Obstructive sleep apnea and atherosclerosis

Heart rate recovery post 6-minute walking test in obstructive sleep apnea: cycle ergometry versus 6-minute walking test in OSA patients

PURPOSE

To examine the clinical usefulness of heart rate recovery (HRR) post 6-minute walking test (6MWT) as a simple marker of cardiovascular risk in obstructive sleep apnea (OSA) patients in comparison to HRR post cycle ergometry, the validated and more sophisticated protocol.

METHODS

Seventy-four participants underwent full overnight polysomnography, cycle ergometry and 6MWT. The HRR at 1, 2 and 3 min (HRR-1, HRR-2 and HRR-3) 6MWT was compared to HRR at 1, 2, and 3 min post cycle ergometry in normal subjects and in moderate and severe OSA patients before and after 6-month CPAP treatment.

RESULTS

The HRR-1, HRR-2 and HRR-3 in 6MWT were significantly different between normal, moderate and severe OSA patients with higher rates achieved in normal. The higher the severity of OSA the lower the HRR was. There were also no differences found between work rate and distance walked during cycle ergometry or 6MWT, respectively, concerning normal, moderate and severe OSA patients. Heart rate recovery was further associated with minimum saturation of oxygen during sleep independently of the duration of apnea episodes of BMI and ESS. The treatment with CPAP had a beneficial effect on HRR both post-6MWT and post cycle ergometry.

CONCLUSIONS

Autonomic nervous system dysfunction in OSA can be found even with submaximal exertion. Heart rate recovery post-6MWT, such as HRR post cycle ergometry, was significantly impaired in OSA patients in comparison to normals and was favorably influenced from CPAP treatment. Furthermore, it was found to be more sensitive compared with distance walked in 6MWT in discriminating severity of OSA. The HRR post-6MWT was found to be an easily measured and reliable marker of OSA severity both before and after CPAP treatment.

Intermittent hypobaric hypoxia promotes atherosclerotic plaque instability in ApoE-deficient mice

AIM

Sudden cardiac death is one of the most frequent causes of death at high altitude. It has been reported that the intermittent normobaric hypoxia experienced by patients with obstructive sleep apnea may enhance the development of atherosclerosis. However, the effect of hypobaric hypoxia, which mimics the ambient air at high altitude, in the development of atherosclerosis has not been investigated.

METHODS

Twenty male ApoE-deficient mice, 8 weeks of age, were subjected to either control conditions or intermittent hypobaric hypoxia (IHH) for 8 weeks. Mice in the IHH group were exposed to a hypobaric chamber that replicated the hypobaric hypoxia conditions found at 4000 m altitude for 8 hours a day.

RESULTS

IHH-exposed mice did not significantly differ from control mice in plasma lipid levels, including triglyceride, total cholesterol, low-density lipoprotein, and high-density lipoprotein. The hematoxylin and eosin-stained sections of the aortic root showed similar plaque size between the groups. However, IHH-treated mice exhibited significantly decreased plaque collagen content, a feature of atherosclerotic plaque stability. Additionally, matrix metalloproteinase (MMP)-9 protein expression was significantly increased, whereas tissue inhibitor of MMP (TIMP)-2 expression was decreased after exposure to IHH.

CONCLUSION

IHH may promote atherosclerotic plaque instability in ApoE-deficient mice by changing the balance of MMPs and TIMPs.

Systematic review on noninvasive assessment of subclinical cardiovascular disease in obstructive sleep apnea: new kid on the block!

Patients with obstructive sleep apnea (OSA) have a high burden of cardiovascular disease (CVD) but a causal relationship between OSA and atherosclerotic CVD remains unclear. We systematically reviewed the literature analyzing the relationship. A review of the Medline database for studies noninvasively evaluating subclinical CVD in OSA was conducted. A total of fifty-two studies were included in this review. Across the studies the prevalence of atherosclerosis, as assessed by coronary artery calcification, carotid intima-media thickness, brachial artery flow-mediated dilation and pulse wave velocity was higher in patients with OSA and correlated with increasing severity and duration of OSA. This study shows OSA is an independent predictor of subclinical CVD as CVD is more likely to occur in patients with long standing and severe OSA. Further research is however necessary to identify specific OSA populations that would benefit from aggressive screening.

Hypoxia in atherosclerosis and inflammation

PURPOSE OF REVIEW

Hypoxia triggers various cellular processes, both in physiological and pathological conditions, and has recently also been implicated in atherosclerosis. This review summarizes the recent evidence for the presence and the role of hypoxia in atherosclerosis. Additionally, it will elucidate on hypoxic signaling, which is interlinked with inflammatory signaling, and discuss recent advances in imaging of hypoxia in atherosclerosis.

