Obstructive sleep apnoea syndrome as a risk factor for hypertension: population study

Nasal CPAP reduces systemic blood pressure in patients with obstructive sleep apnoea and mild sleepiness

BACKGROUND

A randomised controlled study was undertaken to examine the effect of nasal continuous positive airway pressure (CPAP) on 24 hour systemic blood pressure (BP) in patients with obstructive sleep apnoea (OSA).

METHODS

Patients were fitted with an ambulatory BP measuring device as outpatients during normal activities and recorded for 24 hours before starting therapeutic or subtherapeutic (4 cm H(2)O) CPAP treatment. BP monitoring was repeated before completion of 12 weeks of treatment. The primary end point was the change in 24 hour mean BP.

RESULTS

Twenty three of 28 participants in each treatment arm completed the study. There was no significant difference between the two groups in age, body mass index, Epworth Sleepiness Score, apnoea-hypopnoea index, arousal index, and minimum Sao(2). Twenty four patients were hypertensive. The pressure in the therapeutic CPAP group was 10.7 (0.4) cm H(2)O. CPAP usage was 5.1 (0.4) and 2.6 (0.4) hours/night for the therapeutic and subtherapeutic CPAP groups, respectively (p<0.001). After 12 weeks of treatment there were significant differences between the two CPAP groups in mean (SE) changes in 24 hour diastolic BP (-2.4 (1.2) v 1.1 (1.0) mm Hg (95% CI -6.6 to -0.5), p = 0.025); 24 hour mean BP (-2.5 (1.3) v 1.3 (1.1) mm Hg (95% CI -7.2 to -0.2), p = 0.037); sleep time systolic BP (-4.1 (2.1) v 2.2 (1.8) mm Hg (95% CI -11.8 to -0.7), p = 0.028); and sleep time mean BP (-3.6 (1.7) v 1.3 (1.4) mm Hg (95% CI -9.2 to -0.4), p = 0.033).

CONCLUSIONS

Compared with subtherapeutic CPAP, 12 weeks of treatment with therapeutic CPAP leads to reductions in 24 hour mean and diastolic BP by 3.8 mm Hg and 3.5 mm Hg, respectively, in mildly sleepy patients with OSA.

Endothelial Function in Patients with Obstructive Sleep Apnea Syndrome but without Hypertension

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) influences endothelial function and causes hypertension.

OBJECTIVES

Our aim was to evaluate the role of endothelial dysfunction in the pathogenesis of hypertension in OSAS.

METHODS

Twenty-three patients with OSAS but without hypertension and 15 healthy normotensive subjects were investigated. The presence or absence of OSAS was evaluated with a sleep study. Endothelial function was investigated with brachial artery ultrasound examination.

RESULTS

Baseline characteristics were equivalent between the two groups. Minimal oxygen saturation and apnea-hypopnea indexes in the OSAS and control groups were 62.9 +/- 16.5 versus 94.9 +/- 1.1% (p < 0.0001) and 53.1 +/- 20.3 versus 3.8 +/- 0.9 (p < 0.0001), respectively. There was not statistically significant difference between basal brachial artery diameters measured in the morning and in the evening in all groups. Flow-mediated dilation (FMD) values measured in the morning were lower than those measured in the evening in both OSAS patients and the control group: FMD of OSAS patients was 6.04 +/- 3.18% in the morning and 10.38 +/- 4.23% in the evening hours (p = 0.001), and FMD of control subjects was 10.9 +/- 2.6% in the morning and 13.9 +/- 2.32 in the evening hours (p = 0.002). Differences in FMD values measured both in the morning and evening hours in OSAS patients were lower compared with those in control subjects (p < 0.0001 in the morning hours and p = 0.003 in the evening hours).

CONCLUSIONS

We detected a prominent diurnal deterioration in endothelial function in normotensive OSAS patients compared with healthy subjects. This deterioration may occur due to ongoing hypoxemia during the night and it may be a possible cause of hypertension and atherosclerotic cardiovascular diseases in patients with OSAS.

Sleep disorders in end-stage renal disease: ‘Markers of inadequate dialysis?’

Excessive daytime sleepiness and sleep disorders, including sleep apnea syndrome, restless legs syndrome, and periodic limb movement disorder, occur with increased frequency in patients with end-stage renal disease (ESRD). The detection and management of sleep disorders in ESRD patients is often challenging but may have significant clinical benefits. Some of the poor quality of life in ESRD may be attributed to the presence of concomitant sleep disorders, yet the classical symptoms of sleep disorders (poor concentration, daytime sleepiness, and insomnia) are often ascribed to the uremic syndrome itself. Conventional risk factors and screening tools used in the diagnosis of sleep disorders seem to have limited applicability in dialysis patients implicating the unique pathophysiology of sleep disorders in ESRD. Emerging evidence suggests that sleep apnea may contribute to the augmented cardiovascular event rates and to the accelerated development of atherosclerosis in ESRD. Whether treatment of sleep disorders in ESRD patients can affect the high morbidity and mortality of ESRD patients has yet to be elucidated. To date, conventional renal replacement therapies do not appear to have a significant impact on the treatment of sleep disorders in ESRD. The promising therapeutic effects of optimal uremia control in the forms of nocturnal hemodialysis and renal transplantation on sleep disorders require further mechanistic and clinical studies.

Autonomic Cardiac Modulation in Obstructive Sleep Apnea

BACKGROUND

Patients with obstructive sleep apnea (OSA) are characterized by deranged cardiovascular variability, a well-established marker of cardiovascular risk. While long-term treatment with continuous positive airway pressure leads to a significant improvement of cardiovascular variability, little is known of the possibility of achieving the same results with other therapeutic approaches. The aim of our study was to investigate the responses of autonomic indexes of neural cardiac control to another type of OSA treatment based on an oral jaw-positioning appliance.

