Our study showed no significant modifying effect of the functionally relevant beta2-adrenergic receptor polymorphisms on OSA-induced blood pressure, heart rate, or lipid changes. Nevertheless, heterozygosity of these polymorphisms is associated with a lower prevalence of survived myocardial infarction in this group with, on average, a high cardiovascular risk profile.

Clinical characteristics of obstructive sleep apnea in community-dwelling older adults

OBJECTIVES

To examine whether traditional risk factors are common in older adults with obstructive sleep apnea (OSA).

DESIGN

Cross-sectional study.

SETTING

Atlanta, Georgia.

PARTICIPANTS

A convenience sample of 94 community-dwelling adults aged 62 to 91.

MEASUREMENTS

Demographic, medical, and sleep-related information obtained using questionnaires. Epworth Sleepiness Scale (ESS) and 72-hour voiding diary were used to determine daytime sleepiness and nocturia frequency, respectively. Overnight ambulatory sleep recording device was used to screen for OSA.

RESULTS

Fifteen female and 15 male subjects had an apnea-hypopnea index (AHI) of 15 or more per hour of sleep (moderate to severe OSA). Traditional risk factors such as snoring, body mass index, and neck circumference were not significantly associated with OSA. An AHI of 15 or more per hour was independently associated with not feeling well rested in the morning, higher ESS score, and greater frequency of nocturia.

CONCLUSION

Traditional risk factors for OSA were not common presenting symptoms and signs in study subjects with an AHI of 15 or more per hour of sleep; this may contribute to underdiagnosis of OSA in this population. Subjects with an AHI of 15 or more per hour had more sleep-related complaints and excessive daytime sleepiness. Although occult, this suggests that OSA may contribute to disease burden in this group of people.

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.

Hyperlipidemia and lipid peroxidation are dependent on the severity of chronic intermittent hypoxia

Obstructive sleep apnea (OSA) is characterized by chronic intermittent hypoxia (CIH) and associated with dysregulation of lipid metabolisms and atherosclerosis. Causal relationships between OSA and metabolic abnormalities have not been established because of confounding effects of underlying obesity. The goal of the study was to determine if CIH causes lipid peroxidation and dyslipidemia in the absence of obesity and whether the degrees of dyslipidemia and lipid peroxidation depend on the severity of hypoxia. Lean C57BL/6J mice were exposed to CIH for 4 wk with a fractional inspired O2 (FI(O2)) nadir of either 10% (moderate CIH) or 5% (severe CIH). Mice exposed to severe CIH exhibited significant increases in fasting serum levels of total cholesterol (129 +/- 2.9 vs. 113 +/- 2.8 mg/dl in control mice, P < 0.05) and low-density lipoprotein cholesterol (85.7 +/- 8.9 vs. 56.4 +/- 9.7 mg/dl, P < 0.05) in conjunction with a 1.5- to 2-fold increase in lipoprotein secretion, and upregulation of hepatic stearoyl coenzyme A desaturase 1 (SCD-1). Severe CIH also markedly increased lipid peroxidation in the liver (malondialdehyde levels of 94.4 +/- 5.4 vs. 57.4 +/- 5.2 nmol/mg in control mice, P < 0.001). In contrast, moderate CIH did not induce hyperlipidemia or change in hepatic SCD-1 levels but did cause lipid peroxidation in the liver at a reduced level relative to severe CIH. In conclusion, CIH leads to hypercholesterolemia and lipid peroxidation in the absence of obesity, and the degree of metabolic dysregulation is dependent on the severity of the hypoxic stimulus.

Fat snorers and sleepy-heads: were many distinguished characters of the past affected by the obstructive sleep apnea syndrome?

The obstructive sleep apnea syndrome (OSAS) is a clinical condition characterized by the coexistence of irregular breathing at night with excessive daytime sleepiness, and it represents a major social health issue because of its high prevalence and of the growing public awareness of it. The XIX century description of "Fat Joe", the famous character of Charles Dickens's Pickwick Papers, is often retained the first presentation of a person affected by OSAS, since Joe was an obese individual who fell asleep during daytime while performing even extremely simple tasks. However, apart from the fact that Joe's Picwickian syndrome ("the obesity hypoventilation syndrome") needs to be differentiated from true OSAS, already in the Hippocratic Corpus (V-IV century BC) many clues regarding apnea and sleepiness are present, and in 79 AD the Roman author Pliny the Younger clearly reported the death of a man in whom obesity, sleepiness and snoring were co-present in a unique clinical picture. In this paper, elements suggesting OSAS are traced back and evidenced in the XIX and XX centuries in distinguished figures, including Emperor Napoleon Bonaparte, Queen Victoria and President Franklin D. Roosevelt. A posteriori reconstruction of the health status of characters of the past is difficult, and, to an extent, speculative, but the elements here provided appear relevant, since the possible presence of disabling OSAS in important personages of the past may have negatively influenced not only their health status, but also their social life and their work activity.

