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

Sleep apnea is an independent correlate of erectile and sexual dysfunction

INTRODUCTION

Obstructive sleep apnea (OSA) has been linked with erectile dysfunction (ED), but it is unknown whether this association is maintained in the presence of other risk factors for ED.

AIM

The aim of this study was to evaluate the relationship between ED/sexual dysfunction and polysomnographic measures of sleep apnea in patients with known risk factors for ED.

METHODS

Prospective cross-sectional analysis of 401 male patients undergoing in-lab polysomnography for suspected OSA. Erectile (EF) and sexual function were assessed by the 15-item International Index of Erectile Function (IIEF-15) questionnaire.

MAIN OUTCOME MEASURES

Severity of OSA via apnea-hypopnea index (AHI) and mean/lowest nocturnal oxygen saturation (SaO(2)). The IIEF-15 including the sexual domains: EF, intercourse satisfaction, orgasmic function, sexual desire, and overall satisfaction.

RESULTS

OSA (AHI > 5/h) was diagnosed in 92% of patients. ED (EF subdomain < or = 25) was present in 69% of patients with, and 34% of patients without OSA (P < 0.001). Multivariate stepwise regression analyses including known risk factors for ED, such as age, obesity, coronary heart disease, peripheral occlusive disease, hypertension, diabetes, prostate surgery, and beta-blocker treatment, and measures of sleep apnea identified mean nocturnal SaO(2) as independently associated with ED (P = 0.002; mean [95% CI] normalized slope 0.126 [0.047; 0.205]). Age (P < 0.001), peripheral occlusive disease (P = 0.001), prostate surgery (P = 0.018), and hypertension (P = 0.021) were confirmed as risk factors for ED, but did not abolish the sleep apnea-associated risk. Similar results were obtained for sexual dysfunction. Logistic regression analysis using the diagnosis of ED (EF subdomain < or = 25) as binary dependent variable confirmed that mean nocturnal SaO(2) (P = 0.012), as well as age (P < 0.001) were independently associated with ED.

CONCLUSIONS

ED and overall sexual dysfunction were highly prevalent in patients with suspected OSA. Irrespective of known risk factors, mean nocturnal SaO(2) was an additional, independent correlate of these dysfunctions, suggesting that OSA-related intermittent nocturnal hypoxemia specifically contributes to their development.

Cardiovascular and cerebrovascular responses to acute hypoxia following exposure to intermittent hypoxia in healthy humans

Intermittent hypoxia (IH) is thought to be responsible for many of the long-term cardiovascular consequences associated with obstructive sleep apnoea (OSA). Experimental human models of IH can aid in investigating the pathophysiology of these cardiovascular complications. The purpose of this study was to determine the effects of IH on the cardiovascular and cerebrovascular response to acute hypoxia and hypercapnia in an experimental human model that simulates the hypoxaemia experienced by OSA patients. We exposed 10 healthy, male subjects to IH for 4 consecutive days. The IH profile involved 2 min of hypoxia (nadir = 45.0 mmHg) alternating with 2 min of normoxia (peak = 88.0 mmHg) for 6 h. The cerebral blood flow response and the pressor responses to hypoxia and hypercapnia were assessed after 2 days of sham exposure, after each day of IH, and 4 days following the discontinuation of IH. Nitric oxide derivatives were measured at baseline and following the last exposure to IH. After 4 days of IH, mean arterial pressure increased by 4 mmHg (P < 0.01), nitric oxide derivatives were reduced by 55% (P < 0.05), the pressor response to acute hypoxia increased (P < 0.01), and the cerebral vascular resistance response to hypoxia increased (P < 0.01). IH alters blood pressure and cerebrovascular regulation, which is likely to contribute to the pathogenesis of cardiovascular and cerebrovascular disease in patients with OSA.

Endothelial function in obstructive sleep apnea

Untreated obstructive sleep apnea (OSA) is an independent risk factor for hypertension, myocardial infarction, and stroke. The repetitive hypoxia/reoxygenation and sleep fragmentation associated with OSA impair endothelial function. Endothelial dysfunction, in turn, may mediate increased risk for cardiovascular diseases. Specifically, in OSA, endothelial nitric oxide availability and repair capacity are reduced, whereas oxidative stress and inflammation are enhanced. Treatment of OSA improves endothelial vasomotor tone and reduces inflammation. We review the evidence and possible mechanisms of endothelial dysfunction as well as the effect of treatment on endothelial function in OSA.

Effect of uvulopalatopharyngoplasty on endothelial function in obstructive sleep apnea

Objectives: This study evaluates the effects of uvulopalatopharyngoplasty (UPPP) on serum levels of nitric oxide derivatives (NOx) and endothelial function by endothelium dependent flow-mediated dilation (FMD) in obstructive sleep apnea syndrome (OSAS).

Study Design: Prospective study.

Subjects and Methods: Fifteen healthy subjects and 30 subjects with moderately severe to severe OSAS who desired UPPP were prospectively enrolled. FMD was measured by high-resolution B-mode ultrasonography; serum level of NOx from peripheral blood samples was also measured. All subjects participated in sleep studies. These studies were repeated 3 months after UPPP in OSAS patients.

Results: For healthy patients, there was no difference in serum level of NOx and FMD between baseline and 3 months later. The serum levels of NOx in 14 of 30 patients with OSAS – designated surgical responders – increased from 13.9 ± 5.5 μM preoperation to 28.9 ± 8.2 μM postoperatively. FMD increased from 5.2 ± 5.0 preoperatively to 10.0 ± 4.7 postoperatively. For the 16 unresponsive patients, serum NOx and FMD remained impaired after UPPP.

Conclusion: Successful treatment of OSAS with UPPP leads to restoration of FMD and normal serum levels of NOx.

Obstructive sleep apnea syndrome and asthma: what are the links?

