Endothelial function in obstructive sleep apnea and response to treatment

"Sleep disordered breathing and ECG R-wave to radial artery pulse delay, The Multi-Ethnic Study of Atherosclerosis"

BACKGROUND

Electrocardiography R-wave to radial artery pulse delay (RRD) represents pulse transit time inclusive of pre-ejection period (PEP) and arterial pulse propagation time. RRD is proposed to largely reflect arterial stiffness when PEP is accounted for (shorter RRD = higher arterial stiffness). Sleep disordered breathing (SDB) causes intermittent hypoxemia and sympathetic activation, which negatively influences vascular function. We aimed to examine the association of measures of SDB with RRD.

METHODS

Our sample consisted of participants in the Multi-Ethnic Study of Atherosclerosis without prevalent cardiovascular disease who underwent a daytime arterial elasticity exam, cardiac magnetic resonance imaging (MRI), and overnight polysomnography. SDB measures of interest included apnea hypopnea index (AHI) and oxygen desaturation index (ODI) (N = 1173). RRD was regressed on each measure of SDB separately, with adjustment for other cardiovascular risk factors as well as for correlates of the PEP, another component of RRD, by including cardiac MRI measures of contractility and preload.

RESULTS

In multivariate analysis, among measures of SDB, ODI, a marker of intermittent hypoxemia, was inversely associated with RRD (β = -60.2 msec per SD [15.5/hr], p = 0.04). No significant association was found with AHI. In gender stratified analyses, ODI and AHI were predictive of RRD in men only (β = -111.3 msec per SD [15.5/hr], p = 0.01 and β = -100.3 msec per SD [16.1/hr], p = 0.02 respectively).

CONCLUSION

Severity of SDB as measured by ODI was associated with RRD, a marker of arterial stiffness. Thus, association of RRD with measures of SDB appears to be gender-dependent.

Endothelial microvesicles in hypoxic hypoxia diseases

Hypoxic hypoxia, including abnormally low partial pressure of inhaled oxygen, external respiratory dysfunction-induced respiratory hypoxia and venous blood flow into the arterial blood, is characterized by decreased arterial oxygen partial pressure, resulting in tissue oxygen deficiency. The specific characteristics include reduced arterial oxygen partial pressure and oxygen content. Hypoxic hypoxia diseases (HHDs) have attracted increased attention due to their high morbidity and mortality and mounting evidence showing that hypoxia-induced oxidative stress, coagulation, inflammation and angiogenesis play extremely important roles in the physiological and pathological processes of HHDs-related vascular endothelial injury. Interestingly, endothelial microvesicles (EMVs), which can be induced by hypoxia, hypoxia-induced oxidative stress, coagulation and inflammation in HHDs, have emerged as key mediators of intercellular communication and cellular functions. EMVs shed from activated or apoptotic endothelial cells (ECs) reflect the degree of ECs damage, and elevated EMVs levels are present in several HHDs, including obstructive sleep apnoea syndrome and chronic obstructive pulmonary disease. Furthermore, EMVs have procoagulant, proinflammatory and angiogenic functions that affect the pathological processes of HHDs. This review summarizes the emerging roles of EMVs in the diagnosis, staging, treatment and clinical prognosis of HHDs.

Chronic Intermittent Hypoxia-Induced Vascular Dysfunction in Rats is Reverted by N-Acetylcysteine Supplementation and Arginase Inhibition

Chronic intermittent hypoxia (CIH), the main attribute of obstructive sleep apnea (OSA), produces oxidative stress, endothelial dysfunction, and hypertension. Nitric oxide (NO) plays a critical role in controlling the vasomotor tone. The NO level depends on the L-arginine level, which can be reduced by arginase enzymatic activity, and its reaction with the superoxide radical to produce peroxynitrite. Accordingly, we hypothesized whether a combination of an arginase inhibitor and an antioxidant may restore the endothelial function and reduced arterial blood pressure (BP) in CIH-induced hypertensive rats. Male Sprague-Dawley rats 200 g were exposed either to CIH (5% O₂, 12 times/h 8 h/day) or sham condition for 35 days. BP was continuously measured by radio-telemetry in conscious animals. After 14 days, rats were treated with 2(S)-amino-6-boronohexanoic acid (ABH 400 μg/kg day, osmotic pump), N-acetylcysteine (NAC 100 mg/kg day, drinking water), or the combination of both drugs until day 35. At the end of the experiments, external carotid and femoral arteries were isolated to determine vasoactive contractile responses induced by KCL and acetylcholine (ACh) with wire-myography. CIH-induced hypertension (~8 mmHg) was reverted by ABH, NAC, and ABH/NAC administration. Carotid arteries from CIH-treated rats showed higher contraction induced by KCl (3.4 ± 0.4 vs. 2.4 ± 0.2 N/m²) and diminished vasorelaxation elicits by ACh compared to sham rats (12.8 ± 1.5 vs. 30.5 ± 4.6%). ABH reverted the increased contraction (2.5 ± 0.2 N/m²) and the reduced vasorelaxation induced by ACh in carotid arteries from CIH-rats (38.1 ± 4.9%). However, NAC failed to revert the enhanced vasocontraction (3.9 ± 0.6 N/m²) induced by KCl and the diminished ACh-induced vasorelaxation in carotid arteries (10.7 ± 0.8%). Femoral arteries from CIH rats showed an increased contractile response, an effect partially reverted by ABH, but completely reverted by NAC and ABH/NAC. The impaired endothelial-dependent relaxation in femoral arteries from CIH rats was reverted by ABH and ABH/NAC. In addition, ABH/NAC at high doses had no effect on liver and kidney gross morphology and biochemical parameters. Thus, although ABH, and NAC alone and the combination of ABH/NAC were able to normalize the elevated BP, only the combined treatment of ABH/NAC normalized the vascular reactivity and the systemic oxidative stress in CIH-treated rats.

[The dynamics of cerebral vascular reserve in sleep apnea patients during continuous positive airway pressure therapy]

AIM

To explore the possibility of cerebral hemodynamic reserve (CHR) normalization in patients with obstructive sleep apnea syndrome (OSAS), aged over fifty, who received continuous positive airway pressure (CPAP) therapy.

MATERIAL AND METHODS

The main group (20 patients, aged 50-65 years, with severe OSAS) and the control group (20 volunteers without snoring and OSAS matched for age and physical status) were studied. Diagnosis included cardio-respiratory monitoring of nocturnal sleep and ultrasound examination of cerebral blood flow with functional tests (breath holding and hyperventilation) and calculating the coefficient of vasomotor reactivity (CVMR) before the start of CPAP-therapy and after one month therapy.

RESULTS

The significant CVMR decrease in vertebral (VA) and basilar arteries (BA) in patients with OSAS compared to the control group was identified: 38.9±8.5 and 55.7±11.3 for VA, 36.8±15.7 and 54.0±5.4 for BA. After one month CPAP-therapy, no significant coefficient gains was observed: 38.9±8.5 and 42.3±9.1 for VA, 36.8±15.7 and 37.2±7.7 for BA.

CONCLUSION

The reduction of CVMR in patients older than 50 years with severe OSAS suggests the disturbance of CHR. The absence of its recovery within one month of CPAP-therapy may be indicative of the irreversible damage of the cerebral blood flow regulation mechanisms. Continued observations for a longer period are needed.

The Relation between Pregnancy-Associated Plasma Protein A and Obstructive Sleep Apnea Syndrome

Aim

We aimed to investigate the relationship between serum pregnancy-associated plasma protein A (PAPP-A) levels and obstructive sleep apnea syndrome (OSAS).

Materials and Method

44 patients with OSAS and 44 healthy adults were included in this study. The participants having rheumatic or systemic inflammatory disease, advanced liver or kidney failure, diabetes, heart failure, hypertension, pregnancy, prerenal azotemia, known history of coronary artery disease, any pulmonary disease, rhinitis, or atopy, history of major trauma or surgery within the last six 6 months, and inhaled nasal or systemic corticosteroid use or other anti-inflammatory medications and those with <18 years of age were excluded. Serum PAPP-A levels were determined by the Elisa method with the immune sandwich measuring method. Statistical analysis of the study was performed with SPSS 17.0 statistical analysis package program, and p < 0.05 was considered as significant.

