Obstructive sleep apnea and vascular disease

There is emerging evidence linking obstructive sleep apnea (OSA) to vascular disease, including hypertension. This relationship may be independent of co-morbidity, such as obesity. Even apparently healthy OSA patients have evidence of subtle functional vascular abnormalities that are known to occur in patients with hypertension and atherosclerosis. Untreated OSA may possibly contribute to the initiation and/or progression of pathophysiologic mechanisms involved in hypertension, heart failure, cardiac ischemia and stroke. This brief commentary will examine the evidence and mechanisms linking OSA to vascular disease.     

阻塞性睡眠呼吸暂停综合征的临床诊治新进展

阻塞性睡眠呼吸暂停综合征在目前耳鼻喉疾病中发病率日益增高,它以频繁发作的气道梗阻为主要特征,常常伴随着呼吸道气道管径减小,并使呼吸道更易发生进一步的狭窄和塌陷.急性和重复性呼吸暂停的副作用包括氧饱和度降低,胸内压减低,白天嗜睡,自主功能损伤和中枢神经系统损伤.呼吸暂停-减弱及呼吸窘迫检测指标有助于量化疾病的严重程度.呼吸暂停综合症有多种临床表现,其中以白天的嗜睡为主要症状.肥胖是重要发病因素之一.目前较为工人的呼吸暂停综合征包括阻塞性,中枢性和混合型三种,其中阻塞性最为常见.本综述主要从该病的X线表现,诊断和治疗这三个方面进行回顾.     

Obstructive sleep apnea and chronic intermittent hypoxia: a review

Hypoxia is an important topic both physiologically and clinically. Traditionally, physiology research has been focusing on the effect of acute and chronic sustained hypoxia and human adaptive response to high altitude. In the past 20 years, genetic studies by many have expanded our understanding of hypoxia to the molecular level. However, in contrast to our extensive knowledge about acute and chronic sustained hypoxia, we know relatively little about the effect of chronic intermittent hypoxia (CIH). In recent years, CIH has attracted more research attention because of the increasing prevalence of obesity and obstructive sleep apnea (OSA) in the western countries. Clinically, CIH is commonly seen in patients with sleep-disordered breathing including OSA, Cheyne-Stokes respiration and nocturnal hypoventilation. It was estimated that for OSA of at least mild severity prevalence estimates range from 3 to 28% in the general population. OSA is characterized by recurrent upper airway collapse during sleep leading to intermittent nocturnal hypoxia and sleep fragmentation. OSA is associated with significant mortality and morbidity including neurocognitive dysfunction, hypertension, many cardiovascular disorders and metabolic disorders such as diabetes and metabolic syndrome. The intermittent hypoxia in OSA closely mimics what is seen in the ischemia-reperfusion injury. Experimentally, there is no universally accepted definition for CIH. Laboratory protocols vary greatly in duration of hypoxia exposure, numbers of hypoxia episodes per day and the total number of days of exposure. Despite the lack of a uniform definition, recent data suggest that CIH may lead to multiple long-term pathophysiologic consequences similar to what we see in patients with OSA. Recent evidences also demonstrate that there are remarkable differences in the response of the physiologic systems to sustained hypoxia and intermittent hypoxia. This review is aimed to briefly discuss the clinical significance of sleep-disordered breathing and our current understanding of CIH.     

Obstructive sleep apnea and the prevalence and incidence of cancer

Background:

A link between obstructive sleep apnea and cancer development or progression has been suggested, possibly through chronic hypoxemia, but supporting evidence is limited. We examined the association between the severity of obstructive sleep apnea and prevalent and incident cancer, controlling for known risk factors for cancer development.

Methods:

We included all adults referred with possible obstructive sleep apnea who underwent a first diagnostic sleep study at a single large academic hospital between 1994 and 2010. We linked patient data with data from Ontario health administrative databases from 1991 to 2013. Cancer diagnosis was derived from the Ontario Cancer Registry. We assessed the cross-sectional association between obstructive sleep apnea and prevalent cancer at the time of the sleep study (baseline) using logistic regression analysis. Cox regression models were used to investigate the association between obstructive sleep apnea and incident cancer among patients free of cancer at baseline.

Results:

Of 10 149 patients who underwent a sleep study, 520 (5.1%) had a cancer diagnosis at baseline. Over a median follow-up of 7.8 years, 627 (6.5%) of the 9629 patients who were free of cancer at baseline had incident cancer. In multivariable regression models, the severity of sleep apnea was not significantly associated with either prevalent or incident cancer after adjustment for age, sex, body mass index and smoking status at baseline (apnea–hypopnea index > 30 v. < 5: adjusted odds ratio [OR] 0.96, 95% confidence interval [CI] 0.71–1.30, for prevalent cancer, and adjusted hazard ratio [HR] 1.02, 95% CI 0.80–1.31, for incident cancer; sleep time spent with oxygen saturation < 90%, per 10-minute increase: adjusted OR 1.01, 95% CI 1.00–1.03, for prevalent cancer, and adjusted HR 1.00, 95% CI 0.99–1.02, for incident cancer).