Recent data suggest that obstructive sleep apnea syndrome (OSAS) is an independent risk factor for asthma exacerbations. Neuromechanical reflex bronchoconstriction, gastroesophageal reflux, inflammation (local and systemic), and the indirect effect on dyspnea of OSAS-induced cardiac dysfunction have been suggested as mechanisms that lead to worsening asthma control in patients with concomitant OSAS. Vascular endothelial growth factor-induced airway angiogenesis, leptin-related airway changes, and OSAS-induced weight gain also may play a common mechanistic role linking both disorders. Several studies have confirmed that asthmatic patients are more prone to develop OSAS symptoms than are members of the general population. The common asthmatic features that promote OSAS symptoms are nasal obstruction, a decrease in pharyngeal cross sectional area, and an increase in upper airway collapsibility. Clarifying the nature of the relationship between OSAS and asthma is a critical area with important therapeutic implications.

Causes and mechanisms of nondipping hypertension

Growing evidence indicates that nondippers have worsened cardiovascular outcomes than dippers. Ambulatory blood pressure monitoring with a lack of nocturnal BP fall (nondipping) have also been shown to be more closely associated with target organ damage and worsened cardiovascular outcome than in patients with essential hypertension with dipping pattern. The underlying pathogenetic mechanisms potentially linking nondipping with cardiovascular disease are not fully understood. There are multiple possible underlying pathophysiologic mechanisms in the impaired BP decline during the night. Extrinsic and intrinsic factors including abnormal neurohormonal regulation, lack of physical activity, nutritional factors such as increased dietary sodium intake, and smoking of tobacco have been implicated for blunted circadian rhythm of BP. Certain diseases such as diabetes and chronic renal diseases also affect the circadian BP rhythm. Currently, the clinical importance of nondipping is known well; however, the relationship between certain disease states and nondipping has not been fully explained yet. This paper will attempt to address to clarify the underlying basis for nondipping and the specific associations with various disease states.

Vasoconstrictor responses in the upper and lower limbs to increases in transmural pressure

The purpose of this study was to examine upper and lower limb vasoconstrictor responses to changes in transmural pressure in humans. Brachial and femoral blood mean blood velocity (MBV) and vessel diameter (Doppler ultrasound) were measured in 20 supine healthy subjects (10 men and 10 women; 27 +/- 1 yr; mean +/- SE) during four levels of limb suction at -25, -50, -75, and -100 mmHg, respectively. Limb suction led to an initial rise in MBV followed by a rapid fall in flow velocity to a level below MBV baseline, indicating a vasoconstriction effect. Femoral compared with brachial vessels exhibited a greater fall in flow velocity at all levels of suction (-89 +/- 17 vs. -10 +/- 2, -142 +/- 11 vs. -14 +/- 2, -156 +/- 22 vs. -13 +/- 2, and -162 +/- 29 vs. -12 +/- 2 ml/min for -25, -50, -75, and -100 mmHg, respectively; interaction effect, P < 0.05). Even at low tank suction levels (i.e., -10 and -20 mmHg), significant brachial flow velocity vasoconstriction from baseline values was demonstrated, reflecting downstream resistance vessel changes (n = 14). Brachial and femoral diameters did not change during changes in negative tank pressure. During suction, changes in limb volumes were significantly greater in the forearm (1.4 +/- 0.5%, 2.4 +/- 0.8%, 3.5 +/- 1.0%, and 4.3 +/- 1.1%) compared with the calf (0.9 +/- 0.5%, 1.4 +/- 0.7%, 2.0 +/- 0.8%, and 2.8 +/- 1.1%) at all levels of negative tank pressures (-25, -50, -75, and -100 mmHg, respectively). Simultaneous measurements of both upper limbs and both lower limbs suggested that the majority of the reduction in flow was due to myogenic influences except when -100 mmHg of suction was applied to the lower limb. The greater vasoconstriction responses in the leg compared with the arm with suction appear to be influenced by both myogenic and sympathetic mechanisms.

Obstructive sleep apnea syndrome is a systemic disease. Current evidence

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Metabolic syndrome is another highly prevalence emerging public health problem that represents a constellation of cardiovascular risk factors. Each single component of the cluster increases the cardiovascular risk, but the combination of factors is much more significant. It has been suggested that the presence of OSAS may increase the risk of developing some metabolic syndrome features. Moreover, OSAS patients are at an increased risk for vascular events, which represent the greatest morbidity and mortality of all associated complications. Although the etiology of OSAS is uncertain, intense local and systemic inflammation is present. A variety of phenomena are implicated in this disease such as modifications in the autonomic nervous system, hypoxemia-reoxygenation cycles, inflammation, and coagulation-fibrinolysis imbalance. OSAS patients also present increased levels of certain biomarkers linked to endocrine-metabolic and cardiovascular alterations among other systemic consequences. All of this indicates that, more than a local abnormality, OSAS should be considered a systemic disease.

Biology of peripheral blood cells in obstructive sleep apnea--the tip of the iceberg

Obstructive sleep apnea (OSA), a highly prevalent breathing disorder in sleep, characterized by intermittent and recurrent pauses in respiration, has emerged as an independent risk factor for cardiovascular morbidity and mortality. Accumulated evidence implicates Leukocyte-endothelial cell activation and adhesion as critical components that induce inflammation and injury to the vasculature resulting in the development of cardiovascular complications. Similar cellular interactions were described in conditions of ischemia/reperfusion, and various components of the metabolic syndrome as hypercholesterolemia and hypertension. The hallmark of sleep apnea--the multiple cycles of hypoxia/reoxygenation--promote oxidative stress and inflammation. These facilitate increased interactions of blood cells with endothelial cells, resulting in endothelial cell injury and dysfunction. Such events can promote atherosclerosis and the development of cardiovascular morbidities in OSA. However, inter-individual differences in response to intermittent hypoxia and activation of anti-inflammatory cytokine profiles in T lymphocytes can serve as protective mechanisms.

Obstructive sleep apnea and erectile dysfunction: still a neglected risk factor?

INTRODUCTION

Erectile dysfunction (ED) is a well-known entity with determined risk factors, which generally has a negative impact on quality of life. Obstructive sleep-disordered breathing (SDB), often referred to as obstructive sleep apnea, stands among the possible risk factors for ED.