Results

Serum PAPP-A levels of patients with OSAS (2.350 ng/ml (0.641–4.796)) were significantly higher (p < 0.001) when compared with healthy controls (0.971 ng/ml (0.109–2.679)). There was a statistically significant difference in serum PAPP-A levels between groups of OSAS patients according to the classification of OSAS severity. Between the groups of patients with OSAS, serum levels of PAPP-A in moderate group was significantly higher when compared with severe OSAS group (p < 0.001). There was positive correlations between PAPP-A levels and night minimum (p=0.042, r=0.309), and average oxygen levels (p=0.006, r=0.407). There was a negative correlation between PAPP-A levels and AHI (p=0.002, r=−0.460).

Conclusion

Higher PAPP-A levels in OSAS patients that were found in this study show inflammatory component in OSAS.

A review of the associations between obstructive sleep apnea and hypertensive disorders of pregnancy and possible mechanisms of disease

Obesity is prevalent among pregnant women in the United States; 15-20% of obese pregnant women have obstructive sleep apnea. The prevalence of obstructive sleep apnea increases along with body mass index, age and in the presence of other co-morbidities. Untreated obstructive sleep apnea in women is associated with a range of cardiovascular, pulmonary and metabolic co-morbidities; recent studies suggest that women with obstructive sleep apnea in pregnancy may be at significantly greater risk of entering pregnancy with chronic hypertension and/or of developing hypertensive disorders of pregnancy: gestational hypertension; preeclampsia; or eclampsia. This has serious public health implications; hypertensive disorders of pregnancy are a major cause of maternal and neonatal morbidity and mortality and are associated with a greater lifetime risk for cardiovascular disease. The mechanisms that associated obstructive sleep apnea with hypertensive disorders of pregnancy have not been defined, but several pathways are scientifically plausible. In this review, we will present a comprehensive literature review of the following: the associations between obstructive sleep apnea and hypertensive disorders of pregnancy; the proposed mechanisms that may connect obstructive sleep apnea and hypertensive disorders of pregnancy; and the effectiveness of treatment at mitigating these adverse outcomes.

Effects of continuous positive airway pressure on cardiovascular biomarkers in patients with obstructive sleep apnea: a meta-analysis of randomized controlled trials

PURPOSE

Obstructive sleep apnea (OSA) is associated with increased levels of systemic inflammatory markers, increased arterial stiffness, and endothelial dysfunction, which may lead to increased cardiovascular risk. We aimed to quantify the effects of continuous positive airway pressure (CPAP) on cardiovascular biomarkers and to establish predictors of response to CPAP.

METHODS

We searched PubMed and the Cochrane Library from inception to May 31, 2017. Randomized controlled trials (RCTs) assessing the efficacy of CPAP on high-sensitivity C-reactive protein (hs-CRP), interleukin 6 (IL-6), tumor necrosis factor- alpha (TNF-α), augmentation index (AIx), pulse wave velocity (PWV), and flow-mediated dilatation (FMD) in patients with OSA were selected by consensus.

RESULTS

We included 15 RCTs comprising 1090 patients in the meta-analysis. The pooled standard mean difference (SMD) of effect of CPAP on hs-CRP was - 0.64 (95% confidence interval (CI) - 1.19 to - 0.09; P = 0.02). CPAP was associated with a reduction in AIx of 1.53% (95% CI, 0.80 to 2.26%; P < 0.001) and a significant increase in FMD of 3.96% (95% CI 1.34 to 6.59%; P = 0.003). Subgroup analyses found CPAP was likely to be more effective in improving FMD levels in severe OSA patients or patients with effective CPAP use ≥ 4 h/night.

CONCLUSIONS

Among patients with OSA, CPAP improves inflammatory marker hs-CRP, arterial stiffness marker AIx, and endothelial function marker FMD. These biomarkers may provide information related to response to treatment. Future studies will need to clarify the efficacy of these biomarkers in assessing cardiovascular risk reduction among OSA treated with CPAP.

Influence of hypoxia induced by sleep disordered breathing in case of hypertension and atrial fibrillation

Sleep disordered breathing (SDB) has been recognized as one of the important causes or factors of worsening for various cerebro- and cardiovascular diseases. On the other hand, a recent large randomized study and meta-analysis about the effect of continuous positive airway pressure (CPAP) indicated no or only minor effects to improve the outcome of SDB patients. Accumulating evidence has indicated that the key factor of the link between SDB and cardiovascular diseases might be hypoxia caused during repetitive long apneic episodes. Hypertension and atrial fibrillation (AF) are two important cardiovascular diseases that relate to SDB and the therapeutic consequences by CPAP treatment have been studied. As for the mechanism that elevates blood pressure during night, stimulation of chemoreceptors by hypoxia and the resultant increase in sympathetic nervous activity is the first step and repetitive hypoxic stimulation changes the characteristics of chemoreceptors and baroreceptors resulting in daytime hypertension. Pathological changes in the atrial muscle in SDB patients might be a result of repetitive hypoxia and atrial expansion. As for triggering AF, several animal studies revealed that the changes in autonomic nervous system caused by hypoxia and negative intra-thoracic pressure might be crucial. However, a recent observational study could not show the relation between SDB and AF. The difference between the previous studies and this negative study seems to exist in the difference of the severity of SDB or the degree of hypoxia. Such a difference might be also one of the reasons why a recent randomized trial to prove the effect of CPAP in cardio- or cerebrovascular patients failed to improve the patient prognosis. Hence, in this review, the relationship between hypoxia and onset or continuation of hypertension and AF will be reconsidered to understand the fundamental and robust relationship between SDB and these cardiovascular diseases.

Association of obstructive sleep apnea with microvascular endothelial dysfunction and subclinical coronary artery disease in a community-based population

Studies have reported an association between obstructive sleep apnea (OSA) and cardiovascular disease (CVD) morbidity and mortality. Proposed mechanisms include endothelial dysfunction and atherosclerosis. We aimed to investigate the associations of OSA with endothelial dysfunction and subclinical atherosclerotic coronary artery disease (CAD), and assess the impact of race on these associations. We used data from the Heart Strategies Concentrating on Risk Evaluation (Heart SCORE) study, a community-based prospective cohort with approximately equal representation of black and white participants. OSA severity was measured in 765 individuals using the apnea-hypopnea index (AHI). Endothelial dysfunction was measured using the Endo-PAT device, expressed as Framingham reactive hyperemia index (F_RHI). Coronary artery calcium (CAC), a marker of subclinical CAD, was quantified by electron beam computed tomography. There were 498 (65%) female participants, 282 (37%) black individuals, and 204 (26%) participants with moderate/severe OSA (AHI ≥15). In univariate models, moderate/severe OSA was associated with lower F_RHI and higher CAC, as well as several traditional CVD risk factors including older age, male sex, hypertension, diabetes, higher body mass index, and lower high-density lipoprotein cholesterol levels. In a multivariable model, individuals with moderate/severe OSA had 10% lower F_RHI and 35% higher CAC, which did not reach statistical significance ( p=0.08 for both comparisons). There was no significant interaction of race on the association of OSA with F_RHI or CAC ( p-value >0.1 for all comparisons). In a community-based cohort comprised of black and white participants, moderate/severe OSA was modestly associated with endothelial dysfunction and subclinical atherosclerotic CAD. These associations did not vary by race.

Angiotensin Receptor Expression and Vascular Endothelial Dysfunction in Obstructive Sleep Apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with vascular endothelial dysfunction (VED) in otherwise healthy patients. The role of renin-angiotensin system (RAS) in the OSA induced VED is not well understood.

