Endothelial function in obstructive sleep apnea and response to treatment

Secondary arterial hypertension: when, who, and how to screen?

Secondary hypertension refers to arterial hypertension due to an identifiable cause and affects ∼5-10% of the general hypertensive population. Because secondary forms are rare and work up is time-consuming and expensive, only patients with clinical suspicion should be screened. In recent years, some new aspects gained importance regarding this screening. In particular, increasing evidence suggests that 24 h ambulatory blood pressure (BP) monitoring plays a central role in the work up of patients with suspected secondary hypertension. Moreover, obstructive sleep apnoea has been identified as one of the most frequent causes. Finally, the introduction of catheter-based renal denervation for the treatment of patients with resistant hypertension has dramatically increased the interest and the number of patients evaluated for renal artery stenosis. We review the clinical clues of the most common causes of secondary hypertension. Specific recommendations are given as to evaluation and treatment of various forms of secondary hypertension. Despite appropriate therapy or even removal of the secondary cause, BP rarely ever returns to normal with long-term follow-up. Such residue hypertension indicates either that some patients with secondary hypertension also have concomitant essential hypertension or that irreversible vascular remodelling has taken place. Thus, in patients with potentially reversible causes of hypertension, early detection and treatment are important to minimize/prevent irreversible changes in the vasculature and target organs.

Effects of CPAP treatment interruption due to disasters: patients with sleep-disordered breathing in the Great East Japan Earthquake and tsunami area

INTRODUCTION

The 2011 Great East Japan Earthquake caused major disruptions in the provision of health care, including that for patients with sleep-disordered breathing (SDB) using a nasal continuous positive airway pressure (nCPAP) device. This study investigated the ability of SDB patients to continue using the nCPAP device in the weeks immediately following the earthquake, whether inability to use the nCPAP device led to symptom relapse, and measures that should be taken to prevent disruptions in nCPAP therapy during future disasters. Hypothesis If nCPAP devices cannot be used during disasters, SDB patients' health will be affected negatively.

METHODS

Within 14 days of the disaster, 1,047 SDB patients completed a questionnaire that collected data regarding ability to use, duration of inability to use, and reasons for inability to use the nCPAP device; symptom relapse while unable to use the nCPAP device; ability to use the nCPAP device use at evacuation sites; and recommendations for improvement of the nCPAP device.

RESULTS

Of the 1,047 patients, 966 (92.3%) had been unable to use the nCPAP device in the days immediately following the earthquake. The most common reason for inability to use the nCPAP device was power failure, followed by anxiety about sleeping at night due to fear of aftershocks, involvement in disaster-relief activities, loss of the nasal CPAP device, and fear of being unable to wake up in case of an emergency. Among the 966 patients, 242 (25.1%) had experienced relapse of symptoms, the most common of which was excessive daytime sleepiness (EDS), followed by insomnia, headache, irritability, and chest pain.

CONCLUSION

Developing strategies for the continuation of nCPAP therapy during disasters is important for providing healthy sleeping environments for SDB patients in emergency situations.

Symptoms of disturbed sleep predict major adverse cardiac events after percutaneous coronary intervention

BACKGROUND

Disturbed sleep is associated with atherosclerosis in native coronary arteries and may be associated with adverse cardiac events after percutaneous coronary intervention (PCI). We sought to determine the association between symptoms of disturbed sleep and adverse cardiovascular events after PCI.

METHODS

Outpatients who were stable after successful PCI were assessed for symptoms of disturbed sleep with 10 true/false questions. Follow-up was performed at least 4 years after PCI. The primary outcome was a composite of death, myocardial infarction (MI), and repeated revascularization.

RESULTS

Three hundred eighty-eight patients (mean age, 66 ± 11 years) reported on average 3.1 ± 2.1 sleep disturbance symptoms. Follow-up was performed on average 4.4 years after the incident PCI. The primary outcome occurred in 25% of patients. An association was seen between the number of sleep disturbance symptoms and the occurrence of the primary end point. Patients with zero symptoms had a 4-year event rate of 12% compared with a 67% event rate for those with 9 symptoms. On multivariable analysis, sleep symptoms, diabetes mellitus, and the number of diseased coronary vessels were independently associated with the primary end point. Each additional sleep symptom was associated with a hazard ratio (HR) of 1.2 (P = 0.001). The results were driven primarily by the association between symptoms of disturbed sleep and the need for repeated revascularization (repeated PCI HR, 1.9; P = 0.003; coronary artery bypass grafting (CABG) HR, 1.5; P = 0.001).

CONCLUSIONS

Symptoms of disturbed sleep were associated with increased risk of long-term adverse cardiovascular outcomes after successful PCI.

The effect of continuous positive airway pressure therapy on arterial stiffness and endothelial function in obstructive sleep apnea: a randomized controlled trial in patients without cardiovascular disease

BACKGROUND

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity and mortality which may be mediated by increased arterial stiffness and endothelial dysfunction. Continuous positive airway pressure (CPAP) therapy improves excessive daytime somnolence (EDS), but its effect on vascular function in patients without preexisting cardiovascular disease (CVD) is unclear.

METHODS

Fifty-three patients with OSA defined as an apnea-hypopnea index (AHI) of ⩾15 and without CVD were recruited into a double-blind, randomized, placebo-controlled, crossover trial of 12weeks of CPAP therapy, of whom 43 participants completed the study protocol. Arterial stiffness was assessed by measuring the augmentation index (AIx) and pulse wave velocity (PWV) by applanation tonometry and cardiovascular magnetic resonance imaging to determine aortic distensibility. Endothelial function was assessed by measuring vascular reactivity after administration of salbutamol and glyceryl trinitrate.

RESULTS

CPAP therapy lowered systolic blood pressure (SBP) (126mmHg [standard deviation {SD}, 12] vs 129mmHg [SD, 14]; P=.03), with a trend towards reduced AIx (15.5 [SD, 11.9] vs 16.6 [SD, 11.7]%; P=.08) but did not modify endothelial function. When subjects with (n=24) and without (n=19) EDS were separately examined, no effect of CPAP therapy on vascular function was seen.

CONCLUSIONS

In patients without overt CVD, CPAP therapy had a nonsignificant effect on AIx and did not modify endothelial function.

Obstructive sleep apnea syndrome, vascular pathology, endothelial function and endothelial cells and circulating microparticles

Accelerated atherosclerosis and increased cardiovascular risk are frequently reported in patients with obstructive sleep apnea (OSA) syndrome. In this article the authors attempt a review of the current understanding of the relationship between vascular risk and OSA syndrome based on large cohort studies that related the disease to several cardiovascular risk factors and vascular pathologies. We also discuss the pathophysiological mechanisms that may be involved in this relationship, starting with endothelial dysfunction and its mediators. These include an increased oxidative stress and inflammation as well as several disorders of coagulation and lipid metabolism. Moreover, circulating microparticles from activated leukocytes (CD62L_MPs) are higher in patients with OSA and there is a positive correlation between circulating levels of CD62L_MPs and nocturnal hypoxemia severity. Finally, circulating level of endothelial microparticles and circulating endothelial cells seem to be increased in patients with OSA. Also, endothelial progenitor cells are reduced and plasma levels of the vascular endothelial growth factor are increased.

