Polysomnography

What Polysomnography Is and How It Works

Polysomnography (PSG) — commonly known as a sleep study — is a diagnostic investigation carried out overnight in a sleep laboratory, in which the body’s functions during sleep are recorded simultaneously. During the test, parameters such as brain waves, eye movements, jaw muscle activity, heart rhythm, respiratory effort, airflow, blood oxygen level, body position and leg movements are recorded together.

Although sleep may appear to be a single, uniform state, it is in fact a controlled biological cycle made up of distinct stages (N1, N2, N3 and REM). A disturbance at any point in this cycle — at the level of breathing, brain activity, heart rhythm or muscle tone — can have a serious effect on everyday quality of life. Polysomnography provides a real-time, objective picture of these events.

Polysomnography is recognised as the international gold standard for diagnosing sleep apnoea. It also plays a central role in the differential diagnosis of other sleep disorders (insomnia, parasomnias, restless legs syndrome, narcolepsy).

When It Is Considered

Polysomnography may be considered in the following complaints and clinical situations:

• Loud, irregular snoring and pauses in breathing observed by a partner
• Excessive daytime sleepiness — dozing off during the day, fatigue, problems with attention and memory
• Morning headaches and a sense of waking unrefreshed
• Waking with a sensation of choking and dry mouth
• Poorly controlled hypertension, type 2 diabetes, cardiac rhythm disturbances (sleep apnoea may be an underlying factor in these conditions)
• Obesity (particularly a BMI > 30) and a wide neck circumference
• Mouth breathing in children, restless sleep and behavioural problems
• Unexplained daytime fatigue, accompanied by signs of depression
• A sense of restlessness in the legs at night and urge-driven movement at sleep onset
• Unusual behaviour during sleep — acting out dreams, sleepwalking, nightmare disorders
• Pre-operative assessment, particularly for bariatric surgery candidates
• CPAP titration — adjustment of the device pressure in the laboratory setting

The test is not a random screening performed without medical advice; it is requested in connection with the clinical picture.

Types of Test and Which One Is Suitable for You

Polysomnography is not a single type of study; it is performed at different levels according to the needs of the case.

Type I — Full laboratory polysomnography: The gold-standard test, performed under the supervision of a sleep technician and including all parameters. It is the most comprehensive method for reaching a diagnosis.

Type II — Portable full montage: A full parameter recording carried out outside the laboratory. It may be an alternative for patients who find it difficult to remain still, but its availability is limited.

Type III — Limited channel (home sleep test / HSAT): Focused mainly on respiratory parameters and not including a brain-wave recording. It may be used in patients who are highly likely to have moderate-to-severe sleep apnoea. It is insufficient in mild cases or where other sleep disorders are suspected.

Type IV — Single/dual channel (oximetry): Intended for screening. It is not sufficient on its own to establish a diagnosis.

Split-night protocol: Recording for diagnostic purposes until midnight, followed by CPAP titration in the second half of the night if apnoea is detected. In certain patients this offers an advantage in terms of time and cost.

Which test is to be used is determined by the sleep specialist according to the clinical picture. A home test does not replace the laboratory test in every case — laboratory testing is preferred particularly in patients with cardiac comorbidity, suspected additional sleep disorders or in children.

Preparation and the Course of the Test

Standard recommendations before the test:

• Avoiding caffeine, alcohol and sleeping tablets on the day of the test (unless a doctor advises otherwise, in which case that guidance applies)
• Avoiding heavy meals and intense exercise in the evening hours
• Arriving with clean skin, without make-up, cream or hair gel — these affect electrode adhesion
• Comfortable pyjamas and any items normally used to sleep in your usual position (pillow, etc.)
• Bringing a list of all medications taken

Admission to the laboratory generally takes place between 8 p.m. and 10 p.m. The sleep technician applies the electrodes; this takes about 30–45 minutes. The main sensors fitted are:

• EEG (brain waves) — at several points on the scalp
• EOG (eye movements) — around the eyes
• EMG (muscle activity) — under the chin and on the legs
• ECG (heart rhythm) — on the chest
• Respiratory sensors — nasal–oral airflow, chest and abdominal movements
• Pulse oximeter — blood oxygen measurement from the finger
• Position sensor and an overnight camera

It is a painless test. Some patients may find it difficult to fall asleep in an unfamiliar environment and under sensors; this is largely normal, and sleep efficiency is also taken into account when interpreting the results. The test is concluded in the early morning.

