National consensus on diagnosis and treatment of disorders of sleep and wakefulness

2019

Abstract

Introduction. Sleep is a changed state of consciousness that occurs naturally and at certain intervals of time, which together with wakefulness forms the structure of the circadian rhythm. During sleep, the response to external stimuli is significantly reduced, volitional movements are suppressed. Changes in brain activity, body temperature and levels of some hormones are reported.
Sleep architecture. During sleep, several electrophysiologically distinct stages occur, repeating in cycles. The duration of sleep is 6-8 hours, with 4-6 cycles of 90-110 minutes duration being counted during this period. In each cycle, the two main types of sleep are represented in different ratio:
1. Non-REM sleep — it is divided into four stages: stage I is the most superficial, one can be easily awakened. It occupies 2-5% of the total sleep duration. Stage II is the longest (45-55%), sleep is deeper, characteristic K-complexes and sleep spindles appear in the EEG. Stages III and IV are the deepest, occupying 5-15% of sleep and covering mostly the first part of the night. The reactivity of the individual to exogenous stimuli is significantly reduced. In stage I eye movements are slow, while in the other stages (II, III and IV) they are missing partially or completely. Muscle tone decreases gradually, with stages III and IV being the lowest. EEG detects slow wave activity by theta waves (4-7 Hz) and in deep stages by high-amplitude delta waves (0.5-3 Hz).
2. REM sleep — it is associated with rapid eye movements (Rapid Eye Movements), occupies 20-25% of sleep and is quantitatively more present in the second part of sleep. Full muscle atony is reported, in EEG - low-amplitude mixed activity similar to that during wakefulness. Dreams are formed mainly during the REM phase of sleep.
The 'gold standard' in sleep research is polysomnography. It involves the registration of brain activity through EEG, the monitoring of eye movements (electro-oculography), muscle tone, respiratory effort, body position, heart rate, and oxygen saturation. Additionally, a snoring microphone as well as sensors for recording limb movements can be included. The inclusion of synchronized video surveillance in polysomnographic recording improves the diagnostic value of the study. Other studies are limited polygraphy and the multiple sleep latency test.