METHODS

In 10 otherwise healthy subjects with OSA (OSA+) and in 10 subjects without OSA (OSA-) we measured heart rate, BP, and indices of autonomic cardiac regulation derived from time-domain and spectral analysis of R-R interval (RRI), before and after 3 months of treatment with the oral device. High-frequency (HF) power of RRI was taken as an index of parasympathetic cardiac modulation, and the ratio between low-frequency (LF) and HF RRI powers as an indirect marker of the balance between sympathetic and parasympathetic cardiac modulation.

RESULTS

At baseline, in comparison with OSA- subjects, OSA+ subjects displayed a significantly lower RRI variance (p < 0.02) and reduced HF RRI powers (p < 0.001). After 3 months of treatment with the oral device, the OSA+ group showed a marked reduction in apnea-hypopnea index (p < 0.001), a lengthening in RRI and a significant increase in its variance (p < 0,02), an increased HF RRI power (from 134 +/- 26 to 502 +/- 48 ms2, p < 0.001), and a reduction in LF/HF RRI power ratio (from 3.11 +/- 0.8 to 1.5 +/- 0.5). As a result of these changes, after the 3-month treatment there were no more significant differences between the two groups in these parameters. In both OSA+ and OSA- groups, body weight, heart rate, and BP did not change over time.

CONCLUSIONS

Three months of treatment with a specific oral jaw-positioning appliance improves cardiac autonomic modulation in otherwise healthy patients with OSA of mild degree.

Consequences of subchronic and chronic exposure to intermittent hypoxia and sleep deprivation on cardiovascular risk factors in rats

Since studies suggest that both hypoxia and sleep fragmentation are related to cardiovascular alterations induced by obstructive sleep apnea, the present study was designed to evaluate the effects of hypoxia, sleep deprivation, and their combination on biochemical blood parameters in rats. In subchronic experiments (4 days), rats were exposed to intermittent hypoxia (IH) during the light period (2min room air-2min 10% O(2) for 12h/day) and/or paradoxical sleep deprivation (PSD, 24h/day). Consequences of chronic intermittent hypoxia (CIH) exposure were examined after 21 consecutive days of hypoxia protocol from 10:00 to 16:00 followed by a sleep restriction (SR) period of 18h (16:00-10:00). Rats were randomly assigned to seven treatment groups: (1) control (2) IH (3) PSD (4) IH-PSD (5) SR (6) CIH and (7) CIH-SR. PSD reduced triglycerides and very low-density lipoprotein (VLDL) cholesterol concentrations and increased total cholesterol and high-density lipoprotein (HDL) cholesterol. IH did not alter any of these parameters. The combination of IH-PSD did not modify the values of total cholesterol and HDL compared to control group. In the chronic experiment, the animals exposed to CIH displayed a reduction of Vitamin B(6) and an increase of triglycerides and VLDL. Our findings show a duration-dependent effect of hypoxia on triglycerides. Rats in the SR and CIH-SR groups showed a diminished concentration of triglycerides and VLDL. SR rats showed a reduction in the concentration of homocysteine but the animals in the CIH-SR treatment condition did not display any alterations in this parameter. In this latter group, an augmentation of cysteine concentration was observed. These results suggest that sleep deprivation and hypoxia modify biochemical blood parameters in distinct ways.

Obstructive sleep apnea syndrome is associated with metabolic syndrome rather than insulin resistance

The aim of this study was to investigate cross-sectionally the prevalence and covariates of obstructive sleep apnea syndrome (OSAS) and its relationship to metabolic syndrome (MS), insulin resistance (IR), and coronary heart disease (CHD) in a population sample of 1,946 men and women representative of Turkish adults. OSAS was identified when habitual snoring and episodes of apnea were combined with another relevant symptom. MS was diagnosed based on modified criteria of the Adult Treatment Panel III and IR by homeostatic model assessment (HOMA). OSAS was identified in 61 men (6.4%) and 58 women (5.8%), at a similar prevalence, after adjusting for covariates. Among individuals with OSAS, significantly higher odds ratios (ORs), adjusted for age, body mass index (BMI), and waist girth, were observed for MS, hypertension, and prevalent CHD, but not for HOMA or menopause. Significantly higher C-reactive protein existed only in women with OSAS who were also more frequent smokers. In logistic regression models, waist circumference, but not BMI nor hypertension, was significantly associated with OSAS among men. In women, by contrast, current cigarette smoking and hypertension were the significant independent covariates. Regression models controlling for sex, age, and smoking revealed that MS (and not IR per se) was associated significantly with OSAS (OR 1.94) in nondiabetic individuals. To conclude, abdominal rather than overall obesity in men and smoking among women are significant independent determinants of OSAS in Turkish adults. OSAS is associated with MS rather than IR per se. Relatively high prevalence of OSAS is observed in Turkish women in whom it is significantly associated with CHD.

Low Socioeconomic Status Is a Risk Factor for Cardiovascular Disease Among Adult Obstructive Sleep Apnea Syndrome Patients Requiring Treatment

STUDY OBJECTIVE

To evaluate the possible role of low socioeconomic status (SES) as a risk factor for cardiovascular disease (CVD) among obstructive sleep apnea syndrome (OSAS) patients requiring treatment.

DESIGN

Polysomnographic and demographic characteristics and associated morbidity were measured in 686 prospectively recruited adult OSAS patients from two regions in Israel.

SETTING

Two university-affiliated sleep laboratories.