DISCUSSION

Literature review suggests that SDB induces a spectrum of abnormalities in neural, hormonal, and vascular regulation that may contribute to the development of ED. While more studies are required to imply SDB as a risk factor for ED, several case series and expert opinion have contributed evidence for a causal relationship.

CONCLUSION

In clinical practice, men presenting with symptoms of sexual dysfunction often have concomitant sleep disorders requiring treatment. There is now evidence to suggest that treating SDB may be an effective treatment for ED. It is the authors' opinion that patients with erectile dysfunction would benefit from a sleep evaluation.

Cardiovascular Changes in Children with Snoring and Obstructive Sleep Apnoea

Introduction: Adults with obstructive sleep apnoea (OSA) are well documented to be at high risk for cardiovascular abnormalities. Growing evidence suggests that OSA is also associated with cardiovascular consequences in children. The purpose of this review is to examine the available data on this association in children. Methods: Primary studies were extracted from a MEDLINE search limited to those published between 1970 and 2008. The keywords used included child, sleep disordered breathing, sleep apnoea, snoring, blood pressure and hearts. The relevant articles were selected by consensus between 2 authors. Results: The results suggested that OSA was consistently associated with hypertension. Meta-analysis of risk of hypertension in those with high apnoea-hypopnoea index was undertaken. A combined odds ratio equal to 3.15 was found (95% confidence interval, 2.01 to 4.93). There was evidence for increased sympathetic activation, decreased arterial distensibility and ventricular hypertrophy in children with OSA. Conclusion: Childhood OSA is associated with blood pressure dysregulation. The association of OSA with other cardiovascular morbidities requires further study in view of the limited data available currently. Key words: Atherosclerosis, Child, Hypertension

Exogenous nitric oxide regulates activity and synthesis of vascular endothelial nitric oxide synthase

BACKGROUND

Nitric oxide (NO) - a major signalling molecule of the vascular system - is constitutively produced in endothelial cells (EC) by the endothelial NO synthase (eNOS). Since a reduced NO synthesis is an early sign of endothelial dysfunction and NO delivering drugs are used to substitute the impaired endothelial NO production, we addressed the effect of exogenous NO on eNOS in human umbilical venous endothelial cell cultures.

MATERIALS AND METHODS

The synthetic NO donor DETA/NO (trade name, but in the following we refer to detNO), that releases NO in a strictly first order reaction with a half life of 20 h, was used in our experiments.

RESULTS

Short-term (20-30 min) detNO treatment of EC increases the Ser(1177) phosphorylation of the constitutively expressed endothelial NOS and the production of endogenous NO generated by eNOS from [(3)H]arginine. The phosphorylation of eNOS is Akt-dependent and completely reverted by the phosphatidylinositol-3 kinase (PI-3K) inhibitor LY294002. A prolonged continuous exposure of EC to detNO 150 micromol L(-1) over a period of 24-48 h causes a reversible cell cycle arrest at G(1)-phase associated with a larger cell volume and increased cell protein content (hypertrophic phenotype of EC). The eNOS protein and mRNA of the hypertrophic cells and the generation of endogenous NO are reduced but eNOS phosphorylation could still be elevated by stimulation with vascular endothelial growth factor.

CONCLUSIONS

Our data explain clinical studies describing a short-term but not a long-term benefit of NO treatment for patients with cardiovascular risk factors. The results could be a rational approach to develop a generation of NO donors accomplishing a retarded release from NO donors that mimic the low continuous pulsatile stress-induced release of endogenous NO.

Impact of obstructive sleep apnea on the occurrence of restenosis after elective percutaneous coronary intervention in ischemic heart disease

Rationale

There is growing evidence that obstructive sleep apnea is associated with coronary artery disease. However, there are no data on the course of coronary stenosis after percutaneous coronary intervention in patients with obstructive sleep apnea.

Objectives

To determine whether sleep apnea is associated with increased late lumen loss and restenosis after percutaneous coronary intervention.

Methods

78 patients with coronary artery disease who underwent elective percutaneous coronary intervention were divided in 2 groups: 43 patients with an apnea hypopnea – Index < 10/h (group I) and 35 pt. with obstructive sleep apnea and an AHI > 10/h (group II). Late lumen loss, a marker of restenosis, was determined using quantitative coronary angiography after 6.9 ± 3.1 months.

Main results

Angiographic restenosis (>50% luminal diameter), was present in 6 (14%) of group I and in 9 (25%) of group II (p = 0.11). Late lumen loss was significant higher in pt. with an AHI > 10/h (0.7 ± 0.69 mm vs. 0.38 ± 0.37 mm, p = 0.01). Among these 35 patients, 21(60%) used their CPAP devices regularly. There was a marginally lower late lumen loss in treated patients, nevertheless, this difference did not reach statistical significance (0.57 ± 0.47 mm vs. 0.99 ± 0.86 mm, p = 0.08). There was no difference in late lumen loss between treated patients and the group I (p = 0.206).

Conclusion

In summary, patients with OSA and coronary artery disease have a higher degree of late lumen loss, which is a marker of restenosis and vessel remodeling after elective percutaneous intervention.

Treatment of obstructive sleep apnoea leads to enhanced pulmonary vascular nitric oxide release

BACKGROUND

Obstructive sleep apnoea (OSA) is associated with pulmonary hypertension, however neither the pathogenesis of pulmonary vascular disease nor the effect of successful treatment of OSA on pulmonary vascular physiology has been characterised.

METHODS

Seven subjects aged 52 (range 36-63) years with moderate to severe obstructive sleep apnoea (apnoea-hypopnoea index>15/h) had detailed pulmonary vascular reactivity studies, before and after 3 months of successful treatment with nasal continuous positive airways pressure (CPAP). On both occasions, we measured pulmonary pressure, flow velocity, flow and resistance, at baseline and in response to acetylcholine (an endothelium-dependent dilator), sodium nitroprusside (an endothelium-independent dilator), l-NMMA (an antagonist of nitric oxide synthesis) and l-Arginine (the substrate of nitric oxide).

