Polysomnography (Sleep Study)

Polysomnography (sleep study) is an overnight laboratory investigation in which brain waves, eye movements, jaw muscle activity, airflow, blood oxygen level and heart rhythm are recorded simultaneously during sleep. Commonly abbreviated as PSG, it is the reference test used to diagnose sleep apnoea and provides an objective picture of what happens to breathing, the heart and the brain across the night.

Summary: Polysomnography is a painless test carried out over one night in a sleep laboratory. Electrodes and sensors record brain waves (EEG), eye movements (EOG), muscle activity (EMG), airflow, oxygen saturation and heart rhythm (ECG). The Apnoea–Hypopnoea Index (AHI) in the report defines the severity of sleep apnoea: 5–15 mild, 15–30 moderate, 30 and above severe. Findings then guide treatment planning.

Table of Contents

• Why Is a Sleep Study Ordered?
• What Is the Test Night Like?
• What Is Measured During a Sleep Study?
• How Is the Report Read? (AHI)
• In-Lab PSG Versus Home Sleep Test (HSAT)
• What Happens After Diagnosis?
• Sleep Study for International Patients
• Frequently Asked Questions
• When to See a Specialist
• References

Why Is a Sleep Study Ordered?

A sleep study is most often ordered because of the triad of loud snoring through the night, breathing pauses witnessed by a partner, and excessive daytime sleepiness. These complaints are the most typical warning signs of obstructive sleep apnoea. The test is planned on a doctor’s advice and in connection with the clinical picture; it is not a random screening.

A sleep specialist may consider polysomnography in the following situations:

• Loud, irregular snoring and witnessed pauses in breathing at night
• Excessive daytime sleepiness — dozing off during the day, fatigue, problems with attention and memory
• Waking with a sense of choking, a dry mouth and morning headaches
• Unrefreshing sleep and frequent night-time awakenings
• Poorly controlled hypertension, cardiac rhythm disturbances or type 2 diabetes alongside sleep complaints
• Excess weight and a wide neck circumference
• A restless feeling in the legs at night and unusual behaviour during sleep
• Mouth breathing in children, restless sleep and behavioural changes

When one or more of these complaints persists, assessment for a sleep disorder by a physician is appropriate.

What Is the Test Night Like?

On the test night you are admitted to the sleep laboratory in the evening; the setting resembles a quiet, single hotel-style room. A sleep technician fits the electrodes and sensors over about 30–45 minutes. You then sleep in your usual pattern; the recording runs through the night and is concluded in the early morning.

Practical points that ease anxiety:

• You may bring your own pyjamas and familiar items such as your usual pillow.
• The electrodes are attached to the surface of the skin — there is no needle, incision or pain.
• You can turn onto your side and go to the bathroom; the technician manages the cables.

A slightly lower sleep efficiency on the first night does not mean the result is invalid — respiratory events and oxygen drops can be measured reliably even over shorter sleep periods, and the test can be repeated if a recording is inadequate. Before the test, avoid caffeine, alcohol and (unless your doctor advises otherwise) sleeping tablets on the test day, arrive with clean skin free of make-up, cream or hair gel, and carry a list of your medications.

What Is Measured During a Sleep Study?

During polysomnography the body’s main sleep-related functions are recorded at the same time. When these parameters are brought together, a whole-picture view of the sleep stages, the respiratory events and their effect on oxygen and the heart emerges. The standard PSG channels are summarised in the table below.

Recording channel	Abbreviation	What it measures
Brain waves	EEG	Sleep stages (N1, N2, N3, REM) and arousals
Eye movements	EOG	Identification of REM sleep
Muscle activity	EMG	Chin tone and leg movements
Airflow	—	Nasal–oral airflow, apnoea/hypopnoea events
Respiratory effort	—	Chest and abdominal movements
Oxygen saturation	SpO₂	Drops in blood oxygen (desaturation)
Heart rhythm	ECG	Rhythm changes during sleep
Body position	—	Whether events intensify in supine sleep

Through these channels the sleep specialist can objectively see in which stage and position respiratory events increase, how far oxygen falls and how far sleep is fragmented — the most complete single data set in sleep medicine.

How Is the Report Read? (AHI)

The most important figure in the report is the Apnoea–Hypopnoea Index (AHI) — the number of apnoeas (breathing pauses) and hypopnoeas (shallow breaths) per hour of sleep. The AHI is the established measure for classifying the severity of sleep apnoea and forms the basis of the treatment decision.

