This is Your Brain on Sleep Apnea: A Quick Look at the Cognitive Effects of Treated vs Untreated OSA

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This is Your Brain on Sleep Apnea: A Quick Look at the Cognitive Effects of Treated vs Untreated OSA

By Admin

While we hear a lot about sleep apnea’s effects on heart health and metabolic health, some of the disorder’s most immediate effects occur in the brain. Sleep disorders, especially sleep apnea, can have extremely devastating effects on brain health, and CPAP, as an established first-rate treatment option, can not only treat the disorder’s symptoms but can even reverse the damage caused by lack of treatment in the past. As a sleep apnea patient, it is good to have a basic understanding of how sleep apnea affects the brain and its functions, as it may give you an idea of why it is so important to remain compliant to treatment without interruptions. Below is a brief but informative introduction to the effects of sleep apnea on the brain. Links are provided for further information on specific subject areas, and we encourage our readers to stay informed, stay safe, and seek professional guidance if you experience any of the symptoms referred to in this article.

The Brain and Sleep

While there is a lot we still don’t know about the human brain, sleep science has come a long way since the discovery of sleep stages in the 1950s. While tools such as EEG now provide a clearer measure of brain activity during sleep, close observation of the sleep stages gives us invaluable insights into sleep processes that we continue to rely on today. The primary stages are often separated into rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, which has three separate stages of its own. Each stage serves a separate function and involves specific physiological processes. When you sleep, you cycle through these stages at varied intervals depending on your own individual physiology and chronobiological rhythms.

Typically, REM sleep, a period of deep sleep when dreaming often occurs, will last longer during each cycle throughout the night, and each stage progressing toward REM sleep serves to restore the brain’s energies for optimal function The reason this is important is because sleep deprivation or fragmentation disrupts these cycles and limits the brain’s ability to function properly.

When sleep is deprived or fragmented, the brain does not have the time it needs to perform its nightly functions, and toxins can build up as a result, further affecting your ability to think clearly. A series of processes known as the glymphatic system flushes out these toxins and clears the brain for proper functioning upon waking. Disruption of these processes can lead to the grogginess that people feel after insufficient or low-quality sleep. This is also how the brain consolidates and organizes memories from daily experiences. Like the glymphatic system, memory consolidation functions occur gradually through the stages of sleep. It takes time to build up to these processes, and any disruption in the sleep stages, even if the sleeper doesn't wake, can still result in impaired functions.

The Brain and Sleep Apnea

A meta review published in the journal Respirology provides a good summary of research findings on sleep apnea and the brain. Points of consensus among the studies reviewed include the following: deficits in attention and/or vigilance, delayed visual and verbal memory, visuospatial/constructional deficits, and problems with executive function or emotional processing among patients with moderate to severe sleep apnea, while some studies identify problems with working memory, short-term memory, and global cognitive functioning. While many of these issues are related to sleep fragmentation and resulting hypoxia effects, rather than the apnea events themselves, the result is the same.

Research on this link between sleep apnea conditions and brain health has been extensive in recent years, with many studies focusing on specific aspects of the relationship, such as cerebral blood flow, memory problems, brain matter changes, and other functions known to be affected by sleep disruption. Each of these areas of study is outlined below, and links are provided for further reading:

Blood Oxygen and Cerebral Hypoxia

One of the most studied and most damaging effects of sleep apnea is hypoxia or hypoxemia. Hypoxemia is defined as a decrease in the partial pressure of oxygen in the blood whereas hypoxia is defined by reduced levels of tissue oxygenation. Both are problematic, and both result from reductions in blood oxygen levels due to apnea and/or hypopnea events. When this condition progresses to the point that blood oxygen levels in the brain are reduced, the effects can be extremely damaging, potentially causing long-term or permanent alterations of electrical activity needed for everyday cognitive and emotional performance.

According to studies cited by The Lancet, inadequate oxygen supply to the tissues plays a pivotal role in a number of common comorbid conditions associated with sleep apnea, including myocardial infarction, stroke, cancer, metabolic disease and diabetes, and pulmonary obstruction or COPD. In more extreme cases, cerebral hypoxia or cerebrovascular disease can further affect brain health by limiting blood flow and oxygen to life-threatening levels. Any of these factors can affect cognition in a number of ways, including the specificity of the conditions involved, the stage and pathophysiology of the disease processes, and other effects on bodily systems. While blood oxygen saturation is one thing we know a lot about in terms of sleep apnea’s effects on the brain, it is also part of an inherently complex relationship between the brain, the body, and lifestyle choices that affect sleep health on a daily basis.

