During the night, while the patient is sleeping, a particular instrumentation detects and records some fundamental physiological parameters, such as brain activity, respiration, oxygen levels, etc.
Based on how these parameters evolve during the night, a doctor who specializes in sleeping diseases is able to determine if the patient actually suffers from some disorder and what condition it is.
The polysomnography takes place in a hospital center equipped for the procedure: the examination, in fact, must take place in a very special room, equipped with certain instruments.
The risks of the test are minimal and the preparation for the exam is extremely simple, as it does not require any special precautions.

, or paradoxical sleep.

Each cycle consisting of a NON-REM phase and a REM phase typically lasts 90-100 minutes.

Only the correct alternation between the NON-REM phase and the REM phase guarantees a restful rest.

NON-REM phase

The NON-REM (or NREM) phase is characterized by four stages, during which sleep becomes progressively deeper.

The first two stages are, respectively, falling asleep and light sleep; at the third stage, the phase of deep sleep begins, which reaches its climax at the fourth stage.
It is in the fourth stage of the NREM phase that the human organism regenerates itself.

The NON-REM phase is shortened with each cycle: initially, it occupies a large part of the "NREM phase-REM phase" cycle (at least for two cycles); after that, it leaves more and more room for the REM phase.

REM phase

The REM phase is a particular moment of sleep: if on the one hand there is an increase in heart rate and respiratory rate, and the individual dreams and moves his eyes rapidly (hence the acronym REM which means Rapid Eye Movement, ie rapid eye movement), on the other hand, under the influence of specific neurotransmitters, a sort of relaxation / paralysis of the musculature (muscular atony) occurs.

The REM phase initially covers a small portion of the nighttime sleep cycles; towards the morning, however, it gets longer, taking time away from the NREM phase.

  • Blood oxygen levels,
  • The heartbeat,
  • The respiratory rate,
  • Eye movements e
  • The activity of the skeletal muscles (therefore the movements of the upper and lower limbs).
  • As already mentioned, polysomnography performs an "analysis of the variations of the aforementioned parameters in the transition from the NON-REM to the REM phase of sleep.

    Did you know that ...

    In the REM phase, brain activity is more intense than in the NON-REM phase; this is evidenced by dreams, rapid eye movement and an increase in respiratory rate (for all muscles, on the other hand, there is a sort of paralysis) .

    obstructive sleep apnea. Also known as obstructive sleep apnea or OSAS, this condition causes temporary interruptions to breathing during sleep.
  • Sleep-related movement disorders. The individual affected by these problems is the protagonist of involuntary movements, usually with the lower limbs (it is very rare that he moves his arms or hands).
    Two typical examples of sleep-related movement disorders are: restless legs syndrome (RLS) and periodic movements of the lower limbs.
  • Narcolepsy. It is a neurological disease that causes repeated sleep attacks and a constant feeling of daytime sleepiness. Sufferers fall asleep several times throughout the day, even when engaged in engaging activities.
  • Behavioral disorders during the REM phase. People who physically "live" their dreams with leg or arm gestures, swearing, agitation, etc. suffer from these disorders.
  • Behavioral disorders during the NON-REM phase (or nocturnal behavioral disorders of the NON-REM phase). Problems such as sleepwalking and confusional awakening belong to this category.
  • Chronic insomnia. It is the inability to give continuity to nocturnal sleep. Some people suffer from it in a chronic way.
  • Symptoms of Obstructive Sleep Apnea

    • Intermittent snoring, interrupted by apnea episodes (whose duration is around 10-30 seconds);
    • Awakenings at night (arousal), generally following episodes of apnea, which affect the quality of sleep;
    • Restless sleep;
    • Daytime sleepiness, essentially due to night rest fragmented by repeated awakenings;
    • Morning headache.
    of the sensors of the polysomnograph.

    and caffeinated foods or drinks; this is because alcohol and caffeine can disturb nighttime sleep, altering the results of polysomnography.


    It is good practice for the patient to inform the doctor who may prescribe polysomnography of any pharmacological therapies in progress, so as to know, in view of the examination, whether or not he should temporarily stop taking them.



    The room is similar to a hotel room and is equipped with all comforts, so that the patient can feel more at ease.

    Furthermore, it is equipped with a video camera and an audio system: the camera allows the medical staff to observe what happens inside the room during the night; the audio system, on the other hand, is used for communication with the outside, in the event that the patient suffers from some illness.

    Connection to instrumentation

    As anticipated, the connection to the polysomnograph takes place through skin sensors, placed at the end of several cables.
    The cables are long enough for the patient to move around at night.

    The sites of application of the sensors are: scalp, temples, chest and lower limbs.
    A special adhesive or glue is used to connect the sensors to the skin.

    The sensor for measuring oxygen levels represents an exception compared to the others: it is, in fact, a sort of clip to be applied generally to the index finger.

    Measured parameters

    In summary, the parameters measured or monitored during polysomnography are: brain waves (which describe the activity of the brain), eye movements, heart rate, respiration, blood oxygen levels and the activity of the skeletal muscles of upper and lower limbs.

    Duration of registration

    Recording begins when the patient falls asleep and ends when the patient wakes up.

    Typically, if there are no hitches, it lasts all night.


    If the patient feels a sudden illness, he or she has the possibility to communicate it to the medical staff, through the audio system that the room is equipped with for the night.

    Medical personnel are located in the immediate vicinity, just outside the room; therefore, he can intervene immediately.

    Possible problems

    It may happen that the patient feels uncomfortable and struggles to sleep, because the examination and the environment, foreign to him, worry him.

    However, this does not alter the success of the test, as it is sufficient for the patient to sleep for a few hours, not necessarily all night.

    Polysomnography At Home

    For some time now, there has been the possibility of undergoing polysomnography at home, that is, between the walls of the house, in complete comfort.

    It should be noted that several clinics that offer this advantageous service carry out, at the patient's home, only a partial polysomnography, aimed at measuring cardio-respiratory parameters (cardio-respiratory polysomnography).
    For the complete examination (with the measurement of brain activity, etc.), therefore, the patient must always go to the facility.

    The reasons for this choice are essentially due to the impossibility of providing the patient's home with the necessary equipment to perform complete polysomnography.

    ). Unusual gestures and ways of acting during sleep are a possible sign of a REM or NON-REM behavior disorder.

    Recalling that the above are only examples of possible interpretations, the data that emerge from the polysomnography serve to confirm the doctor's suspicions and allow to establish the most appropriate therapeutic treatment.

    Antonio Griguolo

    Graduated in Biomolecular and Cellular Sciences, he obtained a Specialized Master in Journalism and Institutional Communication of Science
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