The standard AHI classification is:

• 5–15: mild sleep apnoea
• 15–30: moderate sleep apnoea
• 30 and above: severe sleep apnoea

The report is not limited to the AHI. Total sleep time and sleep efficiency, the distribution of sleep stages, the minimum oxygen saturation and the Oxygen Desaturation Index (ODI), the type of respiratory events (obstructive, central, mixed), the positional effect and leg movements are also reported. The sleep specialist interprets these data together with the clinical picture; the result is not a single number but a picture of the individual’s sleep pattern. Findings then guide sleep apnoea treatment planning.

In-Lab PSG Versus Home Sleep Test (HSAT)

The core difference between in-lab polysomnography and a home sleep test (HSAT) is the number of parameters recorded: in-lab PSG makes a full recording that includes brain waves, while a home test is limited mainly to breathing and oxygen. Which one is suitable is decided by the sleep specialist according to the clinical picture.

Feature	In-lab PSG	Home sleep test (HSAT)
Parameters recorded	EEG, EOG, EMG, airflow, oxygen, ECG, position	Airflow, effort, oxygen, pulse (no brain waves)
Sleep stages	Recorded	Not recorded
Technician supervision	Present (through the night)	Absent (patient attaches sensors)
Best suited to	Complex cases, children, suspected other sleep disorder, cardiac or pulmonary comorbidity	High likelihood of moderate-to-severe apnoea, otherwise healthy adult
Reliability	Most comprehensive data	Adequate in well-selected cases, limited

A home test is a practical option, but it does not always replace the laboratory test in mild cases, where another sleep disorder is suspected, or in children. For this reason the test type is chosen on an individual basis.

What Happens After Diagnosis?

The polysomnography results, together with the patient’s clinical picture, determine the treatment road map. In moderate-to-severe sleep apnoea a CPAP/BiPAP device may be considered; in selected patients an oral appliance, positional therapy and weight management are options. Where anatomical obstruction stands out, surgical options come onto the agenda.

If a surgical plan is being considered, the usual next step is sleep endoscopy to see the level of obstruction (palate, tongue base, epiglottis) during sleep, so that treatment is directed at the true source of the blockage. For a full overview of assessment and treatment, see the sleep apnoea page.

Sleep Study for International Patients

For patients travelling to Istanbul from abroad, the process usually begins with a remote consultation reviewing symptoms and any prior reports. The clinical assessment and the overnight in-lab recording are then scheduled together during the stay, with the report prepared afterwards so treatment planning can follow in the same visit or by remote follow-up. This describes the process only; the appropriate test type and treatment are always determined by an in-person physician examination.

Frequently Asked Questions

How long does polysomnography take? The recording usually runs 6–8 hours across the night. In addition, fitting the electrodes and sensors in the evening takes about 30–45 minutes. The test is concluded in the early morning and you return to your daily routine.

Is the sleep study painful? No. The electrodes are attached to the surface of the skin — there is no needle or incision, and no pain is felt. Some patients describe the cables or the unfamiliar setting as slightly restless. This is common and is taken into account when the results are interpreted.

When are the results ready and how are they read? The report is usually prepared within a few days. The key figure is the Apnoea–Hypopnoea Index (AHI): 5–15 mild, 15–30 moderate, 30 and above severe. The sleep specialist reads it together with the clinical picture.

What is the difference between a home sleep test and in-lab polysomnography? A home sleep test (HSAT) is a limited recording focused on breathing and oxygen and does not include brain waves. In-lab PSG also records sleep stages and gives more reliable data in complex cases, in children and where another sleep disorder is suspected.

Which conditions can a sleep study detect? It mainly helps diagnose obstructive sleep apnoea, and also assists the differential diagnosis of central sleep apnoea, restless legs syndrome, periodic limb movements, parasomnias and narcolepsy.

How should I prepare for the sleep study? On the day of the test avoid caffeine and alcohol, and arrive with clean skin free of make-up, cream or hair gel. Bring a list of your medications with you. Change any medication only on your doctor’s guidance.

When to See a Specialist

If you have loud snoring, witnessed breathing pauses at night, unrefreshing sleep in the morning, excessive daytime sleepiness, poorly controlled blood pressure or unexplained cardiac rhythm disturbances, assessment for a sleep disorder is appropriate. In children, mouth breathing, restless sleep and behavioural changes should also not be overlooked.

The first consultation may be made with a sleep-focused ENT physician. The doctor assesses the clinical picture and recommends the appropriate test type (in-lab PSG or a home sleep test). Early diagnosis directly affects not only sleep quality but also cardiovascular health, metabolic balance and daytime attention.

References

• American Academy of Sleep Medicine
• PubMed (sleep medicine literature)

This content is for informational purposes only; diagnosis and treatment require an in-person physician examination.