Duygu Erdem¹ Kürşat Murat Özcan²

¹Bülent Ecevit University, Faculty of Medicine, Department of Otorhinolaryngology, Zonguldak, Türkiye
²Ankara Bilkent City Hospital, Department of Otorhinolaryngology, Ankara, Türkiye

Erdem D, Özcan KM. Scoring Sleep Stages in Polysomnography. In: Özcan KM, editor. Sleep-Disordered Breathing: Diagnosis and Treatment. 1^st ed. Ankara: Türkiye Klinikleri; 2025. p.67-75.

ABSTRACT

Numerous different sleep disorders, encompassing various disciplines, have been identified. Sleep-disordered breathing is the most common among all sleep disorders. For sleep-disordered breathing and some other sleep disorders, sleep tests are required for diagnosis, depending on the patient’s clinical condition. Among sleep tests, polysomnography performed in the sleep laboratory is considered as the gold standard to evaluate the patient’s sleep. Experienced and trained sleep laboratory personnel must then manually score data obtained from the overnight test. In polysomnography, electroencephalography, electrooculography, and electromyography data are recorded to assess the patient’s sleep. When evaluating these recorded data, the sleep stages are first scored. Scoring is performed according to the internationally accepted rules outlined in the guidelines of the American Academy of Sleep Medicine. Sleep stages are scored in 30-second bursts called epochs. The appropriate sleep stage for each epoch is determined. Electroencephalography (EEG) wave characteristics and specific EEG patterns are used as the basis for determining which sleep stage to assign to an epoch. Electrooculography and electromyography data are also evaluated in conjunction with EEG characteristics. Alpha waves with a frequency of 8-13 Hz are evaluated in the EEG recording to determine awake status. If alpha waves constitute more than half of the epoch, the epoch is scored as awake. During Stage 1 sleep, the EEG recording consists of low-amplitude mixed-frequency waves. During Stage 2 sleep, the EEG typically shows EEG patterns called sleep spindles and K complexes. Sleep spindles are waves with a frequency of 11-16 Hz that last at least 0.5 seconds. The K complex is a biphasic wave pattern lasting at least 0.5 seconds. It begins with a rapid positive peak and then develops a slower, broader negative peak. Delta waves are typical for stage 3 sleep. Delta waves have an amplitude of at least 75 microvolts and a frequency of 0.5-2 Hz. If delta waves constitute more than 20% of the epoch, the epoch is scored as stage

3. During REM sleep, low-amplitude, mixed-frequency EEG waves, along with rapid eye movements and low muscle activity, are observed. The distribution of sleep stages and their relationship to the respiratory events observed during these stages aid in making decisions for diagnosis and treatment.

Keywords: Sleep stages; Diagnosis; Sleep, REM; Polysomnography; Sleep apnea syndromes