MEASUREMENTS AND RESULTS

The multiple logistic regression (after adjusting for gender, body mass index [BMI], and smoking) revealed that the following are independent determinants for CVD in OSAS patients requiring treatment: each decrease in income level category (odds ratio [OR], 1.4; 95% confidence interval [CI], 1.1 to 1.7), age > or = 1 year (OR, 1.07; 95% CI, 1.04 to 1.1), hypertension (OR, 2.0; 95% CI, 1.3 to 3.1), and hyperlipidemia (OR, 3.7; 95% CI, 2.4 to 5.8); area under the receiver operating characteristic (ROC) = 81.9%. The multivariate determinants describing the low-SES OSAS patients included: minorities and immigrants combined (OR, 6.0; 95% CI, 2.9 to 12), female gender (OR, 2.4; 95% CI, 1.6 to 3.9), increased BMI (OR, 1.9; 95% CI, 1.3 to 2.9), unmarried status (OR, 1.9; 95% CI, 1.2 to 3.1), and years of education (> or = 1 year) [OR, 0.8; 95% CI, 0.7 to 0.8]; area under the ROC = 78.1%.

CONCLUSION

In addition to the already known traditional risk factors, low SES was found to be a novel independent risk factor for CVD among adult OSAS patients requiring treatment.

Follow-up assessment of CPAP efficacy in patients with obstructive sleep apnea using an ambulatory device based on peripheral arterial tonometry

This study aimed to assess the accuracy of a wrist-worn device based on peripheral arterial tonometry (Watch_PAT 100) to detect residual episodes of respiratory disturbance during continuous positive airway pressure (CPAP) therapy. Concurrent polysomnography was used as the reference standard to identify sleep disordered breathing (SDB) events. The study was conducted in three sleep laboratories affiliated with tertiary care academic medical centers. Seventy patients using CPAP to treat obstructive sleep apnea for at least 3 months, following an in-laboratory titration to determine the optimal therapeutic positive airway pressure, participated in this study. Symptoms indicating suboptimal therapy were not required for participation, but self-reported adherence to CPAP therapy was necessary for inclusion. Interventions are not applicable in this study. The accuracy of the PAT-derived respiratory disturbance index (PAT RDI scored by automated algorithm) to detect residual SDB on CPAP was assessed against polysomnography (PSG) using Bland-Altman analysis, receiver-operator characteristic (ROC) curves, and likelihood ratios for increasing (LR+) and decreasing (LR-) the probability of moderate-severe SDB in the study population. Respiratory events on the PSG were quantified using standard criteria for research investigations ("Chicago criteria") to yield a PSG RDI.C. Based on the PSG results, 19% of the participants had moderate-severe SDB (PSG RDI.C>15 events per hour) on their prescribed pressure. For PAT RDI >15 events per hour, the area under the ROC curve was 0.95 (SE 0.03, p < 0.0001, 95% CI 0.89 to 1.00), the LR+ was 8.04 (95% CI 3.64-17.7), and the LR- was 0.17 (95% CI 0.05-0.62). The mean difference between the PAT RDI and PSG RDI.C was three (2SD 14.5) events per hour. Therefore, residual moderate-severe SDB on CPAP was not uncommon in a multicenter population self-reporting adherence to CPAP therapy to treat obstructive sleep apnea. The Watch_PAT device accurately identified participants with moderate-severe SDB while using CPAP in the attended setting of a sleep laboratory.

Lymphocyte activation as a possible measure of atherosclerotic risk in patients with sleep apnea

Obstructive sleep apnea (OSA), a breathing disorder in sleep characterized by intermittent hypoxia and sleep fragmentation, constitutes an independent risk factor for cardiovascular morbidity. Investigating how this breathing disorder modulates immune responses may facilitate understanding one of the risk factors for atherosclerosis. T cells play a significant role in atherogenesis and plaque development via cytokine production and by directly contributing to vascular injury. Using flow cytometry and chromium release assays, we found that CD4 and CD8 T cells of OSA patients undergo phenotypic and functional changes and acquire cytotoxic capabilities. Thus, a shift in CD4 and CD8 T cells toward type 2 cytokine dominance with increased IL-4 expression was noted. IL-10 expression in T cells was negatively correlated with the severity of OSA, as determined by the apnea-hypopnea index (AHI), whereas TNF-alpha was positively correlated. CD8 T cells of OSA patients expressed a fourfold increase in TNF-alpha and CD40 ligand (CD40L), and exhibited an increased OSA severity-dependent cytotoxicity against endothelial cells. The percentage of CD4(+)CD28(null) and cytotoxicity of CD4 T lymphocytes were also significantly higher in OSA patients than in controls. Nasal continuous positive airway pressure (nCPAP) treatment, which ameliorated the severity of OSA, significantly lowered TNF-alpha and CD40L expression, and decreased cytotoxicity in CD8 T cells. In conclusion, increased cytotoxicity and cytokine imbalance in CD4 and CD8 T cells may be involved in atherogenesis in OSA. Nasal CPAP treatment ameliorates some lymphocyte dysfunctions and thus may moderate some atherogenic pathways.

Primary Prevention of Ischemic Stroke

Background and Purpose— This guideline provides an overview of the evidence on various established and potential stroke risk factors and provides recommendations for the reduction of stroke risk.

Methods— Writing group members were nominated by the committee chair on the basis of each writer’s previous work in relevant topic areas and were approved by the American Heart Association Stroke Council’s Scientific Statement Oversight Committee. The writers used systematic literature reviews (covering the time period since the last review published in 2001 up to January 2005), reference to previously published guidelines, personal files, and expert opinion to summarize existing evidence, indicate gaps in current knowledge, and when appropriate, formulate recommendations based on standard American Heart Association criteria. All members of the writing group had numerous opportunities to comment in writing on the recommendations and approved the final version of this document. The guideline underwent extensive peer review before consideration and approval by the AHA Science Advisory and Coordinating Committee.

