Polysomnography - Sleep Physiology

What is Polysomnography?

Polysomnography, often referred to as a sleep study, is a comprehensive recording of the biophysiological changes that occur during sleep. It is used to diagnose a variety of sleep disorders, including obstructive sleep apnea (OSA), narcolepsy, restless legs syndrome (RLS), and insomnia.

How is Polysomnography Conducted?

Polysomnography is typically conducted in a sleep laboratory over the course of one night. During the study, various physiological parameters are monitored, including brain waves (EEG), eye movements (EOG), muscle activity (EMG), heart rhythm (ECG), and breathing patterns. Sensors are placed on the scalp, face, chest, limbs, and finger to collect data.

What Disorders Can Polysomnography Diagnose?

Obstructive Sleep Apnea (OSA): Characterized by repeated episodes of partial or complete blockage of the upper airway during sleep.
Central Sleep Apnea (CSA): Involves intermittent lapses in breathing due to lack of respiratory effort.
Narcolepsy: A chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep.
Periodic Limb Movement Disorder (PLMD): Involves repetitive cramping or jerking of the legs during sleep.
REM Sleep Behavior Disorder (RBD): Characterized by the acting out of dreams during REM sleep.

What are the Components of Polysomnography?

The key components of a standard polysomnography include:

Electroencephalogram (EEG): Records brain wave activity.
Electrooculogram (EOG): Monitors eye movements.
Electromyogram (EMG): Measures muscle activity, particularly in the chin and legs.
Electrocardiogram (ECG): Records heart rate and rhythm.
Pulse Oximetry: Measures blood oxygen saturation.
Respiratory Effort: Assesses chest and abdominal movement.
Airflow: Monitors airflow at the nose and mouth.

What Should Patients Expect During a Sleep Study?

Patients are asked to arrive at the sleep lab in the evening. They can bring personal items such as pajamas, a toothbrush, and a book. After the sensors are attached, patients are encouraged to sleep as normally as possible. The sleep technician monitors the data from a separate room and is available to assist if needed. In the morning, the sensors are removed, and the patient can return home.

How is the Data Analyzed?

The recorded data is analyzed by a sleep specialist. The data provides detailed information on sleep stages, breathing patterns, heart rate, and muscle activity. The specialist looks for abnormalities such as apneas, hypopneas, leg movements, and arousals. A comprehensive report is generated, which includes a diagnosis and recommendations for treatment if necessary.

What are the Limitations of Polysomnography?

While polysomnography is a valuable diagnostic tool, it has some limitations. It is expensive and resource-intensive, requiring specialized equipment and trained personnel. Additionally, the sleep lab environment may not reflect the patient’s typical sleep conditions. Home sleep apnea tests (HSAT) are sometimes used as a more convenient and cost-effective alternative for diagnosing OSA in certain patients.

Conclusion

Polysomnography is a critical tool in the field of sleep medicine, providing essential insights into various sleep disorders. By accurately diagnosing conditions such as OSA, narcolepsy, and RLS, it enables healthcare providers to develop effective treatment plans, thereby improving patients' quality of life.