Chronic intermittent hypoxia alters hypothalamic transcription of genes involved in metabolic regulation

Epidemiological studies show that the obstructive sleep apnea syndrome (OSAS) is strongly associated with obesity, hypertension and diabetes, the three conditions characteristic of the metabolic syndrome. Since metabolic disorders usually involve altered homeostatic mechanisms both centrally and peripherally, it is likely that so it is in OSAS, but the underlying mechanisms remain largely unknown. We used an established rodent model to test whether chronic intermittent hypoxia (CIH) similar to that experienced by OSAS patients leads to distinct and relevant for metabolic regulation transcriptional changes in the posterior hypothalamus. Using quantitative reverse transcription-polymerase chain reaction, we found that rats exposed to CIH for 35 days (n=9) had twice higher levels of the adrenergic alpha2A receptor mRNA than the rats simultaneously submitted to a matching sham treatment (n=9). The mRNA levels of three members of the family of signal transducers and activators of transcription, STAT1, STAT3 and STAT5b, were also increased 2-4 times. The increases occurred only in the perifornical region, whereas no changes were detected in the ventromedial region comprising the ventromedial and arcuate nuclei or the dorsomedial region comprising the dorsomedial and paraventricular nuclei. These results show that, at least at the transcriptional level, CIH exerts a distinct and regionally selective central effect on the expression of selected mRNAs involved in metabolic regulation through adrenergic, leptinergic and inflammatory pathways.

[Obstructive sleep apnea and hypopnea syndrome (OSAHS): association with obesity, gender and age]

Obstructive sleep apnea and hypopnea syndrome (OSAHS) has been the focus of extensive research because of its association with neurocognitive and cardiovascular complications. The aim of this study was to evaluate the frequency and association between OSAHS and the class of obesity, gender and age in outpatients referred to a sleep laboratory. We selected 1,595 patients, 71.7% male. Mean +/- SD age was 46.7 +/- 11.7 years, BMI was 28.1 +/- 5.1 kg/m2 and AIH was 13.9 +/- 15.5 events/ hour of sleep. The patients were considered apneic when the apnea-hypopnea index (AHI) was > 5 events/hour of sleep; OSAHS was present in: (1) 71.1% of men and 50.3% of women (p < 0.001); (2) in 45.3% of patients with normal BMI, in 64.3% of those overweighed and in 80% of obese (p < 0.001). According to age, 61.2% with age < 55 were apneic, as well as 78% of those with age > 55 years old (p < 0.001). We concluded that OSAHS was directly and strongly associated to the male gender, obesity class and to aging.

Office and ambulatory blood pressure are independently associated with albuminuria in older subjects with type 2 diabetes

Blood pressure strongly predicts microalbuminuria and later progression to renal failure in people with diabetes. Ambulatory blood pressure monitoring seems to be superior to office blood pressure in predicting progression to microalbuminuria in type 1 diabetes. The associations of ambulatory blood pressure with office blood pressure and microalbuminuria in type 2 diabetes remain unclear. We studied the association of office blood pressure taken with an automated device and ambulatory blood pressure with spot urine albumin:creatinine ratio in 1180 older people with type 2 diabetes participating in the Informatics for Diabetes Education and Telemedicine Study. Office and awake systolic blood pressure were independently associated with albuminuria (P<0.001 for both) in a multivariate linear regression analysis that adjusted for age, gender, duration of diabetes, hemoglobin A1c, number of antihypertensive medications, and use of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. Twelve percent of participants had well-controlled office blood pressure but not ambulatory blood pressure, whereas 14% had well-controlled ambulatory but not office blood pressure. The prevalence of microalbuminuria and macroalbuminuria in these subgroups was intermediate between those with well-controlled or uncontrolled blood pressure by both methods. We found, in a multiethnic group of older subjects with type 2 diabetes, that office systolic blood pressure and awake systolic ambulatory blood pressure exhibited independent associations with degree of albuminuria.

