Decreased plasma levels of nitric oxide derivatives in obstructive sleep apnoea: response to CPAP therapy

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Obstructive sleep apnoea syndrome: translating science to clinical practice

OSA syndrome is characterized by recurring episodes of upper airway (UA) obstruction during sleep. The UA is subjected to collapse when the negative airway pressure generated by inspiratory activity of the diaphragm and intercostal muscles exceeds the force produced by the UA dilating muscles. Factors that reduce UA calibre lead to increased UA resistance with the generation of a more negative pharyngeal pressure during inspiration, and thereby predispose to UA occlusion during sleep. As a consequence, UA dilating muscles must contract more forcefully to maintain a patent UA, which may predispose to fatigue. Nasal CPAP counteracts these collapsing forces and is associated with resting of the UA muscles. The more recent development of auto-adjusting CPAP (APAP) is a reflection of the understanding that the pressure required to prevent UA collapse fluctuates throughout the night and results in a lower mean pressure that may be more comfortable for some patients. The predominant morbidity of the OSA syndrome is cardiovascular and there is growing understanding of the basic mechanisms involved. Intermittent hypoxia appears to play a central role by activating transcription factors that predispose to atherogenesis, particularly NFkappaB. Sympathetic overactivity also appears to play an important role but the mechanisms involved are unclear.

Circulating adrenomedullin in obstructive sleep apnoea

Adrenomedullin (AM) is a potent endothelial-derived vasodilator secreted under the influence of various stimuli such as hypoxia, shear stress and cytokines. As all of these stimuli might be active under the conditions of obstructive sleep apnoea (OSA), we hypothesized that vascular AM production is increased in these patients. The study included 41 consecutive OSA patients and 28 control subjects without sleep-disordered breathing who were recruited from a pool of patients hospitalized for other reasons. Both groups were matched for anthropometric and comorbid factors. In all patients, i.e. OSA and controls, peripheral venous blood samples were taken at 07:00 hours after diagnostic polysomnography. In subsets of OSA patients, this was repeated after two nights of continuous positive airway pressure (CPAP) therapy (n = 28) and after several months of constant CPAP use (n = 11). The controls and the untreated OSA patients did not have serial blood sampling. In all blood samples, plasma AM levels were measured by an enzyme immunoassay kit. At baseline, the OSA patients had markedly elevated AM concentrations when compared to the controls. There were no differences between normo- and hypertensive OSA patients. After two nights of CPAP therapy, AM levels significantly decreased. Patients on long-term CPAP treatment showed complete normalization of plasma AM concentrations. In conclusion, this pilot study suggests that circulating AM is increased in untreated OSA irrespective of coexistent arterial hypertension and declines after CPAP therapy. AM upregulation might be considered as an adaptive mechanism to counteract the emergence of OSA-related cardiovascular disease.

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

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

Why a polysomnogram should become part of the diagnostic evaluation of stroke and transient ischemic attack

Neurologists need to recognize, diagnose, and treat obstructive sleep apnea (OSA) in patients with stroke or transient ischemic attack (TIA). Increasing medical evidence suggests that OSA is an independent risk factor for stroke and TIA. Stroke (or TIA) is more likely a cause, rather than a consequence, of OSA because PSG studies have shown: 1) apneas in stroke are typically obstructive, not central or Cheyne-Stokes in type; 2) apneas are just as frequent and severe in patients with either TIA or stroke; 3) OSA severity is not influenced by the acuteness or location of the stroke; 4) untreated OSA patients have more strokes, stroke morbidity, and mortality than those who are treated. OSA alone can induce hypertension, especially in younger men. A causal relationship has recently been demonstrated between OSA and hypertension. A distinctive feature of OSA-induced hypertension is loss of the normal nighttime fall in blood pressure ("nondippers"). Data from the Sleep Heart Health Study showed a dose-response association between OSA severity and the presence of hypertension 4 years later. Hypertension or ischemic heart disease usually develops in untreated patients with OSA over time without particular worsening of OSA. Studies have shown sleep itself is not a risk factor for stroke because most stroke and TIAs begin between 6 am and noon, while the individual is awake. However, OSA promptly be considered in stroke beginning during sleep because 88% of strokes that develop during sleep occur in "nondippers." Premature death in OSA patients is most often cardiovascular, but occurs while the patients are awake. The risk of myocardial infarction is increased 20-fold in untreated OSA. Treating OSA patients with continuous positive airway pressure can prevent or improve hypertension, reduce abnormal elevations of inflammatory cytokines and adhesion molecules, reduce excessive sympathetic tone, avoid increased vascular oxidative stress, reverse coagulation abnormalities, and reduce leptin levels. If all this can be achieved by a polysomnogram, then this test should become part of a neurologist's armamentarium for stroke and TIA.