RESULTS

At baseline, pulmonary flow increased in response to acetylcholine and nitroprusside and fell in response to l-NMMA. Following CPAP treatment, the decrease in flow to l-NMMA was significantly greater (to 62+/-6% of control value vs 85+/-6% of pre-treatment; p=0.01), consistent with enhanced basal release of nitric oxide. The acetylcholine response tended to be greater after treatment (174+/-26% of control vs 147+/-12% of pre-CPAP, p=0.22), however the nitroprusside response was unchanged.

CONCLUSION

Successful treatment of obstructive sleep apnoeic episodes in sleep results in enhanced nitric oxide release by the pulmonary microvascular circulation.

Oxidative stress in obstructive sleep apnea: putative pathways to the cardiovascular complications

Obstructive sleep apnea (OSA) is a major public health problem because of its high prevalence in morbidity and mortality. A growing body of evidence suggests that OSA is an important risk factor for cardiovascular diseases. Although the mechanism for the initiation and aggravation of cardiovascular disease has not been fully elucidated, one theorized mechanism is intermittent hypoxia, which is produced by each sleep-disordered breathing event. This repeated hypoxia and reoxygenation cycle is similar to hypoxia-reperfusion injury, which initiates oxidative stress. Recent studies have suggested that OSA is associated with increased levels of oxidative stress or antioxidant deficiencies or both. Oxidative stress is involved in the activation of redox-sensitive transcription factors, which regulate downstream products such as inflammatory cytokines, chemokines, and adhesion molecules. This pathway may be able to explain the pathogenesis of atherosclerosis, a common pathologic factor underlying all types of cardiovascular disease. In addition, endothelial dysfunction derived from oxidative stress can contribute to cardiovascular diseases. This review summarizes current available evidence for and against the occurrence of oxidative stress in OSA and discusses the putative pathways initiating cardiovascular consequences associated with OSA.

Independent association between obstructive sleep apnea and subclinical coronary artery disease

BACKGROUND

Obstructive sleep apnea (OSA) is associated with coronary risk factors, but it is unknown if OSA is associated with development of coronary disease. We evaluated the association between OSA and the presence of subclinical coronary disease assessed by coronary artery calcification (CAC).

METHODS

Consecutive patients with no history of coronary disease who underwent electron-beam CT within 3 years of polysomnography between March 1991 and December 2003 were included. OSA was defined by an apnea-hypopnea index (AHI) > or = 5 events per hour, and patients were grouped by quartiles of AHI severity. Logistic regression modeled the association between OSA severity and presence of CAC.

RESULTS

There were 202 patients (70% male; median age, 50 years; mean body mass index, 32 kg/m(2); 8% diabetic; 9% current smokers; 60% hypercholesterolemic; and 47% hypertensive). OSA was present in 76%. CAC was present in 67% of OSA patients and 31% of non-OSA patients (p < 0.001). Median CAC scores (Agatston units) were 9 in OSA patients and 0 in non-OSA patients (p < 0.001). Median CAC score was higher as OSA severity increased (p for trend by AHI quartile < 0.001). With multivariate adjustment, the odds ratio for CAC increased with OSA severity. Using the first AHI quartile as reference, the adjusted odds ratios for the second, third, and fourth quartiles were 2.1 (p = 0.12), 2.4 (p = 0.06), and 3.3 (p = 0.03), respectively.

CONCLUSIONS

In patients without clinical coronary disease, the presence and severity of OSA is independently associated with the presence and extent of CAC. OSA identifies patients at risk for coronary disease and may represent a highly prevalent modifiable risk factor.

Erectile dysfunction and sleep related disorders

PURPOSE

There are reported links between erectile dysfunction and sleep disorders. We reviewed the physiology of penile erection during sleep and the possible links between the pathophysiology of erectile dysfunction and the most commonly diagnosed sleep disorders.

MATERIALS AND METHODS

A MEDLINE search using the identifiers erectile dysfunction, sleep, sleep disorders, sleep apnea, insomnia and narcolepsy was performed to identify the current literature pertaining to erectile dysfunction and sleep disorders. The peer reviewed literature and relevant surveys from 1985 to 2006 were subsequently reviewed.

RESULTS

An association between erectile dysfunction and sleep disorders appears to exist in survey studies relying on self-report and in small case series. Hormonal, neural and endothelial mechanisms have been implicated in linking sleep disorders with erectile dysfunction. Treatment of sleep disorders, specifically sleep apnea with continuous positive airway pressure, has been shown to improve patient erectile function.

CONCLUSIONS

Clinicians should consider concomitant sleep disorders when evaluating patients with erectile dysfunction, especially in those refractory to routine therapy. Further studies are necessary to clearly define the causative link between sleep disorders and erectile dysfunction.

Cardiovascular morbidity in obstructive sleep apnea: oxidative stress, inflammation, and much more

Sleep-disordered breathing and obstructive sleep apnea (OSA) are highly prevalent disorders throughout the lifespan, which may affect up to 2-10% of the population, and have now been firmly associated with an increased risk for cardiovascular and neurobehavioral complications. Nevertheless, the overall pathophysiologic mechanisms mediating end-organ injury in OSA remain undefined, particularly due to the very frequent coexistence of other disease states, such as obesity, that clearly complicate the potential cause-effect relationships. Two major, and to some extent overlapping, mechanisms have been proposed to explain the morbid consequences of OSA, namely increased generation and propagation of reactive oxygen species and initiation and amplification of inflammatory processes. The evidence supporting the validity of these concepts as well as that detracting from such mechanisms will be critically reviewed in the context of clinical and laboratory-based approaches. In addition, some of the contradictory issues raised by such evaluation of the literature will be interpreted in the context of putative modifications of the individual responses to OSA, as determined by genetic variants among susceptibility-related genes, and also by potential environmental modulators of the phenotypic expression of any particular end-organ morbidity associated with OSA.

