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The Sleep Stages: How Apnea Events Disrupt the Natural Rhythms of the Brain

 

By Admin

 

 

The Sleep Stages

Every night we cycle through stages of sleep that each have a distinct function in maintaining the health of our bodies and minds. For those with sleep apnea issues, the disruptions to these stages can be harmful whether or not you are awakened by an event. In the long term, what is known as sleep architecture, the rate at which a person cycles through the stages of sleep, is affected in ways that can make it harder to sleep even in the absence of apnea events. Whether you have obstructive, central, or mixed sleep apnea, the breathing changes associated with the disorder can also change the way your brain operates in those hours between evening and early morning, affecting everything from heart rate and blood pressure to memory consolidation and emotional health.

Stage One

Also called NREM1 (Non-REM Stage 1), the transition from being awake to being asleep is a lot more complicated than we previously thought. In a normal sleep cycle, stage one only lasts about five minutes, or just short of 5% of the entire cycle, but it is an important transition because it initiates the sleeping process and carries our waking thoughts into the lulling rhythms of sleep onset. It is the lightest stage of sleep, but also the period when the mind and body begin to relax into auto-pilot.

 

Though sleep apnea events can occur during the first stage of sleep, they are much more common during the later stages. Recent discoveries have led to a considerable amount of research on the specific phenomenon of REM apneas, a link that may soon advance our understanding of how sleep apnea affects the memory centers in the brain.

Stage Two

The second stage of sleep is the longest period in the cycle, accounting for approximately 50% of each cycle we sleep through. It is at this stage that firings in the brain called spindles begin to occur in fluctuating rates, as well as activity called K complexes. This is when breathing and heart rate settle into slower rhythms and remain there into the third and fourth stages. While stage one is referred to as NREM 1, stage two is actually the first true non-REM stage of complete sleep. The temperature drops, the muscles relax, and everything slows down into long, steady rhythms.

 

When sleep apnea is involved, the shift in breathing during stage two can be a dangerous moment, and events are increasingly more common with each stage going forward. In particular, the end period of stage two, just before the transition into a deep sleep, is when apnea events are most common at this point in the cycle.

Stages Three and Four (Delta Sleep)

Stages three and four are considered by many to be a single stage of deep sleep. This is the most restorative period of the cycle, responsible for many of the recuperative changes that occur in the brain and body when at rest. Almost coma-like in their characteristics, the deep sleep stages can be difficult to wake from. Slow delta waves begin to take over at this point, and will increase in frequency between the third and fourth stages. In healthy sleeping, each of these stages takes up about 20-25% of the cycle. But for those with sleep apnea, the third and fourth stages can be both dangerous and elusive.

 

Reading descriptions of the third and fourth sleep stages, one would assume that apneas would be a concern at this point. But due to the disruptions caused by abrupt shifts in breathing, sleep apnea patients often fail to sustain their deepest sleep states. This is not simply a problem of sleep quality, but a serious impediment to healing and immunity. Much of the body’s growth and fortifying hormones do their work during these deep stages of sleep, and without those complete minutes of rest, you can wake with fatigue and restlessness, as if you hadn’t slept at all.

REM Sleep

REM, an abbreviation for rapid eye movement, is the primary feature of the final stage in the sleep cycle, lasting about a quarter of a normal sleep cycle’s time. Called Stage R or stage REM for short, this period is known primarily for the darting of the eyes, a behavior that occurs routinely during dreaming. Brain waves are the most active during this stage, and vivid dreams occur much of the time. Heart and breathing rates can become irregular, and chemicals are released that cause paralysis in our bodies, preventing us from acting out our dreams.

 

Studies have not only found that apnea events occur at high numbers during REM sleep, but that sleep apnea patients often spend much of their sleep cycle in this stage, leading some researchers to propose that people with sleep apnea could be skipping stages like deep sleep entirely and instead alternating between other stages throughout the night. Research published in January of this year proposes a link between sleep apnea and problems with memory retention. The type of memories that are disrupted by apnea events, according to the research, are the same types of memories consolidated during REM sleep, making the disruption more likely with each apnea event. This research, led by Dr. Andrew Varga of New York University, has also discovered possible links between sleep apnea and depression, dementia, and Alzheimer’s disease.

 

“For the first time we’ve shown that sleep apnea, an increasingly common medical condition, might negatively impact formation of certain memories, even when the apnea is limited to REM sleep,” said Dr. Varga. What this means for the sleep apnea community is that the fragmented sleeping patterns caused by apnea events can have a direct effect on mental health. As Dr. Varga describes it, untreated sleep apnea is the real issue because the long-term consequences can be even more difficult to treat than the apnea itself.

Future Research

It should be pointed out that studies cited in this article relied upon untreated sleep apnea patients as research subjects. Use of CPAP (Continuous Positive Airway Pressure) and other sleep apnea treatments can potentially limit sleep disruptions caused by the disorder. But it is important to understand the direct effect of apnea on the natural stages of sleep. Researchers will continue to look into the links between apnea, memory, and how the disruption of the sleep cycle contributes to comorbidity and other health concerns over time. The more we know about the harmful aspects of the disorder, the easier it will be to treat effectively in the long term.   

 

Sources

Annual International Conference of the IEE Engineering in Mediine and Biology Society - https://www.ncbi.nlm.nih.gov/pubmed/23366967

Journal of Neuroscience - http://www.jneurosci.org/content/34/44/14571.short

Nationalgeographic.com - https://www.nationalgeographic.com/magazine/2018/08/science-of-sleep/

NYU Langone - https://nyulangone.org/press-releases/innovative-study-utilizing-video-games-shows-sleep-apnea-may-affect-memory-of-everyday-events

PLoS One - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2893208/

Psychcentral.com - https://psychcentral.com/news/2014/10/31/sleep-apnea-affects-rem-sleep-and-memory/76798.html

———. - https://psychcentral.com/news/2019/02/04/sleep-apnea-tied-to-gaps-in-life-memories/142573.html

Sleepcycle.com - https://www.sleepcycle.com/sleep-apnea/sleep-apnea-is-a-big-deal/