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

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

Obesity-related cardiovascular disease: implications of obstructive sleep apnea

Obesity and obstructive sleep apnea (OSA) often coexist. OSA has been linked to cardiovascular disease. Thus, OSA may contribute to the cardiovascular consequences of obesity. In this review, we explore clinical and pathophysiological interactions between obesity, cardiovascular disease and OSA. We discuss the mechanisms whereby OSA may contribute to hypertension, atherosclerosis, insulin resistance and atrial fibrillation associated with obesity, and emphasize the potential implications for understanding why only a subgroup of obese patients develop cardiovascular disease. Identification of the OSA-dependent and OSA-independent pathways in the cardiovascular pathophysiology of obesity may hold clinical and therapeutic promise.

Obstructive Sleep Apnea Syndrome

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Treatment of obstructive sleep apnoea leads to improved microvascular endothelial function in the systemic circulation

BACKGROUND

Obstructive sleep apnoea (OSA) is a common and potentially reversible cause of systemic hypertension. The mechanisms whereby OSA leads to hypertension and the effects of treatment on arterial function, however, are not well established. Microvascular arterial endothelial and smooth muscle function was assessed in subjects with OSA before and after treatment with continuous positive airways pressure (CPAP).

METHODS

Ten subjects of mean (SE) age 49 (8) years with at least moderately severe OSA had detailed forearm vascular reactivity studies before and after 3 months of CPAP treatment. The systemic circulation was assessed by measuring brachial artery pressure, flow and resistance responses to intra-arterial infusions of acetylcholine (ACh; an endothelium dependent vasodilator), sodium nitroprusside (SNP; an endothelium independent vasodilator), L-NMMA (a nitric oxide (NO) antagonist), and L-arginine (the substrate for NO).

RESULTS

Before CPAP, ACh and SNP infusions increased forearm blood flow in a dose dependent manner (p<0.01). After CPAP, endothelium dependent dilation to ACh was significantly increased (434 (23)% of baseline after CPAP v 278 (20)% before CPAP, p<0.001), whereas SNP induced dilation was unchanged. Resting NO production was higher after CPAP, evidenced by a significantly greater reduction in basal flow by L-NMMA (p=0.05). L-Arginine reversed the effect of L-NMMA in all cases.

CONCLUSION

In patients with OSA, treatment with CPAP improves baseline endothelial NO release and stimulates endothelium dependent vasorelaxation in the systemic circulation. This is a potential mechanism for improving systemic and vascular function in patients with OSA treated with CPAP.

Sleep-disordered breathing and cerebrovascular disease: a mechanistic approach

The observations described in this article point to the existence of increased oxidative stress and systemic inflammation in sleep apnea and have paved the way for establishing sleep apnea as an independent risk factor for cardio- and cerebrovascular morbidities. The proposed course of events is summarized in Fig. 1. It is suggested that hypoxia/reoxygenation,characteristic of sleep apnea, promotes the formation of ROS, particularly during the reoxygenation period, and can be deleterious to cells and tissues. ROS, however, regulate the activation of critical transcription factors that are redox sensitive, resulting in increased expression of sets of genes that encode proteins essential to adaptation to hypoxia (via hypoxia inducible factor I [hypoxia inducible factor-la]). Yet, redox-sensitive transcription factors (NFKB and AP-1) that elicit inflammatory pathways also are activated, thereby affecting inflammatory and immune responses by promoting activation of endothelial cells, leukocytes, and platelets. These activated cells express adhesion molecules and proinflammatory cytokines that may lead to endothelial injury and dysfunction and consequently to the development of cardio- and cerebrovascular morbidities. These may be exaggerated in patients who have sleep apnea in response to the intermittent hypoxia.

Inflammatory aspects of sleep apnea and their cardiovascular consequences

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

Antioxidant vitamin C improves endothelial function in obstructive sleep apnea

RATIONALE

Obstructive sleep apnea (OSA) is associated with oxidative stress, endothelial dysfunction, and increased cardiovascular morbidity and mortality.

OBJECTIVE

We tested the hypothesis that endothelial dysfunction in patients with OSA is linked to oxidative stress.

METHODS

In the present study, we measured flow-mediated dilation (FMD) of the brachial artery by ultrasound in 10 otherwise healthy, untreated patients with OSA and 10 age-and sex-matched control subjects without sleep-disordered breathing before and after intravenous injection of the antioxidant vitamin C. The investigator performing the FMD measurements was blinded to the status of the patients.

RESULTS

When compared with control subjects, baseline FMD was significantly reduced in the patients with OSA. After intravenous injection of 0.5 g vitamin C, vasoreactivity remained unchanged in the control subjects. In the patients with OSA, ascorbate led to an increase in FMD to a level comparable to that observed in the control group.

CONCLUSION

The reduced endothelial-dependent vasodilation in untreated patients with OSA acutely improves by the free radical scavenger vitamin C. These results are in favor of oxidative stress being responsible for the endothelial dysfunction in OSA. Antioxidant strategies should be explored for the treatment of OSA-related cardiovascular disease.

The severity of oxygen desaturation is predictive of carotid wall thickening and plaque occurrence

STUDY OBJECTIVES

To characterize carotid intima-media thickness (IMT) and plaque occurrence in patients with newly diagnosed obstructive sleep apnea (OSA) without known cardiovascular disease.

