12/14/11

Editor’s Note

Sleep-disordered breathing – recurrent arousals and intermittent hypoxemia – raised elderly women’s risk of developing cognitive impairment within 5 years.

The hypoxia associated with sleep-disordered breathing, rather than sleep fragmentation or shorter sleep duration, appeared to be behind increased risk for both mild cognitive impairment and dementia, said Kristine Yaffe, MD, of the departments of psychiatry, neurology, and epidemiology at the University of California, San Francisco, and her associates in JAMA (2011;306:613-9).

Both sleep-disordered breathing and cognitive impairment are common in elderly people, but no longitudinal study had ever examined whether the breathing disorder precedes the cognitive impairment. Dr. Yaffe’s team turned to data from the Study of Osteoporotic Fractures, a multicenter cohort assessment of predominantly white women aged 65 years and older at baseline in 1986-88.

For this analysis, Dr. Yaffe and her associates followed 298 subjects who from 2002 to 2004 underwent overnight polysomnography in their homes in Minnesota and Pennsylvania. Of that group, 105 women (35%) met the criteria for sleep-disordered breathing.

A mean of 5 years later, the polysomnography-tested women, mean age 82 years, completed a battery of neuropsychological tests to determine cognitive status. A total of 107 (36%) had developed mild cognitive impairment (60 women) or dementia (47 women).

Significantly more women who had sleep-disordered breathing developed cognitive impairment (45%) than did women who did not have sleep-disordered breathing (31%). The presence of the condition was associated with increased odds of cognitive impairment (odds ratio, 1.80).

Two out of three measures of hypoxia correlated with cognitive impairment. None of the study’s indices of sleep fragmentation and sleep duration – arousal, wakefulness after sleep onset, and total sleep time – correlated with cognitive impairment.

The researchers concluded that hypoxia is the apparent means by which sleep-disordered breathing causes cognitive impairment. "However, it is important to note that because cerebral blood flow may be affected in elderly patients, other mechanisms such as hypercapnia could also be involved," the investigators said. They added that the findings suggest that interventions to address sleep-disordered breathing in general and hypoxia in particular may prevent or improve cognitive impairment.

Previous studies in patients with Alzheimer’s disease have shown that continuous positive airway pressure (CPAP) for sleep-disordered breathing slows or even improves cognitive impairment, Dr. Yaffe and her colleagues noted. The new findings suggest that supplemental oxygen therapy might also be beneficial, they added.

"To fully evaluate the impact of treatment for sleep-disordered breathing in elderly populations, additional trials with larger sample sizes, longer treatment periods, and more diverse populations are required," the researchers said added. "Given the high prevalence of both sleep-disordered breathing and cognitive impairment among older adults, the possibility of an association between the two conditions, even a modest one, has the potential for a large public health impact."

In an editorial accompanying the report, Nicola Canessa, PhD, and Luigi Ferini-Strambi, MD, of the neuroscience and sleep centers at the San Raffaele Scientific Institute, Milan, Italy, said that the new findings support supplemental oxygen for sleep-disordered breathing in the elderly, and the authors recommend further study (JAMA 2011;306:654-5). But they noted that the therapy has not been studied extensively as a treatment of sleep-disordered breathing, and potential dangers include prolongation of apnea, increased hypercarbia and acidosis, and increased ventricular irritability.

In contrast, continuous positive airway pressure (CPAP) is a potential prevention strategy that has been studied in sleep-disordered breathing, they wrote. Both physicians with patients who are candidates for CPAP and authors of future guidelines on managing patients with mild cognitive impairment should consider these new results, Dr. Canessa and Dr. Ferini-Strambi said.

The study was supported by the National Institute on Aging. The Study of Osteoporotic Fractures was supported by the National Institutes of Health. Dr. Yaffe reported ties to Novartis, Pfizer, Medivation, Beeson Scientific Advisory, the National Institute of Mental Health, the Alzheimer’s Association, the Department of Defense, the American Health Assistance Foundation, Japan Geriatrics Society, Wake Forest University, and the State of California Department of Human Services. Her associates reported ties to several pharmaceutical companies.

Mary Ann Moon is a freelance writer based in Clarksburg, Md.