METHODS

Recently diagnosed OSA patients with very low cardiovascular disease (CVD) risk (Framingham score <5%) were studied at diagnosis and after 12 weeks of verified continuous positive airway pressure (CPAP) therapy. Participants underwent biopsy of gluteal subcutaneous tissue at baseline and after CPAP. Microcirculatory endothelial expression of angiotensin receptors type-1 (AT-1) and type-2 (AT-2) was measured in the subcutaneous tissue using quantitative confocal microscopy techniques. The ex-vivo effect of AT-1 receptor blockade (ARB) on endothelial superoxide production was also measured before and after CPAP treatment.

RESULTS

In OSA patients (n = 11), microcirculatory endothelial AT1 expression decreased from 873 (200) (fluorescence units) at baseline to 393 (59) units after 12 weeks of CPAP (P = 0.02). AT2 expression did not decrease significantly in these patients (479 (75) to 329 (58) post CPAP (P = 0.08)). The ex-vivo addition of the losartan to the microcirculatory endothelium resulted in decreased superoxide expression in the vascular walls from 14.2 (2.2) units to 4.2 (0.8) P < 0.001; while it had no effect on post-CPAP patient tissue (P = 0.64).

CONCLUSIONS

In OSA patients with no to minimal CVD risk, VED is associated with upregulation of AT-1 expression that is reversible with CPAP. Endothelial oxidative stress was reversible with ARB. RAS activation may play an important role in the development of early CVD risk in OSA patients.

Sleep-disordered breathing and epicardial adipose tissue in patients with heart failure

BACKGROUND AND AIMS

Sleep-disordered breathing (SDB) is common in patients with heart failure (HF), contributes to the progression of cardiac disease, and is associated with adverse prognosis. Previous evidence indicates that epicardial adipose tissue (EAT) is independently associated with sleep apnea in obese individuals. We explored the relationship between SDB and EAT in HF patients.

METHODS AND RESULTS

EAT thickness was assessed by echocardiography in 66 patients with systolic HF undergoing nocturnal cardiorespiratory monitoring. A significantly higher EAT thickness was found in patients with SDB than in those without SDB (10.7 ± 2.8 mm vs. 8.3 ± 1.8 mm; p = 0.001). Among SDB patients, higher EAT thickness was found in both those with prevalent obstructive sleep apnea (OSA) and those with prevalent central sleep apnea (CSA). Of interest, EAT thickness was significantly higher in CSA than in OSA patients (11.9 ± 2.9 vs. 10.1 ± 2.5 p = 0.022). Circulating plasma norepinephrine levels were higher in CSA than in OSA patients (2.19 ± 1.25 vs. 1.22 ± 0.92 ng/ml, p = 0.019). According to the apnea-hypopnea index (AHI), patients were then stratified in three groups of SDB severity: Group 1, mild SDB; Group 2, moderate SDB; Group 3, severe SDB. EAT thickness progressively and significantly increased from Group 1 to Group 3 (ANOVA p < 0.001). At univariate analysis, only left ventricular ejection fraction and AHI significantly correlated with EAT (p = 0.019 and p < 0.0001, respectively). At multivariate analysis, AHI was the only independent predictor of EAT (β = 0.552, p < 0.001).

CONCLUSIONS

Our results suggest an association between the presence and severity of sleep apneas and cardiac visceral adiposity in HF patients.

Physiological consequences of CPAP therapy withdrawal in patients with obstructive sleep apnoea-an opportunity for an efficient experimental model

Randomised controlled trials (RCTs) of continuous positive airway pressure (CPAP) in obstructive sleep apnoea (OSA) are time consuming, and their findings often inconclusive or limited due to suboptimal CPAP adherence in CPAP-naïve patients with OSA. Short-term CPAP withdrawal in patients with prior optimal CPAP adherence results in recurrence of OSA and its consequences. Thus, this experimental model serves as an efficient tool to investigate both the consequences of untreated OSA, and potential treatment alternatives to CPAP. The CPAP withdrawal protocol has been thoroughly validated, and applied in several RCTs focusing on cardiovascular and metabolic consequences of untreated OSA, as well as the assessment of treatment alternatives to CPAP.

Cardiorespiratory interaction with continuous positive airway pressure

The treatment of choice for obstructive sleep apnoea (OSA) is continuous positive airway pressure therapy (CPAP). Since its introduction in clinical practice, CPAP has been used in various clinical conditions with variable and heterogeneous outcomes. In addition to the well-known effects on the upper airway CPAP impacts on intrathoracic pressures, haemodynamics and blood pressure (BP) control. However, short- and long-term effects of CPAP therapy depend on multiple variables which include symptoms, underlying condition, pressure used, treatment acceptance, compliance and usage. CPAP can alter long-term cardiovascular risk in patients with cardiorespiratory conditions. Furthermore, the effect of CPAP on the awake patient differs from the effect on the patients while asleep, and this might contribute to discomfort and removal of the use interface. The purpose of this review is to highlight the physiological impact of CPAP on the cardiorespiratory system, including short-term benefits and long-term outcomes.

Which place of pharmacological approaches beyond continuous positive airway pressure to treat vascular disease related to obstructive sleep apnea?

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of partial or complete upper airway obstruction, occurring during sleep, leading to chronic intermittent hypoxia (IH), which harms the cardiovascular system. OSA is associated with both functional and structural vascular alterations that contribute to an increased prevalence of fatal and non-fatal cardiovascular events. OSA is a heterogeneous disease with respect to the severity of hypoxia, the presence of daytime symptoms, obesity, and cardiovascular comorbidities. Various clusters of OSA phenotypes have been described leading to more highly personalized treatment. The aim of this review is to describe the various therapeutic strategies including continuous positive airway pressure (CPAP), oral appliances, surgery, weight loss, and especially pharmacological interventions that have been evaluated to reduce vascular alterations in both OSA patients and preclinical animal models. Conventional therapies, predominantly CPAP, have a limited impact on vascular alterations in the presence of co-morbidities. A better knowledge of pharmacological therapies targeting IH-induced vascular alterations will facilitate the use of combined therapies and is crucial for designing clinical trials in well-defined OSA phenotypes.

Serum heparanase levels are associated with endothelial dysfunction in patients with obstructive sleep apnea

BACKGROUND AND AIM

Obstructive sleep apnea syndrome (OSAS) is well-known to be associated with high risk for cardiovascular (CV) diseases. Heparanase has been recently shown to be related to increased inflammation and vulnerability of the atherosclerotic plaques. Herein we aimed to investigate the relationships between OSAS, heparanase and endothelial dysfunction.

MATERIALS AND METHODS

A total of 120 patients with varying severity of OSAS and 31 controls without OSAS were enrolled. Flow-mediated dilatation (FMD) was measured as an indicator of endothelial dysfunction. Serum heparanase levels were measured with ELISA.

RESULTS

Serum heparanase levels increased in a stepwise fashion from controls to patients with more severe OSAS. When FMD was compared with controls and various degrees of severity of OSAS, a stepwise decrease in FMD was observed. Serum heparanase levels were found to be significantly associated with apnea hypopnea index (AHI) (r = .57, P < .001) and FMD (r= -.37, P < .001) in patients with OSAS. Serum heparanase levels were significantly associated with hemoglobin-A1c and body mass index in patients with OSAS. Serum heparanase and uric acid levels were independent predictors of FMD in linear regression analysis (R²  = .506, P < .001; P < .001 and P = .001 respectively).

CONCLUSIONS

Serum heparanase levels were significantly increased in patients with OSAS and associated with the severity of OSAS (AHI) and endothelial dysfunction (FMD). Increased heparanase activity in OSAS may be related to increased cardiovascular risk in patients with OSAS.

Association of Mild Obstructive Sleep Apnea With Cognitive Performance, Excessive Daytime Sleepiness, and Quality of Life in the General Population: The Korean Genome and Epidemiology Study (KoGES)

Study Objectives

Research points to impaired cognitive performance in sleep clinic patients with obstructive sleep apnea (OSA). However, inconsistent findings from various epidemiologic studies make this relationship less generalizable. The current study investigated the association between OSA and functional outcome measures, such as cognition, daytime sleepiness, and quality of life, in a Korean general population sample.