Sleep apnea: epidemiology, pathophysiology, and relation to cardiovascular risk

Several studies have shown the occurrence of an independent association between obstructive sleep apnea syndrome (OSAS) and cardiovascular disease, including arterial hypertension, ischemic heart disease, and stroke. The pathogenesis of the cardiovascular complications of OSAS is still poorly understood, however. Several mechanisms are likely to be involved, including sympathetic overactivity, selective activation of inflammatory molecular pathways, endothelial dysfunction, abnormality in the process of coagulation, and metabolic dysregulation. The latter may involve insulin resistance and disorders of lipid metabolism. The aim of this review, which reports the data presented at a workshop jointly endorsed by the European Society of Hypertension and by the European Union COST action on OSAS (COST B26), is to critically summarize the evidence available to support an independent association between OSAS and cardiovascular disease.

Alveolar-derived exhaled nitric oxide is reduced in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular diseases, in particular systemic arterial hypertension. We postulated that intermittent nocturnal hypoxia in OSAS may be associated to decreased fractional exhaled nitric oxide (FENO) levels from distal airspaces.

METHODS

Multiple flow rate measurements have been used to fractionate nitric oxide (NO) from alveolar and bronchial sources in 34 patients with OSAS, in 29 healthy control subjects, and in 8 hypertensive non-OSAS patients. The effect of 2 days of treatment with nasal continuous positive airway pressure (nCPAP) on FENO was examined in 18 patients with severe OSAS.

RESULTS

We found that the mean [+/- SE] concentrations of exhaled NO at a rate of 50 mL/s was 21.8 +/- 1.9 parts per billion (ppb) in patients with OSAS, 25.1 +/- 3.3 ppb in healthy control subjects, and 15.4 +/- 1.7 ppb in hypertensive control patients. The mean fractional alveolar NO concentration (CANO) in OSAS patients was significantly lower than that in control subjects (2.96 +/- 0.48 vs 5.35 +/- 0.83 ppb, respectively; p < 0.05). In addition, CANO values were significantly lower in OSAS patients with systemic hypertension compared to those in normotensive OSAS patients and hypertensive patients without OSAS. The mean values of CANO significantly improved after nCPAP therapy (2.67 +/- 0.41 to 4.69 +/- 0.74 nL/L, respectively; p = 0.01).

CONCLUSIONS

These findings suggest that alveolar FENO, and not bronchial FENO, is impaired in patients with OSAS and that this impairment is associated with an increased risk of hypertension. NO production within the alveolar space is modified by treatment with nCPAP.

Cardiovascular outcomes of CPAP therapy in obstructive sleep apnea syndrome

Considerable evidence is now available of an independent association between obstructive sleep apnea syndrome (OSAS) and cardiovascular disease. The association is particularly strong for systemic arterial hypertension, but there is growing evidence of an association with ischemic heart disease and stroke. The mechanisms underlying cardiovascular disease in patients with OSAS are still poorly understood. However, the pathogenesis is likely to be a multifactorial process involving a diverse range of mechanisms, including sympathetic overactivity, selective activation of inflammatory molecular pathways, endothelial dysfunction, abnormal coagulation, and metabolic dysregulation, the latter particularly involving insulin resistance and disordered lipid metabolism. Therapy with continuous positive airway pressure (CPAP) has been associated with significant benefits to cardiovascular morbidity and mortality, both in short-term studies addressing specific aspects of morbidity, such as hypertension, and more recently in long-term studies that have evaluated major outcomes of cardiovascular morbidity and mortality. However, there is a clear need for further studies evaluating the impact of CPAP therapy on cardiovascular outcomes. Furthermore, studies on the impact of CPAP therapy have provided useful information concerning the role of basic cell and molecular mechanisms in the pathophysiology of OSAS.

Endothelial dysfunction in obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common disorder and is associated with adverse cardiovascular consequences, including hypertension and coronary artery disease. While the mechanisms responsible for increased risk of cardiovascular events in OSA have not yet been fully elucidated, hypoxia, inflammation, obesity, metabolic dysregulation, and sympathetic activation, may contribute to these consequences. Endothelial dysfunction may be another link between OSA and cardiovascular disease. Dysfunctional endothelium is characterized by an imbalance in production of vasoactive hormones, increased adherence of inflammatory mediators to endothelial cells and hypercoagulability, and is a known risk factor for cardiovascular events. Studies have directly measured vascular endothelial function in patients with OSA and found a muted response compared to controls. Other studies have evaluated biochemical markers of endothelial function including circulating levels of vasoactive and thrombosis mediators and provide further proof of endothelial dysfunction in this disorder. A better appreciation of the role of the dysfunctional endothelium in OSA will help shed light on the pathogenesis of cardiovascular disease in this disorder and may lead to development of novel therapies aimed at preventing untoward outcomes.

Clinical perspective of obstructive sleep apnea-induced cardiovascular complications

Obstructive sleep apnea (OSA) syndrome is a highly prevalent disorder characterized by recurrent upper airway collapse during sleep, and associated with repetitive episodes of transient oxygen desaturation during sleep. It disrupts normal ventilation and sleep architecture, and is typically associated with excessive daytime sleepiness, snoring, and witnessed apneas. Besides being associated with neurocognitive impairment, mood and behavioral effects, and increased risk for work-related and traffic accidents, OSA has also been implicated in the pathogenesis of various cardiovascular diseases, including systemic hypertension, coronary artery disease, congestive heart failure, pulmonary hypertension, stroke, and cardiac arrhythmias. The mechanisms by which OSA affects the cardiovascular system may involve mechanical effects on intrathoracic pressure, increased sympathetic activation, intermittent hypoxia, and endothelial dysfunction. Therapy with continuous positive airway pressure (CPAP) has been demonstrated to improve cardiopulmonary hemodynamics in patients with OSA and may reverse the endothelial cell dysfunction.