DESIGN

Prospective study.

SETTING

Sleep Laboratory and Department of Cardiology of Grenoble University Hospital.

PATIENTS AND INTERVENTION

OSA syndrome is associated with an increased cardiovascular risk. Carotid IMT is recognized as a marker of preclinic atheroma. A small number of studies have analyzed large-artery wall modifications in OSA syndrome. Eighty-three patients (74 men; mean age +/- SD, 48 +/- 11 years; mean body mass index, 27.4 +/- 4.2 kg/m(2)) were included. Mean respiratory disturbance index was 40.7 +/- 19.2/h, mean nocturnal arterial oxygen saturation (Sao(2)) was 93.1 +/- 2.0%, and mean percentage of recording time spent at Sao(2) < 90% was 8.6 +/- 16.8%. Clinical BP was measured following European Society of Hypertension/European Society of Cardiology recommendations, and 24-h ambulatory BP monitoring was assessed. Ultrasonography was used to determine the carotid IMT and atheromatous plaque occurrence.

MEASUREMENTS AND RESULTS

Twenty-five of 83 patients (30%) had carotid wall hypertrophy (IMT > 0.8 mm). In a logistic regression model, mean nocturnal Sao(2) < 92% (odds ratio [OR], 3.9; 95% confidence interval [CI], 1.1 to 12.7) was associated with carotid wall hypertrophy. ORs were even higher after adjustment for BP status (OR, 10.6; 95% CI, 1.6 to 50.9 in normotensive patients) and glucose levels (OR, 4.5; 95% CI, 1.0 to 20.9). Mean nocturnal Sao(2) < 92% and minimal nocturnal Sao(2) < 80% (ORs, 3.1 and 3.1; 95% CIs, 1.0 to 9.4 and 1.0 to 8.5, respectively) were associated with the presence of carotid plaque formation independently of the BP status (hypertensive or normotensive).

CONCLUSIONS

The severity of oxygen desaturation appears to be one of the best predictors for carotid IMT and plaque occurrence in OSA patients without known cardiovascular disease. Thus, carotid IMT and plaque formation appeared as early cardiovascular consequences in OSA patients.

Atrial overdrive pacing for the obstructive sleep apnea-hypopnea syndrome

BACKGROUND

The role of atrial overdrive pacing (AOP) in sleep apnea remains uncertain. We prospectively evaluated the effect of AOP after 24 hours and after one month in patients with the obstructive sleep apnea-hypopnea syndrome and compared it with the use of nasal continuous positive airway pressure (n-CPAP).

METHODS

We studied 16 patients with a moderate or severe case of the obstructive sleep apnea-hypopnea syndrome (baseline mean apnea-hypopnea index, 49) and normal left ventricular systolic function in whom a dual-chamber pacemaker had been implanted. After 48 hours, the patients were randomly assigned to AOP (pacing at 15 bpm above the spontaneous mean nocturnal heart rate) or backup atrial pacing (pacing at a heart rate below 40 bpm); the latter group began n-CPAP therapy one day later. After one month, the two groups switched therapies and were followed for an additional month. Polysomnographic studies were performed at baseline, on the first night after randomization, at crossover, and at the end of the study.

RESULTS

During AOP, no significant changes were observed in any of the respiratory variables measured. The change in the apnea-hypopnea index at one month with AOP was +0.2 (95 percent confidence interval, -2.7 to +2.3; P=0.87). In contrast, all variables improved significantly after one month of n-CPAP (change in the apnea-hypopnea index, -46.3; 95 percent confidence interval, -56.2 to -36.5; P<0.001).

CONCLUSIONS

Nasal continuous positive airway pressure therapy is highly effective for the treatment of the obstructive sleep apnea-hypopnea syndrome, whereas AOP has no significant effect.

[CPAP as adjunctive treatment option for chronic heart failure]

Chronic heart failure with its age-dependent prevalence and incidence is one of the most frequent diseases. Due to high mortality and morbidity there is the necessity of early diagnosis and therapeutic measures being as causal as possible. The medical graded therapy is based on the combination of ACE-inhibitors/AT1-blockers, beta-blockers, diuretics and digitalis. Cardiac resynchronization therapy represents a novel option of treatment for only 25% of patients. Nevertheless the prognosis of patients with chronic heart failure with conventional medical therapy is remaining poor. Additional improvement in the treatment of patient with chronic heart failure remains a priority medical task. The results of this case report argues for CPAP as further adjunctive treatment option in patients with chronic heart failure.

Heart failure and sleep apnoea: to sleep perchance to dream

Heart failure and sleep apnoea are major health problems with an increasingly recognized association; evidence suggests that sleep apnoea may play a role in the progression of heart failure. However, confounding factors such as obesity, hypertension and coronary heart disease make this relationship uncertain and an independent correlation remains unproven. Diagnosis of sleep apnoea is suboptimal, as it is often asymptomatic and polysomnography is expensive and time-consuming. A simple and reliable screening protocol is required. All heart failure patients should be considered to be at high risk of sleep apnoea, as this association might be linked to adverse outcome. Continuous positive airway pressure has shown some beneficial effects, but long-term outcome and improvement in survival remains to be demonstrated. Despite recent advances in the understanding of the complex relationship between heart failure and sleep apnoea, there are a number of areas requiring further investigation, which may have important implications for the management and prognosis of a significant number of patients.

