A Breathe of Fresh Air

by Mind Over Matter V 13:

Oxygen’s Crucial Role in Brain Health

Oxygen is critical to the healthy functioning of the entire body but is especially so for the brain. Although the brain is relatively small (representing approximately 2% of body weight in the average adult human), it uses approximately 20% of oxygen intake to function normally. The brain requires a steady supply of oxygen; without it, brain cells begin to die within as few as five minutes.

Cerebral hypoxia is associated with a host of serious consequences that vary depending on the cause of the lack of oxygen, as well as the severity and duration, and may include memory problems, motor function difficulties, cognitive decline, seizures, dementia, and even death.

There are many causes of lack of oxygen in the brain. Some are acute (i.e., severe and sudden), such as when blood flow to the brain is blocked completely during an ischemic stroke, or when a person is experiencing a severe asthma attack, choking, or drowning. Others are chronic (i.e., long-term), like in cases of chronic obstructive pulmonary disease (COPD) or sleep-disordered breathing.

BRAIN HEALTH IMPLICATIONS OF IMPAIRED BREATHING

Breathing is key to your brain receiving the oxygen it needs. Your lungs take in oxygen when you inhale and release carbon dioxide when you exhale. The oxygen breathed in binds with red blood cells and is carried through your blood circulation system to all parts of your body, including your brain. 

COPD and sleep-disordered breathing are two common disorders that negatively impact breathing, and accordingly affect blood oxygen levels and cognitive function. 

One systematic review and meta-analysis – published in 2018 in the International Journal of Chronic Obstructive Pulmonary Disease – reported that the global prevalence of COPD is 9.23% in men and 6.16% in women. The World Health Organization lists COPD as the third-leading cause of death worldwide, with over 80% of those deaths occurring in low- and middle-income countries. 

In a systematic review published in Sleep Medicine Reviews in 2017, researchers found a wide range in the reported prevalence rates for obstructive sleep apnea in adults in the general population (because of substantial variation in research methodology). The overall prevalence rate ranged from 9% to 38% when considering all levels of severity of sleep apnea and was higher in men. Further, prevalence was found to increase with age and, in some elderly groups, was as high as 90% among the men and 78% in the women.

What is the impact of COPD and obstructive sleep apnea on cognitive function? A meta-review conducted by researchers in Australia reported on the collective findings from 18 systematic reviews and meta-analyses that looked at the impacts of COPD, untreated obstructive sleep apnea, and other sleep-related problems on cognitive function in adults. They found that, compared to people in the control groups, 

PARTICIPANTS WITH OBSTRUCTIVE SLEEP APNEA OR COPD HAD DEFICITS IN A WIDE RANGE OF COGNITIVE AREAS: ATTENTION, MEMORY, EXECUTIVE FUNCTION, PSYCHOMOTOR FUNCTION, AND LANGUAGE ABILITIES. 

These findings were shared in April 2018 in Sleep Medicine Reviews. 

COPD and sleep-disordered breathing have also been linked with increased risk of dementia, and that association appears to be related (at least in part) to the lack of oxygen experienced in both conditions. When oxygen therapy is used in cases of COPD, it reduces the risk of cognitive impairment, dementia, and death. 

Moreover, treating obstructive sleep apnea with continuous positive airway pressure (CPAP) prevents intermittent hypoxia throughout the night, and has been found to improve (or delay the decline in) cognitive function and reduce the risk of dementia. Interestingly, the administration of supplemental oxygen has also been found in different studies to positively affect cognitive processing in healthy adults, both young and old. In other words, optimal oxygen levels can give a cognitive boost to healthy individuals, and not just help those with breathing disorders.

One study – by Dr. Kristine Yaffe and colleagues, published in 2011 in the Journal of the American Medical Association (JAMA) – looked specifically at the cognitive impacts of sleep-disordered breathing in nearly 300 older women, 105 of whom had moderate to severe obstructive sleep apnea (with the remaining women serving as the control group). 

OVER THE FIVE-YEAR STUDY PERIOD, THE WOMEN WITH SLEEP-DISORDERED BREATHING WERE 85% MORE LIKELY TO DEVELOP MILD COGNITIVE IMPAIRMENT (MCI) OR DEMENTIA THAN THE WOMEN IN THE CONTROL GROUP. 

Measures related to hypoxia were found to be associated with the increased risk of developing MCI or dementia, while measures of sleep fragmentation were not, suggesting that insufficient oxygen may be the key culprit underlying the cognitive difficulties experienced by those with untreated sleep-disordered breathing. 

These findings emphasize the importance of diagnosing and treating sleep apnea. Using CPAP or supplemental oxygen therapy addresses this problematic nighttime oxygen loss, and could have a large public health impact, given the high prevalence of sleep-disordered breathing and cognitive impairment among older adults.

HOW BLOOD OXYGEN LEVELS IN THE BRAIN AFFECT MEMORY LOSS

The brain requires an abundant supply of oxygen and when it does not receive enough, there are cognitive consequences. But what exactly is happening inside the brain during periods of insufficient oxygen that negatively impacts memory in particular? A team of researchers from the University of Sussex recently shared study findings that provide some insight into the importance of oxygen for the “brain’s memory centre” (i.e., the hippocampus). 