Methods

A total of 1492 participants from the Korean Genome and Epidemiology Study (KoGES) were included in the analyses. The presence of OSA measured by overnight polysomnography (PSG) was defined by apnea-hypopnea index (AHI) >5. Cognitive performance was determined with scores from a comprehensive neuropsychological battery. Excessive daytime sleepiness and quality of life were additionally measured through subjective reports.

Results

After adjusting for various demographic and medical characteristics, OSA was independently associated with lower performance in the Digit Symbol Test (52.73 ± 17.08 vs. 58.72 ± 18.03, OSA vs. not, p = .02). Hypoxia measures were not related to cognitive performance. OSA was associated with higher odds of displaying excessive daytime sleepiness (odds ratio = 1.72, 95% CI: 1.05-2.80), but there was no significant relationship between OSA and quality of life.

Conclusions

Cognition was unexpectedly unaffected overall. However, OSA was associated with impairment in a multidomain test that taps skills generally associated with frontal lobe function. The results suggest that research on protective and adaptive brain mechanisms to OSA stress can provide unique insights into the brain-sleep interface. As the study runs longitudinally, it will enable future studies on the impact of OSA on cognitive decline.

Obstructive Sleep Apnea and Retinopathy in Patients with Type 2 Diabetes. A Longitudinal Study

RATIONALE

Obstructive sleep apnea (OSA) is associated with several pathophysiological deficits found in diabetic retinopathy (DR). Hence, it's plausible that OSA could play a role in the pathogenesis of sight-threatening DR (STDR).

OBJECTIVES

To assess the relationship between OSA and DR in patients with type 2 diabetes and to assess whether OSA is associated with its progression.

METHODS

A longitudinal study was conducted in diabetes clinics within two U.K. hospitals. Patients known to have any respiratory disorder (including OSA) were excluded. DR was assessed using two-field 45-degree retinal images for each eye. OSA was assessed using a home-based multichannel cardiorespiratory device.

MEASUREMENTS AND MAIN RESULTS

A total of 230 patients were included. STDR and OSA prevalence rates were 36.1% and 63.9%, respectively. STDR prevalence was higher in patients with OSA than in those without OSA (42.9% vs. 24.1%; P = 0.004). After adjustment for confounders, OSA remained independently associated with STDR (odds ratio, 2.3; 95% confidence interval, 1.1-4.9; P = 0.04). After a median (interquartile range) follow-up of 43.0 (37.0-51.0) months, patients with OSA were more likely than patients without OSA to develop preproliferative/proliferative DR (18.4% vs. 6.1%; P = 0.02). After adjustment for confounders, OSA remained an independent predictor of progression to preproliferative/proliferative DR (odds ratio, 5.2; 95% CI confidence interval, 1.2-23.0; P = 0.03). Patients who received continuous positive airway pressure treatment were significantly less likely to develop preproliferative/proliferative DR.

CONCLUSIONS

OSA is associated with STDR in patients with type 2 diabetes. OSA is an independent predictor for the progression to preproliferative/proliferative DR. Continuous positive airway pressure treatment was associated with reduction in preproliferative/proliferative DR. Interventional studies are needed to assess the impact of OSA treatment on STDR.

Repercusiones cardiovasculares del síndrome de apnea-hipopnea obstructiva del sueño (SAHOS)

En la población de sujetos con síndrome de apnea-hipopnea obstructiva del sueño se describen entidades clínicas cardiovasculares asociadas con esta entidad y que afectan su curso y pronóstico. Dentro de estas se encuentran hipertensión arterial, arritmias, enfermedad coronaria, insuficiencia cardíaca, hipertensión pulmonar y tromboembolismo venoso. Del mismo modo, se describen los mecanismos fisiopatológicos de estas asociaciones, su prevalencia e impacto. Dado que afectan el curso de la enfermedad y, por tanto, la severidad de la misma, estas entidades juegan un papel muy importante en la toma de decisiones al momento de ofrecer el mejor manejo en cada caso, el cual debe ser abordado de forma multidisciplinaria.

Sleep apnoea is common in severe peripheral arterial disease

Background

Atherosclerotic conditions have been demonstrated to be associated with sleep- disordered breathing (SDB). Peripheral arterial disease (PAD) represents severe atherosclerosis with a high mortality. In early stages of PAD a substantial prevalence of sleep apnoea has already been shown. Here, we sought to determine the frequency of undiagnosed sleep apnoea in a homogeneous group of advanced PAD patients undergoing percutaneous revascularization.

Methods

59 consecutive patients (mean age: 71.1 ± 9.8 years, 67.8% males) with PAD in Fontaine stages IIb-IV that underwent percutaneous transluminal angioplasty at our department were enrolled for pre-procedural polygraphy.

Results

Patients appertained to Fontaine clinical stage IIb, III and IV in 54.2%, 23.8% and 22.% of cases, respectively, and were principally intervened for femoropopliteal occlusive disease (71.2% of total study population). Polygraphy revealed sleep apnoea in 48 out of 59 patients (81.4%), of whom 60.4% offered a primarily obstructive-driven genesis. Among those patients with polygraphically confirmed sleep apnoea, mean apnoea hypopnoea index (AHI) and mean oxygen desaturation index (ODI) averaged 28.2 ± 19.5/h and 26.7 ± 18.8/h, respectively. 18 patients even offered an AHI ≥30/h that is indicative of severe sleep apnoea. For obstructive-driven apnoeic events, AHI correlated significantly with PAD severity stages (p = 0.042).

Conclusions

In our PAD collective, sleep apnoea was frequent and obstructive sleep apnoea´s severity correlated with PAD severity stages. Long-term results regarding the vasoprotective impact of CPAP treatment on PAD course remains to be determined.

Verifying the Relative Efficacy between Continuous Positive Airway Pressure Therapy and Its Alternatives for Obstructive Sleep Apnea: A Network Meta-analysis

Obstructive sleep apnea (OSA) is a common breathing disorder, and continuous positive airway pressure (CPAP) therapy together with its alternatives has been developed to treat this disease. This network meta-analysis (NMA) was aimed to compare the efficacy of treatments for OSA. Cochrane Library, MEDLINE, and Embase were searched for eligible studies. A conventional and NMA was carried out to compare all therapies. Sleeping characteristics, including Apnea–Hypopnea Index (AHI), Epworth Sleepiness Scale (ESS), arterial oxygen saturation, and arousal index (AI), and changes of blood pressure were selected as outcomes. A total of 84 studies were finally included after rigorous screenings. For the primary outcomes of AHI and ESS, the value of auto-adjusting positive airway pressure (APAP), CPAP, and oral appliance (OA) all showed statistically reduction compared with inactive control (IC). Similar observation was obtained in AI, with treatments of the three active interventions. A lower effect of IC in SaO₂ was exhibited when compared with APAP, CPAP, and OA. Similar statistically significant results were presented in 24 h systolic blood pressure and 24 h DBP when comparing with CPAP. Our NMA identified CPAP as the most efficacious treatment for OSA patients after the evaluation of sleeping characteristics and blood pressures. In addition, more clinical trials are needed for further investigation due to the existence of inconsistency observed in this study.

