Cardiovascular Consequences

In younger adults, SDB has been shown to be a risk factor for hypertension (27-29). Even minimal amounts of SDB (AHI 0.1-4.9), considered by most not to be pathologic, have been shown to increase the risk of developing hypertension compared to an AHI of zero (29). A link between apnea severity and elevations in blood pressure has also been reported. A study by Lavie et al. (27) showed that each additional apneic event per hour of sleep increased the odds of hypertension by 1%, and each oxygen desaturation of 10% increased the odds by 13%.

The relationship between SDB and hypertension in older adults however is not as clear. There are studies that have reported an association between hypertension and SDB in the older adult (30,31), but more recent data from the Sleep Heart Health Study suggested that there was no association between SDB and systolic/ diastolic hypertension in those aged > 60 years (32). A recent study in middle-aged adults found that severe SDB was associated with pulmonary hypertension and that CPAP treatment of the SDB reduced pulmonary systolic pressure (33). Similar studies are needed in the elderly.

There is evidence of SDB being associated with cardiac arrhythmia, myocar-dial infarction, hypercoagulable state, and sudden death (34,35). However, the relationship between SDB and cardiovascular events in the elderly is less clear as most studies have been performed in middle-age adults. The best data come from the Sleep Heart Health Study, which produced strong evidence in support of the association between SDB and ischemic heart disease (34). Results suggested a positive association between the severity of SDB (objectively measured with polysomnography) and the risk of developing cardiovascular disease including coronary artery disease and stroke. In this study, independent of known cardiovascular risk factors, even mild to moderate SDB was associated with the development of ischemic heart disease.

Severity of SDB is an important factor in predicting myocardial infarction in cardiac patients. A study by Hung et al. (36) showed that in male cardiac patients, 66 years old or younger, severe SDB was 25 times more likely to be associated with myocardial infarction compared to mild SDB. There is also evidence that snoring by itself increases the risk of ischemic heart disease in both men and women (37).

Studies have found a high prevalence of SDB in patients with congestive heart failure (38,39). Some research suggests that SDB may exacerbate or even cause the heart failure. The Sleep Heart Health Study found that the severity of SDB was positively associated with the development of congestive heart failure and, like ischemic disease, even mild to moderate SDB was associated with its development (34).

Central sleep apnea and OSA, as well as Cheyne-Stokes respiration, are all common in patients with heart failure. Javaheri et al. (39) reported that 40% to 50% of outpatients, predominantly males, with stable, mild, medically treated congestive heart failure had SDB. In addition, AHI has been shown to be a powerful predictor of poor prognosis in this group of patients (40).

Studies suggest that there is a direct relationship between cerebrovascular conditions and SDB in adults. There are reports of patients with a cerebrovascular accident having higher prevalence of SDB compared to age- and gender-matched controls without SDB (37). The Sleep Heart Health Study found an association between the severity of SDB and the risk of developing cerebrovascular disease and reported that even mild to moderate SDB increases this risk (34). In many patients the SDB persists even after the resolution of the stroke related symptoms, strengthening the argument that the SDB precedes the development of cerebrovascular disease (37). For those patients who have suffered a stroke, the presence of SDB and its severity has been found to be an independent prognostic factor related to mortality, with a 5% increase in mortality risk for each additional unit of AHI (41). In addition, similarly to traditional risk factors for stroke such as hypertension, smoking, and hyperlipidemia, there is evidence of an independent association between self-reported snoring and stroke in the elderly (42).

The nature of the relationship between SDB and cerebrovascular disease in adults and in the elderly is still to be defined; however, as reported earlier, there is evidence that SDB might precede the development of a stroke and may in fact be a risk factor (37).

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