Interpreting the Results

The results of polysomnography are interpreted by a sleep medicine specialist. A standard report is usually prepared within 3–7 days and includes the following:

• Total sleep time and sleep efficiency
• The percentage distribution of sleep stages (N1, N2, N3, REM)
• Apnoea–Hypopnoea Index (AHI): The number of apnoeas and hypopnoeas per hour — the principal indicator of sleep apnoea severity
  • 5–15: mild
  • 15–30: moderate
  • 30 and above: severe
• Oxygen Desaturation Index (ODI) and minimum oxygen saturation
• Patterns of respiratory effort and airflow (obstructive, central, mixed)
• Heart rhythm findings
• Positional effect: The intensity of events during supine sleep
• Leg movements and arousal index
• REM-related events

The sleep specialist interprets this data together with the clinical picture to reach a diagnosis and to recommend a treatment road map. The results are not merely a number, but a picture of the patient’s individual sleep pattern.

The Road Map from Diagnosis to Treatment

The results of polysomnography, together with the patient’s clinical picture, determine the treatment options:

• CPAP / BiPAP device: The gold standard in moderate-to-severe sleep apnoea. The device creates continuous positive pressure in the airway, preventing obstruction.
• Mandibular advancement device (MAD): In mild-to-moderate sleep apnoea and in patients who do not tolerate CPAP
• Positional therapy: In patients whose events intensify during supine sleep
• Weight management: In patients with a high BMI — this may bring about a marked reduction in apnoea severity
• Surgical treatment: In cases where the anatomical source of obstruction is clear. Before surgical planning, the site of obstruction is usually identified with sleep endoscopy (DISE).
• Hypoglossal nerve stimulation: In selected advanced cases
• Other sleep disorders: Medication, cognitive behavioural therapy (in insomnia), neurology consultation (where parasomnia or narcolepsy is suspected)

A follow-up PSG after treatment may be performed for an objective assessment of the outcome.

Risks and Points to Be Aware Of

Polysomnography is a painless, non-invasive and generally safe test. Possible limitations:

• Effect of the unfamiliar environment: In some patients, sleep efficiency is lower on the first night — the test can be repeated if necessary
• Skin sensitivity to electrode adhesives: Temporary redness and, rarely, irritation
• Limited freedom of movement: The presence of sensors and cables may cause discomfort in some patients
• Claustrophobia and anxiety: If reported in advance, appropriate arrangements are made

It should be remembered that medications taken before the test (particularly sedatives, antidepressants and sleeping tablets) may affect the result; stopping or adding medication without a doctor’s guidance is not recommended.

Comparing Polysomnography with Other Sleep Diagnostic Methods

The main methods used in sleep assessment and how they differ:

• Polysomnography (PSG, laboratory): The most comprehensive data set. Sleep stages, brain, heart, breathing, muscle and oxygen all at the same time. The gold standard for diagnosis.
• Home sleep test (HSAT, Type III): Respiration-focused, with no brain-wave recording. Suitable only in cases with a high suspicion of OSA; insufficient if other sleep disorders are present.
• Actigraphy: Measures the sleep–wake cycle from wrist movement. It is helpful in disorders of sleep rhythm but does not diagnose OSA.
• Pulse oximetry: Monitors oxygen only. Intended for screening and insufficient for a definitive diagnosis.
• Sleep endoscopy (DISE): Not a diagnostic test, but a means of identifying the site of obstruction. It comes into play at the surgical planning stage after PSG.
• Cephalometry / 3D imaging: Shows anatomical structure statically, not function.

Polysomnography plays the fundamental role in diagnosis, while the other methods play a complementary role in certain cases.

When to See a Specialist

If there are complaints such as loud snoring, witnessed pauses in breathing at night, waking unrefreshed 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 problems should also not be overlooked.

The first consultation may be made with a sleep specialist ENT doctor or a respiratory medicine specialist. The doctor assesses the clinical picture and recommends the appropriate type of test (laboratory PSG, a home test or another investigation). Early diagnosis directly affects not only sleep quality but also cardiovascular health, metabolic balance, attention and overall life expectancy.