RECENT FINDINGS

Hypoxia is present in atherosclerotic plaques in humans and animal models, and systemic hypoxia promotes atherosclerosis. Hypoxia stimulates proatherosclerotic processes, like deficient lipid efflux, inflammation, interference with macrophage polarization and glucose metabolism. However, the molecular mechanism of hypoxia-mediated atherogenesis remains unclear. Noninvasive imaging directly targeting plaque hypoxia has been applied in animal models of atherosclerosis, but remains to be validated in humans. Meanwhile, the metabolic marker ¹⁸F-fluorodeoxyglucose, used to detect human atherosclerosis in vivo, may serve as an indirect marker of plaque hypoxia due to enhanced glucose uptake in anaerobic metabolism.

SUMMARY

Recent studies underscore the proatherogenic role of hypoxia in macrophage lipid and glucose metabolism, inflammation and polarization. These studies provide new insights into the pathogenesis of atherosclerosis and unravel novel therapeutic targets and new options for noninvasive imaging of human atherosclerotic plaques.

Fingerprinting-based metabolomic approach with LC-MS to sleep apnea and hypopnea syndrome: a pilot study

Sleep apnea and hypopnea syndrome (SAHS) is a multicomponent disorder, with associated cardiovascular and metabolic alterations, second in order of frequency among respiratory disorders. Sleep apnea is diagnosed with an overnight sleep test called a polysomnogram, which requires having the patient in hospital. In addition, a more clear classification of patients according to mild and severe presentations would be desirable. The aim of the present study was to assess the relative metabolic changes in SAHS to identify new potential biomarkers for diagnosis, able to evaluate disease severity to establish response to therapeutic interventions and outcomes. For this purpose, metabolic fingerprinting represents a valuable strategy to monitor, in a nontargeted manner, the changes that are at the base of the pathophysiological mechanism of SAHS. Plasma samples of 33 SAHS patients were collected after polysomnography and analyzed with LC coupled to MS (LC-QTOF-MS). After data treatment and statistical analysis, signals differentiating nonsevere and severe patients were detected. Putative identification of 14 statistically significant features was obtained and changes that can be related to the episodes of hypoxia/reoxygenation (inflammation) have been highlighted. Among them, the patterns of variation of platelet activating factor and lysophospholipids, together with some compounds related to differential activity of the gut microflora (bile pigments and pipecolic acid) open new lines of research that will benefit our understanding of the alterations, offering new possibilities for adequate monitoring of the stage of the disease.

Molecular biomarkers of vascular dysfunction in obstructive sleep apnea

Untreated and long-lasting obstructive sleep apnea (OSA) may lead to important vascular abnormalities, including endothelial cell (EC) dysfunction, hypertension, and atherosclerosis. We observed a correlation between microcirculatory reactivity and endothelium-dependent release of nitric oxide in OSA patients. Therefore, we hypothesized that OSA affects (micro)vasculature and we aimed to identify vascular gene targets of OSA that could possibly serve as reliable biomarkers of severity of the disease and possibly of vascular risk. Using quantitative RT-PCR, we evaluated gene expression in skin biopsies of OSA patients, mouse aortas from animals exposed to 4-week intermittent hypoxia (IH; rapid oscillations in oxygen desaturation and reoxygenation), and human dermal microvascular (HMVEC) and coronary artery endothelial cells (HCAEC) cultured under IH. We demonstrate a significant upregulation of endothelial nitric oxide synthase (eNOS), tumor necrosis factor-alpha-induced protein 3 (TNFAIP3; A20), hypoxia-inducible factor 1 alpha (HIF-1α?? and vascular endothelial growth factor (VEGF) expression in skin biopsies obtained from OSA patients with severe nocturnal hypoxemia (nadir saturated oxygen levels [SaO2]<75%) compared to mildly hypoxemic OSA patients (SaO2 75%-90%) and a significant upregulation of vascular cell adhesion molecule 1 (VCAM-1) expression compared to control subjects. Gene expression profile in aortas of mice exposed to IH demonstrated a significant upregulation of eNOS and VEGF. In an in vitro model of OSA, IH increased expression of A20 and decreased eNOS and HIF-1α expression in HMVEC, while increased A20, VCAM-1 and HIF-1αexpression in HCAEC, indicating that EC in culture originating from distinct vascular beds respond differently to IH stress. We conclude that gene expression profiles in skin of OSA patients may correlate with disease severity and, if validated by further studies, could possibly predict vascular risk in OSA patients.

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.

Effects of CPAP on "vascular" risk factors in patients with obstructive sleep apnea and arterial hypertension

Background

The aim of this study was to assess the effects of continuous positive airway pressure (CPAP) on arterial stiffness, central blood pressure, and reflected pulse wave characteristics in patients with severe obstructive sleep apnea (OSA) and stage 2–3 arterial hypertension.