Memory

Over a century of research has established the fact that sleep health is conducive to memory and alertness in daily life, but more specific studies on the effects of sleep apnea and its resulting fragmentation often have varied results. One reason for this variation is the complex relationship between sleep apnea and other comorbid conditions that may affect memory and cognition. One study, for example, published in the Journal of Sleep Research, combined neuropsychological testing with brain imaging data to assess the effects of apnea events over time. The results showed clear attentional lapses and memory gaps, but the specific origin of the impairments remained unclear. Studies like these are extremely important because they provide an opportunity to test the effects of untreated sleep apnea, which is a growing problem affecting millions of Americans.

One explanation suggests that people with sleep apnea have difficulties converting short-term memories into long term memories. Sleep is thought to play a role in this type of memory storage, allowing for more effective long-term recall. When sleep is altered by apnea events, the sufferer will have incomplete memory storage processes, especially with the addition of respiratory events and blood oxygen reductions. These types of limitations not only cause memory problems, but can also lead to confusional states similar to dementia.

Brain Matter Changes

One of the most surprising effects of sleep apnea is the reduction of gray matter and other physical changes of the brain. Studies have not only found gray matter deficits in individuals with sleep apnea, but have suggested that they may play a role in the disruption of autonomic and respiratory control as well as memory and cognition. This could potentially explain the phenomenon known as treatment-emergent central sleep apnea (CSA), a form of complex sleep apnea in which the treatment of OSA gives rise to CSA episodes.

Gray matter is located primarily in the cerebral cortex, where the brain does most of its processing of information. Rather than the myelinated (a form of insulation) axons that make up most of the brain’s white matter, gray matter consists primarily of neuronal cell bodies that do not have the white coating. These two areas of the brain are interconnected and both play a role in sleep processes. While gray matter changes receive more attention, there have also been studies on white matter changes that are just as alarming, relating deficits in both regions to repeated apnea events. This means that untreated sleep apnea can potentially change the shape of a patient’s brain, causing semi-permanent brain damage. While the relationship between sleep apnea and brain matter deficits is less consistent among patients with mild to moderate conditions, the link becomes much stronger with moderate to severe apnea and related hypoxemia. Only in recent years have doctors realized the effectiveness of CPAP therapy in reversing this type of brain damage caused by apnea, but patients still have differing responses to therapy, and the extent of residual damage is one possible explanation for the variation in treatment outcomes.

The Brain and CPAP

Almost across the board CPAP has shown positive increments in each of the areas mentioned above, including those in the meta-review list published in Respirology. Even gray matter reductions, which can change the shape of a patient’s brain, have shown considerable improvements after consistent use of CPAP for just three months. In fact, researchers have been surprised by just how significant the reversals can be, especially when proper sleep is restored after a period of fragmentation. When this occurs, a period of REM rebound often occurs, allowing patients to achieve deep states of sleep to make up for lost time.

According to a study on brain topography, extensive damage caused by sleep apnea, such as alterations of brain electrical activity, visuospatial abilities, long-term memory, and motor performances caused by chronic hypoxia could be reversed by CPAP therapy. According to the study, this includes significant damage in the brain’s fiber pathways responsible for mood regulation, memory consolidation, and autonomic functions such as respiration and blood pressure. In short, nearly every consequence of sleep apnea, however significant, can show potential improvements through routine PAP therapy compliance. And this is in line with numerous studies confirming that CPAP treatment, when used regularly, can almost completely alleviate the symptoms of the disease.

If you find yourself experiencing any of the above symptoms, there is a chance that you have sleep apnea without even knowing it. Schedule an appointment with your regular doctor and ask for more information about sleep studies and sleep apnea testing. There is always the option of starting with an at-home sleep monitoring device or application, but you should always seek the advice and recommendations of a healthcare professional. It is never too early to begin a potentially life-saving treatment, and it’s never too late to make a difference.