Obstructive Sleep Apnea Syndrome

OBJECTIVES

We studied structural and functional cardiac alterations in obstructive sleep apnea (OSA), their relationship to the severity of OSA, and the effects of treatment with continuous positive airway pressure (CPAP).

BACKGROUND

Obstructive sleep apnea may influence the cardiac function by several mechanisms in the awake patient.

METHODS

Left and right ventricular morphology and function were studied using echocardiography before and after treatment with CPAP in symptomatic patients (Epworth sleepiness score, 10 +/- 4.8) with severe OSA (apnea-hypopnea index [AHI], 42 +/- 24). The patients (n = 43, 32 men) had no known cardiac disease and were obese (body mass index, 31.6 +/- 5.4 kg/m2). The same echocardiographic parameters were studied in age-matched overweight patients (n = 40; body mass index, 26.4 +/- 2.3 kg/m2).

RESULTS

The patients were hypertensive (systolic blood pressure, 153 +/- 25 mm Hg), with a higher resting heart rate (77 +/- 10 beats/min, p = 0.008) compared with age-matched control patients (n = 40). There was right ventricular dilatation, hypertrophic interventricular septum, reduced left ventricular stroke volume, tissue Doppler-determined systolic and diastolic velocities of the left and right ventricle, and normal pulmonary artery pressure. The structural and functional parameters were significantly associated with AHI (p < 0.004). Multiple stepwise regression showed the interventricular septum thickness, right ventricular free wall, and mitral annulus tissue Doppler systolic velocities to be predictive of a higher AHI (p < 0.001). Six months after treatment with CPAP, significant improvements were observed in the symptoms and hemodynamics, as well as left and right ventricular morphology and function.

CONCLUSIONS

The structural and functional consequences of OSA on the heart are influenced by the severity of AHI. These effects are reversible if the apneic episodes are abolished.

Modifying effects of the R389G beta1-adrenoceptor polymorphism on resting heart rate and blood pressure in patients with obstructive sleep apnoea

OSA (obstructive sleep apnoea) stimulates sympathetic nervous activity and elevates resting HR (heart rate) and BP (blood pressure). In the present study in a cohort of 309 untreated OSA patients, the resting HR and BP during the daytime were correlated with AHI (apnoea/hypopnea index) and compared with patients with R389R (n = 162), R389G (n = 125) and G389G (n = 22) genotypes of the beta1-adrenoreceptor R389G polymorphism. We analysed the impact of the genotype on the decline of HR and BP in a subgroup of 148 patients (R389R, n = 86; R389G, n = 54; G389G, n = 8) during a 6-month follow-up period under CPAP (continuous positive airway pressure) therapy during which cardiovascular medication remained unchanged. In untreated OSA patients, we found an independent relationship between AHI and resting HR (beta = 0.096, P < 0.001), systolic BP (beta = 0.09, P = 0.021) and diastolic BP (beta = 0.059, P = 0.016). The resting HR/BP, however, did not differ among carriers with the R389R, R389G and G389G genotypes. CPAP therapy significantly reduced HR [-2.5 (-1.1 to -4.0) beats/min; values are mean difference (95% confidence intervals)] and diastolic BP [-3.2 (-1.5 to -5.0) mmHg]. The decline in HR was more significantly pronounced in the R389R group compared with the Gly(389) carriers [-4.1 (-2.3 to -5.9) beats/min (P < 0.001) compared with -0.2 (2.1 to -2.6) beats/min (P = 0.854) respectively; Student's t test between groups, P = 0.008]. Diastolic BP was decreased significantly (P < 0.001) only in Gly389 carriers (R389G or G389G) compared with R389R carriers [-5.0 (-2.3 to -7.6) mmHg compared with -2.0 (0.4 to -4.3) mmHg respectively]. ANOVA revealed a significant difference (P = 0.023) in HR reduction between the three genotypes [-4.1 (+/-8.4) beats/min for R389R, -0.5 (+/-9.3) beats/min for R389G and +1.9 (+/-7.2) beats/min for G389G]. In conclusion, although the R389G polymorphism of the beta1-adrenoceptor gene did not influence resting HR or BP in untreated OSA patients, it may modify the beneficial effects of CPAP therapy on these parameters.

