A patient undergoing polysomnography shows high-amplitude, low-frequency delta waves (0.5–4 Hz) occupying >20% of the recording epoch. This pattern characterizes which sleep stage?

• A Stage N3 (Slow-wave or deep NREM sleep) ✓
• B Stage N1 (NREM sleep)
• C Stage N2 (NREM sleep) with sleep spindles
• D REM sleep

Explanation

Stage N3 (slow-wave sleep, SWS or deep sleep) is defined by delta waves (0.5–4 Hz, >75 microvolts amplitude) comprising ≥20% of the scoring epoch. Stage N1 shows theta waves and vertex sharp waves; N2 shows sleep spindles (12–14 Hz) and K-complexes on a low-amplitude background; REM sleep shows low-amplitude mixed-frequency waves resembling wakefulness (with rapid eye movements and muscle atonia).

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.