A study published in the July 1, 2008, issue of the journal Sleep provides visual evidence of the severe structural damage that occurs in numerous regions of the brain in people with obstructive sleep apnea (OSA).
Results show that obstructive sleep apnea patients have extensive alterations in “white matter,” nerve tissue in the brain containing fibers that are insulated with myelin — a white, fatty sheath. These structural changes appear both in brain regions that have functional importance for characteristics such as mood, memory, and cardiovascular regulation; and in fiber pathways interconnecting these regions.
“Showing that the fibers are damaged means that many areas that work together to make one feel happy, to adjust blood pressure correctly to circumstances, and to remember properly can affect each other,” said principal investigator Ronald Harper, Ph.D, distinguished professor of neurobiology at the David Geffen School of Medicine at UCLA. “That possibility, that we are now contending with an entire system of structures that serve memory, mood, and blood pressure, rather than individual structures, was surprising.”
The study involved 41 patients with moderate-to-severe obstructive sleep apnea and 69 control subjects matched by age. Diffusion tensor imaging (DTI), a newer modality of magnetic resonance imaging (MRI), was performed to analyze the microstructure of the brain tissue. From this data fractional anisotropy (FA) was derived to measure fiber integrity, resulting in a whole brain FA “map.”
Study subjects with obstructive sleep apnea had lower FA in multiple areas of the brain including regions of the cerebellum, the thalamus and the prefrontal cortex. According to the authors, lower FA primarily represents damage, shrinking or loss of myelin in groups of axons — nerve fibers that transmit impulses away from the body of nerve cells. Such damage may affect the function of these brain regions, while similar changes to the fiber pathways may compromise the relaying of information between regions.
The authors speculate that at least some of these changes result from the fluctuation of oxygen levels caused by pauses, lasting at least 10 seconds, and sometimes as long as 90 seconds or longer, in the breathing of people with obstructive sleep apnea during sleep prior to therapy with a positive airway pressure device.
In this study the subjects with obstructive sleep apnea averaged 15 to 101 partial or complete pauses in breathing per hour of sleep during one night of monitoring at the UCLA Sleep Disorders Laboratory. Blood flow in the brain is reduced during these pauses, the authors also note, and high blood pressure is associated with obstructive sleep apnea; both of these conditions also create a potential for tissue damage.
In a related study published in the June 27, 2008, issue of the journal Neuroscience Letters, the same UCLA research team reported finding that people with sleep apnea also have tissue loss in the mammillary bodies, brain regions that help store memory.
“The findings make it all the more imperative that obstructive sleep apnea be treated as soon as possible to prevent further injury,” said Harper. “The long-term effects of OSA are terribly damaging to memory and thinking processes. Moreover, control of blood pressure is heavily impacted by the breathing condition, and if multiple areas, each connected with one another, are affected, regulation of blood pressure will be all the more difficult if OSA continues.”
The authors conclude that the structural changes found in the study probably represent injury that accumulated over time; it is uncertain if these changes are permanent, or if they can be reversed by treating obstructive sleep apnea.
“The changes in the brain connections we see with this technique may be to some degree reversible,” said lead author Paul Macey, Ph.D, an assistant professor in residence in the UCLA School of Nursing and Brain Research Institute. “However, some of the changes are probably due to fibers and cells having died.”
The most common treatment for obstructive sleep apnea is continuous positive airway pressure (CPAP), which provides a steady stream of air through a mask that is worn during sleep. This airflow keeps the airway open to prevent pauses in breathing and restore normal oxygen levels.
While many people with obstructive sleep apnea snore loudly and frequently, following by periods of silence when airflow is reduced or blocked, and then come to a conclusion when the person begins to make choking, snorting, or gasping sounds when the person’s airway reopens.
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.
Related Posts
Sleep apnea-related memory loss tied to tissue loss, study shows (June 12, 2008)
Links of interest
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