Methods

Forty-four patients with hypertension and severe OSA (apnea/hypopnea index > 30) received stepped dose titration of antihypertensive treatment, consisting of valsartan 160 mg + amlodipine 5–10 mg + hydrochlorothiazide 25 mg. CPAP therapy was added after 3 weeks of continuous antihypertensive treatment with BP < 140/90 mmHg or after adjusting triple treatment in patients with resistant arterial hypertension. The patients were randomized to effective CPAP (4–15 mm H₂O) or placebo CPAP (pressure 4 mm H₂O) for three weeks, then crossed over to the alternative treatment in a single-blind manner. Office blood pressure (BP), ambulatory BP monitoring, ambulatory arterial stiffness index (AASI), aortic BP, carotid-femoral pulse wave velocity (cfPWV), and systolic wave augmentation index were measured using a Sphygmocor® device at baseline, after antihypertensive treatment, placebo CPAP, and effective CPAP.

Results

Baseline cfPWV was above the normal range in 94% of patients. After reaching target BP, the cfPWV decreased by 1.9 ± 1.0 msec (P = 0.007). Effective CPAP achieved a further cfPWV reduction of 0.7 msec (P = 0.03). Increased arterial stiffness (pulse wave velocity > 12 msec) persisted in 35% of patients on antihypertensive treatment and effective CPAP, in 56% of patients on antihypertensive treatment alone, and in 53% of patients on placebo CPAP. Only the combination of antihypertensive treatment with effective CPAP achieved a significant reduction in augmentation index and AASI, along with a further reduction in aortic and brachial BP.

Conclusion

Effective CPAP for 3 weeks resulted in a significant additional decrease in office BP, ambulatory BP monitoring, central BP, and augmentation index, together with an improvement in arterial stiffness parameters, ie, cfPWV and AASI, in a group of hypertensive patients with OSA.

Factors associated with increased carotid intima-media thickness in obstructive sleep apnea/hypopnea syndrome

BACKGROUND

Obstructive sleep apnea/hypopnea syndrome (OSAHS) is strongly associated with the increase of cardiovascular and cerebrovascular disorders. Carotid intima-media thickness (IMT) is used as a surrogate marker for subclinical or early atherosclerosis. Knowledge regarding early atherosclerosis in patients with OSAHS is scarce, and factors predicting carotid IMT have not been well studied.

OBJECTIVE

To compare IMT in patients with OSAHS versus controls and explore the factors associated with increased IMT in OSAHS.

METHODS

One hundred fifty-six OSAHS patients and 35 controls without history of vascular events, hypertension, and diabetes mellitus who underwent polysomnography were consecutively enrolled. Carotid IMT was measured using B-mode ultrasonography. Body mass index, waist circumference, hip circumference, waist-to-hip circumference ratio, Epworth Sleepiness Scale, and polysomnographic variables including arousal index, apnea/hypopnea index, mean oxygen saturation, and lowest oxygen saturation were assessed. Fasting plasma glucose, blood lipid profile, and high-sensitivity C-reactive protein were measured.

RESULTS

Average carotid IMT of OSAHS patients was significantly thicker than controls (0.66 vs. 0.58 mm, P=0.002) and multivariable logistic regression analysis revealed that arousal index [odds ratio (OR), 0.77; confidence interval (CI), 0.63-0.95; P=0.01] and lowest oxygen saturation (OR, 1.91; CI, 1.24-2.95; P=0.003) were significantly associated with OSAHS patients. Among the OSAHS patients, age (OR, 1.16; CI, 1.10-1.22; P<0.0001), fasting plasma glucose (OR, 1.05; CI, 1.01-1.10; P=0.04), low-density lipoprotein cholesterol (OR, 1.03; CI, 1.02-1.05; P<0.0001), and high-sensitivity C-reactive protein (OR, 1.48; CI, 1.13-1.95; P=0.005) were significantly associated with patients with IMT≥0.65 mm.

CONCLUSIONS

IMT was thicker in OSAHS patients without history of vascular events, hypertension, and diabetes mellitus. This study demonstrates that early atherosclerosis exists in this group of patients.

Oral pressure therapy for treatment of obstructive sleep apnea: clinical feasibility

PURPOSE

This feasibility study examined the initial-use safety and effectiveness of a new noninvasive oral pressure therapy (OPT) system developed to treat obstructive sleep apnea (OSA).

METHODS

The OPT system consists of a console that connects with flexible tubing to a premanufactured polymer mouthpiece. Through the mouthpiece, a pump in the console creates oral vacuum intended to move the soft palate anteriorly to decrease obstruction of the airway during sleep. The mouthpiece was produced in ten different sizes to accommodate a range of oral dimensions. Subjects with OSA in this single-center, single-night study underwent a polysomnography (PSG) study at baseline, followed by PSG during use of OPT.