Predictors of erectile function improvement in obstructive sleep apnea patients with long-term CPAP treatment

The long-term effect of treatment with continuous positive airway pressure (CPAP) on erectile function was assessed in 60 patients with obstructive sleep apnea syndrome (OSAS). Severity of OSAS was evaluated by respiratory disturbance index (RDI) and minimal oxygen saturation (OxiMin). Severity of erectile dysfunction (ED) was assessed with the five question International Index of Erectile Function (IIEF-5) before and after CPAP treatment. Subjects were categorized into three groups on the basis of the change in IIEF-5 score: Group 1, no change (n=37); Group 2, improvement from 10+/-5.65 to 19.1+/-5.7, P<0.01 (n=12); Group 3, worsening from 19.9+/-4.7 to 9.5+/-7.8, P<0.01 (n=11). Group 2 had significantly higher RDI and lower OxiMin than the other groups, and was also more compliant and satisfied with CPAP. Change in IIEF-5 with CPAP treatment was negatively correlated (Pearson coefficient) with OxiMin (r=-0.374), and positively correlated with adherence to CPAP treatment (r=0.689). In conclusion, in selected patients, CPAP treatment for OSAS may by itself have a positive effect on erectile function by improving respiration during sleep. Predictors of erectile improvement include high RDI, low OxiMin, and CPAP compliance.

Os radicais livres de oxigênio e as doenças pulmonares

Os radicais livres de oxigênio são moléculas que apresentam elétrons não pareados em sua órbita externa, capazes de transformar outras moléculas com as quais se encontram, como proteínas, carbohidratos, lípides e o ácido desoxirribonucleico. Essas moléculas são geradas em situações clínicas onde microambientes de hipóxia são seguidos por microambientes de reoxigenação. Nesse grupo estão o choque hemodinâmico, a septicemia, a resposta inflamatória sistêmica, as hepatites fulminantes, o transplante de órgãos, e a insuficiência respiratória, entre outras condições. Neste trabalho discutimos os principais conceitos sobre os radicais livres de oxigênio: os principais tipos, sua formação e a forma como atuam sobre todas as estruturas celulares provocando lesão tecidual significativa. Os principais sistemas de defesa antioxidante existentes para combater o estresse oxidativo são comentados, com destaque para a glutationa, superóxido dismutase, catalase, glutationa peroxidase e N-acetilcisteína. A influência dos radicais livres de oxigênio sobre as principais doenças pulmonares também é discutida, com ênfase nos produtos do cigarro, doença pulmonar obstrutiva crônica, asma, apnéia obstrutiva do sono e síndrome do desconforto respiratório agudo.

[Functional dynamics of the right ventricle and pulmonary circulation in obstructive sleep apnea. Therapeutic consequences]

Obstructive sleep apnea (OSA) is common with an incidence of at least 500,000 patients in the German population. Typical symptoms are daytime sleepiness, headache in the morning, and snoring. Presumably obstructive sleep apnea via various mechanisms increases cardiovascular morbidity. Hypoxemia causes nocturnal hypertension in most of the patients. Nevertheless, about 20% of the patients develop daytime pulmonary hypertension and right heart dysfunction. Clinical and animal studies demonstrated right ventricular hypertrophy as a consequence of intermittent hypoxemia and pulmonary hypertension. Right ventricular hemodynamics differ essentially from left ventricular hemodynamics. Right ventricular function is substantially influenced by right ventricular afterload, which is mainly determined by pulmonary vascular resistance, and slightly influenced by preload. Application of continuous positive airway pressure (CPAP) via a nose mask normalizes nocturnal breathing disorders and reduces pre- and afterload, especially in patients with cardiomegaly. Therefore, CPAP generates positive effects on the myocardium.

Circulating free nitrotyrosine in obstructive sleep apnea

Obstructive sleep apnea (OSA) has been increasingly linked to cardiovascular disease, endothelial dysfunction, and oxidative stress, generated by repetitive nocturnal hypoxemia and reperfusion. Circulating free nitrotyrosine has been reported as a novel biomarker of nitric oxide (NO)-induced oxidative/nitrosative stress. Nitrosative stress has been implicated as a possible mechanism for development of cardiovascular diseases. We tested the hypothesis that repetitive severe hypoxemia resulting from OSA would increase NO-mediated oxidative stress. We studied 10 men with newly diagnosed moderate to severe OSA who were free of other diseases, had never been treated for OSA, and were taking no medications. Nitrotyrosine measurements, performed by liquid chromatography-tandem mass spectrometry, were made before and after untreated apneic sleep. We compared free nitrotyrosine levels in these patients with those obtained at similar times in 10 healthy male control subjects without OSA, with similar age and body mass index. Evening baseline nitrotyrosine levels were similar before sleep in the control and OSA groups [0.16 +/- 0.01 and 0.15 +/- 0.01 ng/ml, respectively, P = not significant (NS)]. Neither normal nor disturbed apneic sleep led to significant changes of plasma nitrotyrosine (morning levels: control group 0.14 +/- 0.01 ng/ml; OSA group 0.15 +/- 0.01 ng/ml, P = NS). OSA was not accompanied by increased circulating free nitrotyrosine either at baseline or after sleep. This observation suggests that repetitive hypoxemia during OSA does not result in increased NO-mediated oxidative/nitrosative stress in otherwise healthy subjects with OSA.

