Sleep can be defined as “a special genetically determined state of the human body (and warm-blooded animals, ie mammals and birds), characterized by a natural sequential change of certain polygraphic pictures in the form of cycles, phases and stages” (VM Kovalzon ).
This complex definition of sleep testifies, firstly, that sleep is an integral part of a person’s being, because the need to sleep is genetically predetermined and, secondly, that the state of sleep can be determined only with the help of special objective methods.
For an objective study of sleep and its disorders, polysomnography is used – a method that includes parallel registration of an electroencephalogram (EEG) (usually multichannel), electrooculogram (EOG), electromyogram (EMG), electrocardiogram (ECG), blood pressure (BP), motor activity ( general and in the extremities), respiratory movements of the chest and abdominal wall, oro- nasal air flow, the level of oxygen saturation in the blood, the severity of snoring, body temperature, erection of the penis, video monitoring . The first three of the above indicators (EEG, EOG and EMG) are basic for identifying the stages and phases of sleep. Based on the analysis of these indicators, a hypnogram is constructed , reflecting the dynamics of the stages and phases of sleep during the registration period .
Human sleep is a continuum (sequence) of functional states of the brain – stages 1, 2, 3, and 4 of slow wave sleep (REM) and REM sleep (REM).
Stage 1 of FMS is characterized by a slowdown in the frequency of the main rhythm (characteristic of the relaxed wakefulness of a given person), the appearance of beta and theta EEG waves; a decrease in heart rate (HR), respiratory rate (RR), muscle tone, blood pressure.
Stage 2 FMS (stage of “sleepy spindles”)
– so named after the main EEG phenomenon – “sleepy spindles” – sinusoidal oscillations with a frequency of 11.5-15 Hz , an amplitude of more than 25 μV and a duration of 0.5-1.5 seconds, in addition, K- complexes – waves of high amplitude (2-3 times higher than the amplitude of the background EEG, mainly represented by theta waves), two or multiphase; from the point of view of vegetative and EMG indicators, the trends described for the 1st stage of FMS are developing; apnea episodes lasting less than 10 seconds may occur in small numbers.
3 and 4 stages
called delta sleep, since the main EEG phenomenon is delta activity (in the 3rd stage it ranges from 20% to 50%, and in the 4th stage more than 50% of the analysis epoch); breathing in these stages is rhythmic, slow, blood pressure is reduced, EMG has a low amplitude.
characterized by rapid eye movements (REM), very low EMG amplitude, “sawtooth” theta rhythm, combined with an irregular EEG; at the same time, a “vegetative storm” is noted with respiratory and cardiac arrhythmias, fluctuations in blood pressure, episodes of apnea (normally lasting less than 10 seconds), erection of the penis and clitoris.
The stages of FMS and FBS make up one sleep cycle, and such cycles in a healthy person are from 4 to 6 per night; these cycles are not the same: in the first two, FMS is maximally represented, and in the morning – FBS (Fig. 1).
The main function of FMS is restorative (accumulation of energy, primarily phosphatergic bonds, synthesis of peptides and nucleic acids, in this phase there are peaks of secretion of growth hormone, prolactin, melatonin, and FBS is information processing and building a program of behavior.
In physiological aging, the structure of sleep undergoes the following changes: the total duration of sleep decreases, the duration of the superficial stages increases, the time of falling asleep and the time of wakefulness within sleep increases, the motor activity in sleep increases, sleep fragmentation occurs, there is a greater preservation of FBS in relation to FMS, polyphasicity of sleep is revealed (the presence of day and night sleep) and daytime micro-sleep Complaints about poor night sleep in people over 60 are 3-4 times more common than in middle age.