RESULTS

Fifty-six men and 20 women, aged 50.8 ± 12.0 years (mean ± standard deviation [SD]), had OSA with apnea-hypopnea indices (AHI) greater than five events per hour at baseline. Body weight averaged 98.0 ± 18.2 kg (mean ± SD), body mass index ranged from 22.6 kg/m(2) to 57.9 kg/m(2) and averaged 32.5 ± 5.8 kg/m(2) (mean ± SD). OPT was generally well tolerated without any serious adverse events. Baseline AHI was 38.7 ± 27.5 events/hour (mean ± SD) and was reduced with treatment to 24.6 ± 25.7 events/hour (P < 0.001, Cohen's d 0.53). Treatment produced AHI less than or equal to ten events/hour in 38% of the subjects. Oxygen desaturation index was 30.1 ± 23.7 events/hour at baseline versus 15.8 ± 19.1 events/hour with treatment (P < 0.001, Cohen's d 0.66). The minimum oxygen saturation increased with treatment from 77.9 ± 8.3 to 82.2 ± 7.9 (P < 0.001, Cohen's d 0.53). Stage-N1 sleep shifts, total sleep-stage shifts, and awakenings were significantly reduced with treatment.

CONCLUSION

This single-center, single-night feasibility study demonstrates that OPT can improve OSA in certain subjects identifiable by PSG during systematic usage. In appropriately responsive patients, OPT shows potential as a clinically useful new alternative for treatment of OSA without the need for custom manufacture of an oral device component.

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.

A feasibility evaluation of oral pressure therapy for the treatment of obstructive sleep apnea

Objective:

This feasibility study examined the initial-use safety and potential utility of a novel noninvasive oral pressure therapy (OPT) system designed to reduce airway obstruction during sleep.

Methods:

This was a single-center, proof-of-concept, single-treatment-night study in which subjects with obstructive sleep apnea (OSA) underwent a baseline polysomnography (PSG) study followed by PSG during use of an OPT system. The OPT system is composed of a bedside console, a polymer mouthpiece, and a flexible tube connecting the mouthpiece to the console. The console contains a pump that creates vacuum intended to pull the soft palate anteriorly and stabilize the tongue to reduce obstruction during sleep.

Results:

Fifty-four men and 17 women, aged 53.2 ± 11.5 years (mean ± SD) had a baseline apnea–hypopnea index (AHI) greater than 5 events per hour. OPT was generally well tolerated with no serious adverse events. OPT significantly decreased AHI from 34.4 ± 28.9 events per hour (mean ± SD) at baseline to 20.7 ± 23.3 ( p < 0.001). Treatment produced an AHI less than 10 in 48% of the subjects. OPT significantly improved oxygen desaturation index ( p < 0.001) and increased the percentage of the night with oxygen saturation of 90% or greater ( p = 0.028). Stage-N1 sleep shifts, total sleep-stage shifts, awakenings and the percentage of sleep time spent in N1 sleep were significantly reduced with treatment.

Conclusion:

This proof-of-concept study suggests that OPT can produce clinically relevant relief of OSA in certain subjects who are readily identified by PSG during trial use of the noninvasive system. OPT shows promise as a new treatment option for OSA in appropriate patients.

Chronic intermittent hypoxia exposure induces atherosclerosis in ApoE knockout mice: role of NF-κB p50

Current animal models of chronic intermittent hypoxia (CIH)-induced atherosclerosis have limitations. Mechanisms of CIH-induced atherosclerosis are poorly understood. This study tested new mouse models of CIH-induced atherosclerosis and defined the role of NF-κB p50 in CIH-induced atherosclerosis. Mice deficient in apolipoprotein E (ApoE-KO) or in both ApoE and p50 genes (ApoE-p50-DKO) were exposed to sham or CIH. Atherosclerotic lesions on aortic preparations were analyzed. CIH exposure caused atherosclerosis in ApoE-KO mice fed a normal chow diet and with no preexisting atherosclerotic condition in an exposure time-dependent manner. CIH caused more pronounced atherosclerotic lesions in ApoE-p50-DKO mice on a normal chow diet without preexisting atherosclerosis. ApoE-KO and ApoE-p50-DKO mice exposed to CIH for 30 and 9 weeks, respectively, displayed similar areas of atherosclerotic lesions on cross sections of aortic root. P50 gene deletion in ApoE-p50-DKO mice significantly augmented CIH-induced serum levels of tumor necrosis factor-α and IL-6, aortic tumor necrosis factor-α, and inducible nitric oxide synthase expression and aortic infiltration of Mac3-positive macrophages. CIH caused a greater elevation in serum cholesterol level in ApoE-p50-DKO than in ApoE-KO mice. CIH down-regulated hepatic low-density lipoprotein receptor and HMG-CoA reductase expression in ApoE-p50-DKO but not in ApoE-KO mice. We found two new mouse models that are useful for studying mechanisms and pathways of CIH-induced atherosclerosis. We showed that NF-κB p50 protects against CIH-induced atherosclerosis by inhibiting vascular inflammation and hypercholesterolemia.