The researchers compared brain activity and blood flow in the hippocampus versus the visual cortex of mice. Compared to the visual cortex, the hippocampus was found to have lower resting blood flow and blood oxygenation. Additionally, blood vessels in the hippocampus dilated less frequently and to a smaller degree in response to increased neuronal activity than in the visual cortex. 

The researchers then looked at simulations of oxygen diffusion and concluded that these differences in how the blood vessels operate in the hippocampus may restrict oxygen availability in this region of the brain. The differences could also help to explain why the hippocampus is so sensitive to damage in neurological conditions such as Alzheimer’s disease, where reduced oxygen levels might promote the toxic accumulation of proteins that cause brain damage. 

“These findings provide a potential explanation for why memory loss is an early symptom in Alzheimer’s disease. The brain finely regulates oxygen supply through neurovascular coupling, a process where active neurons signal to dilate local blood vessels to increase blood flow and oxygen/glucose supply to the active brain regions. Yet our study showed that neurovascular function in the hippocampus is different than in another part of the brain; the hippocampus appears to be not as good at shifting its oxygen supply in response to fluctuating energy demands from neurons,” said Dr. Catherine Hall, Senior Lecturer in Psychology at the University of Sussex and lead researcher on this study.

“INCREASING BLOOD FLOW IN THE HIPPOCAMPUS MIGHT BE A REALLY EFFECTIVE WAY TO PREVENT DAMAGE FROM HAPPENING IN THAT CRITICAL AREA FOR MEMORY; AND IF THAT’S TRUE, IT PROVIDES FURTHER SUPPORT FOR THE IMPORTANCE OF ALL OF THE HEALTHY LIFESTYLE CHOICES TYPICALLY ADVISED FOR HEART HEALTH, LIKE REGULAR EXERCISE AND A HEALTHY DIET.”

TIPS FOR GETTING MORE OXYGEN TO YOUR BRAIN

·       If you have an untreated breathing disorder, such as COPD or sleep-disordered breathing, see your doctor as soon as possible. There are effective treatments available that can help you breathe better, get more of the oxygen you need, and help prevent, halt, or even reverse cognitive decline related to the disorder.

·       Make lifestyle choices that support healthy cardiovascular function – for example, exercise, eat nutritious food, do not smoke, and limit your alcohol intake. Additionally, if you have high blood pressure or cholesterol, take any medications that your doctor has prescribed.

·       Meditate with an emphasis on slow, deep breathing to help reduce stress and improve your oxygen intake.

·       Grow plants indoors. The Lung Health Institute lists the following five plants as great options for increasing oxygen indoors and purifying the air: Chinese Evergreen, Gerbera Daisy, Money Plant, Snake Plant, and Areca Palm. 

·       When weather allows and the outdoor air quality is good, open up your windows to let in fresh air and make breathing easier. 

(Hypoxia refers to a deficiency in the amount of oxygen reaching bodily tissues. Cerebral hypoxia refers to insufficient oxygen supply in the brain.)

Chronic obstructive pulmonary disease (COPD) is a group of lung conditions, including emphysema and chronic bronchitis, which limit air flow and make breathing difficult. Common symptoms include shortness of breath, wheezing, and mucus production.

Sleep-disordered breathing is an umbrella term for several chronic conditions, including obstructive sleep apnea, where a person stops breathing during sleep (either partially or completely), thereby causing intermittent hypoxia. In addition to hypoxia, a person with sleep-disordered breathing experiences sleep fragmentation from recurrent arousals from sleep. Both hypoxia and sleep fragmentation can negatively impact cognitive function.

The coronavirus disease (COVID-19) is another cause of hypoxia. Of particular concern are those individuals with serious cases of the virus who have abnormally low blood oxygen levels, but do not exhibit symptoms such as shortness of breath or trouble breathing. Despite experiencing potentially life-threateningly low oxygen levels, they may feel fine and not seek medical attention. Researchers call this “silent hypoxia” because the low oxygen levels are quietly inflicting damage in the absence of obvious symptoms. 

In their study of 1,095 people hospitalized with COVID-19 in the United States, Dr. Neal Chatterjee and colleagues found that blood-oxygen saturation and respiration rate were associated with higher mortality rates. These findings – published in April 2021 in Influenza and Other Respiratory Viruses – led the researchers to recommend that those with COVID-19 should be aware of the following measures, which can easily be monitored at home:

·       The simplest measure to watch is respiratory rate, which does not require any equipment; simply have someone count your number of breaths per minute at a time when you are not paying attention, and if you hit 23 breaths per minute, contact your doctor.

·       Watch for low blood oxygen levels using a pulse oximeter, a clip-like device that fits over a fingertip and monitors oxygen saturation of red blood cells. Contact your doctor if you get a reading below 92%. This is of particular importance for people who are at higher risk of adverse COVID-19 outcomes, such as older or obese individuals.