It is increasingly recognized that many adults have sleep disordered breathing patterns characterized as obstructive sleep apnea and hypopnea. There appears to be a high prevalence of these abnormalities in patients with cardiovascular disease, in the range of 30-50% (148). There is evidence that the disorder may increase the relative risks of myocardial infarction (149,150), sudden death (151), and cardiovascular death (152). One small study of 40 patients admitted with acute myocardial infarction found a significantly higher prevalence of sleep apnea in patients with myocardial infarction onset in the morning (153).
Apneic events during sleep result in acute increases in blood pressure, vascular resistance, and sympathetic nervous system activity, and some events may be associated with hypoxemia (148). In 17 patients with moderate and severe obstructive sleep apnea, platelet aggregation induced by epinephrine was increased at midnight and 6 am (compared to 8 pm), in contrast to an overnight decrease in this variable in 15 age-matched controls (154). A similarly small study found an overnight increase in whole blood viscosity in obstructive sleep apnea patients compared to controls (155). Therefore, it is not surprising that studies have identified myocardial ischemic episodes in association with obstructive sleep apnea (156,157). Despite these suggestive data, one recent review identified methodologic difficulties in a number of the epidemiologic studies prior to 1996 and cast doubt on the significance of obstructive sleep apnea as an independent risk factor for acute cardiac events (158).
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