Results— Schemes for assessing a person’s risk of a first stroke were evaluated. Risk factors or risk markers for a first stroke were classified according to their potential for modification (nonmodifiable, modifiable, or potentially modifiable) and strength of evidence (well documented or less well documented). Nonmodifiable risk factors include age, sex, low birth weight, race/ethnicity, and genetic factors. Well-documented and modifiable risk factors include hypertension, exposure to cigarette smoke, diabetes, atrial fibrillation and certain other cardiac conditions, dyslipidemia, carotid artery stenosis, sickle cell disease, postmenopausal hormone therapy, poor diet, physical inactivity, and obesity and body fat distribution. Less well-documented or potentially modifiable risk factors include the metabolic syndrome, alcohol abuse, drug abuse, oral contraceptive use, sleep-disordered breathing, migraine headache, hyperhomocysteinemia, elevated lipoprotein(a), elevated lipoprotein-associated phospholipase, hypercoagulability, inflammation, and infection. Data on the use of aspirin for primary stroke prevention are reviewed.

Conclusion— Extensive evidence is available identifying a variety of specific factors that increase the risk of a first stroke and providing strategies for reducing that risk.

Obstructive sleep apnea and insulin resistance: a role for microcirculation?

Obstructive sleep apnea is an increasingly recognized medical problem. The recent attention to its frequency in the general population and its important role in metabolic, vascular, and behavioral aspects have sharply increased the number and nature of investigations, thereby revealing new aspects that open new approaches in research. Whereas obstructive sleep apnea is a well-known phenomenon accompanying obesity and diabetes, new findings strongly suggest that this close relationship may also operate in the opposite direction. Indeed obstructive sleep apnea may be a primary feature inducing or aggravating a series of vascular and metabolic disturbances closely resembling the metabolic syndrome. This review will discuss established and potential mechanisms responsible for these changes. Obstructive sleep apnea indeed appears to gather all the elements necessary to induce insulin resistance, hypertension, and possibly heart failure. After careful analysis of these modifications and considering how they are intertwined, we propose that microcirculation could represent the common denominator mediating the progression of this pathology, as it is eventually the case in the metabolic syndrome and diabetes domain. This plausible hypothesis is discussed in detail and should be verified by appropriate preclinical and clinical protocols, which are now achievable by using noninvasive techniques in humans.

A case of sleep apnea syndrome manifesting severe hypertension with high plasma norepinephrine levels

A 55-year-old female was admitted to our hospital with severe hypertension (274/140 mmHg). Endocrinological examination revealed that her plasma levels of norepinephrine (NE) was elevated with high levels of urinary NE, normetanephrine and vanillylmandelic acid (VMA), suggesting the presence of pheochromocytoma. However, neither computed tomography nor MIBG scintigraphy detected any catecholamine-producing tumor in or outside the adrenal glands. She was screened with full polysomnography because of heavy snoring, and the diagnosis of severe obstructive sleep apnea syndrome (OSAS) was made. She was treated with calcium channel blocker for three weeks, but severe hypertension persisted. After treatment with nasal continuous positive airway pressure (CPAP) was added, her blood pressure gradually lowered week by week. Concomitantly, the levels of plasma and urinary NE, urinary normetanephrine and urinary VMA were normalized following nasal CPAP therapy for 2 weeks. Additional treatments with alpha-adrenergic blocker further decreased her home blood pressure. After a year, she continued nasal CPAP therapy and her blood pressure was nearly below 160/100 mmHg. Urinary NE level was slightly above normal range and other catecholamines stayed within the normal range. This case shows that patients with OSAS could develop severe hypertension through elevated sympathetic tone, mimicking pheochromocytoma. Nasal CPAP therapy is recommended not only to improve hypertension and catecholamine excess but also to distinguish the condition from pheochromocytoma.

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.

Oxidative stress and oxidant signaling in obstructive sleep apnea and associated cardiovascular diseases

Obstructive sleep apnea (OSA) has emerged as a major public health problem and increasing evidence indicates that untreated OSA can lead to the development of various cardiovascular disorders. One important mechanism by which OSA may promote cardiovascular diseases is intermittent hypoxia, in which patients are subjected to repeated episodes of brief oxygen desaturation in the blood, followed by reoxygenation. Such cycles of hypoxia/reoxygenation may result in the generation of reactive oxygen species. Some studies have demonstrated the presence of oxidative stress in OSA patients as well as in animals subjected to intermittent hypoxia. Further, modulations of nitric oxide and biothiol status might also play important roles in the pathogenesis of OSA-associated diseases. Reactive oxygen species and redox events are also involved in the regulation of signal transduction for oxygen-sensing mechanisms. This review summarizes currently available information on the evidence for and against the occurrence of oxidative stress in OSA and the role of reactive oxygen species in cardiovascular changes associated with OSA.

Effects of continuous positive airway pressure versus supplemental oxygen on 24-hour ambulatory blood pressure

Obstructive sleep apnea (OSA) is associated with recurrent episodes of nocturnal hypoxia and increased risk for development of systemic hypertension. Prior studies have been limited, however, in their ability to show reduction in blood pressure after continuous positive airway pressure (CPAP) therapy, and the effect of supplemental oxygen alone on blood pressure in OSA has not been evaluated. We performed a randomized, double-blind, placebo-controlled study comparing the effects of 2 weeks of CPAP versus sham-CPAP versus supplemental nocturnal oxygen on 24-hour ambulatory blood pressure in 46 patients with moderate-severe OSA. We found that 2 weeks of CPAP therapy resulted in a significant reduction in daytime mean arterial and diastolic blood pressure and nighttime systolic, mean, and diastolic blood pressure (all Ps <0.05). Although nocturnal supplemental oxygen therapy improved oxyhemoglobin saturation, it did not affect blood pressure. We conclude that CPAP therapy reduces both daytime and nighttime blood pressure in patients with OSA, perhaps through mechanisms other than improvement of nocturnal oxyhemoglobin saturation.

