Research has shown that a common cause of impairment of cognitive function in healthy individuals is the lack of oxygen during sleep.
IT USED to be taken for granted that forgetfulness comes with age. However, research in recent years has provided more information about the underlying causes for deterioration in memory. Contrary to the common belief that relentless memory loss is an inevitable consequence of advancing age, recent research suggests that memory loss can potentially be prevented.
Changes in brain associated with memory impairment
Physicians have been using magnetic resonance imaging (MRI) of the brain to understand changes in the brain that are associated with impairment of cognitive function or memory loss.
Some of the findings seen in the MRI scans of the brain in those who have memory loss and dementia is the presence of reduced grey matter concentration in parts of the brain that are responsible for cognitive ability, concentration, and other vital functions of the brain and the presence of intensely bright white spots (white matter hyperintensities or WMH).
A recent study by Columbia University's Taub Institute for Research on Alzheimer's Disease and the Aging Brain led by Frank Provenzano published in the
JAMA Neurology journal in February 2013 reported that the presence and status of WMH in the brain was a significant predictor of which people with mildly impaired cognitive ability would progress to Alzheimer's disease.
Another study published in the same journal by Bruce Reed from the University of California Davis Alzheimer's Disease Center demonstrated that the presence of small-vessel brain damage in the grey matter had a negative impact on memory, problem-solving ability, and organisational ability. Small-vessel brain damage was visualised as WMH and minor strokes (brain infarcts) in MRI.
Identifying those at risk of memory loss
A study by Lisa Silbert of the Oregon Health and Science University, presented at the American Academy of Neurology meeting in May 2012, showed that MRI can demonstrate the progression of WMH in brains of the elderly as early as 10 years before the onset of mild cognitive impairment.
The researchers also found that total brain volume also decreased five years prior to symptoms of mild cognitive impairment. By monitoring WMH status in the brain, physicians can determine the groups at risk of memory loss and institute measures directed at the diseases that may predispose a person to the development of dementia.
These studies indicate that the small- vessel damage in the brain manifesting as the presence of WMH, grey matter loss, and minor strokes is an important cause of cognitive impairment and may potentially be preventable.
While the presence of uncontrolled high-blood pressure and diabetes mellitus can cause small-vessel damage in the brain, for many apparently healthy individuals with neither of these diseases, an MRI scan of their brains may also demonstrate WMH and grey matter in their brains.
Memory loss in healthy people
Research in the last few years has shown that a common cause of impairment of cognitive function in apparently healthy individuals is the lack of oxygen during sleep.
If you feel tired during the day, have daytime sleepiness, cannot concentrate, tend to be forgetful and snore, you may be having obstruction of your airway during sleep resulting in decreased oxygen level, a condition termed as obstructive sleep apnea (OSA). In more severe cases, as a result of breathing through the mouth, dryness of the throat, choking sensations or coughing may occur during sleep.
Studies have shown that those with moderate to severe OSA demonstrate evidence of brain metabolic injury. Both structural and functional imaging studies have shown consistently that there is a strong correlation between OSA and damage to the hippocampus and the frontal lobes - areas of the brain that play an important role in cognitive abilities.
The presence of OSA also increases the risk of stroke as OSA is associated with high-blood pressure, abnormal heart rhythm, heart disease, and diabetes. Studies have shown that the presence of OSA is associated with an increased incidence of stroke.
A Japanese study by Suzuki published in the journal
Sleep in 2004 suggested that vibration from snoring increased plaque formation in the carotid artery (neck arteries leading to the brain) and this was reduced after correction of OSA. In a study by Minoguchi in 2007, 25 per cent of silent strokes were seen on MRI in moderate to severe OSA patients.
Preventing memory loss
For those with high-blood pressure and diabetes mellitus, optimal control will reduce the likelihood of small-vessel damage in the brain. For healthy individuals with OSA symptoms, avoid sleeping on your back as that will increase the likelihood that the palate will fall backwards towards the back of the throat and obstruct the passage of air.
Some studies have shown that people who use breathing devices, such as continuous positive airway pressure (CPAP) to push oxygen through the airways during sleep, have shown an improvement in both cognitive function and MRI brain findings.
However, the device needs a mask to be worn tightly during sleep and hence compliance is poor. It makes more sense to try to open up your blocked nasal passage than to try to push oxygen through blocked nasal passages via a CPAP device.
More recently, a newer technique has been used to open up the blocked nasal passages which obstruct the entry of air during sleep. By the use of radio frequency techniques, the swollen tissue in the nose can be shrunken to open up the nasal passages. This relatively painless outpatient procedure, that can be completed within minutes, may be a simple way to improve your oxygenation during sleep, thereby preventing deterioration in memory.
However, before you rush off to get your nose "fixed" if you think that your memory is failing you, you may wish to have a discussion with your physician first about having a sleep study to confirm the presence of OSA and an MRI scan of the head which will not only be able to demonstrate brain changes resulting from long-term oxygen deprivation, but will also allow visualisation of any obstruction of the nasal passages and palatal obstruction of the airway.
- Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia (a journal of the British Medical Journal Publishing Group); chairman, scientific advisory board, Asia Pacific Heart Association; and honorary professor and senior medical adviser, Peking University Heart Centre
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