What is sleep breathing?
Sleep breathing simply refers to the physiological function of breathing which occurs during our sleep at night. Breathing is a key process that happens subconsciously. It is required for staying alive and is therefore controlled by a specific region of the brain known as the breathing centre, one of the critical life centres.
As we relax and fall deeper and deeper asleep, our muscles lose tension and our body consumes less oxygen. As a result, breathing slows down and evens out. In the deepest stages of sleeping, though, breathing rate increases, becomes irregular and stronger.
Breathing obstruction may be great enough for you to fully wake up and choke for air. Such moments of terminated breathing cause actual oxygen deprivation.
What happens while we sleep?
Since our body is programmed to regulate itself and sustain us even while we are unconscious and asleep, we don’t pay attention to the organic processes that happen at night. Nevertheless, there are a number of important physiological events taking place. This includes:
- The synthesis of hormones – reproductive hormones, growth hormone, cortisol (stress response hormone), melatonin (sleep hormone), leptin and ghrelin (appetite control hormones) and others;
- The homeostasis of nutrients – glucose and lipid regulation, or in other words the balanced distribution of carbohydrates and fats in the body;
- Immune system activity – production and functioning of natural killer cells, those responsible for destroying harmful substances, infection and cancerous cells in our body;
- Memory consolidation – the transformation of short-term memories into long-term memories and preparation to absorb new information the next day for memory storage;
- Genetic repair – insufficient sleep leads to distortion of genes, resulting in lower activity in some and higher activity in others. For example, genes responsible for chronic inflammation and stress become hyperactive, which leads to cardiovascular diseases.
Sleep is vital for the physiology of all these processes. However, it is not just any type of sleep that is sufficient to initiate them. As you have probably heard, your sleep is not uniform throughout the night. It comprises of multiple cycles and multiple stages of variant duration. Each stage has its own use and importance.
Sleep stages and cycles
Our sleep at night is generally inconsistent as it follows a pattern of various states of wakefulness. These states of alternating sleep and wakefulness make up cycles. Usually we go through four or six cycles of sleep each night.7
The duration of cycles, as well as total sleep time, vary from person to person and usually decrease with age. It is considered that a cycle lasts around 70 – 120 minutes. The cycle itself is made up of four distinct stages of sleep. These stages depend on the state of breathing, heart rate and muscle tone and their consequent activity. As a result, our sleep cycle is separated into light sleep and deep phases of sleep. There are also two main categories of sleep: REM and non-REM sleep.
You have probably heard this term loosely thrown around. REM simply stands for “Rapid Eye Movement”. So how is our sleep REM or not? Our sleep cycle is made up of four stages of sleep: 3 non-REM stages and 1 REM stage. The first two stages are considered as light sleep and the last two are the deeper phases of sleep. That is why it is easier to be woken up during the first two stages.
The duration of stages differs and the length of each stage changes throughout the night. In the beginning of the night, non-REM sleep is longest. The second half of the night gets taken over by REM sleep.
The cycles themselves change in length, becoming longer with each next one. The first cycle is usually around 1 and a half hours long. Meanwhile, the later cycles reach up to 2 hours.
Stage 1 non-REM sleep
This stage is the initial step to falling asleep and represents the person dozing off. It is the shortest out of all the stages and easiest the be awoken from. The further into the night with each cycle, the shorter this stage becomes, lasting on average from 1 to 5 minutes.
The body is not entirely relaxed, there are occasional twitches and jolts but brain activity and breathing begin to slow down. If you are undisturbed, it becomes easy to transition into the next stage.
Stage 2 non-REM sleep
At this stage, the body relaxes further. This is accompanied by muscle relaxation, further reduction in breathing and pulse rate and even a decrease in body temperature. This is when eye movement stops, and twitching is uncommon.
Unlike the first stage, stage 2 becomes longer with each new cycle. So, the duration ranges between 10 to 60 minutes. It is considered that half of your sleeping time is spent in stage 2.
Stage 3 non-REM sleep
This is the deep stage of sleep and it is crucial for recovery. It is the critical stage that represents restorative sleep. It becomes more difficult to wake the person up, as the body is very relaxed and the muscle, heart and breathing activities are minimal. During stage 3 your breathing and pulse are at their lowest.
Brain activity has also gradually slowed down, although there are occasional bursts of activity recognisable. These pulses regulate the sleep and prevent you from accidental awakening.
During deep sleep most of the restorative physiological processes mentioned earlier take place. This is the best state for growth and composition of the immune system. Moreover, it is vital for cognitive functioning and is known to be responsible not only for memory processes but also creativity and insightful thinking.9
Stage 3 is the longest in the beginning of the night, during the initial sleep cycles. It ranges between 20 and 40 minutes on average.