Phenotypic characteristics associated with hypertension in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) causes secondary hypertension. However, the reasons why the prevalence of hypertension among OSA patients varies widely (35-70%) are not clear. We sought to investigate the phenotypic characteristics of patients with and without hypertension among OSA patients who were matched for disease severity. We studied 152 OSA patients (76 normotensive and 76 hypertensive) diagnosed by polysomnography. Detailed phenotypic characteristics, including laboratorial analysis, were determined in all patients. Univariate analysis followed by multiple logistic regression analysis was used to identify variables that were independently associated with hypertension. The apnea-hypopnea index in normotensive and hypertensive patients was similar (48+/-26 and 48+/-26 events/h, respectively) as well as minimum arterial oxygen saturation (76+/-10 and 75+/-10%, respectively) and total sleep time with oxyhaemoglobin saturation <90% (25+/-25 and 28+/-26%, respectively). Hypertensive patients were older (57+/-11 vs 47+/-12 years; P<0.001), had a higher body mass index (BMI; 34+/-7 vs 30+/-5 kg/m(2); P<0.001), had a higher frequency of women (37 vs 8%; P<0.001), had a higher incidence of diabetes (25 vs 6%; P=0.002) and a higher family history of hypertension (75 vs 42%; P=0.01) than did the normotensive patients. Multiple logistic regression analysis indicated that age (P=0.004), familial history of hypertension (P=0.004), BMI (P=0.04) and female sex (P=0.03) were the independent variables associated with hypertension. We concluded that increasing age and BMI, familial history of hypertension as well as female gender are phenotypic characteristics associated with hypertension among OSA patients with similar disease severity.

Inflammatory aspects of sleep apnea and their cardiovascular consequences

Obstructive sleep apnea (OSA) is a common medical condition that occurs in a considerable percentage of the population. Substantial evidence shows that patients with OSA have an increased incidence of hypertension compared with individuals without OSA, and that OSA is a risk factor for the development of hypertension. It is established that OSA may be implicated in stroke and transient ischemic attacks. OSA is associated with coronary heart disease, heart failure, and cardiac arrhythmias. Pulmonary hypertension may be associated with OSA, especially in patients with pre-existing pulmonary disease. Although the exact cause that links OSA with cardiovascular disease is unknown, there is evidence that OSA is associated with a group of proinflammatory and prothrombotic factors that have been identified as important in the development of atherosclerosis. OSA is associated with increased daytime and nocturnal sympathetic activity. Autonomic abnormalities seen in patients with OSA include increased resting heart rate, decreased R-R interval variability, and increased blood pressure variability. Both atherosclerosis and OSA are associated with endothelial dysfunction, increased C-reactive protein, interleukin 6, fibrinogen, plasminogen activator inhibitor, and reduced fibrinolytic activity. OSA has been associated with enhanced platelet activity and aggregation. Leukocyte adhesion and accumulation on endothelial cells are common in both OSA and atherosclerosis. Clinicians should be aware that OSA may be a risk factor for the development of cardiovascular disease.

Pre-eclampsia is associated with sleep-disordered breathing and endothelial dysfunction

Pre-eclamptic toxaemia (PET) may be associated with both endothelial dysfunction (ED) and sleep-disordered breathing (SDB). It was hypothesised that females with PET would demonstrate both SDB and ED, and that a correlation between these two would suggest a potential causative association. A total of 17 females with PET and 25 matched females with uncomplicated pregnancy were studied. They underwent a nocturnal ambulatory sleep study (using Watch_PAT100) and noninvasive evaluation of endothelial function utilising the reactive hyperaemia test (using Endo_PAT 2000). A higher ratio of post- to pre-occlusion pulse-wave amplitude (endothelial function index (EFI)) indicated better endothelial function. Females with PET had a significantly higher respiratory disturbance index (RDI) and lower EFI than controls (18.4+/-8.4 versus 8.3+/-1.3.h(-1), and 1.5+/-0.1 versus 1.8+/-0.1, respectively). Blood pressure significantly correlated with RDI and with EFI. EFI tended to correlate with RDI. In conclusion, these results suggest that both sleep-disordered breathing and endothelial dysfunction are more likely to occur in females with pre-eclamptic toxaemia than in females with uncomplicated pregnancies. The current authors speculate that respiratory disturbances contribute to the functional abnormality of the blood vessels seen in females with pre-eclamptic toxaemia, although causality cannot be determined based on this study.

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

OBJECTIVE

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

DESIGN

Cross-sectional clinical study.

PATIENTS

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

MEASUREMENTS

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

RESULTS

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

CONCLUSION

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

Relationship between sleep-disordered breathing and lifestyle-related illnesses in subjects who have undergone health-screening

OBJECTIVE

Simplified sleep polysomnography was performed in 207 adult men to examine the relationship between the frequency of sleep-disordered breathing (SDB) and lifestyle-related illness.

METHODS

Each subject was checked for SDB using a simplified sleep polysomnograph (Auto-Set Portable; Teijin Limited, Tokyo, Japan). Apnea and hypopnea were detected with a nasal cannula type airflow sensor. Hypoxemia was checked with a percutaneous oxygen saturation (SpO2) monitor. We analyzed the relationships between SDB and body mass index (BMI) and hypertension, hyperlipidemia, liver dysfunction, fatty liver, and abnormal glucose metabolism.

RESULTS

Fifty-nine subjects (29%) showed SDB with apnea hypopnea index (AHI) over 15 times/h. The frequency of obesity (BMI > or = 25), hypertension, hypercholesterolemia, fasting blood glucose level, and HbA1c were significantly higher in patients with SDB than in normal individuals (AHI < 5 times/h). The frequencies of hypertension, hyperlipidemia, and abnormal glucose metabolism were compared between the obesity-free normal AHI group and the SDB group, and only that of hypertension was significantly different between the two groups.

