The main method for studying human sleep is POLISOMNOGRAPHY (PSG). POLYSOMNOGRAPHY is a method of recording vital signs during sleep. This name is derived from the words poly – plural, somnos – sleep, grapho – write. Usually PSG is performed during a night’s sleep. The purpose of the polysomnographic study is to objectify the activity of the human body during sleep. For this, a number of indicators are recorded. The most important ones are the following:
- Electroencephalogram (EEG) – a recording of the electrical activity of the brain
- Electrooculogram (EOG) – recording of eye movements
- Electromyogram (EMG) – a record of muscle tension (most often the chin)
The combination of these three indicators makes it possible at any time to determine at what stage of sleep a person is. Based on the results of the sleep recording, a sleep timeline is built – a hypnogram , and then various sleep characteristics (time of falling asleep, duration of sleep stages, etc.) are calculated and compared with the normative ones.
PSG allows you to answer 2 main questions:
- Are the patient’s sleep indicators in line with the norm? (in this case, a visual analysis of the hypnogram is performed , and the quantitative data are compared with the age norm).
- What phenomena occur during sleep and can be the cause of its disturbance? (eg apnea, muscle twitching, epileptic discharges).
In order to obtain data not only on the structure of sleep, but also on the harmful phenomena associated with sleep mentioned in paragraph 2, several more indicators are recorded with PSG:
- Exhaled air flow from the mouth and nostrils
- Respiratory movements of the chest and abdomen
- Breathing noise (snoring)
- Blood oxygen saturation level
- Body position in bed
- Heart rate
HOW DOES THE STUDY GO?
The research is carried out in the Sleep Center, in a specially equipped single ward. In the evening, the patient comes to the Center, fills out a special questionnaire and gets ready for bed. Then sensors are applied (glued) to him, he goes to bed and sleeps. Throughout the night, the indicators of his sleep are recorded on a computer and a VCR, and an employee of the Center monitors his condition. The next morning, the sensors are removed from the patient and they are told when to come for the results.
OTHER POLISOMNOGRAPHY OPTIONS
To diagnose snoring and sleep apnea, simplified versions of polysomnography can be used – night and day cardiorespiratory monitoring. In this case, only sensors for assessing breathing during sleep are superimposed. Sleep time is determined by video monitoring data . In the daytime, when it is difficult to fall asleep, the patient receives a short-acting sleeping pill that does not change the breathing pattern during sleep.
MULTIPLE SLEEP LATENCE TEST (MTLS)
This study is used to quantify daytime sleepiness. During the daytime, the patient is put to bed 5 times with the sensors superimposed as in PSG. Then the time of falling asleep is averaged and compared with the standard. This test is used to diagnose narcolepsy.