Interpretation:

In a large cohort, the severity of obstructive sleep apnea was not independently associated with either prevalent or incident cancer. Additional studies are needed to elucidate whether there is an independent association with specific types of cancer.Obstructive sleep apnea is a sleep-related breathing disorder characterized by repetitive episodes of upper-airway obstruction during sleep. Through sleep fragmentation, hypoxemia, hypercapnia, swings in intrathoracic pressure and increased sympathetic activity, these episodes lead to symptoms and health consequences.¹ In 2009, 23% of Canadian adults reported risk factors for obstructive sleep apnea, and 5% of the population 45 years and older reported being told by a health professional that they had the condition.²Obstructive sleep apnea has been postulated to cause cancer^3,4 or cancer progression,⁵ possibly through chronic intermittent hypoxemia,⁶ thus making it a potential modifiable risk factor for cancer development.⁷ However, the longitudinal evidence on this association is limited. Four cohort studies evaluated the longitudinal association between obstructive sleep apnea (expressed by the apnea–hypopnea index, oxygen desaturation or symptoms) and cancer development or cancer-related mortality (Appendix 1, available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.140238/-/DC1).^3–5,8 All had limitations. Of the 3 that reported a positive association,^3,5,8 2 studies included a small number of participants with severe obstructive sleep apnea, had a relatively small number of events and did not consider competing risk of death from other causes;^5,8 and 2 used less reliable sleep-testing devices to define obstructive sleep apnea,^3,8 which may have introduced measurement bias. In the only study that did not show an association between obstructive sleep apnea and cancer,⁴ the former was diagnosed on the basis of self-reported symptoms, which could have resulted in misclassification of exposure.There is a need for a sufficiently large cohort study with a long enough follow-up to allow for the potential development of cancer that adjusts for important potential confounders, examines common cancer subtypes and has a rigorous assessment of both obstructive sleep apnea and cancer.^7,9,10 Our study was designed to improve upon the methods of published studies. We examined the association between the severity of obstructive sleep apnea (expressed by the apnea–hypopnea index or oxygen desaturation) and prevalent or incident cancer after controlling for known cancer risk factors.     

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.     

Pathogenesis of obstructive sleep apnea.

The pathogenesis of obstructive sleep apnea (OSA) has been under investigation for over 25 years, during which a number of factors that contribute to upper airway (UA) collapse during sleep have been identified. Structural/anatomic factors that constrict space for the soft tissues surrounding the pharynx and its lumen are crucial to the development of OSA in many patients. Enlargement of soft tissues enveloping the pharynx, including hypertrophied tonsils, adenoids, and tongue, is also an important factor predisposing to UA collapse, inasmuch as this can impinge on the pharyngeal lumen and narrow it during sleep. Other factors, including impairment of UA mechanoreceptor sensitivity and reflexes that maintain pharyngeal patency and respiratory control system instability, have also been identified as possible mechanisms facilitating UA instability. This suggests that OSA may be a heterogeneous disorder, rather than a single disease entity. Therefore, the extent to which various pathogenic factors contribute to the phenomenon of repetitive collapse of the UA during sleep probably varies from patient to patient. Further elucidation of specific pathogenic mechanisms in individuals with OSA may facilitate the development of new therapies that can be tailored to individual patient needs according to the underlying mechanism(s) of their disease.     

Disorders of glucose metabolism in sleep apnea.

Sleep is a complex behavioral state that occupies one-third of the human life span. Although viewed as a passive condition, sleep is a highly active and dynamic process. The sleep-related decrease in muscle tone is associated with an increase in resistance to airflow through the upper airway. Partial or complete collapse of the airway during sleep can lead to the occurrence of apneas and hypopneas during sleep that define the syndrome of sleep apnea. Sleep apnea has become pervasive in Western society, affecting approximately 5% of adults in industrialized countries. Given the pandemic of obesity, the prevalence of Type 2 diabetes mellitus and metabolic syndrome has also increased dramatically over the last decade. Although the role of sleep apnea in cardiovascular disease is uncertain, there is a growing body of literature that implicates sleep apnea in the pathogenesis of altered glucose metabolism. Intermittent hypoxemia and sleep fragmentation in sleep apnea can trigger a cascade of pathophysiological events, including autonomic activation, alterations in neuroendocrine function, and release of potent proinflammatory mediators such as tumor necrosis factor-alpha and interleukin-6. Epidemiologic and experimental evidence linking sleep apnea and disorders of glucose metabolism is reviewed and discussed here. Although the cause-and-effect relationship remains to be determined, the available data suggest that sleep apnea is independently associated with altered glucose metabolism and may predispose to the eventual development of Type 2 diabetes mellitus.     