Sleep-related breathing disorders

Sleep-related breathing disorders are a heterogeneous group of conditions that may be associated with alterations in the structure of sleep, in sleep quality, and in gas exchange during sleep. Obstructive sleep apnea represents the most frequent cause of sleep-related breathing disorders, which encompass a diversity of conditions that either complicate coexisting disease or present as primary disorders. Many of these disorders have consequences during both sleep and wakefulness and may produce substantial burden of symptoms and disease in untreated individuals.

Diagnosis and treatment of sleep disorders in older adults

Among the most common complaints of older adults are difficulty initiating or maintaining sleep. These problems result in insufficient sleep at night, which then results in an increased risk of falls, difficulty with concentration and memory, and overall decreased quality of life. Difficulties sleeping, however, are not an inevitable part of aging. Rather, these sleep complaints are often secondary to medical and psychiatric illness, the medications used to treat these illnesses, circadian rhythm changes, or other sleep disorders. The task for the geriatric psychiatrist is to identify the causes of these complaints and then initiate appropriate treatment.

Apolipoprotein E and obstructive sleep apnea: evaluating whether a candidate gene explains a linkage peak

Evidence from both linkage analyses and association-based analyses has implicated Apoliprotein E (ApoE) as a disease susceptibility locus for obstructive sleep apnea. To further assess the putative role of ApoE in sleep apnea, we performed genotyping, association, and linkage analyses in a cohort assembled to investigate the genetic epidemiology of sleep apnea. Among a subset of the Caucasian families, ten microsatellites, spanning 20 cM, were genotyped in a region near ApoE on chromosome 19 where previous suggestive linkage had been demonstrated using a 9.1-cM genome-wide scan. Haseman-Elston regression analysis, conducted with these fine mapping markers (n=196 sibling pairs, 56 families), showed evidence for linkage to marker AFM210yg9 (p=0.00034), which was increased over that observed with the original scan. ApoE genotyping also was performed on a larger set of data (n=1,211 from 271 families, ages 3-85 years) from the cohort with available DNA. To determine whether the ApoE genotype explains the linkage peak, we included the ApoE genotype as a covariate in regression models. Inclusion of ApoE E2 allele as a covariate reduced the regression coefficient by 18%, suggesting that ApoE does not substantively explain the linkage signal. Finally, we repeated an association-based analysis in the larger sample of 1,211 individuals, and observed a higher prevalence of sleep apnea among individuals with the ApoE E2 allele. Overall, the evidence suggests that there is a disease susceptibility locus for obstructive sleep apnea in the region of ApoE, but ApoE itself is unlikely to be the causative locus.

The history, science, and innovation of Holter technology

Holter technology has endured for more than 40 years, and proven to be a valuable adjunctive noninvasive diagnostic technology to record the ambulatory or long-term electrocardiogram in the study of living creatures. During this span of time, many scientists, physicians, and innovators contributed to the development and evolution of Holter technology. This essay seeks to document a view of the history and evolution of the technology during that time, and concomitantly give recognition to the scientists, physicians, and engineers who contributed so greatly.

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.

Antioxidant nutrient intake and supplements as potential moderators of cognitive decline and cardiovascular disease in obstructive sleep apnea

Cognitive deficits and cardiovascular disease (CVD) are comorbid conditions frequently associated with obstructive sleep apnea (OSA). Oxygen free radical release and its differential regulation of cytokine synthesis and immune modulation resulting from OSA-related hypoxic events have been hypothesized as the underlying mechanism(s) for the cognitive deficits and CVD in OSA. A number of studies have suggested that increased levels of oxidative stress and/or antioxidant deficiencies may also be risk factors in cognitive decline and CVD. The influence of antioxidant nutrients and supplements, such as Vitamins B6, B12, C, E, folic acid, alpha-lipoic acid and Coenzyme Q(10) on cognitive decline and CVD have been investigated. The influence of antioxidant nutrients or supplements on OSA remains to be investigated. Even if dietary or supplemental antioxidants do not prove to be effective therapies for OSA, dietary assessment and prescription to increase dietary intake of neuro- and cardio-protective nutrients may make it possible to reduce some of the cognitive and cardiovascular sequelae associated with OSA.