Impact of obstructive sleep apnoea and intermittent hypoxia on cardiovascular and cerebrovascular regulation

NEW FINDINGS

What is the topic of this review? This review examines the notion that obstructive sleep apnoea (OSA) and intermittent hypoxia (IH) have hormetic effects on vascular health. What advances does it highlight? Clinical (OSA patient) and experimental animal and human models report that IH is detrimental to vascular regulation. However, mild IH and, by extension, mild OSA also have physiological and clinical benefits. This review highlights clinical and experimental animal and human data linking OSA and IH to vascular disease and discusses how hormetic effects of OSA and IH relate to OSA severity, IH intensity and duration, and patient/subject age. Obstructive sleep apnoea (OSA) is associated with increased risk of cardiovascular and cerebrovascular disease, a consequence attributed in part to chronic intermittent hypoxia (IH) resulting from repetitive apnoeas during sleep. Although findings from experimental animal, and human, models have shown that IH is detrimental to vascular regulation, the severity of IH used in many of these animal studies [e.g. inspired fraction of oxygen (FI,O2) = 2-3%; oxygen desaturation index = 120 events h^-1 ] is considerably greater than that observed in the majority of patients with OSA. This may also explain disparities between animal and recently developed human models of IH, where IH severity is, by necessity, less severe (e.g. FI,O2 = 10-12%; oxygen desaturation index = 15-30 events h^-1 ). In this review, we highlight the current knowledge regarding the impact of OSA and IH on cardiovascular and cerebrovascular regulation. In addition, we critically discuss the recent notion that OSA and IH may have hormetic effects on vascular health depending on conditions such as OSA severity, IH intensity and duration, and age. In general, data support an independent causal link between OSA and vascular disease, particularly for patients with severe OSA. However, the data are equivocal for older OSA patients and patients with mild OSA, because advanced age and short-duration, low-intensity IH have been reported to provide a degree of protection against IH and ischaemic events such as myocardial infarction and stroke, respectively. Overall, additional studies are needed to investigate the beneficial/detrimental effects of mild OSA on the various vascular beds.

Inflammatory responses to acute elevations of carbon dioxide in mice

Health risks are described from elevated indoor air carbon dioxide (CO₂), which often ranges from 1,000 to 4,000 ppm, but the mechanisms are unknown. Here, we demonstrate that mice exposed for 2 h to 2,000 or 4,000 ppm CO₂ exhibit, respectively, 3.4 ± 0.9-fold (SE, n = 6) and 4.1 ± 0.7-fold (n = 10) elevations in circulating microparticles (MPs); neutrophil and platelet activation, and vascular leak in brain, muscle, and distal colon. Interleukin (IL)-1β content of MPs also increases after 2,000 ppm by 3.8 ± 0.6-fold (n = 6) and after 4,000 ppm CO₂ by 9.3 ± 1.1-fold (n = 10) greater than control. CO₂-induced vascular damage is abrogated by treating mice with an antibody to IL-1β or an IL-1β receptor inhibitor. Injecting naïve mice with CO₂-induced MPs expressing a protein found on mature neutrophils recapitulates vascular damage as seen with elevated CO₂, and destruction of MPs in CO₂-exposed mice abrogates vascular injuries without altering neutrophil or platelet activation. We conclude that environmentally relevant elevations of CO₂ trigger neutrophils to generate MPs containing high concentrations of IL-1β that cause diffuse inflammatory vascular injury.NEW & NOTEWORTHY Elevated levels of CO₂ are often found in indoor air and cause adverse health effects, but the mechanisms have not been identified. In a murine model, environmentally relevant levels of CO₂ were found to cause diffuse vascular damage because neutrophils are stimulated to produce microparticles that contain high concentrations of interleukin-1β.

Impact of sleep disordered breathing on short-term post-operative outcome after elective coronary artery bypass graft surgery: a prospective observational study

Sleep disordered breathing (SDB) is common in patients with coronary disease, but its impact on post-operative recovery after coronary artery bypass graft surgery (CABG) is unclear. We therefore determined the effects of SDB on post-operative outcome after elective CABG.

In this prospective two-centre study, 219 patients due to receive elective CABG underwent cardiorespiratory polygraphy for SDB prior to surgery and were monitored for post-operative complications. The primary end-point was a composite of 30-day mortality or major post-operative complications (cardiac, respiratory, surgical, infectious, acute renal failure or stroke). Key secondary end-points were single components of the primary end-point.

SDB was present in 69% and moderate/severe SDB in 43% of the CABG patients. There was no difference in the composite of 30-day mortality or major postoperative complications between patients with and without SDB (OR 0.97, 95% CI 0.49–1.96) and between patients with moderate/severe SDB and no/mild SDB (OR 1.07, 95% CI 0.55–2.06). However, moderate/severe SDB was associated with higher rates of mortality (crude OR 10.1, 95% CI 1.22–83.5), sepsis (OR 2.96, 95% CI 1.17–7.50) and respiratory complications (OR 2.85, 95% CI 1.46–5.55).

Although SDB was not associated with higher overall morbidity/mortality, moderate/severe SDB may increase the risk of death, and septic and respiratory complications, after elective CABG.

Patients with Obstructive Sleep Apnea Display Decreased Flow-Mediated Dilatation: Evidence from a Meta-Analysis

Background

Endothelial dysfunction, which can be measured by flow-mediated dilatation (FMD), is an early clinical marker of atherosclerosis, which is considered to be the main cause of the observed cardiovascular complications in obstructive sleep apnea (OSA) patients. The association between OSA and endothelial dysfunction has been reported in a number of studies; however, the findings are not entirely consistent. Our aim was to meta-analytically synthesize the existing evidence to explore the association between OSA and endothelial dysfunction.

Material/Methods

Data from PubMed, EMBASE, the Cochrane library, and Google Scholar for all trials that investigated the relationship between endothelial dysfunction and OSA were systematically reviewed. The minimum inclusion criteria for the studies were reporting of the Apnea-Hypopnea Index (AHI) and FMD measurements (as an indicator of endothelial dysfunction) for both OSA and control groups. Data from case-control studies that met the inclusion criteria were extracted.

Results

Twenty-eight studies comprising a total of 1496 OSA patients and 1135 controls were included in the meta-analysis. A random-effects model was used. The weighted mean difference in the FMD measurements was −3.07 and the 95% confidence interval was −3.71 to −2.43 (P<0.01). Meta-regression analysis showed that age, sex, body mass index (BMI), blood pressure, glucose, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol did not explain the heterogeneity.

Conclusions

This meta-analysis showed that patients with OSA have decreased FMD, which may contribute to the development of atherosclerosis.

Consequences of Obstructive Sleep Apnea: Cardiovascular Risk of Obstructive Sleep Apnea and Whether Continuous Positive Airway Pressure Reduces that Risk

Obstructive sleep apnea (OSA) is present in up to 25% of otherwise healthy individuals. OSA is associated with intermittent hypoxia, oxidative stress, sympathetic activation, and an inflammatory response. These perturbations mediate the role of OSA as an independent and modifiable risk factor for cardiovascular disease (CVD). OSA can induce CVD or accelerate the progression of CVD into an end-stage disorder, including heart failure and stroke. Current clinical recommendations are based on existing clinical trial data and the clinical experience of our program; current and future clinical trials will help to optimize management of OSA in the setting of CVD.

Sleep apnea in total joint arthroplasty patients and the role for cardiac biomarkers for risk stratification: an exploration of feasibility

Obstructive sleep apnea (OSA) is highly prevalent in patients undergoing total joint arthroplasty (TJA) and is a major risk factor for postoperative cardiovascular complications and death. Recognizing this, the American Society of Anesthesiologists urges clinicians to implement special considerations in the perioperative care of OSA patients. However, as the volume of patients presenting for TJA increases, resources to implement these recommendations are limited. This necessitates mechanisms to efficiently risk stratify patients having OSA who may be susceptible to post-TJA cardiovascular complications. We explore the role of perioperative measurement of cardiac troponins (cTns) and brain natriuretic peptides (BNPs) in helping determine which OSA patients are at increased risk for post-TJA cardiovascular-related morbidity.