C-reactive protein is elevated in heart failure patients with central sleep apnea and Cheyne-Stokes respiration

BACKGROUND

Manifestation of central sleep apnea (CSA) with Cheyne-Stokes respiration is of major prognostic impact in chronic heart failure (CHF). Inflammatory processes have been linked to a progression of cardiovascular diseases, including heart failure. While an association of C-reactive protein (CRP) levels to obstructive sleep apnea has been documented before, there is a lack of information regarding variation of CRP levels in patients with CSA.

OBJECTIVES

The objective of this study was to investigate a potential association of CRP levels to CSA severity in CHF patients.

METHODS

High sensitivity CRP levels were analyzed in 966 patients with CHF (BMI 26.3 ± 4.6, New York Heart Association class 2.6 ± 0.5, left ventricular ejection fraction 29.4 ± 7.9%, N-terminal pro-brain natriuretic peptide, NT-proBNP, level 2,209 ± 3,315 pg/ml) without sleep-disordered breathing (SDB; Apnea-Hypopnea Index, AHI, <5/h) or various degrees of CSA, documented by in-hospital cardiorespiratory polygraphy or polysomnography.

RESULTS

The CRP concentration in CHF patients was 0.550 ± 0.794 mg/dl in patients without SDB (AHI 0-4/h, n = 403) versus 0.488 ± 0.708 mg/dl in patients with mild CSA (AHI 5-14/h, n = 123, p = n.s.) and 0.660 ± 0.963 mg/dl in patients with moderate CSA (AHI 15-29/h, n = 160, p = n.s.). In patients with severe CSA (AHI ≥ 30/h, n = 280), significantly higher CRP concentrations were documented (0.893 ± 1.384 mg/dl, p < 0.05). Stepwise regression analysis revealed AHI, NT-proBNP and heart rate to be independently associated with elevated CRP levels.

CONCLUSION

Severe CSA in CHF patients is associated with elevated levels of CRP, a systemic marker of inflammation and cardiovascular risk. This might explain in part the negative prognostic impact of CSA in these patients.

Association between obstructive sleep apnea severity and endothelial dysfunction in an increased background of cardiovascular burden

The objective of this study is to examine whether increasing obstructive sleep apnea (OSA) severity is associated with worsening endothelial function. The design is a cross-sectional examination of the baseline assessment of a multi-centre randomized controlled clinical trial examining the effects of oxygen, continuous positive airway pressure (CPAP) therapy or lifestyle modifications on cardiovascular biomarkers. Participants were recruited from cardiology clinics at four sites. Participants with an apnea-hypopnea index (AHI) of 15-50 and known cardio/cerebrovascular disease (CVD) or CVD risk factors were included. OSA severity indices [oxygen desaturation index (ODI), AHI and percentage of sleep time below 90% oxygen saturation (total sleep time <90)] and a measure of endothelium-mediated vasodilatation [Framingham reactive hyperaemia index (F-RHI) derived from peripheral arterial tonometry (PAT)] were assessed. The sample included 267 individuals with a mean AHI of 25.0 ± 8.5 SD and mean F-RHI 0.44 ± 0.38. In adjusted models, the slope of the relationship between ODI and F-RHI differed above and below an ODI of 24.6 (P = 0.04), such that above an ODI of 24.6 there was a marginally significant decline in the geometric mean of the PAT ratio by 3% [95% confidence interval (CI): 0%, 5%; P = 0.05], while below this point, there was a marginally significant incline in the geometric mean of the PAT ratio by 13% (95% CI: 0%, 27%; P = 0.05) per 5-unit increase in ODI. A similar pattern was observed between AHI and F-RHI. No relation was noted with total sleep time <90 and F-RHI. There was evidence of a graded decline in endothelial function in association with higher levels of intermittent hypoxaemia.

[Sleep apnea and heart failure]

Sleep apnea can influence cardiac function, by which the development of heart failure is facilitated. Vice versa, chronic heart failure increases the risk for sleep apnea. Consequently, in patients with symptomatic chronic heart failure, sleep apnea is a frequent comorbidity occuring in up to 75% of cases. More than half of those suffer from central sleep apnea, whereas in the general population, obstructive sleep apnea is far more frequent. Both, the obstructive and the central sleep apnea lead to oxygen desaturations during the night which are followed by increases in serum catecholamines. Possibly, this is the main mechanism why the prognosis of patients with symptomatic heart failure and sleep apnea is much worse than that of patients without sleep apnea. Therefore, a screening of all heart failure patients for sleep apnea is mandatory. Currently, large studies are underway which investigate whether the treatment of sleep apnea, esp. central sleep apnea, will beneficially influence the clinical course of heart failure (SERVE-HF, ADVENT-HF). A new therapeutic approach for central sleep apnea is the phrenic nerve stimulation.

Significance of endothelial dysfunction in sleep-related breathing disorder

The endothelium functions not only as a semi-selective barrier between body tissue and circulation; it also plays an active role in the maintenance of a healthy vasculature. Endothelial dysfunction is increasingly found to play a pivotal role in the pathogenesis of atherosclerosis. Impaired endothelium-dependent vasodilation, as a marker of endothelial dysfunction, predates and predicts cardiovascular disease. Endothelial dysfunction is thought to result from oxidative stress, inflammatory gene activation and cytokine cascade, as well as impairment of endothelial repair mechanisms. In the context of sleep-related breathing disorders, obstructive sleep apnoea (OSA) is postulated to contribute independently to cardiovascular morbidity and mortality. Thus, endothelial dysfunction is an important target of research in vascular pathogenesis and also serves as an intermediary outcome indicator in clinical trials evaluating cardiovascular sequelae in OSA. Basic or translational studies have identified cellular and molecular mechanisms of potential relevance to endothelial dysfunction in OSA, while epidemiological or clinical studies have shown endothelial dysfunction attributable to sleep-disordered breathing, which could improve with effective treatment of OSA. Endothelial dysfunction is poised to serve as a call for timely intervention with possibility of halting or even reverting vascular injury in sleep-related breathing disorders. Much remains to be explored about the complex pathways of endothelial dysfunction and its clinical manifestations in subjects with OSA, which are likely to involve multiple contributing factors. Evidence-based information will allow us to construct the framework for guiding individualized clinical management and public health strategies for OSA, as well as cardiometabolic diseases.