Sleep apnea: clinical investigations in humans

Sleep apnea syndrome (SAS), a common disorder, is characterized by repetitive episodes of cessation of breathing during sleep, resulting in hypoxemia and sleep disruption. The consequences of the abnormal breathing during sleep include daytime sleepiness, neurocognitive dysfunction, development of cardiovascular disorders, metabolic dysfunction, and impaired quality of life. There are two types of SAS: obstructive sleep apnea syndrome (OSAS) and central sleep apnea syndrome (CSAS). OSAS is a prevalent disorder in which there is snoring, repetitive apneic episodes, and daytime sleepiness. Anatomical conditions causing upper airway obstruction (obesity or craniofacial abnormalities such as retrognathia or micrognathia) can cause OSAS. CSAS, much less common than OSAS, is a disorder characterized by cessation of breathing which is caused by reduced respiratory drive from the central nervous system to the muscles of respiration. The latter condition is common in patients with heart failure and cerebral neurologic diseases. The diagnosis of SAS requires assessment of subjective symptoms and apneic episodes during sleep documented by polysomnography. Treatments of OSAS include continuous positive airway pressure (CPAP), oral appliances, and surgery; patients with CSAS are treated with oxygen, adaptive servo-ventilation, or CPAP. With assessment and treatment of the SAS, patients usually have resolution of their disabling symptoms, subsequently resulting in improved quality of life.

The effects of adaptive servo ventilation on cerebral vascular reactivity in patients with congestive heart failure and sleep-disordered breathing

STUDY OBJECTIVE

Hypercapnic cerebral vascular reactivity (HCVR) is reduced in patients with congestive heart failure (CHF) and sleep-disordered breathing (SDB); this may be associated with an increased risk of stroke. We tested the hypothesis that reversal of SDB in CHF patients using adaptive servo ventilation (ASV) would increase morning HCVR.

DESIGN

Interventional, cross-over clinical study.

SETTING

Research sleep laboratory.

PATIENTS

Ten CHF patients with SDB, predominantly obstructive sleep apnea.

INTERVENTIONS

The HCVR was measured from the change in middle cerebral artery velocity, using pulsed Doppler ultrasound. HCVR was determined during the evening (before) and morning (after) 1 night of sleep on ASV and 1 night of spontaneous sleep (control).

MEASUREMENTS AND RESULTS

Compared with the control situation, ASV decreased the apnea-hypopnea index (group mean +/- SEM, control: 48 +/- 12, ASV: 4 +/- 1 events per hour). HCVR was 23% lower in the morning, compared with the evening, on the control night (evening: 1.3 +/- 0.2, morning: 1.0 +/- 0.2 cm/sec per mm Hg, P < 0.05) and 27% lower following the ASV night (evening: 1.5 +/- 0.2, morning: 1.1 +/- 0.2 cm/sec per mm Hg, P < 0.05). The effect of ASV on the evening-to-morning reduction in HCVR was not significant, compared with the control night (0.02 cm/sec per mm Hg, 95% confidence interval: -0.28, 0.32 P = 0.89).

CONCLUSIONS

In CHF patients with SDB, HCVR was reduced in the morning compared with the evening. However, removal of SDB for 1 night did not reverse the reduced HCVR. The relatively low morning HCVR could be linked with an increased risk of stroke.

Sleep apnea: why a good night's sleep is good for your health

Recent studies have suggested that sleep apnea-a form of sleep-disordered breathing in which sleep is repeatedly interrupted by episodes of decreased or absent breathing-may be linked to pathogenesis and progression of numerous disease states. In particular, cardiovascular conditions such as hypertension, myocardial ischemia, and congestive heart failure are associated with sleep disordered breathing. There also may be a link between diabetes and sleep apnea. While pharmacologic treatments have shown little efficacy, treatment with continuous positive airway pressure often is beneficial. Increasingly, clinicians are considering sleep apnea as a potential risk factor for many diseases and conditions.

Obstructive sleep apnea, cardiovascular disease, and inflammation—is NF-κB the key?

Obstructive sleep apnea (OSA) affects a large portion of the population and is associated with repeated airway collapse leading to chronic intermittent hypoxia, exaggerated swings in intrathoracic pressure and post apneic arousal. OSA is associated with heightened sympathoadrenal tone and is a risk factor for cardiovascular mortality and morbidity. In addition to well-known mechanical and autonomic effects, OSA appears to be associated with systemic inflammation. This could provide one mechanism leading to cardiovascular disease (CVD). A central factor in the inflammatory cascade is nuclear factor kappa B (NF-kappaB), which is involved in the transcription of numerous genes involved in the inflammatory cascade. The object of this article is to review recent literature on some of the aspects of OSA related to a proinflammatory state and the possible role of NF-kappaB as one mechanism providing a link between sleep apnea and CVD.

Lungenerkrankungen und Herzfunktion

The most severe cardiac sequel to lung disease is the load on the right ventricle due to pulmonary hypertension with the development of a cor pulmonale. This is characterized by hypertrophy and/or dilatation of the right ventricle because of a primary impairment of lung function and/or lung structure. The most important pathomechanisms for the development of pulmonary hypertension are vessel obliteration, mechanical lesions, primary vascular or extra-vascular inflammation and hypoxic vasoconstriction. Chronic obstructive pulmonary disease (COPD) is one of the most important reasons for chronic cor pulmonale. A further very common reason is obstructive sleep apnea syndrome, especially if combined with a COPD. In this case, the prevalence of cor pulmonale can reach 80%. The development of a chronic cor pulmonale is the most striking negative prognostic factor for these patients. Only 30% of COPD patients with cor pulmonale survive longer than 5 years, and only early detection of the disturbances to respiration which might potentially lead to cor pulmonale and their subsequent therapy are able to improve the patient's prognosis. Furthermore, pulmonary diseases may also have an impact on the left heart side in terms of an impairment of left heart function or by inducing severe arrhythmias . Thus, lung diseases may have both a significant impact on right and left heart performance.

Sildenafil combined with continuous positive airway pressure for treatment of erectile dysfunction in men with obstructive sleep apnea

OBJECTIVES

To assess efficacy and safety of the combination of sildenafil and continuous positive airway pressure (CPAP), and satisfaction with treatment for erectile dysfunction (ED) in men with obstructive sleep apnea (OSA).