Chronic intermittent hypoxia induces atherosclerosis by NF-κB-dependent mechanisms

Chronic intermittent hypoxia (CIH) causes atherosclerosis in mice fed a high cholesterol diet (HCD). The mechanisms by which CIH promotes atherosclerosis are incompletely understood. This study defined the mechanistic role of NF-κB pathway in CIH+HCD induced atherosclerosis. Wild type (WT) and mice deficient in the p50 subunit of NF-κB (p50-KO) were fed normal chow diet (ND) or HCD, and exposed to sham or CIH. Atherosclerotic lesions on the en face aortic preparation and cross-sections of aortic root were examined. In WT mice, neither CIH nor HCD exposure alone caused, but CIH+HCD caused evident atherosclerotic lesions on both preparations after 20weeks of exposure. WT mice on ND and exposed to CIH for 35.6weeks did not develop atherosclerotic lesions. P50 gene deletion diminished CIH+HCD induced NF-κB activation and abolished CIH+HCD induced atherosclerosis. P50 gene deletion inhibited vascular wall inflammation, reduced hepatic TNF-α level, attenuated the elevation in serum cholesterol level and diminished macrophage foam cell formation induced by CIH+HCD exposure. These results demonstrate that inhibition of NF-κB activation abrogates the activation of three major atherogenic mechanisms associated with an abolition of CIH+HCD induced atherosclerosis. NF-κB may be a central common pathway through which CIH+HCD exposure activates multiple atherogenic mechanisms, leading to atherosclerosis.

Association of epicardial fat thickness with the severity of obstructive sleep apnea in obese patients

BACKGROUND

The correlation between obesity and severity of obstructive sleep apnea (OSA) is controversial. Although fat excess is a predisposing factor for the development of OSA, it has not been determined whether fat distribution rather than obesity per se is associated with OSA severity. Epicardial fat thickness (EFT) is an independent index of visceral adiposity and cardiometabolic risk. We investigated the relation between fat distribution and cardiometabolic risk factors, including EFT and common carotid intima-media thickness (cIMT), with the severity of OSA in obese patients.

METHODS

One hundred and fifteen obese patients (56 males, 59 females) with polysomnographic evidence of OSA (≥ 5 apnea/hypopnea events per hour) of various degrees, without significant differences in grade of obesity as defined by body mass index (BMI), were evaluated. The following parameters were measured: BMI, body composition by dual energy X-ray absorptiometry, EFT, right ventricular end-diastolic diameter (RVEDD) and cIMT by ultrasound, and parameters of metabolic syndrome (waist circumference, arterial blood pressure, fasting glucose, HDL-cholesterol and triglycerides).

RESULTS

EFT, RVEDD, cIMT and trunk/leg fat mass ratio showed a positive correlation with OSA severity in univariate analysis (r=0.536, p<0.001; r=0.480, p<0.001; r=0.345, p<0.001; r=0.330, p<0.001, respectively). However, multiple linear regression analysis showed that EFT was the most significant independent correlate of the severity of OSA (R(2)=0.376, p=0.022).

CONCLUSIONS

The present study suggests that, in obese patients, EFT may be included among the clinical parameters associating with OSA severity. The association of EFT with OSA, both cardiovascular risk factors, is independent of obesity as defined by classical measures.

Effects of continuous positive airway pressure (CPAP) treatment for obstructive sleep apnea in arterial stiffness: a meta-analysis

Obstructive sleep apnea (OSA) is associated with increased arterial stiffness, a cumulative indicator of arterial health. Continuous positive airway pressure (CPAP) is the gold standard treatment for OSA. We conducted a meta-analysis of the available literature investigating the effect of CPAP on arterial stiffness in patients with OSA. Fifteen articles (n = 615 patients) assessing indices of arterial stiffness were identified. Five different meta-analyses were performed assessing: a) all indices of arterial stiffness, b) augmentation index (AIx), c) all pulse wave velocities (PWV), d) brachial-ankle PWV and e) carotid-femoral PWV. Pooled standardized mean differences (SMDs) and weighted mean differences (WMDs) were appropriately calculated through fixed or random effects models after assessing between-study heterogeneity. A significant improvement of all indices of arterial stiffness was observed after CPAP treatment (SMD = -0.74; 95%CI: -1.08 to -0.41). AIx and PWVs were also significantly improved (WMD = -4.86; 95%CI: -7.31 to -2.41 and WMD = -0.87; 95%CI: -0.98 to -0.77, respectively), as well as brachial-ankle PWV and carotid-femoral PWV (WMD = -0.86; 95%CI: -0.97 to -0.75 and WMD = -1.21; 95%CI:-1.92 to -0.50, respectively). Neither the proportion of compliant patients nor the duration of CPAP use altered the effect of arterial stiffness reduction after CPAP treatment. In conclusion, our meta-analyses showed significant improvements in all indices of arterial stiffness after CPAP treatment in patients with OSA. As clinical use of arterial stiffness is growing in popularity, the efficacy of this useful tool in assessing cardiovascular risk reduction among patients with OSA treated with CPAP needs to be further explored.