Pathophysiologic mechanisms of cardiovascular disease in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Patients with OSAS experience repetitive episodes of hypoxia and reoxygenation during transient cessation of breathing that provoke systemic effects. Furthermore, there may be increased levels of biomarkers linked to endocrine-metabolic and cardiovascular alterations. Epidemiological studies have identified OSAS as an independent comorbid factor in cardiovascular and cerebrovascular diseases, and physiopathological links may exist with onset and progression of heart failure. In addition, OSAS is associated with other disorders and comorbidities which worsen cardiovascular consequences, such as obesity, diabetes, and metabolic syndrome. Metabolic syndrome is an emerging public health problem that represents a constellation of cardiovascular risk factors. Both OSAS and metabolic syndrome may exert negative synergistic effects on the cardiovascular system through multiple mechanisms (e.g., hypoxemia, sleep disruption, activation of the sympathetic nervous system, and inflammatory activation). It has been found that CPAP therapy for OSAS provides an objective improvement in symptoms and cardiac function, decreases cardiovascular risk, improves insulin sensitivity, and normalises biomarkers. OSAS contributes to the pathogenesis of cardiovascular disease independently and by interaction with comorbidities. The present review focuses on indirect and direct evidence regarding mechanisms implicated in cardiovascular disease among OSAS patients.

Effect of CPAP treatment on endothelial function and plasma CRP levels in patients with sleep apnea

BACKGROUND

Continuous positive airway pressure (CPAP) is the most effective method for treating obstructive sleep apnea syndrome (OSAS) and alleviating symptoms. Improved sleep quality with effective CPAP therapy might also contribute to attenuated systemic inflammation and improved endothelial function, with subsequent reduction of cardiovascular risk. The aim of this study was to assess the effect of 3-month CPAP therapy on brachial artery flow-mediated dilation (FMD) and plasma C-reactive protein (CRP) levels in patients with OSAS.

MATERIAL/METHODS

Our study group consisted of 38 male patients with no prior history of cardiovascular disease. Twenty patients with an Apnea-Hypopnea Index (AHI) ≥15 were assigned to receive CPAP treatment and 18 subjects with an AHI<5 were included in the control group. Six patients failed to comply with the CPAP treatment. Measurement of FMD and blood analysis was performed at baseline and 3 months after CPAP therapy.

RESULTS

Baseline FMD values were negatively correlated with age, BMI, AHI, DSI,% of time <90% Sa02, and CRP (p<0.05). Plasma CRP values were positively correlated with BMI, AHI, DSI and% of time <90% Sa02 (p<0.05). In the group of patients who complied with the CPAP treatment, there was a significant increase in the FMD values (9.18 ± 0.55 vs. 6.27 ± 0.50) and a decrease in the levels of CRP (0.67 ± 0.15 vs. 0.84 ± 0.18) (p<0.05).

CONCLUSIONS

Appropriate CPAP therapy improved both CRP and FMD values, suggesting its potentially beneficial role in reducing cardiovascular risk in OSAS patients.

Endothelial dysfunction and hypertension in obstructive sleep apnea - Is it due to intermittent hypoxia?

BACKGROUND

Obstructive sleep apnea (OSA) is a prevalent disorder causing hypertension. Endothelial dysfunction appears to underlie development of hypertension. It is not known whether hypoxia during sleep is necessarily the prerequisite process for endothelial dysfunction and hypertension in OSA. We therefore examined the relationship between endothelial-dependent vasodilatory capacity, hypoxia and circulating angiogenesis inhibitors in OSA.

METHODS AND RESULTS

We studies 95 subjects with and without OSA and hypertension. Endothelial-dependent vasodilation was assessed using brachial artery flow-mediated vasodilation method (FMD). Plasma angiogenesis inhibitors, endoglin (sEng) and fms-like tyrosine kinase-1 (sFlt-1), were measured using ELISA. The apnea-hypopnea indexes were 41 ± 5 and 48 ± 4 events/hr in normotensive OSA (N-OSA) and hypertensive OSA (H-OSA), respectively, indicating severe OSA. The sleep time spent with SaO2 < 90% (T < 90%) were 34 ± 8 and 40 ± 9 min, respectively. FMD was markedly impaired in H-OSA (8.0% ± 0.5) compared to N-OSA (13.5% ± 0.5, P < 0.0001), H-non-OSA (10.5% ± 0.8, P < 0.01), and N-non-OSA (16.1% ± 1.0, P < 0.0001). There was no correlation between T < 90% and FMD. Both OSA groups had elevated levels of sFlt-1 (62.4 ± 5.9 and 63.9 ± 4.7 pg/ml) compared to N-non-OSA (32.1 ± 6.5, P = 0.0008 and P = 0.0004, respectively) and H-non-OSA (41.2 ± 7.0, P < 0.05 and P = 0.03, respectively). In contrast, sEng was only elevated in H-OSA (4.20 ± 0.17 ng/ml) compared with N-OSA (3.64 ± 0.14, P = 0.01) and N-non-OSA (3.48 ± 0.20, P = 0.01). There was a modest but statistically significant inverse correlation between sEng and FMD in only H-OSA group (r = -0.38, P < 0.05).

CONCLUSION

These data show that patients with OSA and hypertension have marked impairment of FMD, independent of hypoxia exposure, which is associated with increased sEng.

Obstructive sleep apnea: a cardiometabolic risk in obesity and the metabolic syndrome

Obstructive sleep apnea (OSA) is an underdiagnosed condition characterized by recurrent episodes of obstruction of the upper airway leading to sleep fragmentation and intermittent hypoxia during sleep. Obesity predisposes to OSA, and the prevalence of OSA is increasing worldwide because of the ongoing epidemic of obesity. Recent evidence has shown that surrogate markers of cardiovascular risk, including sympathetic activation, systemic inflammation, and endothelial dysfunction, are significantly increased in obese patients with OSA versus those without OSA, suggesting that OSA is not simply an epiphenomenon of obesity. Moreover, findings from animal models and patients with OSA show that intermittent hypoxia exacerbates the metabolic dysfunction of obesity, augmenting insulin resistance and nonalcoholic fatty liver disease. In patients with the metabolic syndrome, the prevalence of moderate to severe OSA is very high (∼60%). In this population, OSA is independently associated with increased glucose and triglyceride levels as well as markers of inflammation, arterial stiffness, and atherosclerosis. A recent randomized, controlled, crossover study showed that effective treatment of OSA with continuous positive airway pressure for 3 months significantly reduced several components of the metabolic syndrome, including blood pressure, triglyceride levels, and visceral fat. Finally, several cohort studies have consistently shown that OSA is associated with increased cardiovascular mortality, independent of obesity. Taken together, these results support the concept that OSA exacerbates the cardiometabolic risk attributed to obesity and the metabolic syndrome. Recognition and treatment of OSA may decrease the cardiovascular risk in obese patients.

Association of nocturnal hypoxemia with progression of CKD

BACKGROUND AND OBJECTIVES

Nocturnal hypoxemia is highly prevalent among patients with CKD. Nocturnal hypoxemia contributes to systemic inflammation, oxidative stress, endothelial cell dysfunction, and activation of the renin-angiotensin system, which are common pathologic mechanisms of CKD progression. This study investigated whether nocturnal hypoxemia is independently associated with CKD progression.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This two-center retrospective cohort study included 161 patients with stages 3-4 CKD enrolled from January of 2009 to July of 2011 with a body mass index less than 25.0 kg/m(2). The 4% oxygen desaturation index, the number of events per hour in which oxygen saturation decreases by >4% during sleep, was measured, and the declining rate of the estimated GFR was followed over 1 year. The severity of nocturnal hypoxemia was categorized as none (oxygen desaturation index<5.0), mild (5.0≤oxygen desaturation index<15.0), or moderate to severe (15.0≤oxygen desaturation index).