PATIENTS AND METHODS

Forty men suffering from OSA and concurrent ED were treated with CPAP after a thorough investigation. After a 4-week run-in period, the patients were randomly allocated to treatment for 6 weeks; 20 men to the combination group, receiving additionally 100 mg sildenafil on demand for intercourse, and 20 men to CPAP alone. After a 1-week washout phase, the two groups switched to the other treatment arm for an additional 6 weeks period. End points for efficacy evaluation were the percentage of successful attempts for intercourse based on an event log and the overall satisfaction with sildenafil in the treatment of ED.

RESULTS

The patients recorded a total of 149 attempts for intercourse during the run-in phase with a success rate of 19.5%. During the 12 weeks of treatment, the success rate of intercourse attempts was 24.8% when only on CPAP and 61.1% when in combination with sildenafil (P < 0.001). Of the studied men, 70% were satisfied with the use of sildenafil while 30% remained unhappy with this additional treatment.

CONCLUSIONS

Sildenafil in combination with CPAP appears clearly superior to CPAP alone. The efficacy of this combination is superior to that of sildenafil alone, as reported in previous studies. Both treatment modalities are safe and well tolerated. However, approximately one-third of the patients remain unsatisfied even from the combination treatment. Further treatment options are needed.

Hemodynamic and molecular response to intermittent hypoxia (IH) versus continuous hypoxia (CH) in normal humans

The hemodynamic response to hypoxia may be influenced by exposure pattern and inducible biological signals, such as nitric oxide synthase (iNOS) expression. The systemic blood pressure (BP) and heart rate (HR) response to intermittent and continuous hypoxia (IH and CH) were examined as was the relationship between these responses and iNOS expression in 10 normal subjects. BP and HR were recorded during exposure to IH or CH (total hypoxic time=60 min/dayx3 days for each exposure profile), whereas arterial oxygen saturation (SpO2) was maintained at 80-90%. Total RNA was isolated from peripheral blood lymphocytes before exposure on Day 1 and 2 hours after the last exposure on Day 3, and it was assayed for iNOS messenger RNA (mRNA) expression using quantitative polymerase chain reaction (PCR). HR, systolic BP (SBP), and diastolic BP (DBP) increased during both experimental conditions (P<0.05), with no difference by exposure pattern or evidence of facilitation over 3 days. No significant change occurred in iNOS mRNA during IH or CH when pre- and post-exposure values were compared. However, iNOS expression at the end of Day 3 was negatively correlated with the average end-exposure DBP (r=-0.79) and mean BP (MBP; r=-0.76) on Days 1-3 of the IH (P<0.05), but not CH exposure. It is concluded that both IH and CH are associated with significant but comparable hemodynamic changes. The negative correlation between BP and iNOS mRNA with IH, but not CH, may suggest differential modulation of the hemodynamic response to the 2 exposure patterns.

The impact of long-term conventional treatment for overlap syndrome (obstructive sleep apnea and chronic obstructive pulmonary disease) on concurrent erectile dysfunction

PURPOSE

To assess the improvement of concurrent erectile dysfunction (ED) in men with overlap syndrome (obstructive sleep apnea and chronic obstructive pulmonary disease), treated with continuous positive airway pressure (CPAP) and bronchodilators.

MATERIAL AND METHODS

We evaluated 48 men of a mean age of 52.8+/-10 years suffering from both obstructive sleep apnea (OSA) and chronic obstructive pulmonary disease (COPD), and concurrent ED. They were treated with conventional for pulmonary obstruction therapy (CPAP and bronchodilators) for 6 months and then their erectile function (EF) status was reassessed. ED was considered as improved, if ED intensity score increased for at least five points compared to that of baseline. The determinants for improvement of ED were also evaluated, as well as patient's personal degree of satisfaction with the treatment they received as far as the disorder was concerned.

RESULTS

EF was improved in 12 patients (25%), but only two thirds of them were satisfied with the grade of improvement after treatment. ED improvement was related positively with age and apnea/hypopnea index and negatively with ED duration. ED intensity score, O(2) saturation at night and BMI were not significantly related to the outcome of EF improvement.

CONCLUSIONS

Conventional treatment for OSA and COPD, has a positive effect on concurrent ED on the minority of patients. This effect is possibly due to the improvement of respiration during sleep with CPAP and of oxygenation with bronchodilators continuously. Of the improved men, one third was not satisfied with the impact of this treatment modality on their EF. It is likely that specific for ED treatment is needed in these individuals.

Endothelial cell apoptosis in obstructive sleep apnea: a link to endothelial dysfunction

RATIONALE

Patients with obstructive sleep apnea (OSA) are at increased risk for cardiovascular diseases. Injury of endothelial cells has been advanced as an initial trigger to atherosclerosis.

OBJECTIVES

To study the association between circulating apoptotic endothelial cells and vasomotor dysfunction as a function of sleep apnea.

METHODS

Brachial artery flow-mediated dilation was determined in 14 subjects with documented OSA and 10 healthy control subjects at baseline and 8 weeks after continuous positive airway pressure (CPAP) therapy. Quantification of circulating apoptotic endothelial cells (CD146(+) Annexin V(+)) was performed by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

Compared with healthy subjects, patients with OSA had higher numbers of circulating CD146(+) Annexin V(+) cells (39.2 +/- 13.6 cells/mL and 17.8 +/- 9.4, respectively; p < 0.001). Increased apoptotic endothelial cells correlated moderately with abnormal vascular function (r = -0.61; p = 0.001). A significant correlation was observed between CD146 Annexin V(+) cells and the apnea-hypopnea index (r = 0.56; p = 0.004). After 8 weeks of treatment with CPAP, the numbers of circulating apoptotic endothelial cells were reduced significantly from 39.2 +/- 13.6 to 22.3 +/- 12.9 apoptotic cells per milliliter (p < 0.001) and correlated with improvement in endothelium-dependent vasodilation (r = 0.49; p = 0.07).

CONCLUSIONS

In patients with OSA, impairment of endothelial-dependent vasodilation correlated with the degree of endothelial cell apoptosis. CPAP therapy led to significant decline in circulating apoptotic endothelial cells. These findings provide an additional mechanism for the predisposition of patients with OSA to premature vascular disease.