Effects of continuous positive airway pressure therapy on plasma aldosterone levels in patients with obstructive sleep apnea: A meta-analysis

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular diseases. Aldosterone was reported to be increased in patients with OSA and correlated with OSA severity. Many studies investigated the effect of continuous positive airway pressure (CPAP) therapy on plasma aldosterone concentrations (PAC) in OSA patients. The results, however, were inconsistent. In the present study, we aimed to evaluate the effects of CPAP therapy on PAC by performing a meta-analysis. Literature search was carried out in electronic databases including PubMed/Medline, Cochrane Library, Embase and Web of Science. Eligible full-text articles were identified, and important data were extracted. Pooled analysis was performed using the STATA12.0 and RevMan 5.2. Standardized mean difference (SMD) was calculated to estimate the treatment effects. A total of eight studies involving 219 patients were included for our final analysis. PAC was found unchanged after CPAP treatment in OSA patients (SMD=-0.36, 95% CI:-0.91 to 0.18, Z=1.32, P=0.19). Meanwhile, CPAP therapy showed no impact on PAC (SMD=-0.21, 95% CI:-0.85 to 0.42, Z=0.66, P=0.51) in a separate meta-analysis including 3 randomized controlled trials. In conclusion, the evidence for the use of CPAP therapy to decrease PAC in OSA patients is low, and further studies are still warranted.

Continuous positive airway pressure treatment does not normalize the prolonged reflex inhibition to inspiratory loading in obstructive sleep apnea

In obstructive sleep apnea (OSA), the short-latency inhibitory reflex (IR) of inspiratory muscles to airway occlusion is prolonged in proportion to the severity of the OSA. The mechanism underlying the prolongation may relate to chronic inspiratory muscle loading due to upper airway obstruction or sensory changes due to chronic OSA-mediated inflammation. Continuous positive airway pressure (CPAP) therapy prevents upper airway obstruction and reverses inflammation. We therefore tested whether CPAP therapy normalized the IR abnormality in OSA. The IR responses of scalene muscles to brief airway occlusion were measured in 37 adult participants with untreated, mostly severe, OSA, of whom 13 were restudied after the initiation of CPAP therapy (usage >4 h/night). Participants received CPAP treatment as standard clinical care, and the mean CPAP usage between initial and subsequent studies was 6.5 h/night (range 4.1-8.8 h/night) for a mean of 19 mo (range 4–41 mo). The duration of the IR in scalene muscles in response to brief (250 ms) inspiratory loading was confirmed to be prolonged in the participants with OSA. The IR was assessed before and after CPAP therapy. CPAP treatment did not normalize the prolonged duration of the IR to airway occlusion (60 ± 21 ms pretreatment vs. 59 ± 18 ms posttreatment, means ± SD) observed in participants with severe OSA. This suggests that the prolongation of IR reflects alterations in the reflex pathway that may be irreversible, or a specific disease trait.

Role of sleep quality in the metabolic syndrome

Emerging evidence has assigned an important role to sleep as a modulator of metabolic homeostasis. The impact of variations in sleep duration, sleep-disordered breathing, and chronotype to cardiometabolic function encompasses a wide array of perturbations spanning from obesity, insulin resistance, type 2 diabetes, the metabolic syndrome, and cardiovascular disease risk and mortality in both adults and children. Here, we critically and extensively review the published literature on such important issues and provide a comprehensive overview of the most salient pathophysiologic pathways underlying the links between sleep, sleep disorders, and cardiometabolic functioning.

Speckle tracking echocardiography in chronic obstructive pulmonary disease and overlapping obstructive sleep apnea

Background

COPD and congestive heart failure represent two disease entities of growing global burden that share common etiological features. Therefore, we aimed to identify the degree of left ventricular (LV) dysfunction in COPD as a function of COPD severity stages and concurrently placed particular emphasis on the presence of overlapping obstructive sleep apnea (OSA).

Methods

A total of 85 COPD outpatients (64.1±10.4 years, 54.1% males) and 20 controls, matched for age, sex, and smoking habits, underwent speckle tracking echocardiography for LV longitudinal strain imaging. Complementary 12-lead electrocardiography, laboratory testing, and overnight screening for sleep-disordered breathing using the SOMNOcheck micro^® device were performed.

Results

Contrary to conventional echocardiographic parameters, speckle tracking echocardiography revealed significant impairment in global LV strain among COPD patients compared to control smokers (−13.3%±5.4% vs −17.1%±1.8%, P=0.04). On a regional level, the apical septal LV strain was reduced in COPD (P=0.003) and associated with the degree of COPD severity (P=0.02). With regard to electrocardiographic findings, COPD patients exhibited a significantly higher mean heart rate than controls (71.4±13.0 beats per minute vs 60.3±7.7 beats per minute, P=0.001) that additionally increased over Global Initiative for Chronic Obstructive Lung Disease stages (P=0.01). Albeit not statistically significant, COPD led to elevated N-terminal pro-brain natriuretic peptide levels (453.2±909.0 pg/mL vs 96.8±70.0 pg/mL, P=0.08). As to somnological testing, the portion of COPD patients exhibiting overlapping OSA accounted for 5.9% and did not significantly vary either in comparison to controls (P=0.07) or throughout the COPD Global Initiative for Chronic Obstructive Lung Disease stages (P=0.49). COPD-OSA overlap solely correlated with nocturnal hypoxemic events, whereas LV performance status was unrelated to coexisting OSA.

Conclusion

To conclude, COPD itself seems to be accompanied with decreased LV deformation properties that worsen over COPD severity stages, but do not vary in case of overlapping OSA.

Obstructive sleep apnea syndrome should be considered as a cause of nocturia in younger patients without other voiding symptoms

INTRODUCTION

This study aimed to evaluate urination frequency among patients with obstructive sleep apnea syndrome (OSAS) and the effect of continuous positive airway pressure (CPAP) treatment.

METHODS

We evaluated 138 men with moderate-to-severe OSAS by using polysomnography. Urination status was assessed at baseline and three months using the International Prostate Symptom Score and Overactive Bladder Symptom Score. Nocturia was defined as ≥2 nighttime urinations and patients were classified into Group A (<50 years old with nocturia), Group B (≥50 years old with nocturia), and Group C (patients without nocturia). OSAS severity and other urinary symptoms were also evaluated.

RESULTS

Patients with nocturia exhibited more severe OSAS, compared to patients without nocturia (apnea-hypopnea index [AHI]: 52.0 vs. 44.7; p=0.021). Group A had the worst AHI, but did not have additional voiding symptoms, compared to Group B (p<0.001). The number of urinations was significantly correlated with OSAS severity in <50-year-old patients (p=0.013). CPAP reduced the number of urinations in Group A (75% of patients) and Group B (90% of patients). Patients with and without improved nocturia exhibited significant differences in their baseline OSAS severity (AHI: 53.7 vs. 37.3; p=0.042).

CONCLUSIONS

OSAS severity was associated with the number of urinations in <50-year-old patients. CPAP decreased the nocturia frequency in 85% of patients with nocturia and was most effective in patients with severe AHI. However, additional studies should evaluate voiding volume in order to elucidate the mechanism of nocturia in patients with OSAS.

Obstructive sleep apnea is independently associated with subclinical coronary atherosclerosis among middle-aged women

PURPOSE

Obstructive sleep apnea (OSA) is associated with coronary disease among men. However, this association is not clear for women. In this study, we evaluate the association between OSA and presence of subclinical atherosclerosis assessed by tomographic coronary calcium score in middle-aged women.

METHODS

We evaluated consecutive women aged between 45 and 65 years in perimenopause or postmenopause period (with menstrual irregularity-amenorrhea > 60 days), without manifest cardiovascular disease (heart failure, coronary disease, and stroke), from two gynecologic clinics. All patients underwent clinical evaluation, computed tomographic examination for coronary artery calcium (CAC > 100 Agatston units), and portable sleep study. Multiple logistic regression models were used to evaluate the association between OSA and CAC, controlling for traditional risk factors including Framingham Risk Score (FRS), body mass index (BMI), and diabetes.

RESULTS

We studied 214 women (age 56 years (52-61); BMI 28 kg/m² (25-31), 25 % diabetes, 62 % hypertension). OSA (apnea-hypopnea index (AHI) ≥5 events/h) was diagnosed in 82 women (38.3 %). CAC was more prevalent in patients with moderate/severe OSA (AHI ≥15 events/h) than in patients without or with mild OSA, 19 % vs 4.5 and 1.6 %, respectively (p < 0.01). Moderate to severe OSA was associated with CAC in unadjusted (odds ratio = 6.25, 95 % CI 1.66-23.52; p < 0.01) and adjusted (odds ratio = 8.19, 95 % CI 1.66-40.32; p = 0.01) logistic regression analysis.