Prevalence of calcified carotid artery atheromas on the panoramic images of patients with syndrome Z, coexisting obstructive sleep apnea, and metabolic syndrome

OBJECTIVES

The objective of this study was to compare the prevalence of calcified carotid artery atheromas (CCAAs) on panoramic images of individuals (n = 31) with obstructive sleep apnea (OSA) with individuals (n = 117) with syndrome Z (SZ: OSA with concomitant metabolic syndrome [MetS]).

STUDY DESIGN

Images of patients with OSA or SZ referred from the Sleep Service to Dentistry were evaluated. Descriptive statistics and t tests (Bonferroni correction) were conducted to determine significant differences between atheroma prevalence and proatherogenic factors (age, apnea-hypopnea index, body mass index, lipid profile, blood pressure, glucose) between OSA and SZ groups.

RESULTS

Individuals with OSA had an atheroma prevalence of 35% and those with SZ 42% (P = .52). Individuals with SZ also had significantly more severe atherogenic profiles (obesity, dyslipidemia, hyperglycemia) than OSA patients (P ≤ .05). Greatest CCAA prevalence (63%) was evidenced by SZ patients with severe OSA and moderate MetS.

CONCLUSION

Individuals with SZ have significantly greater atherogenic burden and slightly higher prevalence of CCAAs when compared with individuals with OSA.

Noninvasive ventilation in mild obesity hypoventilation syndrome: a randomized controlled trial

OBJECTIVE

Open studies suggest that treatment of obesity hypoventilation syndrome (OHS) by noninvasive ventilation (NIV) restores sleep quality and daytime vigilance and reduces cardiovascular morbidity. However, to our knowledge no randomized controlled trial (RCT) comparing NIV to conservative measures is available in the field. The goal of this study was to assess in patients with OHS, during an RCT, effects of 1-month NIV compared with lifestyle counseling on blood gas measurements, sleep quality, vigilance, and cardiovascular, metabolic, and inflammatory parameters.

METHODS

Thirty-five patients in whom OHS was newly diagnosed were randomized either to the NIV group or the control group represented by lifestyle counseling. Assessments included blood gas levels, subjective daytime sleepiness, metabolic parameters, inflammatory (hsCRP, leptin, regulated upon activation normal T-cell express and secreted [RANTES], monocyte chemoattractant protein-1, IL-6, IL-8, tumor necrosis factor-α, resistin) and antiinflammatory (adiponectin, IL-1-RA) cytokines, sleep studies, endothelial function (reactive hyperemia measured by peripheral arterial tonometry [RH-PAT]), and arterial stiffness.

RESULTS

Despite randomization, NIV group patients (n = 18) were older (58 ± 11 years vs 54 ± 6 years) with a higher baseline Paco(2) (47.9 ± 4.2 mm Hg vs 45.2 ± 3 mm Hg). In intention-to-treat analysis, compared with control group, NIV treatment significantly reduced daytime Paco(2) (difference between treatments: -3.5 mm Hg; 95% CI, -6.2 to -0.8) and apnea-hypopnea index (-40.3/h; 95% CI, -62.4 to -18.2). Sleep architecture was restored, although nonrespiratory microarousals increased (+9.4/h of sleep; 95% CI, 1.9-16.9), and daytime sleepiness was not completely normalized. Despite a dramatic improvement in sleep hypoxemia, glucidic and lipidic metabolism parameters as well as cytokine profiles did not vary significantly. Accordingly, neither RH-PAT (+0.02; 95% CI, -0.24 to 0.29) nor arterial stiffness (+0.22 m/s; 95% CI, -1.47 to 1.92) improved.

CONCLUSIONS

One month of NIV treatment, although improving sleep and blood gas measurements dramatically, did not change inflammatory, metabolic, and cardiovascular markers.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT00603096; URL: www.clinicaltrials.gov.

The association of obesity with insulin resistance in male patients with obstructive sleep apnea syndrome in Korea

OBJECTIVE

Obstructive sleep apnea syndrome (OSAS) has been associated with cardiovascular complications and insulin resistance has been implicated in the pathogenesis and progression of atherosclerosis. We investigated whether insulin resistance is associated with OSAS independent of obesity.

METHODS

A total of 183 male patients with OSAS and 52 healthy controls were assessed by nocturnal polysomnography (NPSG). After NPSG, serum concentrations of total cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, glucose and insulin were measured. Insulin resistance was determined by calculating the homeostasis model assessment for insulin resistance (HOMA-IR).