Hypertension research in sleep apnea

Obstructive sleep apnea (OSA) is characterized by repetitive partial and total collapse of the upper airway that induces stressful arousals throughout sleep to reestablish breathing. Although estimates vary, prevalence has been reported as high as 20% in the adult population. OSA is common in several chronic diseases, the most common of which is obesity. Evidence is strong that OSA increases the risk of hypertension and both fatal and nonfatal cardiovascular events. Several mechanisms linking OSA to hypertension have been proposed, with increased sympathetic activation implicated as the prime mediator. This review summarizes recent data on the influence of OSA on blood pressure, the effect of standard OSA therapy on improving blood pressure, and the potential of lifestyle modification for further decreasing hypertension risk. Challenges confronting the investigation of blood pressure outcomes in response to treatment in OSA patients are discussed.

Effects of continuous positive airway pressure on cerebral vascular response to hypoxia in patients with obstructive sleep apnea

RATIONALE

The mechanism leading to increased risk of stroke in patients with obstructive sleep apnea (OSA) is unknown. It may occur through alteration in the regulation of cerebral blood flow, reflected in part by the response of the cerebral vasculature to hypoxia. We hypothesized that the cerebrovascular response to hypoxia is reduced in patients with OSA.

OBJECTIVE

To determine the cerebral blood flow response to hypoxia in patients with OSA.

METHODS

The cerebral blood flow response to 20 minutes of isocapnic hypoxia was measured in eight male patients with OSA before and after 4 to 6 weeks of continuous positive airway pressure (CPAP) therapy and in 10 matched healthy control subjects.

MEASUREMENTS AND MAIN RESULTS

The cerebral blood flow response to hypoxia was significantly lower in patients with OSA compared with control subjects (0.56 +/- 0.10 vs. 0.97 +/- 0.09% [mean +/- SE] change in blood flow velocity per % desaturation; p=0.007). After CPAP therapy, the cerebral blood flow response to hypoxia was similar between patients with OSA and control subjects (1.08 +/- 0.15 vs. 0.92 +/- 0.13% change in blood flow velocity per % desaturation; p=0.4). Moderately strong correlations were found between the cerebral blood flow response to hypoxia and the apnea-hypopnea index (r=-0.57; p=0.04) and nocturnal oxyhemoglobin saturation (r=0.48; p=0.01).

CONCLUSIONS

The cerebral blood flow response to hypoxia is significantly reduced in patients with OSA. Treatment of OSA with CPAP increases the cerebral blood flow response to hypoxia to normal levels. An attenuated cerebrovascular response to hypoxia in patients with OSA may contribute to their elevated risk of stroke.

Effect of CPAP on brachial-ankle pulse wave velocity in patients with OSAHS: An open-labelled study

Pulse wave velocity (PWV) is a good indicator of arterial stiffness and an important predictor of cardiovascular events. Recent studies have revealed that PWV increases in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) and it also correlates with its severity. However, the therapeutic effect of continuous positive airway pressure (CPAP) on PWV remains undetermined. To clarify this point, we started CPAP treatment on 17 OSAHS patients. Brachial-ankle PWV was measured before starting CPAP, and at 2 months and 4 months after the start of CPAP. Before the CPAP treatment, mean brachial-ankle PWV of the patients was 15.6+/-0.6 m/s, and mean Epworth sleepiness scale (ESS) score was 8.6+/-1.0. Brachial-ankle PWV was found to positively correlate with heart rate, systolic and diastolic blood pressures, mean blood pressure, and arousal index. During the study period, the CPAP treatment did not have a significant effect on heart rate, blood pressures and serum total cholesterol levels. However, it significantly improved ESS score at 4 months after the start of CPAP (P=0.001), while it effectively decreased brachial-ankle PWV at 2 months and at 4 months after the start of CPAP (P=0.010 and P=0.027, respectively). The CPAP treatment was shown to decrease brachial-ankle PWV without affecting blood pressures in OSAHS patients. Although the precise mechanism for this effect is unclear, our finding suggests a close relationship between OSAHS and arterial stiffness, while also reemphasizing the clinical importance of CPAP treatment.

Intermittent hypoxia and vascular function: implications for obstructive sleep apnoea

Obstructive sleep apnoea (OSA) has been implicated as a risk factor for the development of hypertension, stroke and myocardial infarction. The main cause of cardiovascular and cerebrovascular disease in OSA is thought to be exposure to intermittent hypoxia, which can lead to oxidative stress, inflammation, atherosclerosis, endothelial dysfunction and hypertension. These proposed mechanisms have been drawn from basic research in animal and human models of intermittent hypoxia in addition to clinical investigation of patients with OSA. This review outlines the association between OSA and vascular disease, describes basic mechanisms that may be responsible for this association and compares the results from studies of OSA subjects with those in experimental models of intermittent hypoxia.

Sleep and the metabolic syndrome

The metabolic syndrome represents a clustering of several interrelated risk factors of metabolic origin that are thought to increase cardiovascular risk. It is still uncertain whether this clustering results from multiple underlying risk factors or whether it has a single cause. One metabolic abnormality that may underlie several clinical characteristics of the metabolic syndrome is insulin resistance. This review discusses the evidence that sleep disturbances (obstructive sleep apnoea, sleep deprivation and shift work) may independently lead to the development of both insulin resistance and individual clinical components of the metabolic syndrome. The converse may also be true, in that metabolic abnormalities associated with the metabolic syndrome and insulin resistance may potentially exacerbate sleep disorders. The notion that sleep disturbances exert detrimental metabolic effects may help explain the increasing prevalence of the metabolic syndrome and insulin resistance in the general population and may have important implications for population-based approaches to combat the increasing epidemic of metabolic and cardiovascular disease.

Cardiac pacing in sleep apnoea: diagnostic and therapeutic implications

The sleep apnoea syndrome is a particularly common health problem associated with increased cardiovascular morbidity and mortality, as well as harmful socioeconomical and familial complications. In this article, the diagnostic and therapeutic role of cardiac pacing in this syndrome is discussed.