CONCLUSIONS

The present study revealed a high frequency of SDB among Japanese individuals. The results also suggest that as SDB becomes severe, it becomes more closely linked to the onset of lifestyle-related illnesses, such as hypertension, hypercholesterolemia and abnormal glucose metabolism.

NT-pro-BNP in obstructive sleep apnea syndrome is decreased by nasal continuous positive airway pressure

OBJECTIVE

The aim of this study was to evaluate the impact of obstructive sleep apnea syndrome (OSAS) on B-type natriuretic peptide (BNP) and to determine the effect of nasal continuous positive airway pressure (nCPAP) treatment on BNP levels.

BACKGROUND

Increased sympathetic activity, repetitive rises in blood pressure, and apnea-induced wall stress may contribute as a trigger to release BNP in OSAS. However, there is uncertainty about whether OSAS affects BNP and whether application of nasal continuous positive airway pressure (nCPAP) ventilation affects release of BNP.

PATIENTS AND METHODS

A prospective study in 69 consecutive patients with suspected sleep disordered breathing referred to our sleep laboratory was conducted. OSAS was confirmed in 26 normotensive and 34 hypertensive patients and ruled out in nine normotensive patients (controls) by polysomnography (PSG).

RESULTS

Baseline N-terminal fragment of BNP prohormone (NT-pro-BNP) did not differ significantly between OSAS patients (hypertensive: mean +/-SEM 60.8+/-9.9 pg/ml, normotensive: 43.2+/-6.8 pg/ml) and controls (36.5+/-8.5 pg/ml). Application of CPAP resulted in a significant decrease of NT-pro-BNP in hypertensive (60.8+/-9.9 pg/ml to 47.6+/-7.4 pg/ml, p=0.023) and normotensive OSAS (43.2+/-6.8 pg/ml to 29.6+/-5.3 pg/ml, p=0.0002). In contrast, controls showed no significant differences in NT-pro-BNP after a second PSG (36.5+/-8.5 pg/ml to 40.7+/-12.3 pg/ml, p=0.597).

CONCLUSIONS

Normotensive and hypertensive OSAS was not associated with a significant elevation of NT-pro-BNP. Application of nCPAP decreased NT-pro-BNP levels significantly in normotensive and, in particular, hypertensive OSAS. These findings may provide further evidence of the potential for nCPAP to improve cardiovascular comorbidity and co-mortality in OSAS and sleep disordered breathing, in general.

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.

Bilaterale Palliduminfarkte bei Schlaf-Apnoe-Syndrom

Patients suffering from sleep apnea syndrome are known to be at higher risk of cardiac and cerebral infarction. In this case report, we describe bilateral pallidal lesions, which are normally seen after sudden asphyxia due to cardiac arrest or carbon monoxide intoxication. Some epidemiological and pathophysiological observations are cited.

Surgical treatment of obstructive sleep apnea

THE PRIMARY TREATMENT for obstructive sleep apnea (OSA) has been continuous positive airway pressure (CPAP) therapy, but the minimum acceptable number of hours of nightly CPAP use remains unclear. INTEGRATED SOFT TISSUE and bone surgery may be a viable alternative for patients who have rejected CPAP as a treatment option. Formal sleep testing has shown that surgery and CPAP therapy are equally successful at resolving OSA. REPEAT SLEEP TESTING conducted several years after patients have undergone combined soft tissue and bone surgery has demonstrated consistent and reliable surgical results. Patients with OSA should be offered surgery as an alternative to life-long CPAP treatment or as an option when CPAP therapy has not been successful.

Sleep disordered breathing and its treatment in congestive heart failure

Sleep disordered breathing (SDB) is a common problem with adverse cardiorespiratory, endocrinological, and endothelial effects. Recent studies demonstrate an even higher prevalence of SDB in congestive heart failure (CHF) than in a randomly selected population, with up to 40% and 11% having Cheyne Stokes respiration-central sleep apnoea and obstructive sleep apnoea-hypopnoea syndromes, respectively. Randomised controlled trials of nocturnal respiratory support for SDB associated with CHF for up to three months demonstrate significant benefits in terms of improvements in left ventricular ejection fraction, markers of sympathetic system activity, and quality of life. Further randomised controlled trials of larger scale and longer duration are required to establish the role and benefit of this intervention for the treatment of this debilitating condition. The evidence for the higher prevalence of SDB in CHF, its pathogenesis, its pathophysiological consequences, and the emerging benefits of respiratory support are reviewed.

A preliminary study on application of portable monitoring for diagnosis of obstructive sleep apnea

Portable monitoring (PM) for diagnosis of obstructive sleep apnea has developed recently. Many studies were performed in the laboratory setting, with simultaneous polysomnographic recordings or required technical assistance in the home setting. And the data were automatically analyzed. In this study, we attempted to evaluate whether PM could be useful in fully unattended home setting, and whether the auto analysis of the data is reliable. Home setting examination by Stardust II, a novel PM device, was performed unattendedly on consecutive 62 patients who complained of snoring. The questionnaire survey on the difficulty of fitting and operation, and the discomfort was conducted by visual analog scale. Automatically and manually analyzed results were compared. The examination was successfully performed by all subjects. The difficulty of fitting and operation, and the discomfort were 2.9+/-1.9, 1.8+/-1.2 and 3.6+/-2.1, respectively. Auto analysis differed significantly from manual analysis not only in apnea/hypopnea index (AHI), but also in the construction of sleep disordered respiratory events. Although AHI in automatic and manual analysis had a good correlation (r=0.949; P<0.001), their agreement was poor, especially in mild and moderate cases. However, setting AHI=50 as a cut-off point in auto analysis, sensitivity and specificity could reach 100% and 92.5%, respectively. Accordingly, PM is useful to identify obstructive sleep apnea in an unattended home setting condition. Considering the significant difference between automatic and manual analysis, we suggest that the data analysis should be performed manually.