Erectile dysfunction in men with obstructive sleep apnea syndrome: a randomized study of the efficacy of sildenafil and continuous positive airway pressure

The aim of this study was to compare the efficacy of sildenafil and continuous positive airway pressure (CPAP) in men with erectile dysfunction (ED) and obstructive sleep apnea syndrome (OSAS). In all, 30 men were randomly treated for 12 weeks either with sildenafil 100 mg before intercourse (15 men) or CPAP during night time sleep (15 men). Under sildenafil, 97/180 (53.9%) of attempted intercourses were successful compared to 33/138 (23.9%) under CPAP. The mean IIEF (erectile function domain score) was 12.9 and 9.3 after sildenafil and CPAP treatment, respectively (P=0.007), compared to 7.9 and 7 at baseline. In all, 53.3% of patients were satisfied with sildenafil and 20% with CPAP for ED treatment (P=0.058). Although sildenafil was superior to CPAP, comorbidities and OSAS per se possibly resulted in a lower effectiveness of sildenafil compared to that in the general population of ED men. While about half of the patients were not satisfied even with the more effective treatment, we conclude that a combination of the two therapeutic tools or a different therapeutic mode should be studied further.

Hypertension and obstructive sleep apnea

Obstructive sleep apnea is a common disorder that is often unrecognized and underappreciated. Emerging evidence suggests that there is a causal link between obstructive sleep apnea and hypertension. This relationship appears to be independent of other comorbidities that have been previously linked to hypertension, such as obesity. The majority of studies support the contention that alleviation of sleep disordered breathing has a clinically significant beneficial impact on decreasing both nighttime and daytime blood pressure. A pathophysiologic basis for patients with sleep apnea having an increased risk for hypertension is not fully elucidated. However, there is consistent evidence that autonomic mechanisms are implicated. Sympathetic activation along with humoral responses to repetitive episodes of hypoxemia and apnea over the longer term may cause vasoconstriction, endothelial dysfunction, and possibly hypertension. Patients with sleep apnea are often obese and may be predisposed to weight gain. Hence, obesity may further contribute to hypertension in this patient population.

Chronic intermittent hypoxia impairs endothelium-dependent dilation in rat cerebral and skeletal muscle resistance arteries

The goal of the present study was to evaluate the effects of relatively short-term chronic intermittent hypoxia (CIH) on endothelial function of resistance vessels in the skeletal muscle and cerebral circulations. Sprague-Dawley rats were exposed to 14 days of CIH (10% fraction of inspired oxygen for 1 min at 4-min intervals, 12 h/day, n = 6). Control rats (n = 6) were housed under normoxic conditions. After 14 days, resistance arteries of the gracilis muscle (GA) and middle cerebral arteries (MCA) were isolated and cannulated with micropipettes, perfused and superfused with physiological salt solution, and equilibrated with 21% O2-5% CO2 in a heated chamber. The arteries were pressurized to 90 mmHg, and vessel diameters were measured via a video micrometer before and after exposure to ACh (10-7-10-4 M), sodium nitroprusside (10-6 M), and acute reduction of Po2 in the perfusate/superfusate (from 140 to 40 mmHg). ACh-induced dilations of GA and MCA from animals exposed to CIH were greatly attenuated, whereas responses to nitroprusside were similar to controls. Dilations of both GA and MCA in response to acute reductions in Po2 were virtually abolished in animals exposed to CIH compared with controls. These findings suggest that exposure to CIH reduces the bioavailability of nitric oxide in the cerebral and skeletal muscle circulations and severely blunts vasodilator responsiveness to acute hypoxia.

Nitric oxide (NO) and obstructive sleep apnea (OSA)

Nitric oxide (NO) and obstructive sleep apnea are inseparable. Obstructive sleep apnea could be described as the intermittent failure to transport the full complement of nasal NO to the lung with each breath. There NO matches perfusion to ventilation. NO is utilized by the efferent pathways that control the unequal, inspiratory battle between the pharyngeal dilators and the closing negative pressures induced by the thoracic musculature. Recurrent cortical arousals are a major short-term complication, and the return to sleep after each arousal uses NO. The long-term complications, namely hypertension, myocardial infarction, and stroke, might be due to the repeated temporary dearth of NO in the tissues, secondary to a lack of oxygen, one of NO's two essential substrates.