Familial lethal sleep apnea

Summary Three of six siblings presented with sleep apnea between 18 and 26 months of age. Twin females and a male had normal growth and development without antecedent neurologic or apparent metabolic disorder. The females presented at 25 and 27 months respectively with irregular respiration and episodes of apnea. Twin A succumbed to an apneic episode while sleeping. Central sleep apnea was diagnosed in twin B at the Stanford Sleep Clinic. She died following an apneic episode three months after evaluation. The male presented at 18 months with fatal sleep apnea. A fourth child was evaluated for sleep apnea at 7 weeks of age with several hospitalizations before her death at 31 months. She and remaining family members were extensively studied for inherited neurologic disorders including subacute necrotizing encephalomyopathy (SANE, Leigh disease). This family with lethal sleep apnea presents an association with SANE with minimal neurologic signs and symptoms and neuropathologic involvement. Lesions were conined to the respiratory centers of the lower brain stem, making sleep apnea explicable. This child and family members tested positive or borderline for inhibitor substance thiamine triphosphate (TTP). All testing for TTP inhibitor substance was performed in Professor Jack R. Cooper's laboratory, Department of Pharmacology, Yale University School of Medicine, New Haven, Conn. These cases present an interesting and instructive lesson emphasizing the need for extensive evaluation of children with unsuspected sleep apnea with early demise.     

Characteristics of sleep structure in patients with sleep apnea]

The course of different sleep phases has been studied in group of patients. A decrease in duration of deep sleep phase and increase in the number of awakenings are found in them.     

Clinical features and treatment of obstructive sleep apnea.

OBJECTIVE: To review the clinical features and treatment of obstructive sleep apnea (OSA). DATA SOURCE AND SELECTION: All articles on OSA published in French and English between 1970 and 1990 and indexed in Index Medicus were reviewed. Studies addressing the epidemiologic features and clinical aspects of OSA were selected, and special emphasis was given to articles reporting the effects of treatment on morbidity and mortality rates. MAIN RESULTS: OSA is characterized by episodes of upper airway obstruction during sleep that result in repetitive hypoxemia and sleep disruption. OSA leads to various neuropsychologic and cardiovascular complications, including daytime hypersomnolence, cognitive impairment, systemic and pulmonary hypertension and cardiac arrhythmias. There is suggestive evidence that the death rate among affected people is increased. The true incidence of OSA is unknown, but estimates have varied from 1% upwards among men. The current treatment with the greatest overall effectiveness and acceptability is nasal continuous positive airway pressure. CONCLUSION: This common, readily treatable disorder is associated with serious complications and therefore must be widely recognized by health professionals.     

Impaired cerebral autoregulation in obstructive sleep apnea

Obstructive sleep apnea (OSA) increases the risk of stroke independent of known vascular and metabolic risk factors. Although patients with OSA have higher prevalence of hypertension and evidence of hypercoagulability, the mechanism of this increased risk is unknown. Obstructive apnea events are associated with surges in blood pressure, hypercapnia, and fluctuations in cerebral blood flow. These perturbations can adversely affect the cerebral circulation. We hypothesized that patients with OSA have impaired cerebral autoregulation, which may contribute to the increased risk of cerebral ischemia and stroke. We examined cerebral autoregulation in patients with and without OSA by measuring cerebral artery blood flow velocity (CBFV) by using transcranial Doppler ultrasound and arterial blood pressure using finger pulse photoplethysmography during orthostatic hypotension and recovery as well as during 5% CO(2) inhalation. Cerebral vascular conductance and reactivity were determined. Forty-eight subjects, 26 controls (age 41.0+/-2.3 yr) and 22 OSA (age 46.8+/-2.3 yr) free of cerebrovascular and active coronary artery disease participated in this study. OSA patients had a mean apnea-hypopnea index of 78.4+/-7.1 vs. 1.8+/-0.3 events/h in controls. The oxygen saturation during sleep was significantly lower in the OSA group (78+/-2%) vs. 91+/-1% in controls. The dynamic vascular analysis showed mean CBFV was significantly lower in OSA patients compared with controls (48+/-3 vs. 55+/-2 cm/s; P <0.05, respectively). The OSA group had a lower rate of recovery of cerebrovascular conductance for a given drop in blood pressure compared with controls (0.06+/-0.02 vs. 0.20+/-0.06 cm.s(-2).mmHg(-1); P <0.05). There was no difference in cerebrovascular vasodilatation in response to CO(2). The findings showed that patients with OSA have decreased CBFV at baseline and delayed cerebrovascular compensatory response to changes in blood pressure but not to CO(2). These perturbations may increase the risk of cerebral ischemia during obstructive apnea.