Mortality

Researchers have suggested that patients with SDB may be at increased risk of death compared to those without SDB. Bliwise et al. (60) followed a cohort of noninstitu-tionalized older subjects (mean age 66) for 12 years and found that there was a 2.7 times risk of shorter survival for those with SDB.

A polysomnographic study that reviewed death certificates of patients (mostly in their 60-70 years of age) who had died of cardiac-related death, found that those who had died from midnight to 6 a.m. had a significantly higher AHI than those who died during other time intervals during the day. This study reported that for patients with SDB, the relative risk of sudden death from cardiac causes was 2.57 from midnight to 6 a.m. (35). This is particularly telling about the possible relationship between SDB, heart failure and death if one considers that in general the risk of sudden death from cardiac causes is highest from 6 am to noon and lowest from midnight to 6 a.m. (61).

The estimates of mortality in patients with SDB are high. It is possible that SDB in the elderly is one of several factors which, in combination, lead to increased mortality. There are reports of increased mortality rates in patients with heart failure who develop SDB in combination with Cheyne-Stokes breathing (62,63). Hoch et al. (64) reported that in elderly patients suffering from depression and cognitive impairment, SDB was associated with an excess mortality rate of 450%.

Ancoli-Israel et al. (65) found that community-dwelling elderly with greater SDB (RDI > 30) had significantly shorter survival rates than those with mildmoderate or no SDB. In other studies, however, AHI was not found to be an independent predictor of mortality (65,66). These studies found that cardiovascular and pulmonary conditions, including hypertension, were independent predictors of death. Ancoli-Israel et al. reported that elderly men with congestive heart failure (CHF) had more severe SDB than those with no heart disease. Furthermore, men with both conditions, heart failure and SDB, had shortened life-spans compared to those men with only CHF, only SDB or neither (Fig. 1) (67).

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