Cardiovascular consequences of obstructive sleep apnea

Sleep apnea is associated with several cardiovascular disease conditions. A causal relationship between sleep apnea and each of these diseases is likely, but remains to be proven. The clearest evidence implicating OSA in the development of new cardiovascular disease involves data that show an increased prevalence of new hypertension in patients with OSA followed over 4 years [3]. Circumstantial evidence and data from small study samples suggest that OSA, in the setting of existing cardiovascular disease, may exacerbate symptoms and accelerate disease progression. The diagnosis of OSA always should be considered in patients with refractory heart failure, resistant hypertension, nocturnal cardiac ischemia, and nocturnal arrhythmias, especially in individuals with risk factors for sleep apnea (e.g., central obesity, age, and male gender). Treating sleep apnea may help to achieve better clinical control in these diseases and may improve long-term cardiovascular prognosis.

Obstructive sleep apnea and cardiovascular disease

Obstructive sleep apnea (OSA) is a common disorder associated with an increased risk of cardiovascular disease and stroke. As it is strongly associated with known cardiovascular risk factors, including obesity, insulin resistance, and dyslipidemia, OSA is an independent risk factor for hypertension and has also been implicated in the pathogenesis of congestive cardiac failure, pulmonary hypertension, arrhythmias, and atherosclerosis. Obesity is strongly linked to an increased risk of OSA, and weight loss can reduce the severity of OSA. The current standard treatment for OSA-nasal continuous positive airway pressure (CPAP)-eliminates apnea and the ensuing acute hemodynamic changes during sleep. Long-term CPAP treatment studies have shown a reduction in nocturnal cardiac ischemic episodes and improvements in daytime blood pressure levels and left ventricular function. Despite the availability of effective therapy, OSA remains an underdiagnosed and undertreated condition. A lack of physician awareness is one of the primary reasons for this deficit in diagnosis and treatment.

Obstructive sleep apnoea syndrome--an oxidative stress disorder

Obstructive sleep apnoea syndrome (OSA) is associated with increased cardiovascular morbidity and mortality. However, the underlying mechanisms are not entirely understood. This review will summarize the evidence that substantiates the notion that the repeated apnoea-related hypoxic events in OSA, similarly to hypoxia/reperfusion injury, initiate oxidative stress. Thus, affecting energy metabolism, redox-sensitive gene expression, and expression of adhesion molecules. A limited number of studies substantiate this hypothesis directly by demonstrating increased free radical production in OSA leukocytes and increased plasma-lipid peroxidation. A great number of studies, however, support this hypothesis indirectly. Increase in circulating levels of adenosine and urinary uric acid in OSA are implicated with increased production of reactive oxygen species (ROS). Activation of redox-sensitive gene expression is suggested by the increase in some protein products of these genes, including VEGF, erythropoietin, endothelin-1, inflammatory cytokines and adhesion molecules. These implicate the participation of redox-sensitive transcription factors as HIF-1 AP-1 and NFkappaB. Finally, adhesion molecule-dependent increased avidity of OSA monocytes to endothelial cells, combined with diminished NO bioavailability, lead to exaggerated endothelial cell damage and dysfunction. Cumulatively, these processes may exacerbate atherogenic sequelae in OSA.

Stroke and sleep apnoea: cause or consequence?

The relationships between obstructive sleep apnoea syndrome (OSAS) and stroke are still under discussion, but increasing evidence demonstrates that the OSAS is an independent risk factor for stroke. However, in rare cases, OSAS could be a consequence of strokes, especially if located in the brainstem. Many recent studies have found a 70 to 95% frequency of OSAS (defined by an apnoea/hypopnoea index >10) in patients with acute stroke. Age, body mass index, diabetes, and severity of stroke have been identified as independent predictors of stroke. Furthermore, the presence of OSAS in stroke patients could lead to a poor outcome. The potential mechanisms linking OSAS and stroke are probably multiple (arterial hypertension, cardiac arrhythmia, increased atherogenesis, coagulation disorders, and cerebral haemodynamic changes). Despite numerous uncertainties, OSAS should be systematically screened at the moment it is clinically suspected in patients with acute stroke. However, the optimal timing (early or differed) for treatment with nasal continuous positive airway pressure remains to be determined.

Prevalence of sleep-disordered breathing and continuous positive airway pressure compliance: results in chinese patients with first-ever ischemic stroke

OBJECTIVE

To assess the prevalence of sleep-disordered breathing (SDB), continuous positive airway pressure (CPAP) acceptance, and CPAP compliance in patients who have experienced ischemic stroke.

DESIGN

A case-controlled study.

SETTING

A university hospital.