Stage 4 REM sleep
The type of sleep occurring at the REM stage is entirely different. Ironically, the activity of the brain raises up, mimicking that of being awake. This is also the reason for this stage being responsible for most vivid dreams.
Although dreaming may occur at any stage of the night, the most intense, extreme and intricate dreams are experienced during REM sleep. REM sleep is also important for critical cognitive abilities, learning capabilities and memory consolidation activities.10
The other body functions, which previously slowed down, are also reactivated. The pulse, for example, reaches almost the same rate as when awake. Breathing picks up again and may actually become irregular. This is a critical pointer for night breathing analysis.
The opposite happens to the muscles. After gradually being relaxed, they finally reach a state of atonia, which is an actual temporary and partial paralysis. It is done for personal safety, and helps to control our limbs during vivid dreaming.
The muscles that keep active are essentially respiratory and eye muscles. The movement of eyes behind eyelids is a typical indicator of REM sleep and thus gives it its name, “Rapid Eye Movement”. Respiratory muscles remain active to control our breathing patterns and this is another pointer of importance of sleep breathing.
It is not very easy to reach REM sleep. Even under normal circumstances, it is considered that you should be asleep for around 1 and a half hours before you reach the 4th stage of sleep. The REM stage, though, gets longer with each cycle. So, lasting on average from 10 to 60 minutes, you can expect that during the second half of the night, your REM sleep might reach up to an hour long. It is considered that adults spend around one quarter of their sleep in the REM stage.
So how do we breathe at night?
Control of breathing activities is a highly intricate process. We have seen that rates of respiratory events vary through the various stages of sleep. So, in order to achieve fruitful, restorative sleep, breathing has to function accordingly at both fast and slow rates.
The different processes taking place during the various stages of sleep require oxygen so breathing is regulated in order to have appropriate levels of oxygenation of the blood. Furthermore, it is important to get rid of the carbon dioxide in the body. This is another process which happens during respiration, and avoids hypercapnia, which is an increased level of carbon dioxide in the blood.
The body keeps tabs on this by constantly checking that there is a right balance of oxygen and carbon dioxide. It is done by simply checking the levels of oxygenation of the blood as it flows through the brain and the breathing centre.
The brain keeps sending signals to your lungs and breathing muscles to sustain the required respiration.
What if breathing fails?
There are multiple factors associated with a fluctuation of oxygen concentration in the body. Nevertheless, the difference is immediately picked up by the brain and it starts to regulate the body in order to resume correct breathing.
Most of such conditions are due to various breathing disorders, such as an obstruction of the airway. Something can block the passage of air and your brain cannot allow you to just choke to death. So, it sends a signal to wake you up and make you clear up your throat from whatever has blocked it.
One of the most popular sleep-related breathing disorders is sleep apnoea. This condition causes the obstruction of the airway due to relaxation of muscles in the throat. As this happens, breathing stops and oxygen levels fall. The brain sends a signal for waking up, the muscles tense up again and the airways open, allowing air to flow freely.
Why irregular sleep breathing is so harmful?
The blockage of airways and restricted breathing due to sleep apnoea happens so regularly and slightly that the brain doesn’t need for you to fully wake up for it to be regulated. As a result, many people are unaware that they might have problems breathing at night.
However, sleep is still distracted and you are awakened from the deep restorative stages of it, or perhaps haven’t even gotten the chance to reach REM sleep. As previously mentioned, breathing has to be stronger and deeper for the 4th stage of sleep. This results in insufficient sleep of poor quality.
At certain times, the obstruction is great enough for you to have to fully wake up and chock for air. Such moments of terminated breathing cause actual oxygen deprivation.
This is a devious cycle of not being able to enter deep sleep due to constant awakening and need for breathing and at the same time not being able to reach the part of sleep that is associated with faster, deeper breathing (the REM sleep).
There is a way to know!
Since this all happens somewhere deep in our brain and the process is so intricate, we cannot always just know if our sleep breathing is impaired. However, now there is a real and simple technology allowing us to test our sleep breathing!
The Sunrise device has been developed specifically for analysis of sleep breathing, among other sleep metrics. This allows it to be a certified medical device for diagnosing sleep apnoea. Moreover, it is able to give crucial information about the different sleep stages, as well as REM sleep.
The added benefit of it being a home test is that such intricate metrics of sleep breathing can most accurately be registered only in the condition of comfort found within one’s home.
It is possible to take the sleep test by yourself at home and have fast and simple answers about your sleep breathing in your hands the next morning. No need to complicate your life even further!