RESULTS

The mean estimated GFR of the total cohort at baseline was 31 ml/min per 1.73 m(2). Eighty patients (49.7%) were diagnosed with nocturnal hypoxemia; 64 patients were diagnosed with mild nocturnal hypoxemia, and 16 patients were diagnosed with moderate-to-severe nocturnal hypoxemia. The estimated GFR declined three- to fourfold faster in patients with moderate-to-severe nocturnal hypoxemia than patients with no or mild nocturnal hypoxemia (the mean values [95% confidence intervals] were -2.14 [-1.06 to -3.21], -3.02 [-1.31 to -4.74], and -8.59 [-2.00 to -15.2] ml/min per 1.73 m(2) per year in the no, mild, and moderate-to-severe nocturnal hypoxemia groups, respectively; P=0.003). Nocturnal hypoxemia remained a significant predictor of decline in estimated GFR after adjustment for various baseline clinical factors.

CONCLUSIONS

In nonobese patients with CKD, nocturnal hypoxemia is an independent risk factor of a rapid decline in kidney function.

Endothelial function is well preserved in obese patients with mild obstructive sleep apnea

PURPOSE

Endothelial dysfunction is one of the early markers of cardiovascular complications in obstructive sleep apnea (OSA). The aim of our study was to evaluate whether overweight patients with mild OSA displayed endothelial dysfunction, and to assess the effect of 1-year lifestyle intervention with an early very low calorie diet in endothelial function.

METHODS

At baseline, the study population consisted of 83 overweight patients with mild OSA and 46 weight-matched non-OSA subjects. OSA patients were further randomized into a 1-year supervised lifestyle intervention group or control group which received routine lifestyle counselling. Endothelial function measured by brachial artery flow-mediated dilatation (FMD), apnea-hypopnea index (AHI), body mass index (BMI), and metabolic parameters were assessed at baseline and 12 months.

RESULTS

No correlations between endothelial function and mild OSA were detected. However, patients with impaired endothelial function had lower mean saturation and impaired endothelial function correlated significantly with glucose intolerance and dyslipidemia. After the lifestyle intervention and successful weight reduction, AHI, BMI, serum triglycerides and insulin improved significantly; however, no improvement in FMD was detected.

CONCLUSIONS

Mild OSA was not observed to be associated with endothelial dysfunction. Although in mild OSA endothelial function is still preserved, lifestyle intervention with weight reduction did achieve an improvement in other obesity-related risk factors for cardiovascular diseases, thus highlighting the importance of early intervention.

Relationship of depression, stress and endothelial function in stable angina patients

Endothelial dysfunction has been considered as one of potential mechanisms by which depression and stress might contribute to the development of coronary artery disease (CAD). Recent studies suggest that circulating endothelial progenitor cells (EPCs) and brachial artery flow-mediated dilation (FMD) are related to endothelial function and progression of CAD. We investigated the relationships between the level of circulating CD34/KDR(+) EPCs and CD133/KDR(+) EPCs, brachial FMD, and scores of depression and stress measured with the Depression Anxiety Stress Scales in 288 stable angina patients without major psychiatric disorders. As defined by the ≥75th percentile, 100 (35%) subjects had high depression score (≥8), and 84 (29%) subjects had high stress score (≥10). Subjects with high depression or stress score had significantly lower FMD (1.86±0.14 vs. 3.63±0.17%, p<0.001; 2.05±0.18 vs. 3.48±0.17%, p<0.001) and percentage of circulating CD34/KDR(+) EPCs (0.97±0.11 vs. 1.94±0.17%, p<0.001; 1.09±0.13 vs. 1.68±0.16%, p=0.005), but not CD133/KDR(+) EPCs (0.52±0.04 vs. 0.66±0.06%, p=0.057; 0.61±0.05 vs. 0.59±0.05%, p=0.833), as compared with subjects with normal depression or stress score. Multivariate regression analysis indicated that high depression score (OR 1.09, 95% CI: 1.04-1.15, p<0.001), but not stress score or percentage of circulating EPCs, independently predicted impaired brachial FMD. In conclusions, our results demonstrated that in stable angina patients without major psychiatric disorders, a high depression or stress score was related to attenuated brachial FMD and depletion of circulating EPCs. However, only the depression score, but not the stress score or the level of EPCs, was an independent predictor for decreased brachial FMD.

Obstructive sleep apnea in children is associated with severity-dependent deterioration in overnight endothelial function

BACKGROUND

Restorative sleep is expected to promote improved endothelial function (EF) in the morning compared to the evening. However, in adults with obstructive sleep apnea (OSA) EF is not only adversely affected, but it worsens during the night. Data in pediatric OSA are scarce, and overnight changes have not been explored. Therefore, we sought to examine potential associations between pediatric OSA and overnight changes in EF.

METHODS

59 habitually snoring children with various degrees of sleep-disordered breathing (age range, 4-16 years) underwent EF assessment (reactive hyperemia test by EndoPAT, Itamar Medical, Israel) in the evening before and the morning after an overnight polysomnography (PSG). Two brachial occlusion periods (1 min and 5 min) also were tested. Potential associations between evening-to-morning changes in EF and polysomnographic parameters were explored.

RESULTS

Evening-to-morning changes in children with OSA displayed severity-dependent deterioration of EF, and occlusions lasting 1 or 5 min during the reactive hyperemia test yielded similar findings.

CONCLUSIONS

In children deterioration in EF during the night significantly correlated with the severity of OSA. Furthermore, the reactive hyperemia test can be reliably performed with only 60 seconds of arterial flow occlusion in children. These findings support our hypothesis that similarly to adults, sleep apnea in children results in endothelial dysfunction (ED). We speculate that pediatric OSA is less commonly associated with cardiovascular complications possibly due to the shorter duration of the syndrome.

Obstructive sleep apnea and coronary artery disease: from pathophysiology to clinical implications

Coronary artery disease (CAD) and obstructive sleep apnea (OSA) are both complex and significant clinical problems. The pathophysiological mechanisms that link OSA with CAD are complex and can influence the broad spectrum of conditions caused by CAD, from subclinical atherosclerosis to myocardial infarction. OSA remains a significant clinical problem among patients with CAD, and evidence suggesting its role as a risk factor for CAD is growing. Furthermore, increasing data support that CAD prognosis may be influenced by OSA and its treatment by continuous positive airway pressure (CPAP) therapy. However, stronger evidence is needed to definitely answer these questions. This paper focuses on the relationship between OSA and CAD from the pathophysiological effects of OSA in CAD, to the clinical implications of OSA and its treatment in CAD patients.