MEASUREMENTS AND RESULTS

We recruited 23 women and 28 men, who were admitted to the hospital within 4 days of stroke onset, with a mean (+/- SD) age of 64.2 +/- 13.0 years and a body mass index (BMI) of 24.3 +/- 4.4 kg/m(2) for this study. Twenty-seven patients (53%) and 9 patients (17.6%), respectively, reported a history of snoring and severe daytime sleepiness prior to experiencing a stroke, while the mean Epworth sleepiness scale score was 6.8 +/- 3.6. Polysomnography revealed 34 patients (67%) with an apnea-hypopnea index (AHI) of > or = 10 events per hour, 31 patients (61%) with an AHI of > or = 15 events per hour, and 25 patients (49%) with an AHI of > or = 20 events per hour. Significant obstructive SDB, defined as an AHI of > or = 20/h, was more prevalent in ischemic stroke patients than in control subjects (49% vs 24%, respectively; p = 0.04) and was associated with a higher BMI (p = 0.046). Among the 34 patients with an AHI of > or = 10/h, CPAP titration was tolerated by 16 patients, but only 4 patients who had typical sleep apnea features proceeded to home CPAP treatment with objective compliance over a period of 3 months of 2.5 +/- 0.6 h per night. A subgroup of 20 patients not receiving CPAP showed partial spontaneous improvement of SDB at 1 month (baseline AHI, 32.3 +/- 17.6 events per hour; AHI at 1 month, 23.0 +/- 18.8 events per hour; p = 0.01) with a trend toward improvement for the obstructive but no significant change for the central events, whereas no improvement in AHI was noted for the four patients receiving CPAP.

CONCLUSION

There is a high prevalence of obstructive SDB in patients who have experienced acute ischemic stroke, which, in many cases, is different from classic obstructive sleep apnea syndrome, and this is reflected by the lack of significant sleepiness, poor CPAP acceptance, and partial spontaneous improvement at 1 month.

Pulmonary haemodynamics in obstructive sleep apnoea

In patients with obstructive sleep apnoea syndrome (OSAS), pulmonary haemodynamics can show both transient perturbations during sleep and permanent alterations. During sleep, repeated fluctuations in pulmonary artery pressure and pulmonary wedge pressure, coincident with apnoeas, can be observed. Calculation of transmural pressure values is preferable to intravascular pressures in OSAS, due to the marked swings in intrathoracic pressure associated with obstructive apnoeas. Pulmonary artery pressure may progressively increase during sleep, particularly in close sequences of highly desaturating apnoeas. Apnoea-induced hypoxia appears as the most important determinant of this pulmonary artery pressure behaviour. Stroke volume and cardiac output during obstructive apnoeas show changes mainly related to intrathoracic pressure variations. Permanent precapillary pulmonary hypertension at rest is observed in <50% OSAS patients, and is poorly reversible after OSAS treatment. It correlates best with diurnal respiratory function parameters. However, the finding of pulmonary hypertension in some patients with near normal diurnal lung function led to suggest that sleep respiratory disorders may contribute to permanent pulmonary haemodynamic impairment in predisposed subjects. Knowledge on right ventricle hypertrophy in OSAS is inconsistent. As to right ventricle failure, it is clinically evident in subjects with associated lung disease or morbid obesity, while it may be detected instrumentally in subjects without such alterations, presumably as effect of apnoeas themselves. Besides, it appears more fully reversible after long-term OSAS treatment than pulmonary hypertension.

Severe obstructive sleep apnea is associated with left ventricular diastolic dysfunction

INTRODUCTION

Hypertension is common in patients with obstructive sleep apnea (OSA). However, the effect of OSA on ventricular function, especially diastolic function, is not clear. Therefore, we have assessed the prevalence of diastolic dysfunction in patients with OSA and the relationship between diastolic parameters and severity of OSA.

METHODS

Sixty-eight consecutive patients with OSA confirmed by polysomnography underwent echocardiography. Diastolic function of the left ventricle was determined by transmitral valve pulse-wave Doppler echocardiography. Various baseline characteristics, severity of OSA, and echocardiographic parameters were compared between patients with and without diastolic dysfunction.

RESULTS

There were 61 male and 7 female patients with a mean age of 48.1 +/- 11.1 years, body mass index of 28.5 +/- 4.3 kg/m(2), and apnea/hypopnea index (AHI) of 44.3 +/- 23.2/h (mean +/- SD). An abnormal relaxation pattern (ARP) in diastole was noted in 25 patients (36.8%). Older age (52.7 +/- 8.9 years vs 45.1 +/- 11.3 years, p = 0.005), hypertension (56% vs 20%, p = 0.002), and a lower minimum pulse oximetric saturation (SpO(2)) during sleep (70.5 +/- 17.9% vs 78.8 +/- 12.9%, respectively; p = 0.049) were more common in patients with ARP. By multivariate analysis, minimum SpO(2) < 70% was an independent predictor of ARP (odds ratio, 4.34; 95% confidence interval, 1.23 to 15.25; p = 0.02) irrespective of age and hypertension. Patients with AHI > or = 40/h had significantly longer isovolumic relaxation times than those with AHI < 40/h (106 +/- 19 ms vs 93 +/- 17 ms, respectively; p = 0.005).

CONCLUSION

Diastolic dysfunction with ARP was common in patients with OSA. More severe sleep apnea was associated with a higher degree of left ventricular diastolic dysfunction in this study.