Sleep and medical disorders

Extensive evidence links cardiovascular disease and sleep disordered breathing. OSA has adverse effects on blood pressure, cardiovascular status,and mortality. Effective CPAP therapy can improve blood pressure and cardiac function in patients who have OSA. Patients who have congestive heart failure have a high prevalence of sleep-disordered breathing, with OSA occurring in 30% of such patients and Cheyne-Stokes respiration in 40%.CPAP is the preferred mode of therapy for both types of sleep-disordered breathing in patients who have coexistent congestive heart failure. Nocturnal worsening of asthma is a common manifestation of this disease that indicates increased disease severity. Therapy focuses on judicious use of long-acting bronchodilators, and the presence of OSA should also be considered. COPD is frequently associated with impaired sleep, likely because of chronic dyspnea and sleep-associated hypoxemia. Appropriate therapy again includes long-acting bronchodilators and possibly nocturnal supplemental oxygen. Gastroesophageal reflux during sleep may lead to prolonged episodes of esophageal acid exposure and may be a common sequela of OSA, perhaps triggering nocturnal worsening of asthma. Endstage renal disease and chronic dialysis are commonly associated with a host of troublesome sleep problems,including OSA, RLS, PLMD, and daytime sleepiness.

Interaction of chemoreceptor and baroreceptor reflexes by hypoxia and hypercapnia - a mechanism for promoting hypertension in obstructive sleep apnoea

Asphyxia, which occurs during obstructive sleep apnoeic events, alters the baroreceptor reflex and this may lead to hypertension. We have recently reported that breathing an asphyxic gas resets the baroreceptor-vascular resistance reflex towards higher pressures. The present study was designed to determine whether this effect was caused by the reduced oxygen tension, which affects mainly peripheral chemoreceptors, or by the increased carbon dioxide, which acts mainly on central chemoreceptors. We studied 11 healthy volunteer subjects aged between 20 and 55 years old (6 male). The stimulus to the carotid baroreceptors was changed using graded pressures of -40 to +60 mmHg applied to a neck chamber. Responses of vascular resistance were assessed in the forearm from changes in blood pressure (Finapres) divided by brachial blood flow velocity (Doppler) and cardiac responses from the changes in RR interval and heart rate. Stimulus-response curves were defined during (i) air breathing, (ii) hypoxia (12% O(2) in N(2)), and (iii) hypercapnia (5% CO(2) in 95% O(2)). Responses during air breathing were assessed both prior to and after either hypoxia or hypercapnia. We applied a sigmoid function or third order polynomial to the curves and determined the maximal differential (equivalent to peak sensitivity) and the corresponding carotid sinus pressure (equivalent to 'set point'). Hypoxia resulted in an increase in heart rate but no significant change in mean blood pressure or vascular resistance. However, there was an increase in vascular resistance in the post-stimulus period. Hypoxia had no significant effect on baroreflex sensitivity or 'set point' for the control of RR interval, heart rate or mean arterial pressure. Peak sensitivity of the vascular resistance response to baroreceptor stimulation was significantly reduced from -2.5 +/- 0.4 units to -1.4 +/- 0.1 units (P < 0.05) and this was restored in the post-stimulus period to -2.6 +/- 0.5 units. There was no effect on 'set point'. Hypercapnia, on the other hand, resulted in a decrease in heart rate, which remained reduced in the post-stimulus period and significantly increased mean blood pressure. Baseline vascular resistance was significantly increased and then further increased in the post-control period. Like hypoxia, hypercapnia had no effect on baroreflex control of RR interval, heart rate or mean arterial pressure. There was, also no significant change in the sensitivity of the vascular resistance responses, however, 'set point' was significantly increased from 74.7 +/- 4 to 87.0 +/- 2 mmHg (P < 0.02). This was not completely restored to pre-stimulus control levels in the post-stimulus control period (82.2 +/- 3 mmHg). These results suggest that the hypoxic component of asphyxia reduces baroreceptor-vascular resistance reflex sensitivity, whilst the hypercapnic component is responsible for increasing blood pressure and reflex 'set point'. Hypercapnia appears to have a lasting effect after the removal of the stimulus. Thus the effect of both peripheral and central chemoreceptors on baroreflex function may contribute to promoting hypertension in patients with obstructive sleep apnoea.

Oxidative stress and left ventricular function with chronic intermittent hypoxia in rats

RATIONALE AND OBJECTIVES

Obstructive sleep apnea (OSA) is associated with oxidative stress and myocardial dysfunction. We hypothesized that the chronic intermittent hypoxia (CIH) component of OSA is sufficient to lead to these adverse effects.

METHODS AND RESULTS

Rats were exposed to CIH (nadir O2, 4-5%) for 8 hours/day, 5 days/week, for 5 weeks. Results were compared with similarly handled controls (HC). Outcomes included blood pressure (tail cuff plethysmograph), echocardiographic and invasive measures of left-ventricular (LV) function, and indices of oxidative stress that included levels of myocardial lipid peroxides and Cu/Zn superoxide dismutase. Blood pressure was greater in CIH (n=22) than in HC (n=22) after 2 weeks of exposure (136+/-12 vs. 128+/-8 mm Hg; p<0.05). However, the difference disappeared by 5 weeks (127+/-13 vs. 127+/-13 mm Hg). LV weight/heart weight was greater with CIH (CIH, 0.52+/-0.05; HC, 0.47+/-0.06; p<0.005). Echocardiograms revealed LV dilation, as well as decreased LV fractional shortening (CIH, 29.7+/-9.8%; HC, 37.4+/-7.1%; p<0.001). LV end-diastolic pressure was increased with CIH (CIH, 13.7+/-5.5; HC, 8.0+/-2.9 mm Hg; p<0.001), decreased LV dp/dtmax (CIH, 5072+/-2191; HC, 6596+/-720 mm Hg/second; p<0.039), and decreased cardiac output (CIH, 48.2+/-10.5; HC, 64.1+/-10.9 ml/minute; p<0.001). LV myocardial lipid peroxides were greater (CIH, 1,258+/-703; HC 715+/-240 microm/mg protein; p<0.05) and LV myocardial superoxide dismutase levels were lower (CIH, 10.3+/-4.9; HC, 18.6+/-8.2 U/mg protein; p<0.05) with CIH.