RESULTS

Subjects were divided into normal control, mild-to-moderate OSA group (n=96) and severe OSA group (n=87). There were no significant differences among groups in age, body mass index (BMI), neck circumference or waist circumference. Serum concentrations of total cholesterol, LDL cholesterol, triglycerides, glucose, insulin and HOMA-IR scores of normal controls did not differ from those of the mild-to-moderate or severe OSAS groups. HOMA-IR significantly correlated with anthropometric variables, oxygen desaturation index, triglyceride and LDL cholesterol. Stepwise multiple linear regression analysis showed that waist circumference (β=0.35) and triglycerides (β=0.27) were significant determinants of HOMA-IR (adjusted R(2)=20%, p<0.01).

CONCLUSION

Insulin resistance was related to obesity itself rather than OSAS severity or nocturnal hypoxemia-related variables. In preventing cardiovascular complications in OSAS patients, weight reduction should be considered.

Leukotriene B4 receptor-1 mediates intermittent hypoxia-induced atherogenesis

RATIONALE

Obstructive sleep apnea, which is characterized by intermittent hypoxia (IH) during sleep, has emerged as an independent risk factor for cardiovascular disease, including atherosclerosis. Leukotriene B4 (LTB4) production is increased in patients with obstructive sleep apnea and negatively correlates to hypoxic levels during sleep, with continuous positive airway pressure therapy decreasing LTB4 production.

OBJECTIVES

Determine the potential role of LTB4 in IH-induced atherosclerosis in a monocyte cellular model and a murine model.

METHODS

THP-1 cells were exposed to IH for 3, 6, 24, and 48 hours. Macrophage transformation and foam cell formation were assessed after IH exposures. Apolipopotein E (ApoE)(-/-) or BLT1(-/-)/ApoE(-/-) mice were fed an atherogenic diet and exposed to IH (alternating 21% and 5.7% O(2) from 7 am to 7 PM each day) for 10 weeks. Atherosclerotic lesion formation in en face aorta was examined by oil red O staining.

MEASUREMENTS AND MAIN RESULTS

IH increased production of LTB4 and the expression of 5-lipoxygenase and leukotriene A4 hydrolase, the key enzymes for producing LTB4. IH was associated with transformation of monocytes to activated macrophages, as evidenced by increased expression of CD14 and CD68. In addition, IH exposures promoted increased cellular cholesterol accumulation and foam cell formation. The LTB4 receptor 1 (BLT1) antagonist U-75302 markedly attenuated IH-induced changes. Furthermore, IH promoted atherosclerotic lesion formation in ApoE(-/-) mice. IH-induced lesion formation was markedly attenuated in BLT1(-/-)/ApoE(-/-) mice.

CONCLUSIONS

BLT1-dependent pathways underlie IH-induced atherogenesis, and may become a potential novel therapeutic target for obstructive sleep apnea-associated cardiovascular disease.

Increased arterial stiffness in obstructive sleep apnea: a systematic review

Obstructive sleep apnea is a prevalent disease that is associated with significant morbidity and mortality, particularly due to cardiovascular disease. An emerging cardiovascular risk factor, arterial stiffness, may also be involved in the cardiovascular complications of obstructive sleep apnea. The purpose of this review was to summarize the current literature regarding the effect of obstructive sleep apnea on arterial stiffness. We conducted a systematic literature review using PubMed, Embase and the Cochrane Library. We identified 24 studies that met search criteria investigating the effect of obstructive sleep apnea on arterial stiffness. Arterial stiffness was found to be increased in obstructive sleep apnea patients compared with controls or increased in severe compared with mild sleep apnea. In some studies, a positive correlation was identified between the degree of arterial stiffness and sleep apnea severity. In the two randomized, controlled trials and the two nonrandomized trials identified, treatment of obstructive sleep apnea with continuous positive airway pressure led to significant decreases in arterial stiffness. Obstructive sleep apnea appears to have an independent effect on arterial stiffness, which may be one of the mechanisms accounting for sleep apnea-associated cardiovascular risk.

Obstructive sleep apnea syndrome and fatty liver: Association or causal link?

Obstructive sleep apnea (OSA) is a complex disorder that consists of upper airway obstruction, chronic intermittent hypoxia and sleep fragmentation. OSA is well known to be associated with hypoxia, insulin resistance and glucose intolerance, and these factors can occur in the presence or absence of obesity and metabolic syndrome. Although it is well established that insulin resistance, glucose intolerance and obesity occur frequently with non-alcoholic fatty liver disease (NAFLD), it is now becoming apparent that hypoxia might also be important in the development of NAFLD, and it is recognized that there is increased risk of NAFLD with OSA. This review discusses the association between OSA, NAFLD and cardiovascular disease, and describes the potential role of hypoxia in the development of NAFLD with OSA.

Choroidal blood-flow responses to hyperoxia and hypercapnia in men with obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) impacts on macrovasculature and autonomic function and may therefore interfere with ocular microvascular regulation. We hypothesized that choroidal vascular reactivity to hyperoxia and hypercapnia was altered in patients with OSA compared with matched control subjects and would improve after treatment with continuous positive airway pressure (CPAP).