Serum levels of vascular endothelial growth factor are elevated in patients with obstructive sleep apnea and severe nighttime hypoxia

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity and mortality; however, some patients with OSA do not develop cardiovascular disease even in the presence of severe nocturnal oxygen desaturations. Vascular endothelial growth factor (VEGF) is a hypoxia-sensitive glycoprotein stimulating neoangiogenesis. We hypothesized that VEGF production is increased in OSA because of repetitive nocturnal hypoxia. Three different groups were investigated: 10 OSA patients with severe nighttime hypoxia (Group A), 10 OSA patients with moderate hypoxia (Group B), and 10 healthy volunteers (Group C). Serum levels of VEGF were measured by ELISA from peripheral venous blood samples obtained at 7 AM. Group A had significantly (p < 0.01) increased VEGF serum levels when compared with Group B and Group C (mean +/- SEM: 410 +/- 77 pg/ml versus 224 +/- 38 pg/ml and 245 +/- 61 pg/ml). The degree of nocturnal oxygen desaturation in OSA significantly correlated with the VEGF concentrations (r = 0.67, p < 0.01). In conclusion, serum levels of VEGF are elevated in severely hypoxic patients with OSA and are related to the degree of nocturnal oxygen desaturation. This might constitute an adaptive mechanism to counterbalance the emergence of OSA-related cardiovascular disease.

Sleep disordered breathing and hypertension

Patients with sleep apnea may be at increased risk for cardiovascular disease. Recently, the link between hypertension and sleep apnea has been strengthened by findings of two large epidemiologic studies. Neurohumoral and hemodynamic responses to repetitive episodes of hypoxemia and apnea may offer a pathophysiologic basis for patients with sleep apnea having an increased risk for hypertension. Sympathetic, humoral, and cellular responses to sleep apnea over the long term may cause vascular dysfunction and consequent hypertension. These responses may be exacerbated by sleep deprivation, which occurs commonly in patients with sleep apnea because of poor sleep architecture. Patients with sleep apnea are often obese and may be predisposed to weight gain. Hence, obesity may further contribute to cardiovascular risk in this patient population. Alleviation of sleep disordered breathing may be accompanied by lower blood pressure in hypertensive patients with sleep apnea.

Plasma homocysteine levels in obstructive sleep apnea: association with cardiovascular morbidity

OBJECTIVES

Obstructive sleep apnea (OSA) is associated with cardiovascular morbidity and mortality. Plasma levels of homocysteine are also associated with cardiovascular morbidity and mortality. We therefore investigated homocysteine and conventional cardiovascular risk factors in OSA patients with and without cardiovascular morbidity in comparison with normal control subjects and ischemic heart disease (IHD) patients without OSA.

SETTING

Technion Sleep Medicine Center, Haifa, Israel.

METHODS AND PARTICIPANTS

Levels of homocysteine, cholesterol, low-density lipoprotein, high-density lipoprotein, triglycerides, creatinine, vitamins B(12) and B(6), and folic acid were determined in 345 participants after overnight fasting. These included OSA patients with IHD (n = 49), with hypertension (n = 61), or without any cardiovascular disease (n = 127). Two control groups were employed: IHD patients without or with low likelihood for sleep apnea (n = 35), and healthy control subjects (n = 73).

RESULTS

After adjustment for age, body mass index, creatinine, and existence of diabetes mellitus, OSA patients with IHD had significantly higher homocysteine levels (14.6 +/- 6.77 micromol/L) than all other groups including the IHD-only patients. Hypertensive OSA patients had comparable homocysteine levels to IHD patients (11.80 +/- 5.28 micromol/L and 11.92 +/- 5.7 micromol/L, respectively), while patients with OSA only had comparable levels to normal control subjects (9.85 +/- 2.99 micromol/L and 9.78 +/- 3.49 micromol/L, respectively). No differences in conventional cardiovascular risk factors or in vitamin levels were found between groups.

CONCLUSIONS

Patients with the combination of IHD and OSA have elevated homocysteine levels. We hypothesize that these results may be explained by endothelial dysfunction combined with excess free-radical formation in OSA patients.

Obstructive sleep apnea and hypertension: from correlative to causative relationship

Sleep-disordered breathing, manifested by repetitive episodes of partial or complete cessation of breathing during sleep associated with brief arousal and autonomic activation, is estimated to affect as many as 4% of adult men and 2% of adult women. Studies conducted during the 1980s revealed a strong association between sleep-disordered breathing and hypertension. The results of these early studies, which relied on relatively small samples of patients, have been confirmed in recent years by large-scale epidemiologic studies that are controlled for all possible confounding factors. This paper reviews the evidence suggesting a causative relationship between hypertension and disordered breathing in sleep. The authors discuss the possible underlying mechanisms of the two entities and address the clinical implications of this relationship. They conclude by recommending a proactive approach to the diagnosis of breathing disorders in sleep, in order to prevent the cardiovascular sequelae of this syndrome.