Sleep disordered breathing as a risk of cardiac events in subjects with diabetes mellitus and normal exercise echocardiographic findings

Sleep disordered breathing (SDB) is associated with type 2 diabetes mellitus (T2DM) and cardiovascular disease; however, the contribution of SDB to incident heart failure (HF), coronary artery disease (CAD), and atrial fibrillation (AF) in patients with T2DM is unknown. We followed up 834 consecutive asymptomatic patients with T2DM (age 56 ± 11 years, 369 women) with normal exercise echocardiographic findings for ≤8 years using electronic health records. The demographics, cardiac risk factors, symptoms, diagnoses, and medications were collected at the echocardiography and validated from the electronic health records. SDB was confirmed by a comprehensive sleep evaluation and/or polysomnography before echocardiography. SDB was diagnosed in 188 patients (21%) at baseline; 116 were untreated. During a median follow-up of 4.9 years (interquartile range 3.9 to 6.1), 22 congestive HF, 72 CAD, and 40 AF incident events were observed. In the Cox proportional hazards models, SDB was associated with incident CAD (hazard ratio 1.8, 95% confidence interval 1.1 to 3.0, p = 0.01; adjusted hazard ratio 1.9, 95% confidence interval 1.2 to 3.2, p <0.01) and AF (hazard ratio 2.6, 95% confidence interval 1.4 to 4.7, p = 0.01; adjusted hazard ratio 2.9, 95% confidence interval 1.5 to 5.9, p <0.01). Limiting SDB to only those patients diagnosed using polysomnography (n = 132), SDB was associated with incident CAD (hazard ratio 1.9, 95% confidence interval 1.1 to 3.3, p = 0.03; adjusted hazard ratio 2.2, 95% confidence interval 1.2 to 3.9, p = 0.01) and HF (hazard ratio 2.7, 95% confidence interval 1.1 to 7.0, p = 0.03; adjusted hazard ratio 3.5, 95% confidence interval 1.4 to 9.0, p <0.01). Female gender, age, elevated blood pressure, and left ventricular mass were additional correlates of CAD in those with asymptomatic T2DM. In conclusion, the association of SDB with incident CAD, AF, and HF in patients with T2DM justifies more liberal screening for SDB in patients with T2DM, realizing that SDB is a potentially modifiable risk factor.

Impaired brachial artery flow-mediated vasodilation in response to handgrip exercise-induced increases in shear stress in young smokers

Smoking is an established risk factor for cardiovascular disease. It has also been shown to result in endothelial dysfunction as assessed by flow-mediated dilation (FMD) in response to reactive hyperemia (RH)-induced increases in shear stress. Handgrip exercise (HGEX) is an emerging alternative method to increase shear stress for FMD assessment (HGEX-FMD) and the purpose of this study was to identify the impact of smoking on HGEX-FMD in young healthy subjects. Brachial artery RH-FMD and HGEX-FMD (10-minute bout of HGEX) was assessed in eight smokers (S) and 14 non-smokers (NS) (age 21 ± 2 years). Brachial artery diameter and mean blood velocity were assessed with echo and Doppler ultrasound, respectively. Shear stress was estimated by shear rate (SR = brachial artery blood velocity/diameter). The SR stimulus did not differ between groups for either test (RH-FMD (SR area under the curve until peak diameter measurement), p = 0.897; HGEX-FMD (average SR over 10-minute exercise bout), p = 0.599). The RH-FMD magnitude was not significantly different between groups (S: 7.7 ± 2.2% vs NS: 7.9 ± 2.4%, p = 0.838); however, the HGEX-FMD magnitude was significantly impaired in smokers (S: 6.1 ± 3.4% vs NS: 9.6 ± 3.6%, p = 0.037). In conclusion, HGEX-FMD assessment detected vascular dysfunction in young healthy smokers while RH-FMD did not. This suggests that HGEX-FMD may be useful in the early detection of smoking-induced impairments in endothelial function. Further research is required to explore this phenomenon in other populations and to isolate underlying mechanisms.

Obstructive sleep apnea, oxidative stress and cardiovascular disease: lessons from animal studies

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular (CV) diseases such as arterial hypertension, heart failure, and stroke. Based on human research, sympathetic activation, inflammation, and oxidative stress are thought to play major roles in the pathophysiology of OSA-related CV diseases. Animal models of OSA have shown that endothelial dysfunction, vascular remodelling, and systemic and pulmonary arterial hypertension as well as heart failure can develop in response to chronic intermittent hypoxia (CIH). The available animal data are clearly in favour of oxidative stress playing a key role in the development of all of these CV manifestations of OSA. Presumably, the oxidative stress is due to an activation of NADPH oxidase and other free oxygen radicals producing enzymes within the CV system as evidenced by data from knockout mice and pharmacological interventions. It is hoped that animal models of OSA-related CV disease will continue to contribute to a deeper understanding of their underlying pathophysiology and will foster the way for the development of cardioprotective treatment options other than conventional CPAP therapy.

Effects of continuous positive airway pressure on endothelial function and circulating progenitor cells in obstructive sleep apnoea: a randomised sham-controlled study

OBJECTIVE

Obstructive sleep apnoea (OSA) is characterised by reoccurring apnoeas and hypopneas, causing repetitive hypoxia and reoxygenation, and is associated with endothelial dysfunction and reduced levels of circulating progenitor cells (CPCs). The potential to improve endothelial function and CPC levels in people with OSA by preventing hypoxic episodes with Continuous Positive Airway Pressure (CPAP) was investigated in a sham-controlled CPAP study.

METHODS

Men with moderate-to-severe OSA (mean ± SD: age=49 ± 12 y, apnoea hypopnea index (AHI)=37.6 ± 16.4 events/h, body mass index=31.5 ± 5.7 kg/m(2)) who were CPAP naïve without diabetes mellitus were randomised in a 12-week double-blind sham-controlled parallel group study to receive either active (n=25) or sham (n=21) CPAP. CPCs, isolated from blood, were measured by flow cytometry and by co-staining cultured cells (7 days) with acetylated low-density lipoprotein (acLDL) and lectin. Endothelial function was assessed by peripheral arterial tonometry (PAT).

RESULTS

Compared to sham, CPAP significantly decreased AHI (mean between-group difference -36.0 events/h; 95%CI, -49.7 to -22.3, p<0.0001) after 12 weeks. Despite this improvement in AHI, CPAP had no effect on change in CPC levels (including CD34(+)/KDR(+) (565 cells/mL; -977 to 2106, p=0.45), CD34(+)/KDR(+)/CD45(-) (37.0 cells/mL; -17.7 to 85.7, p=0.13), acLDL(+)/lectin(+) (-43.1 cells/field, -247 to 161, p=0.67)) or change in endothelial function (0.27; -0.14 to 0.67, p=0.19) compared to sham therapy.

CONCLUSIONS

Despite the improvement in OSA parameters and ablation of apnoeic events by CPAP, CPC counts and endothelial function in men with moderate-to-severe OSA were not significantly improved after 12 weeks of therapeutic CPAP when compared to sham control.

Arterial stiffness and endothelial function in obstructive sleep apnoea/hypopnoea syndrome

BACKGROUND

Obstructive sleep apnoea-hypopnoea syndrome (OSAHS) is associated with increased cardiovascular morbidity and mortality. Our study examined arterial stiffness and endothelial function in subjects with OSAHS with no known cardiovascular disease compared to well-matched controls.

