Sleep Disorders and Sleep Deprivation: An Unmet Public

Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem
http://www.nap.edu/catalog/11617.html
70 SLEEP DISORDERS AND SLEEP DEPRIVATION
mined by polysomnography, and adjustments were made for a variety of
confounding factors, including hypertension. That the hypertension adjustment
did not eliminate the effect suggests that hypertension is not the exclusive
means by which OSA may lead to cardiovascular disease. A limitation
of cross-sectional and case-control analyses is that cause and effect cannot
be determined: heart disease may have resulted in OSA or vice versa. However,
an observational cohort study of 1,022 individuals, where 68 percent
of individuals had OSA (apnea-hypopnea index of 5 or higher), showed
that OSA syndrome significantly increased the risk of stroke or death from
any cause, and the increase is independent of other risk factors, including
hypertension (Yaggi et al., 2005). Other studies have confirmed the risk of
OSA syndrome with stroke or death from any cause (Ayas et al., 2003;
Gami et al., 2005). Furthermore, other large prospective studies also have
shown an association between snoring—a marker for OSA—and incidence
of cardiovascular diseases (Jennum et al., 1995; Hu et al., 2000), providing
temporal associations in support of OSA playing a causal role in the development
of heart diseases. As will be discussed in the next section, OSA is
associated with glucose intolerance and diabetes, both of which are independent
risk factors for cardiovascular disease.
Studies of the benefits of CPAP further support an association between
cardiovascular disease and OSA. Marin and colleagues (2005), in a large,
observational study of 10 years’ duration, found that patients with untreated
severe OSA (apnea-hypopnea index greater than 30), relative to those receiving
CPAP treatment, with similar apnea-hypopnea index severity, had a
higher incidence of fatal and nonfatal cardiovascular events. The events
included myocardial infarction, stroke, and coronary artery bypass surgery.
The untreated patients had refused CPAP but were followed regularly. A
second study found an increased mortality rate from cardiovascular disease
in individuals who did not maintain CPAP treatment over a 5-year followup
period (Doherty et al., 2005). However, the number of new cases of
cardiovascular disease was independent of CPAP treatment compliance.
Although observational evidence of this type is not conclusive proof, because
it may be subject to confounding by indication and other biases, it
still lends weight to the strength of the association.
Most studies finding elevated cardiovascular disease risk have been conducted
in adults. Whether or not children with sleep-disordered breathing
are at risk for cardiovascular effects is not known. Children with OSA, as
noted previously, do experience changes in blood pressure profiles, heart
rate variability, and ventricular wall changes as measured by echocardiography
(Marcus et al., 1998; Amin et al., 2005). The paucity of longitudinal
data on OSA in children, in whom levels of OSA may vary during growth
and development and in whom responses to therapies such as tonsillectomy
may be variable (Morton et al., 2001), limits the ability to speculate on the
Copyright © National Academy of Sciences. All rights reserved.