Obstructive sleep apnea and cardiovascular disease: role of the metabolic syndrome and its components

Abstract

Although obstructive sleep apnea and cardiovascular disease have common risk factors, epidemiologic studies show that sleep apnea increases risks for cardiovascular disease independently of individuals' demographic characteristics (i.e., age, sex, and race) or risk markers (i.e., smoking, alcohol, obesity, diabetes, dyslipidemia, atrial fibrillation, and hypertension). Individuals with severe sleep apnea are at increased risk for coronary artery disease, congestive heart failure, and stroke. The underlying mechanisms explaining associations between obstructive sleep apnea and cardiovascular disease are not entirely delineated. Several intermediary mechanisms might be involved including sustained sympathetic activation, intrathoracic pressure changes, and oxidative stress. Other abnormalities such as disorders in coagulation factors, endothelial damage, platelet activation, and increased inflammatory mediators might also play a role in the pathogenesis of cardiovascular disease. Linkage between obstructive sleep apnea and cardiovascular disease is corroborated by evidence that treatment of sleep apnea with continuous positive airway pressure reduces systolic blood pressure, improves left ventricular systolic function, and diminishes platelet activation. Several systematic studies are necessary to explicate complex associations between sleep apnea and cardiovascular disease, which may be compounded by the involvement of diseases comprising the metabolic syndrome (i.e., central obesity, hypertension, diabetes, and dyslipidemia). Large-scale, population-based studies testing causal models linking among sleep apnea, cardiovascular morbidity, and metabolic syndrome are needed.

Figure 1

Proposed pathway linking sleep loss to cardiovascular disease. Of note, obesity triggers the onset of sleep apnea in a significant number of cases.

Figure 2

Prevalence of metabolic syndrome components and cardiovascular disease among patients with a diagnosis of sleep apnea; risks of cardiovascular disease for patients with sleep apnea are also indicated.

Figure 3

Interrelationships between metabolic diseases comprising the metabolic syndrome and sleep apnea. Together, these diseases are referred to as Syndrome Z in the field of sleep medicine. Available epidemiologic and clinical evidence suggests that all of these conditions interact with each other through complex, yet undifferentiated pathophysiological pathways, thereby increasing risks for cardiovascular disease.

Figure 4

Benefits of sleep apnea treatment, which may include CPAP/bilevel PAP therapy (sometimes used in combination with behavior modification), use of oral-dental devices, or surgical procedures (e.g., UPPP and LAUP).

Figure 5

Prevalence of metabolic diseases linked to obesity based on ethnicity: black (B) vs. white (W). Data were retrieved from the Center for Disease Control (CDC), National Health and Nutrition Examination Survey (NHANES), the Genetic Epidemiology Network of Arteriopathy (GENOA) and the Sleep Heart Health Study (SHHS).