Polysomnography (PSG) is a non-invasive test useful for studying the behavior of patients during sleep. The exam allows you to mainly analyze respiratory, heart and brain activity during sleep. The polysomnograph is the tool used for recording these parameters and is connected to the person undergoing the examination.

Polysomnography is the gold standard exam for diagnosing sleep apnea. The exam can also be used for monitoring the therapy of patients diagnosed with respiratory disorders.


Polysomnography: historical notes

The first studies on the use of an exam adopted to monitor sleep phases appeared shortly after the 1960s. In fact, at that time, the first scientific research on sleep and its phases began by Kleitman, an American physiologist who had been dealing with sleep for almost thirty years. The same, with the help of one of his collaborators, had begun to study the slow eye movements that occurred in children who were about to fall asleep.

During these studies, the physiologist also noticed the appearance of rapid eye movement discharges (Rapid Eye Movement) identical to those that occur in a waking state. Another of his students, William Dement, destined to become one of the pillars of sleep medicine, showed that these rapid eye movements were linked to dream activity. It was Dement who demonstrated that synchronous sleep episodes and REM sleep episodes alternate cyclically during sleep according to a characteristic pattern.

Dement, under the direction of Kleitman, had come to this consideration because he had recorded human sleep for the first time continuously and completely. The same man was able to record the sleep of a man from the moment of falling asleep to that of awakening using instruments for measuring eye movement and brain activity respectively (EOG and EEG) to rudimentary measuring instruments.

The two researchers in this way therefore had also redefined the sleep recording techniques used up to that moment. This intuition provided clinicians with the instrument of measurement, polysomnography, which would allow them to objectively study human sleep and its pathologies.


Sleep and its phases

Human sleep is not a uniform process but includes two states. From a neurophysiological point of view, sleep is divided into:

  • REM phase (Rapid Eye Movements)
  • non REM phase (NREM Non – Rapid Eye Movement)

The REM phase is also referred to as “paradoxical” sleep and the non-REM phase is also referred to as “orthodox” sleep. The two phases alternate cyclically with cycles of similar duration. During the NON-REM phase our brain and our body rest and regenerate. During the REM phase, however, our body rests, but our brain reactivates with the appearance of dream activity. In this situation the subject dreams.

The NREM phase is also characterized by four stages that follow each other up to the REM phase in which there is a single stage. After falling asleep, the subject progressively passes from stage 1 to stage 4 and then, after about 90 minutes, reaches the first phase of REM sleep which lasts about 15 minutes; this concludes the first cycle lasting about 100 minutes. Subsequently in the following cycles the NON-REM phase has an increasingly shorter duration, leaving room for the REM phase. In general, in a young adult, about three quarters of nocturnal sleep includes NREM sleep (5% stage N1, 50% stage N2 and 20% stage N3), while the other quarter consists of REM sleep.

The most characteristic phenomenon of the REM phase is the dream. About 85% of subjects awakened during REM sleep will report having dreamed. For these reasons, in the REM phase, the brain consumes oxygen and glucose as during wakefulness. Furthermore, during NREM sleep, some mental images may arise, but upon awakening they are not remembered.



Polysomnography: what the exam consists of. The different levels of investigation.

The polysomnographic nocturnal instrumental evaluation can be performed with different recording methods, both in the laboratory and in the clinic, with personnel or without surveillance personnel, with decreasing complexity and costs.

Mainly for the polysomnographic examination there is a subdivision between:

The table below summarizes the main polysomnographic channels that are used during a polysomnographic exam.


Parameter and description

1. Electroencephalogram (EEG):  Information on the central nervous system through the measurement of brain electrical activity

2. Electrooculogram (EOG): Monitoring of eye movements useful in sleep staging

3. Electromyography (EMG): Information on the functionality of the peripheral nervous system and the muscular system

4. Electrocardiogram (ECG): Information on cardiac activity, by recording heart rate and rhythm.

5. Air flow Monitoring of respiratory activity through a nasal cannula. You can get information on airway flow. Specifically, information about normal flow events, low flow events (hypoapneas) or apnea flow stop events.

6. O2 saturation: Evaluates the oxygenation of the blood using the pulse oximeter, allowing us to record the desaturation events associated with apneas.

7. Snoring: The noise value caused by snoring during sleep

8. Respiratory effort: It considers the abdominal and thoracic movements to give information on breathing, it allows to distinguish obstructive from central apneas (from neurological damage).

