What is hypnogram?

Hypnogram is a graphical representation of sleep stages in relation to time. It is requires full polysomnography at sleep laboratory, including EEG, EMG and simultaneous recording of eye movements. Sleep disorders specialist can diagnose various disorders of your sleep stages, both qualitative and quantitative.

Method of calculating hypnogram

Based on guidelines of the American Academy of Sleep Medicine (AASM), in order to determine sleep stages, Sleep Physician scores your sleep at intervals of 30 seconds. Then summarizes hypnogram with the aid of software. It is a process that requires time and knowledge, as the whole duration of your sleep is scored in periods of half a minute.

Normal hypnogram

During our sleep, cycles of non-REM (non-Rapid Eye Movement) sleep alternate with cycles of  REM (Rapid Eye Movement). A normal adult requires about 7-9 hours of sleep daily. If deprived of sleep the previous days, this will be illustrated in hypnogram. If he takes drugs affecting the structure of sleep, it will also be recorded. Conversely, if there is no pathological factor, hypnogram usually consists of 4-6 sleep cycles lasting about 90 minutes each. Deep sleep (NREM step 3) occurs mainly in the first half of our sleep and dreams predominate prevalent in the second half (REM). Hence many times when we wake up, we remember our dreams, because we just may wake after REM sleep.

Is it so important to record hypnogram during a sleep study?

The prevailing opinion today is that not only it is important but is is also necessary. It has been found that daily somnolence predisposes to work-related and road traffic accidents due to sleep fragmentation. In other words, if hypnogram shows abnormal sleep architecture, i.e. many arousals, many sleep stages changes etc, it has been proven by studies that the subject has a reduced quality of life, increased risk of accidents, and more daytime sleepiness. So it is not enough to know whether someone has for example apneas during sleep, but also whether these apneas are associated with abnormal sleep architecture, as shown by hypnogram.