METHODS

Twenty subjects with OSAHS (defined as apnoea-hypopnoea index [AHI] > or =15 and Epworth Sleepiness Scale score > or =11) without cardiovascular disease and 20 well-matched controls underwent a comprehensive evaluation of arterial stiffness and endothelial function. Arterial stiffness was measured by applanation tonometry and cardiovascular magnetic resonance imaging (MRI) and endothelial function assessed by measuring vascular reactivity after administration of glyceryl trinitrate and salbutamol.

RESULTS

Subjects with OSAHS had increased arterial stiffness (augmentation index 19.3 [10.9] vs. 12.6 (10.2)%; p=0.017) and impaired endothelial function (change in augmentation index following salbutamol -4.3 (3.2) vs. -8.0 (4.9)%; p=0.02) compared to controls. Aortic distensibility, a measure of arterial stiffness, was negatively correlated with the AHI.

CONCLUSIONS

Our findings suggest that even in the absence of known cardiovascular disease, subjects with OSAHS have increased arterial stiffness and impaired endothelial function and are at increased risk for cardiovascular disease.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Correlation between endothelial dysfunction, Rho-associated protein kinase activity, C-reactive protein and obstructive sleep apnoea syndrome in male patients

OBJECTIVE

This study investigated the association between obstructive sleep apnoea syndrome (OSAS) and flow-mediated dilatation (FMD), Rho-associated protein kinase (ROCK) activity, and C-reactive protein (CRP) concentrations in male patients.

METHODS

Consecutive patients with symptoms suggestive of OSAS were recruited and divided into non-OSAS (n = 18) and OSAS (n = 32) groups. FMD was measured in the brachial artery; blood samples were taken to measure ROCK activity and CRP concentrations.

RESULTS

ROCK activity and CRP concentrations were significantly higher, and FMD was significantly lower, in the OSAS group than in the non-OSAS group. There was a correlation between ROCK activity and FMD. In stepwise multiple regression analyses, the proportion of sleep time spent with an oxygen saturation < 90% was a significant determinant of ROCK activity, while body mass index was the only significant determinant of CRP concentration. The oxygen desaturation index was a significant determinant of FMD.

CONCLUSIONS

OSAS increased ROCK activity and was a major determinant of endothelial dysfunction.

Hypertension and obstructive sleep apnea

Obstructive sleep apnea (OSA) is increasingly being recognized as a major health burden with strong focus on the associated cardiovascular risk. Studies from the last two decades have provided strong evidence for a causal role of OSA in the development of systemic hypertension. The acute physiological changes that occur during apnea promote nocturnal hypertension and may lead to the development of sustained daytime hypertension via the pathways of sympathetic activation, inflammation, oxidative stress, and endothelial dysfunction. This review will focus on the acute hemodynamic disturbances and associated intermittent hypoxia that characterize OSA and the potential pathophysiological mechanisms responsible for the development of hypertension in OSA. In addition the epidemiology of OSA and hypertension, as well as the role of treatment of OSA, in improving blood pressure control will be examined.

Chronic intermittent hypoxia down-regulates endothelial nitric oxide synthase expression by an NF-κB-dependent mechanism

OBJECTIVES

Patients with obstructive sleep apnea have an impaired endothelium-dependent vasodilator response. The mechanisms underlying this impairment remain unclear. We tested the hypothesis that chronic intermittent hypoxia (CIH) impairs endothelium-dependent vasodilatation by NF-κB-mediated down-regulation of endothelial nitric oxide synthase (eNOS) expression.

METHODS

Wild type (WT) mice and mice deficient in NF-κB p50 or TNF-α gene were exposed to sham or CIH. Aortic NF-κB activity and aortic expression of TNF-α were determined. Aortic and mesenteric artery levels of eNOS expression were examined and their correlation to endothelium-dependent vasodilator response in vitro and vasodepressor response in vivo were analyzed.

RESULTS

WT mice exposed to CIH for five to eight weeks showed significantly reduced eNOS protein expression in aortas and mesenteric arteries, associated with significantly blunted vasodilator and vasodepressor responses to acetylcholine, but not to sodium nitroprusside. CIH activated NF-κB, which preceded TNF-α up-regulation and eNOS down-regulation. NF-κB p50 gene deletion blocked NF-κB activation, inhibited TNF-α expression, prevented eNOS down-regulation and reversed the impaired endothelium-dependent vasodepressor response induced by CIH. TNF-α knockout prevented CIH-induced eNOS down-regulation and restored the endothelium-dependent vasodepressor response.

CONCLUSIONS

CIH exposure impairs endothelium-dependent vasodilator mechanism by stimulating NF-κB-mediated TNF-α generation, which in turn, down-regulates eNOS expression, resulting in an impaired endothelium-dependent vasodilatation.

Altered profile of circulating endothelial progenitor cells in obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is independently associated with endothelial dysfunction, which may be perpetuated by alteration in endothelial repair capacity. Our study evaluates changes in endothelial progenitor cell (EPC) profile in relation to OSA and the role of advanced glycation end-products (AGE) in this relationship.

Methods

Consecutive Chinese adults undergoing sleep studies, who had no medical illnesses or regular medications, were enrolled. Subjects with morbid obesity or grossly elevated lipoprotein levels were excluded from analysis. Circulating EPC was measured with flow cytometry analysis.

Results

Seventy-two subjects, 64 % with OSA defined by apnea–hypopnea index (AHI) ≥ 5, were analyzed. CD34+ cell counts were positively correlated with oxygen desaturation index (ODI) (r = 0.250, p = 0.041) and duration of oxygen desaturation <90 % (T90) (r = 0.261, p = 0.033) and negatively with minimal oxygen saturation (r = −0.247, p = 0.044) after adjusting for age, glucose, body weight, and smoking status. AGE was positively correlated with indices of OSA severity (AHI, r = 0.249, p = 0.042; ODI, r = 0.244, p = 0.047; T90, r = 0.243, p = 0.047; minimal oxygen saturation, r = −0.251, p = 0.041) and negatively with CD133+ cells (r = −0.281, p = 0.021). On stepwise multiple linear regression analysis, minimal oxygen saturation (p = 0.013) and CD133+ cell counts (p = 0.029) were found to be significant determinants of AGE level (R² = 0.147).

Conclusions

Nocturnal hypoxemia in OSA subjects was associated with increase in endothelial cells (CD34+) which may promote vascular repair. Accumulation of AGE in OSA may lead to diminution in early EPC (CD133+) and endothelial repair capacity over time, thus contributing to vascular pathogenesis.

Elevated levels of endothelial cell-derived microparticles following short-term withdrawal of continuous positive airway pressure in patients with obstructive sleep apnea: data from a randomized controlled trial

BACKGROUND

Obstructive sleep apnea has been associated with impaired endothelial function; however, the mechanisms underlying this association are not completely understood. Cell-derived microparticles may provide a link between obstructive sleep apnea and endothelial dysfunction.

OBJECTIVES

This randomized controlled trial aimed to examine the effect of a 2-week withdrawal of continuous positive airway pressure (CPAP) therapy on levels of circulating microparticles.