9. Body position: Indicates the sleeping position (supine and / or lateral position). It is important for the differential diagnosis between positional and supine dependent apneas

10 *. CO2

11 *. Systemic blood pressure

12 *. Endoesophageal pressure

* optional channel




Cardiorespiratory polysomnography

This method allows the direct identification of respiratory events. During the examination, the parameters related to the respiratory function are monitored and in particular:


  • Snoring
  • The heart rate
  • Oxygen saturation
  • The nasal and oronosal flow
  • abdominal and chest movements
  • Body position during sleep
  • This method does not require dedicated environments or the continuous assistance of expert staff.


Therefore, after the positioning of the polysomnograph by qualified personnel, the patient can also sleep at home or in the ward. Complete cardiorespiratory polysomnography allows the diagnosis of all sleep breathing disorders, including sleep apnea, snoring and especially in the case of children, hypertrophy of the adenoids and tonsils, etc. Cardiorespiratory polysomnography is the gold standard exam for diagnosing sleep apnea.

According to the guidelines of the AIPO-AIMS (the Italian Association of Hospital Pulmonologists and the Italian Association of Sleep Medicine), complete cardiorespiratory monitoring, with the recording of all cardiorespiratory parameters, is called complete cardiorespiratory monitoring or level recording. III and allows direct identification of respiratory events. On the other hand, in the case of partial recordings or in the absence of the recording of abdominal toric movements we speak of nocturnal oximetry or even level IV recording.

Overnight oximetry is not an instrumental evaluation method accepted by international guidelines for the diagnosis of OSAS. On the other hand, it can be used for a control in the follow up of patients who already use night ventilation or to select patients for further instrumental investigations being a very simple and inexpensive examination to perform.

Through the cardiorespiratory polysomnographic examination it is not possible to identify the periods of sleep or to distinguish between NREM / REM sleep and the various sleep phases.


Neurological polysomnography

During the examination, the parameters related to respiratory function and necessary for sleep staging are monitored and in particular:

  • EEG with at least two unipolar leads;
  • EOG;
  • Submental EMG;
  • respiratory noise and oronasal airflow;
  • thoraco-abdominal movements;
  • heart rate and electrocardiogram;
  • SaO2;
  • body position;
  • movement of the limbs through the electromyogram of the anterior tibial muscles;
  • CO2 (optional);
  • systemic blood pressure (optional);
  • endoesophageal pressure (optional).


This method requires dedicated environments with particular structural characteristics (for example soundproofing) and requires the supervision of dedicated technical or nursing staff. In fact, the polysomnographic examination must be performed in a sleep laboratory under the direct control of the technician for the entire recording time. The staff, while the patient sleeps only in one room, monitors the quality of the tracing and the patient in an adjoining room all night.

According to the guidelines of the AIPO-AIMS (the Italian Association of Hospital Pulmonologists and the Italian Association of Sleep Medicine), complete nocturnal polysomnography in the laboratory is identified as a level I recording. This method allows for the recording of sleep parameters and any other respiratory and non-respiratory parameter. In this case the patient sleeps in a room alone, while the recording system is placed in an adjoining room to be able to monitor and intervene on the track without disturbing the patient. In the case of a polysomnogram in the absence of continuous assistance from expert personnel, it is referred to as level II recording.



Pediatric polysomnography

The diagnosis and evaluation of children with suspicion of sleep disorders is carried out by performing polysomnography on children. Pediatric polysomnography is a non-invasive nocturnal instrumental examination required for the evaluation of sleep apnea in children.

Sleep apnea is a child’s sleep disorder in which breathing is partially or completely blocked repeatedly during sleep. The condition is due to the narrowing or blockage of the upper airways during sleep also due to the tonsils and adenoids.

Specifically, the examination is performed in exactly the same way as it is performed in the adult even if the instrumentation used is specific to the size of the child.

Early diagnosis and treatment are important to prevent complications that can affect children’s growth, cognitive development, and behavior.



Polysomnographic examination: when and why to perform the examination

The examination is necessary for sleep analysis and when patients with sleep disorders suspect they are mainly affected by:

  • sleep apnea
  • nocturnal epilepsy
  • dysomnia (insomnia, hypersomnia, narcolepsy)
  • parasomnias (bruxism, nocturnal enuresis, pavor nocturnus, sleepwalking)
  • Movement of the limbs, especially the legs (restless legs syndrome (RLS))

It is necessary to rely on a sleep specialist before carrying out the examination. The results of the examination are used to confirm the doctor’s suspicions and allow the most appropriate therapeutic treatment to be established.


Sonnocare is a sleep medicine center specialized in the treatment of sleep disorders. The center carries out activities and tests for the diagnosis and definition of the therapeutic process of the main sleep pathologies.