CONCLUSION

Moderate to severe OSA is independently associated with the presence of CAC in middle-aged women. These results reinforce the concept that women are also susceptible to the cardiovascular consequences of OSA.

Endothelial function and carotid intima media thickness in obstructive sleep apnea without comorbidity

PURPOSE

The objective of this study was to evaluate endothelial function and carotid intima media thickness (CIMT) in moderate to severe obstructive sleep apnea (OSA) without comorbidities.

METHODS

It is an observational case control study in which endothelial function was assessed using flow-mediated dilatation (FMD) and peripheral arterial tonometry (PAT), and carotid artery ultrasound was used to measure CIMT in study group subjects that included 20 normotensive, non-diabetic, treatment naïve, and moderate to severe OSA patients, and 20 normotensive, non-diabetic, and non-OSA subjects served as a control group. Study was conducted in Polysomnography Laboratory, Department of Internal Medicine, All India Institute of Medical Sciences (AIIMS) Hospital, New Delhi.

RESULTS

FMD was significantly lower in the moderate to severe OSA group compared to non-OSA group (mean ± SD, 8.3 ± 2.8 vs. 13.4 ± 4.1 %; p = 0.0001). Reactive hyperemia index (RHI) was also significantly lower in the OSA group (1.55 ± 0.27 vs. 2.01 ± 0.48, p = 0.0007). CIMT was observed to be significantly higher in the OSA group compared to the non-OSA group (0.54 ± 0.09 vs. 0.48 ± 0.08 mm; p = 0.049). In the OSA group, FMD, RHI, and CIMT did not show a significant correlation with OSA disease severity indices [apnea hypopnea index (AHI), oxygen desaturation index (ODI), and minimum O₂ saturation].

CONCLUSION

Endothelial function in macrovascular and microvascular circulation is significantly impaired in moderate to severe OSA patients without comorbidities. These patients also show evidence of subclinical atherosclerosis, in the form of increased CIMT.

The Link Between Obstructive Sleep Apnea and Cardiovascular Disease

Obstructive sleep apnea (OSA) is common in the general population and highly prevalent in patients with cardiovascular disease. In this paper, we review (1) the pathophysiological mechanisms of OSA that may causally contribute to cardiovascular disease; (2) current evidence regarding the association between OSA and hypertension, stroke, ischemic heart disease, heart failure, atrial fibrillation, and cardiovascular mortality; and (3) the impact of continuous positive airway pressure (CPAP) treatment on cardiovascular risk factors and outcomes. We emphasize the importance of obesity as a comorbidity of OSA and a confounder in the association between OSA and cardiovascular disease. We also discuss the importance of addressing obesity in patients with OSA, as a strategy to reduce the burden of cardiovascular risk factors in this population. Implications for the approach of patients' OSA in clinical practice and future research directions are discussed.

8-isoprostanes and resistin as markers of vascular damage in non-hypersomnolent obstructive sleep apnoea patients

BACKGROUND

Oxidative stress and inflammation are assumed as the main pathological triggers for vascular damage in hypersomnolent obstructive sleep apnoea (OSA) patients, whereas their exact role in less symptomatic population is currently unknown.

AIM

To determine whether oxidative stress (urinary 8-isoprostane concentration) and inflammation (plasma resistin levels) are associated with vascular damage in non-hypersomnolent (Epworth Sleep Score <11) OSA patients.

METHODS

A total of 325 consecutive patients have undergone standard polysomnography, and 256 of them were diagnosed with OSA. Excessive daytime sleepiness was assessed by the Epworth Sleepiness Scale (ESS). Only 86 patients with ESS <11 participated in the study. The control group was presented by 45 subjects without OSA. Endothelial function was assessed by ultrasonographic measurement of flow-mediated dilatation (FMD). Intima-media thickness (IMT) and ankle-brachial index (ABI) were determined by ultrasonography. Urinary 8-isoprostanes (Cayman Chemical, USA) were measured, applying mass spectrometry. Resistin (RayBio_ Human ResistinCat#:ELH-Resistin-001) plasma levels were detected by ELISA.

RESULTS

In patients with OSA, flow-mediated dilatation was significantly lower than in control subjects (4·62% ±1·9) and (7·1% ±2·8), respectively (P: 0·013). The prevalence of plaques in a.carotis communis was higher in OSA (16% versus 4%). The same is observed regarding a.tibialis posterior (81% vs. 29%). The average IMT and ABI in OSA and in the control group were, respectively, (IMT - 800 µm versus. 666 µm); (ABI -1·06 versus 1·20). Urinary isoprostanes were higher in OSA patients (0·091 versus 0·078) and correlated negatively to FMD (r: -0·825, P: 0·00), IMT (r: -0·324, P: 0·003) and ABI (r: -0·226, P: 0·043). No association between resistin and the degree of vascular injury was found.

CONCLUSIONS

In comparison with the control group, increased prevalence of endothelial dysfunction and vascular damage was established in OSA patients without excessive daytime sleepiness. Urinary 8-isoprostanes (oxidative stress markers) are closely associated with FMD (endothelial dysfunction), IMT and ABI (vascular damage). Resistin plasma levels correlated neither to FMD, nor to IMT or ABI.

Endothelial dysfunction and coronary artery disease: assessment, prognosis, and treatment

Progress in the modification of conventional coronary risk factors and lifestyle behavior has reduced the incidence of atherosclerotic coronary artery disease; nonetheless, it continues to be the leading cause of mortality in the world. This might be attributed to the defective risk stratifying and prevention strategy for coronary artery disease. In the current clinical setting, atherosclerotic coronary artery disease risk is estimated on the basis of identifying and quantifying only traditional risk factors; it does not take into consideration nontraditional risk factors. In addition, most of the prevailing therapies for atherosclerosis are targeted toward traditional risk factors rather than atherosclerosis itself. It is desirable to develop a method that can directly assess the activity of atherogenesis at every moment. Endothelial function is an integrated index of all atherogenic and atheroprotective factors present in an individual including nontraditional factors and heretofore unknown factors, and it is reported to have additional predictive value for future cardiovascular events to traditional risk factors. Moreover, endothelial function has a pivotal role in all phases of atherosclerosis, from initiation to atherothrombotic complication, and is reversible at every phase, indicating that endothelial function-guided therapies might be effective and feasible in cardiovascular practice. Thus, the introduction of endothelial function testing into clinical practice might enable us to innovate individualized cardiovascular medicine. In this review, we summarize the current knowledge on the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function. Finally, we focus on the effects of major antiatherosclerotic disease therapies on endothelial function and argue the possibility of noninvasive assessment of endothelial function aiming at individualized cardiovascular medicine.

Effect of CPAP Withdrawal on myocardial perfusion in OSA: A randomized controlled trial

BACKGROUND AND OBJECTIVE

Obstructive sleep apnoea (OSA) is highly prevalent and associated with an increased incidence of cardiovascular events. Endothelial dysfunction is the proposed causative mechanism. Continuous positive airway pressure (CPAP) is presumed to improve cardiovascular outcome in OSA. CPAP withdrawal was recently shown to lead to peripheral endothelial dysfunction. However, it is not known whether short-term CPAP withdrawal reduces myocardial perfusion in OSA.

METHODS

In this double-blind randomized controlled study, 45 patients with moderate to severe OSA previously adherent to CPAP were assigned to either subtherapeutic or continuing therapeutic CPAP for 2 weeks. The primary outcome was adenosine-induced myocardial blood flow (MBF) as a measure of endothelial function, assessed by (13) N-ammonia positron emission tomography. Secondary outcomes were measures of dermal and renal microvascular function, morning blood pressure (BP) and heart rate.