METHODS

Forty-one obstructive sleep apnea patients established on CPAP treatment were randomized to either CPAP withdrawal (subtherapeutic CPAP) or continuing therapeutic CPAP, for 2 weeks. Polysomnography was performed and circulating levels of microparticles were analyzed by flow cytometry at baseline and 2 weeks.

RESULTS

CPAP withdrawal led to a recurrence of obstructive sleep apnea. Levels of CD62E+ endothelium-derived microparticles increased significantly in the CPAP withdrawal group compared to the continuing therapeutic CPAP group (median difference in change +32.4 per µl; 95% CI +7.3 to +64.1 per µl, p = 0.010). CPAP withdrawal was not associated with a statistically significant increase in granulocyte, leukocyte, and platelet-derived microparticles when compared with therapeutic CPAP.

CONCLUSIONS

Short-term withdrawal of CPAP therapy leads to a significant increase in endothelium-derived microparticles, suggesting that microparticle formation may be causally linked to obstructive sleep apnea and may promote endothelial activation.

Obstructive sleep apnea syndrome (OSAS) and hypertension: pathogenic mechanisms and possible therapeutic approaches

Obstructive sleep apnea syndrome (OSAS), a chronic condition characterized by collapse of the pharynx during sleep, has been increasingly recognized as a health issue of growing importance over the last decade. Recently emerging evidence suggests that there is a causal link between OSAS and hypertension, and hypertension represents an independent risk factor in OSAS patients. However, the pathophysiological basis for patients with OSAS having an increased risk for hypertension remains to be elucidated. The main acute physiological outcomes of OSAS are intermittent hypoxia, intrapleural pressure changes, and arousal from sleep, which might induce endothelial dysfunction, sympathetic activation, renin-angiotensin-aldosterone system activation, lipid metabolism dysfunction, and increased oxidative stress. This brief review focuses on the current understanding of the complex association between OSAS and hypertension.

Obstructive sleep apnea syndrome: blood viscosity, blood coagulation abnormalities, and early atherosclerosis

Obstructive sleep apnea syndrome (OSAS) is an independent risk factor for atherosclerosis and arterial thrombosis, which are associated with high cardiovascular (CV) morbidity and mortality. In studies performed in clinical populations with elevated CV event risk profiles, the occurrence of moderate to severe OSAS was very often accompanied by a worsened vascular function and increased prevalence of structural abnormalities. Recent investigations of atherosclerosis in OSAS have focused on thrombotic tendency and blood viscosity, providing new insight into mechanisms of the disease. Despite that knowledge about the mechanisms of development of CV disease in patients with OSAS is still incomplete, observations confirm a relationship between sleep-disordered breathing and the rheological properties (flow properties) of blood. While platelet dysfunction and hypercoagulability (PDMPs, PaI-1, and SF) play important roles in the pathogenesis of vascular disease, there are limited studies on the potential role of blood viscosity in the development of vascular disease in OSAS.

The effect of continuous positive airway pressure treatment on blood pressure: a systematic review and meta-analysis of randomized controlled trials

STUDY OBJECTIVES

We sought to provide an updated systematic review and meta-analysis of studies investigating the effect of positive airway pressure (PAP) treatment for obstructive sleep apnea (OSA) on systolic and diastolic blood pressure (SBP, DBP).

METHODS

Two independent investigators undertook a systematic search of the PubMed database (1980-2012) to identify randomized controlled trials comparing therapeutic PAP to sham-PAP, pill placebo, or standard care over at least one week in adult OSA patients without major comorbidities. The mean, variance, and sample size for diurnal and nocturnal SBP and DBP data were also extracted independently from each study. Random effects meta-analyses were conducted, followed by pre-specified subgroup and meta-regression analyses.

RESULTS

32 studies were identified, with data available from 28 studies representing n = 1,948 patients. The weighted mean difference in diurnal SBP (-2.58 mm Hg, 95% CI -3.57 to -1.59 mm Hg) and DBP (-2.01 mm Hg, 95% CI -2.84 to -1.18 mm Hg) both significantly favored PAP treatment over control arms, with similar results seen in nocturnal readings. Statistically significant reductions in BP were seen in studies whose patients were younger, sleepier, had more severe OSA, and exhibited greater PAP adherence. Meta-regression indicated that the reductions in DBP with PAP were predicted by mean baseline BP (β = -0.22, p = 0.02) and Epworth Sleepiness Scale scores (β = -0.27, p = 0.04).

CONCLUSIONS

PAP treatment for OSA is associated with modest but significant reductions in diurnal and nocturnal SBP and DBP. Future research should be directed towards identifying subgroups likely to reap greater treatment benefits as well as other therapeutic benefits provided by PAP therapy.

Obstructive sleep apnea syndrome

Obstructive sleep apnea (OSA) syndrome is a common but often unrecognized disorder caused by pharyngeal collapse during sleep and characterized by frequent awakenings, disrupted sleep and consequent excessive daytime sleepiness. With the increasing epidemic of obesity, the most important risk factor for OSA, prevalence of the disease will increase over the coming years thus representing an important public-health problem. In fact, it is now recognized that there is an association between OSA and hypertension, metabolic syndrome, diabetes, heart failure, coronary artery disease, arrhythmias, stroke, pulmonary hypertension, neurocognitive and mood disorders. Diagnosis is based on the combined evaluation of clinical manifestations and objective sleep study findings. Cardinal symptoms include snoring, sleepiness and significant reports of sleep apnea episodes. Polysomnography represents the gold standard to confirm the clinical suspicion of OSA syndrome, to assess its severity and to guide therapeutic choices. Behavioral, medical and surgical options are available for the treatment. Continuous positive airway pressure (CPAP) represents the treatment of choice in most patients. CPAP has been demonstrated to be effective in reducing symptoms, cardiovascular morbidity and mortality and neurocognitive sequelae, but it is often poorly tolerated. The results of clinical studies do not support surgery and pharmacological therapy as first-line treatment, but these approaches might be useful in selected patients. A better understanding of mechanisms underlying the disease could improve therapeutic strategies and reduce the social impact of OSA syndrome.

Medical disorders impacted by obstructive sleep apnea

Normal-sleeping individuals experience a lower metabolic rate and relative cardiovascular quiescent state with lower heart rate and blood pressure that naturally occurs during sleep compared with the waking state. In patients with obstructive sleep apnea (OSA), this quiescent state becomes disrupted. Research has shown a higher risk for several medical disorders, most ominous being a myocardial infarction or stroke. This article serves as an overview to the cardiovascular, cerebrovascular, metabolic, and gastroesophageal effects of OSA.

