Sleep apnea-related memory loss tied to tissue loss, study shows

For the first time, UCLA researchers have discovered that people with sleep apnea show tissue loss in brain regions that help store memory. Reported in the June 27, 2008 edition of the journal Neuroscience Letters, the findings emphasize the importance of early detection of the disorder, which afflicts an estimated 20 million Americans.

Sleep apnea occurs when a blocked airway repeatedly halts the sleeper’s breathing, resulting in loud bursts of snoring and chronic daytime fatigue. Memory loss and difficulty focusing are also common complaints. Prior studies have linked the disorder to a higher risk of stroke, heart disease and diabetes.

"Our findings demonstrate that impaired breathing during sleep can lead to a serious brain injury that disrupts memory and thinking," said principal investigator Ronald Harper, a distinguished professor of neurobiology at the David Geffen School of Medicine at UCLA.

The study focused on structures called mammillary bodies, so named because they resemble small breasts, on the underside of the brain.

The UCLA team scanned the brains of 43 sleep apnea patients, using magnetic resonance imaging (MRI) to collect high-resolution images of the entire brain, including slices of the mammillary bodies.

The structures’ small size and proximity to bone and fluid make them difficult to measure by conventional MRI. So the researchers manually traced the mammillary bodies from the high-resolution scans and calculated their volumes from the hand-drawn outlines.

When they compared the results to images of 66 control subjects matched for age and gender, the scientists discovered that the sleep apnea patients’ mammillary bodies were nearly 20 percent smaller, particularly on the left side.

"The findings are important because patients suffering memory loss from other syndromes, such as alcoholism or Alzheimer disease, also show shrunken mammillary bodies," said lead author Rajesh Kumar, a UCLA assistant researcher in neurobiology.

"Physicians treat memory loss in alcoholic patients with massive amounts of thiamine, or vitamin B1," he added. "We suspect that the dose helps dying cells to recover, enabling the brain to use them again."

The scientists’ next step is to determine how sleep apnea causes tissue loss in the mammillary bodies.

Harper hypothesizes that repeated drops in oxygen lead to the brain injury. During an apnea episode, the brain’s blood vessels constrict, starving its tissue of oxygen and causing cellular death. The process also incites inflammation, which further damages the tissue.

"The reduced size of the mammillary bodies suggests that they’ve suffered a harmful event resulting in sizable cell loss," Harper said. "The fact that patients’ memory problems continue despite treatment for their sleep disorder implies a long-lasting brain injury."

In a future study, Harper and Kumar will explore whether taking supplemental vitamin B1 helps restore sleep apnea patients’ memory. The vitamin helps move glucose into the cells, preventing their death from oxygen starvation.

"UCLA researchers used sophisticated imaging technology to identify brain lesions associated with impaired memory in individuals with obstructive sleep apnea," said Elizabeth G. Nabel, director of the National Heart, Lung and Blood Institute, which funded the study. "These results underscore the importance of early diagnosis and treatment of sleep-disordered breathing, which can have long-term effects on patients’ health and well-being."

Obstructive sleep apnea occurs when the muscles in the throat, soft palate and tongue relax during sleep and sag, narrowing the airway. The tongue slides to the back of the mouth, blocking the windpipe and cutting off oxygen to the lungs.

The sleeper wakes up, gasping for air, and falls back into a fitful sleep. The cycle can repeat itself hundreds of times per night.

Study co-authors included Bramley Birrer, Paul Macey, Mary Woo and Frisca Yan-Go of UCLA, and Rakesh Gupta from the Sanjay Gandhi Institute of Medical Sciences, India.

Almost everyone is likely to snore at one time or another, and while most people with apnea snore, not everyone who snores has apnea. It has been found in all age groups. Estimates of snoring vary widely based on how it is defined.

Habitual snoring has been found in about 24 percent of adult women and 40 percent of adult men. Both men and women are more likely to snore as they age. Men, however, become less likely to snore after the age of 70.

Obstructive sleep apnea is best treated by the use of a positive airway pressure device, such as a continuous positive airway pressure device, or CPAP, or a bi-level positive airway pressure device, or bi-level. Some people mistaken refer to all bi-level devices as BiPAP machines, although the word BiPAP is a registered trademark of Respironics, Inc., for a specific line of bi-level devices. The term xPAP is used when speaking of positive airway pressure machines, overall, when one specific type of machine is not being discussed.

Other treatments for apnea exist, though the success rate at eliminating the apneas — especially without surgery — are not close to the almost 100 percent success rate of xPAP devices. They include oral devices, including custom devices made by dentists; surgeries; and an implant that’s been on the market for a few years with mixed comments.

Links of interest

Have you had bouts of insomnia lasting two weeks or more? Do you walk around in a constant fog, feeling sleepy, fatigued, and as though you have no energy? Perhaps you "feel" older than you are, or maybe it’s all you can do to stay awake while driving. If any of that, or similar issues are familiar, or if you snore or have disrupted sleep, even if just a few simple, repeat trips to the bathroom during the night, check out these two online tests to help you get to the root of the issue. While they will not make a diagnosis for you, they will help you, your physician, or, more appropriately, a sleep specialist, find out what’s causing you the problem sleepiness.

• Epworth Sleepiness Scale
• World Class Snoring Quiz

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