RESULTS

Despite return of OSA associated with significant increases in BP (+9.1 mm Hg, 95% CI +4.9 to +13.4 mm Hg, P < 0.001) and heart rate (+9.6 bpm, 95% confidence interval (CI) +4.6 to +14.6 bpm, P < 0.001), CPAP withdrawal had no significant effect on maximal myocardial perfusion capacity (hyperaemic MBF -0.01 ml/min/g, 95% CI -0.33 to +0.24 ml/min/g, P = 0.91), nor renal and dermal microvascular function.

CONCLUSION

In patients with OSA, a short-term CPAP withdrawal does not lead to detectable impairment of coronary endothelial function, as has been demonstrated in the brachial artery, despite a clinically relevant increase in BP of nearly 10 mm Hg. There was also no evidence of an impairment of renal or dermal microvascular function.

Arginase-endothelial nitric oxide synthase imbalance contributes to endothelial dysfunction during chronic intermittent hypoxia

OBJECTIVE

Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnoea, is associated with impaired vascular function despite unaltered response to nitric oxide donors. This study addressed whether arginase contributes to the endothelial dysfunction in CIH rats.

METHODS

Adult male Sprague-Dawley rats were exposed for 21 days to CIH (5% oxygen, 12 times/h, 8 h/day). The internal carotid arteries were isolated to study endothelial nitric oxide synthase (eNOS) and arginase-1 levels by western blot and immunohistochemistry, and their vasoactive responses using wire myography. Relaxation to sodium nitroprusside (SNP; nitric oxide donor) in the presence or absence of soluble guanylyl cyclase inhibitor, and acetylcholine with and without a NOS inhibitor [N(G)-nitro-L-arginine (L-NA)] and the arginase inhibitor BEC were determined.

RESULTS

Arteries from the CIH rats presented higher active contraction induced by KCl (3.5 ± 0.4 vs. 2.3 ± 0.2 N/m2), augmented media-to-lumen ratio (∼40%), decreased relaxation to acetylcholine (12.8 ± 1.5 vs. 30.5 ± 4.6%) and increased sensitivity to SNP (pD2 7.3 ± 0.1 vs. 6.7 ± 0.1). Arginase inhibition reversed the impaired acetylcholine-induced relaxation in CIH arteries (49.5 ± 7.4%), an effect completely blocked by L-NA. In the carotid arteries, arginase-1 protein level was increased, whereas eNOS levels decreased in the CIH arteries.

CONCLUSION

The current results suggest that endothelial dysfunction in CIH-induced hypertension may result from imbalanced arginase-1 to eNOS expression, vascular remodelling and increased contractile capacity, rather than decreased vascular response to nitric oxide.

Effect of CPAP on New Endothelial Dysfunction Marker, Endocan, in People With Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is associated with increased cardiovascular (CV) morbidity and mortality. Endocan is a surrogate endothelial dysfunction marker that may be associated with CV risk factors. In this study, we tested whether serum endocan is a biomarker for OSA. Serum endocan levels were measured at baseline in 40 patients with OSA and 40 healthy controls and after 3 months of continuous positive airway pressure (CPAP) treatment in the patients with OSA. All participants were evaluated by full polysomnography. Flow-mediated dilatation (FMD) and carotid intima media thickness (cIMT) were measured in all participants. Endocan levels were significantly higher in patients with OSA than in healthy controls. After adjusting confounders, endocan was a good predictor of OSA. Endocan levels correlated with OSA severity (measured by the apnea-hypopnea index [AHI]). After 3 months of CPAP treatment, endocan levels significantly decreased. Endocan levels were significantly and independently correlated with cIMT and FMD after multiple adjustments. The cIMT and FMD also had significant and independent correlation with AHI. Endocan might be a useful marker for the predisposition of patients with OSA to premature vascular disease.

Sleep Characteristics in Early Stages of Chronic Kidney Disease in the HypnoLaus Cohort

STUDY OBJECTIVES

To evaluate the association between early stages of chronic kidney disease (CKD) and sleep disordered breathing (SDB), restless legs syndrome (RLS), and subjective and objective sleep quality (SQ).

METHODS

Cross-sectional analysis of a general population-based cohort (HypnoLaus). 1,760 adults (862 men, 898 women; age 59.3 (± 11.4) y) underwent complete polysomnography at home.

RESULTS

8.2% of participants had mild CKD (stage 1-2, estimated glomerular filtration rate [eGFR] ≥ 60 mL/min/1.73 m(2) with albuminuria) and 7.8% moderate CKD (stage 3, eGFR 30-60 mL/min/1.73 m(2)). 37.3% of our sample had moderate-to-severe SDB (apnea-hypopnea index [AHI] ≥ 15/h) and 15.3% had severe SDB (AHI ≥ 30/h). SDB prevalence was positively associated with CKD stages and negatively with eGFR. In multivariate analysis, age, male sex, and body mass index were independently associated with SDB (all P < 0.001), but kidney function was not. The prevalence of RLS was 17.5%, without difference between CKD stages. Periodic leg movements index (PLMI) was independently associated with CKD stages. Subjective and objective SQ decreased and the use of sleep medication was more frequent with declining kidney function. Older age, female sex, and the severity of SDB were the strongest predictors of poor SQ in multivariate regression analysis but CKD stage was also independently associated with reduced objective SQ.

CONCLUSIONS

Patients with early stages of CKD have impaired SQ, use more hypnotic drugs, and have an increased prevalence of SDB and PLM. After controlling for confounders, objective SQ and PLMI were still independently associated with declining kidney function.

A clinical approach to obstructive sleep apnea as a risk factor for cardiovascular disease

Obstructive sleep apnea (OSA) is associated with cardiovascular risk factors, cardiovascular diseases, and increased mortality. Epidemiological studies have established these associations, and there are now numerous experimental and clinical studies which have provided information on the possible underlying mechanisms. Mechanistic proof-of-concept studies with surrogate endpoints have been performed to demonstrate that treatment of OSA by continuous positive airway pressure (CPAP) has the potential to reverse or at least to attenuate not only OSA but also the adverse cardiovascular effects associated with OSA. However, no randomized studies have been performed to demonstrate that treatment of OSA by CPAP improves clinical outcomes in patients with cardiovascular risk factors and/or established cardiovascular disease and concomitant OSA. In the present review, we summarize the current knowledge on the role of OSA as a potential cardiovascular risk factor, the impact of OSA on cardiac function, the role of OSA as a modifier of the course of cardiovascular diseases such as coronary artery disease, atrial fibrillation, and heart failure, and the insights from studies evaluating the impact of CPAP therapy on the cardiovascular features associated with OSA.

Cerebral hemodynamics is altered in patients with sleep apnea/hypopnea syndrome

According to recent epidemiologic studies, patients with sleep apnea/hypopnea syndrome (SAHS) are at increased risk of cardiovascular diseases, including stroke. However, the mechanisms are not well defined. Nocturnal apneas can trigger acute cerebral ischemia in predisposed patients and impaired vasodilatation is present in SAHS, but few studies have explored vascular cerebral dysfunction and often gave inconclusive results. The aims of our study were to assess whether patients with SAHS have impairment of cerebral hemodynamics with respect to controls, and to investigate a possible relationship with clinical data. We studied two groups, one of 76 SAHS patients and another one of 76 non-SAHS subjects matched for age, sex and main cardiovascular risk factors. All participants underwent a daytime transcranial Doppler study of right middle cerebral artery to record cerebral blood flow velocity and cerebrovascular reactivity by means of breath-holding test (BHT). SAHS patients have a reduction in mean cerebral blood flow velocity (MFV) (52 ± 9 vs 60 ± 12 cms/s, p < 0.001) and BHT (31 ± 12 vs 36 ± 11 %, p = 0.005) when compared to non-SAHS controls. Moreover, MFV correlated negatively with the presence of coronary disease, and BHT with female sex and arterial pressure. On the other hand, in the SAHS group, MFV correlated negatively with oxygen desaturation severity. Patients with SAHS have impaired MFV and cerebrovascular reactivity when compared to controls. Interestingly, poorly controlled or unknown hypertension and severe nocturnal hypoxemia caused additional cerebral hemodynamic disturbances to these patients.