CONCLUSIONS

CIH leads to oxidative stress and LV myocardial dysfunction.

Chronic liver injury during obstructive sleep apnea

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

Disorders of sleep: an overview

Only recently has the medical profession focused on the importance of sleep and health. There are increasing numbers of studies linking sleep disorders with neurobehavioral and cardiovascular morbidity and possibly mortality. Although sleep disorders are diverse and affect a substantial number of patients, they are often misdiagnosed or underdiagnosed. Common presenting symptoms to physicians include hypersomnia and insomnia. A systematic workup helps to diagnose the underlying cause.

Obstructive Sleep Apnea-Hypopnea Syndrome

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

[Validation of a respiratory polygraphy system in the diagnosis of sleep apnea syndrome]

OBJECTIVE

To validate a cardiorespiratory polygraphy system (BITMED NGP 140) by comparing it to conventional polysomnography in the diagnosis of sleep apnea-hypopnea syndrome.

PATIENTS AND METHODS

Polysomnography and cardio-respiratory polygraphy were performed simultaneously on 103 consecutive patients referred because of suspected sleep apnea-hypopnea syndrome. The Bland and Altman method and intraclass correlation coefficients were used to assess agreement between the 2 methods of measurement. Receiver operating characteristic (ROC) curves were used to calculate the yield of cardiorespiratory polygraphy compared to that of conventional polysomnography.

RESULTS

Ninety-two valid studies were obtained for 72 men and 20 women (mean [SD] age: 52.4 [12] years). By the Bland and Altman method, the difference between the respiratory event index obtained with the BITMED NGP140 and the apnea-hypopnea index (AHI) obtained by conventional polysomnography was 7.6 (13.2) in the manual analysis (95% confidence interval [CI], 4.9-10.4) and 12 (15.3) (95% CI, 8.8-15.3) in the automatic analysis. For a corrected AHI (AH/total time in bed) mean differences were -2.2 (5.9) and 2.4 (8.2) for manual and automatic analysis. The intraclass correlation coefficients were greater than 0.94. The areas under the ROC curves of the respiratory event index were greater than 0.97 for all cut points. For an AHI of 30 or higher, the best cut-off point determined by manual cardiorespiratory polygraphy analysis was 27 (sensitivity, 98% and specificity, 98%). For the different cut-off points cardiorespiratory polygraphy correctly classified between 92% and 98% of patients in both the manual and automatic analyses.

CONCLUSIONS

The BITMED NGP140 had good agreement with conventional polysomnography for the measurement of respiratory events and provided high diagnostic yield.

Oxidative Stress in Obstructive Sleep Apnea

STUDY OBJECTIVES

To investigate the relationship between the severity of obstructive sleep apnea (OSA) and oxidative stress, which plays an important role in the pathogenesis of cardiovascular disease, and to elucidate the factors contributing to this relationship.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 128 consecutive subjects referred to the sleep laboratory of our hospital for screening or treatment of OSA.

INTERVENTIONS

Not applicable.

MEASUREMENTS

The severity of sleep-disordered breathing was evaluated by polysomnography. We measured urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as an in vivo parameter of oxidative stress. Known risk factors for oxidative stress (age, obesity, smoking, hyperlipidemia, hypertension, and diabetes mellitus) were also investigated.

RESULTS

Seventy subjects had nonsevere OSA (an apnea-hypopnea index [AHI] < 30), and 58 subjects had severe OSA (AHI >or= 30). Urinary 8-OHdG excretion was significantly higher in the severe OSA group (p = 0.03). Furthermore, urinary 8-OHdG excretion was significantly correlated with parameters of sleep-disordered breathing, including AHI, the apnea index, the oxygen desaturation index (ODI), the duration of oxygen saturation < 90%, and the respiratory arousal index. However, only ODI was significantly correlated with urinary 8-OHdG excretion after adjustment for confounding factors that are considered to be related to oxidative stress.

CONCLUSIONS

The severity of OSA is independently associated with oxidative stress. Among various sleep-disordered breathing parameters, ODI is most closely related to oxidative stress.

Comparison of blood pressure measurements in children with and without habitual snoring

Higher or similar systolic and/or diastolic blood pressure has been recorded in children with sleep apnea compared to subjects with primary snoring or in those with primary snoring compared to controls. To investigate the association between blood pressure and habitual snoring, we studied children in four randomly selected schools in central Greece. A symptom questionnaire was answered by parents, and children's weight, height, and blood pressure were measured. Seven hundred and sixty children (4-14 years old; 352 female) were recruited. Fifty of 760 (6.6%) participants were snoring more than 3 nights/week (habitual snorers). Mean (+/- SD) systolic blood pressure was 106.9 (+/-10.6) mmHg in habitual snorers vs. 107 (+/- 12) in nonhabitual snorers (P > 0.05). Mean diastolic blood pressure was 61.9 (+/- 7.6) in the former vs. 61.8 (+/- 6.8) in the latter (P > 0.05). While age, gender, and body mass index were significant predictors of systolic blood pressure in a general linear model, snoring was not. Similarly, that gender and body mass index but not snoring were significant predictors of diastolic blood pressure. In a community sample of children, habitual snorers do not have higher morning systolic or diastolic blood pressure than nonhabitual snorers.