Relationship between atrial conduction delay and obstructive sleep apnea

Prolonged P-wave duration, indicating atrial conduction delay, is a marker of left atrial abnormality and is reported as a potent precursor of atrial fibrillation (AF). Several studies have shown that obstructive sleep apnea (OSA) is associated with AF. We evaluated the relationship between OSA and prolonged P-wave duration. Consecutive subjects who underwent overnight polysomnography and showed a normal sinus rhythm, had no history of AF or ischemic heart disease, and showed no evidence of heart failure were enrolled. Apnea-hypopnea index (AHI) is defined as the number of apnea and hypopnea events per hour of sleep. P-wave duration was determined on the basis of the mean duration of three consecutive beats in lead II from a digitally stored electrocardiogram. A total of 250 subjects (middle-aged, predominantly male, mildly obese, with a mean P-wave duration of 106 ms) were enrolled. In addition to age, male gender, body mass index (BMI), hypertension, dyslipidemia, and uric acid and creatinine levels, AHI (r = 0.56; P < 0.001) had significant univariable relationship with P-wave duration. Multivariate regression analysis showed that age, BMI, male gender, and AHI (partial correlation coefficient, 0.47; P < 0.001) were significantly independently correlated to P-wave duration. Severity of OSA is significantly associated with delayed atrial conduction time. Obstructive sleep apnea may lead to progression of atrial remodeling as an AF substrate.

Independent association between obstructive sleep apnea and noncalcified coronary plaque demonstrated by noninvasive coronary computed tomography angiography

BACKGROUND

Coronary artery atherosclerosis has been associated with obstructive sleep apnea (OSA). However, the type and severity of plaque formation have not been characterized. This study evaluated the association of coronary noncalcified plaques and severity of stenosis in patients with OSA.

HYPOTHESIS

METHODS

This study was a retrospective analysis of 81 patients, 49 with OSA and 32 without OSA, who had undergone multidetector-row helical computed tomography scanning. The board-certified radiologist was blinded to the diagnosis of OSA and reviewed the scans for plaque characterization, severity of stenosis, and number of vessels involved.

RESULTS

Of the 81 patients reviewed, the mean apnea-hypopnea index in the OSA group was 42.2 vs 7.5 in the non-OSA group. The groups did not significantly differ in the distribution of comorbid conditions. We found that among the patients with OSA, 63% had noncalcified/mixed plaques, as opposed to 16% in the non-OSA group (P < 0.0001), with unadjusted odds ratio of 9.3 (3.0, 28.4). After adjustment for other risk factors such as age, sex, race, hypercholesterolemia, and history of smoking, the association remained strong, with an odds ratio of 7.0 (1.9, 26.5; P < 0.05).

CONCLUSIONS

Our study finds that the frequency of noncalcified/mixed plaques is much higher in patients with OSA than in non-OSA patients. Patients with OSA also have more severe stenosis and a higher number of vessels involved. This study adds to a growing body of data regarding our understanding of the association of OSA and atherosclerosis.

OSA and atherosclerosis

Untreated obstructive sleep apnea (OSA) is increasingly recognized as a risk factor contributing to cardiovascular morbidity and mortality. Research in recent decades has uncovered many components of the complex pathological events leading to the atherosclerotic vascular diseases in OSA, which involve heightened oxidative stress as a result of intermittent hypoxia, vascular inflammation, activation of platelet and coagulation cascades, endothelial dysfunction and ultimately the formation of atherosclerotic plagues. The close association of OSA and conventional cardiovascular risk factors including hypertension, diabetes mellitus, dyslipidemia and obesity adds to the adverse cardiovascular sequelae. Further studies are required to clarify further on the pathophysiological processes, and the effect size of OSA therapy, and other potential preventive strategies.

Effect of AT1 receptor blockade on intermittent hypoxia-induced endothelial dysfunction

Chronic intermittent hypoxia (CIH) raises arterial pressure, impairs vasodilator responsiveness, and increases circulating angiotensin II (Ang II); however, the role of Ang II in CIH-induced vascular dysfunction is unknown. Rats were exposed to CIH or room air (NORM), and a subset of these animals was treated with losartan (Los) during the exposure period. After 28 days, vasodilatory responses to acetylcholine or nitroprusside were measured in isolated gracilis arteries. Superoxide levels and Ang II receptor protein expression were measured in saphenous arteries. After 28 days, arterial pressure was increased and acetylcholine-induced vasodilation was blunted in CIH vs. NORM, and this was prevented by Los. Responses to nitroprusside and superoxide levels did not differ between CIH and NORM. Expression of AT(2)R was decreased and the AT(1)R:AT(2)R ratio was increased in CIH vs. NORM, but this was unaffected by Los. These results indicate that the blood pressure elevation and endothelial dysfunction associated with CIH is dependent, at least in part, on RAS signaling.

Activation of heme oxygenase and suppression of cGMP are associated with impaired endothelial function in obstructive sleep apnea with hypertension

BACKGROUND

Obstructive sleep apnea (OSA) is a highly prevalent disorder that increases the risk of systemic hypertension and cardiovascular diseases. Heme oxygenase (HO) has been shown to be upregulated in patients with OSA and its overexpression in mice causes hypertension. End products of HO are carbon monoxide (CO) and bilirubin. CO exerts a pleiotropic action on vasoregulation. Despite high prevalence and incident of hypertension in OSA, its pathophysiology is not well-understood, particularly in regard to varying susceptibility of patients to hypertension. We investigated the role of HO in endothelial dysfunction and hypertension in OSA.

METHODS

We determined flow-mediated vasodilatation (FMD) as a measure of endothelial-dependent vasodilatory capacity, exhaled CO, bilirubin, and guanosine 3',5'-cyclic monophosphate (cGMP) in 63 subjects with OSA (normotensive 27, hypertensive 36) and in 32 subjects without OSA (normotensive 19, hypertensive 13).

RESULTS

Hypertensive OSA demonstrated marked impairment in FMD (8.0 ± 0.5% vasodilatation) compared to 10.5 ± 0.8% in hypertensives non-OSA (P < 0.01) and 13.5 ± 0.5% in normotensive OSA (P < 0.001) and 16.1 ± 1.1% in normotensive non-OSA (P < 0.0001). HO was upregulated and plasma nitric oxide (NO) was significantly increased in hypertensive OSA compared to normotensive OSA and hypertensive non-OSA. Conversely, serum cGMP was markedly decreased in hypertensive OSA (12.9 ± 1.8 pmol/ml vs. 20.6 ± 3.7 in normotensive OSA, P = 0.032). There was an inverse relationship between FMD and CO and bilirubin concentrations (r = 0.43, P = 0.0001 and r = 0.28, P = 0.01, respectively).

CONCLUSIONS

These data show that increased CO in the setting of elevated NO concentrations is associated with decreased cGMP, impaired FMD, and hypertension in patient with OSA.

Obstructive sleep apnea and stroke

Obstructive sleep apnea (OSA) is a common disorder that has been associated with many cardiovascular disease processes, including hypertension and arrhythmias. OSA has also been identified as an independent risk factor for stroke and all-cause mortality. OSA is highly prevalent in patients with transient ischemic attacks and stroke. Routinely screening patients with transient ischemic attacks or stroke for sleep apnea is becoming more common. In stroke patients with OSA, treatment with continuous positive airway pressure may prevent subsequent cardiovascular events and improve neurologic outcomes. This review explores the pathophysiology of the association between OSA and stroke, and the clinical implications of identification and treatment of OSA in patients with stroke.