METHODS

Sixteen healthy men were matched 1:1 for body mass index, sex, and age with 16 men with newly diagnosed OSA without comorbidities. Subjects underwent sleep studies, 24-hour blood pressure monitoring, arterial stiffness measurements, and cardiac and carotid echography. Overall, patients were middle-aged, lean, and otherwise healthy except for having OSA with a limited amount of desaturation, with, at most, subclinical lesions of the cardiovascular system, stage 1 hypertension, or both. Choroidal laser Doppler flowmetry provides a unique opportunity to assess microvascular function by measuring velocity, (ChBVel), volume (ChBVol), and relative subfoveal choroidal blood flow (ChBF). Vascular choroidal reactivity was studied during hyperoxia and hypercapnia (8% CO2) challenges before and after treatment with nasal CPAP.

RESULTS

Patients with OSA and control subjects exhibited similar choroidal reactivity during hyperoxia (stability of choroidal blood flow) and hypercapnia (significant increases in ChBVel of 13.5% and in ChBF of 16%). Choroidal vasoreactivity to CO2 was positively associated with arterial stiffness in patients with OSA. Gas choroidal vasoreactivity was unchanged after 6 to 9 months of CPAP treatment.

CONCLUSION

This study showed unimpaired choroidal vascular reactivity in otherwise healthy men with OSA. This suggests that patients with OSA, without comorbidities, have long-term adaptive mechanisms active in ocular microcirculation.

Intermittent and sustained hypoxia induce a similar gene expression profile in human aortic endothelial cells

Obstructive sleep apnea may cause vascular inflammation and atherosclerosis, which has been attributed to intermittent hypoxia (IH). Recent data suggest that IH, but not sustained hypoxia (SH), activates proinflammatory genes in HeLa cells. Effects of IH and SH on the gene expression profile in human aortic endothelial cells (HAEC) have not been compared. We perfused media with alternating flow of 16% and 0% O2 (IH) or constant flow of 4% O2 (SH-4%), 8% O2 (SH-8%), or 16% O2 (control) for 8 h. Illumina gene microarrays were performed, with subsequent verification by real-time PCR. Proinflammatory cytokines in the media were measured by ELISA. Both IH and SH-4% upregulated proinflammatory genes, including heat shock protein 90-kDa B1, tumor necrosis factor superfamily member 4, and thrombospondin 1. Among all proinflammatory genes, only IL-8 mRNA showed significantly higher levels of expression (1.78-fold) during IH, compared with SH-4%, but both types of hypoxic exposure elicited striking three- to eightfold increases in IL-8 and IL-6 protein levels in the media. IH and SH-4% also upregulated antioxidant genes, including heme oxygenase-1 and nuclear factor (erythroid-derived 2)-like 2 (NRF2), whereas classical genes regulated by hypoxia-inducible factor 1 (HIF-1), such as endothelin and glucose transporter GLUT1, were not induced. SH-8% induced changes in gene expression and cytokine secretion that were similar to those of IH and SH-4%. In conclusion, short exposures to IH and SH upregulate proinflammatory and antioxidant genes in HAEC and increase secretion of proinflammatory cytokines IL-8 and IL-6 into media in similar fashions.

Obstructive sleep apnea, immuno-inflammation, and atherosclerosis

Obstructive sleep apnea (OSA) is a highly prevalent sleep disorder leading to cardiovascular and metabolic complications. OSA is also a multicomponent disorder, with intermittent hypoxia (IH) as the main trigger for the associated cardiovascular and metabolic alterations. Indeed, recurrent pharyngeal collapses during sleep lead to repetitive sequences of hypoxia-reoxygenation. This IH induces several consequences such as hemodynamic, hormonometabolic, oxidative, and immuno-inflammatory alterations that may interact and aggravate each other, resulting in artery changes, from adaptive to degenerative atherosclerotic remodeling. Atherosclerosis has been found in OSA patients free of other cardiovascular risk factors and is related to the severity of nocturnal hypoxia. Early stages of artery alteration, including functional and structural changes, have been evidenced in both OSA patients and rodents experimentally exposed to IH. Impaired vasoreactivity with endothelial dysfunction and/or increased vasoconstrictive responses due to sympathetic, endothelin, and renin-angiotensin systems have been reported and also contribute to vascular remodeling and inflammation. Oxidative stress, inflammation, and vascular remodeling can be directly triggered by IH, further aggravated by the OSA-associated hormonometabolic alterations, such as insulin resistance, dyslipidemia, and adipokine imbalance. As shown in OSA patients and in the animal model, genetic susceptibility, comorbidities (obesity), and life habits (high fat diet) may aggravate atherosclerosis development or progression. The intimate molecular mechanisms are still largely unknown, and their understanding may contribute to delineate new targets for prevention strategies and/or development of new treatment of OSA-related atherosclerosis, especially in patients at risk for cardiovascular disease.