Sleep pressure

Under the Sleep pressure medicine understands a control loop that regulates tiredness and triggers physically-related sleepiness. During the waking phase, metabolic products are deposited in the brain that trigger increasing sleep pressure. During sleep, the glyphatic system cleanses the brain of these deposits.

What is the sleep pressure?

Sleep has essential functions. These tasks include the regeneration of body cells, but also mental regeneration and the storage of learning experiences. Too little sleep therefore affects physical and mental health. Persistent insomnia can therefore even be fatal for the human organism.

To ensure that people regularly get enough sleep and that there are no harmful consequences for their health, sleep and the need for sleep are subject to several physical control loops. In this context, medicine understands sleep pressure to mean physically induced sleepiness. Together with the internal clock of the biorhythm, sleep pressure regulates the duration and timing of sleep.

The regulation of the sleep-wake rhythm is the responsibility of the internal clock. Unlike the internal clock, the sleep pressure does not depend on the daily rhythm, but increases consistently during the waking phase. The longer a person is awake, the more intensely he feels sleep pressure.

The physiological cause of the increasing drowsiness is probably the metabolic products that accumulate in the brain during the waking phase. Above a certain amount, these metabolic products make people tired. The sleep pressure regulates the purely physical need for sleep.

Function & task

Sleep pressure contributes to survival. By regulating the duration of sleep and controlling tiredness, the mechanism ensures, for example, that sufficient cell regeneration can take place during sleep.

During the day all kinds of molecular metabolic products accumulate in the brain. The brain has only limited energies and decides when planning energy for one of two functional states: the waking state or the sleeping state. In the waking phase, the brain is able to concentrate on its surroundings and it works. People are aware of this work and can be understood by them, for example, based on their own thoughts.

Although people may consciously not suspect anything of this during sleep, the brain does not rest in any way while asleep - it continues to work and tidies up at night, unlike during the day. The clean-up work consists of sorting information in sleep phases such as the REM sleep phase. The sleeper can sometimes understand this sorting on the basis of dreams.

However, this is not the only cleanup job the brain does during sleep. The glyphatic system is considered to be a kind of garbage disposal of the brain. It also clears the control center of molecular metabolic products that accumulate during the day. The cleansing system is a network of tiny channels that contain what is known as cerebrospinal fluid and correspond to a type of lymphatic system in the brain.

As organizers, support and auxiliary cells of the nervous system, the glial cells take over control of the network. They ensure that all rubbish collects in the channels during sleep and can be washed into the bloodstream with the brain water. The metabolic products are removed about twice as quickly during sleep as when awake, since the liquor circulates faster in the resting phase.

The nocturnal cleaning of the brain is closely related to sleep pressure. The human being feels increasing tiredness, the more metabolic products accumulate in the brain. The peak of sleep pressure is just before falling asleep. In the first three to four hours of the sleep phase, the sleep pressure is reduced, since the harmful metabolic products are probably also broken down during this period.

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Illnesses & ailments

Sleep disorders have not yet been conclusively researched. In the past few decades, sleep medicine has established its own specialty that takes into account and documents the crucial tasks of sleep.

Sleep pressure plays an important role in sleep disorders. For example, reducing sheep pressure lets people wake up momentarily after around four hours. However, many people with insomnia wake up much more often at night.

Difficulty falling asleep despite high sleep pressure is also a common phenomenon. A general lack of sleep pressure is somewhat less common. Sleep quality is directly related to sleep pressure. If, for example, people go through too few deep sleep phases and their sleep generally remains superficial, the metabolic products, and with them sleep pressure, can only break down at a slower rate. The consequences of this are daytime sleepiness, inability to concentrate and reduced performance on the following day.

Sleep disorders due to decreased sleep pressure are often caused by irregular sleep-wake times. Sleeping in late on the weekends, for example, can, in some cases, reduce sleep pressure so much that it makes it difficult to fall asleep.

The accumulation of metabolic products in the brain, which first triggers sleep pressure and thus indicates the need for self-cleaning, is currently being researched. This research is, for example, devoted to the question of the extent to which sleep pressure could play a role in diseases such as Alzheimer's and epilepsy and which therapeutic options would be conceivable in this context.