Polysomnography and sleep studies

Sleep Architecture - The REM Team

• Also called “paradoxical sleep”: active mind (EEG resembles wakefulness) with a paralyzed body (atonia).
• Occurs every 90 minutes, with duration increasing through the night.
• Key Polysomnography (PSG) Features:
  • EEG: Low-voltage, mixed-frequency activity with characteristic “sawtooth waves.”
  • EOG: Bursts of conjugate rapid eye movements.
  • EMG: Atonia (lowest muscle tone), preventing dream enactment.
• Associated with vivid dreaming, memory consolidation, and penile/clitoral tumescence.

⭐ In major depression, REM sleep latency is often decreased, and the percentage of REM sleep is increased.

PSG Components - Wires and Waves

• EEG (Electroencephalogram): Measures brain waves.
  • Alpha waves: Relaxed wakefulness (eyes closed).
  • Beta waves: Alert, active wakefulness (eyes open).
  • Theta waves: Predominate in N1 & N2 sleep.
  • Delta waves (<4 Hz): Define N3 (slow-wave sleep).
  • K-complexes & Sleep Spindles: Pathognomonic for N2 sleep.
• EOG (Electrooculogram): Records eye movements, crucial for identifying REM sleep.
• EMG (Electromyogram): Monitors submental (chin) muscle tone. Shows progressive relaxation through NREM and profound atonia during REM.
• Additional Leads: ECG, respiratory airflow/effort, pulse oximetry (SpO₂).

⭐ Sawtooth waves on EEG are a characteristic finding of REM sleep, often appearing just before bursts of rapid eye movements.

Key Metrics - Reading the Squiggles

• EEG (Brain Waves):
  • N1: Theta waves
  • N2: Sleep spindles & K-complexes
  • N3: Delta waves (slow-wave sleep)
  • REM: Low-amplitude, mixed-frequency "sawtooth" waves
• EOG (Eyes): Rapid eye movements define REM sleep.
• EMG (Chin Muscle): Atonia (paralysis) is characteristic of REM.

⭐ Absence of REM atonia on EMG is a key finding in REM Sleep Behavior Disorder, where patients physically act out vivid, often unpleasant dreams.

Clinical Correlations - Sleep Disorder Signatures

• Obstructive Sleep Apnea (OSA):
  • Repetitive apneas/hypopneas with continued respiratory effort.
  • Apnea-Hypopnea Index (AHI) ≥ 15/hr, or ≥ 5/hr with symptoms.
  • Results in ↓ O₂ saturation and sleep fragmentation.
• Narcolepsy:
  • Shortened REM sleep latency (≤ 15 min).
  • Multiple Sleep Latency Test (MSLT) shows mean latency < 8 min & ≥ 2 sleep-onset REM periods (SOREMPs).
• NREM Parasomnias (Sleepwalking/Terrors):
  • Occur during slow-wave sleep (N3), typically in the first third of the night.
• REM Sleep Behavior Disorder (RBD):
  • REM sleep without normal muscle atonia.

⭐ High-Yield: RBD is a strong predictor for future neurodegenerative disease, particularly α-synucleinopathies like Parkinson's disease or Lewy body dementia.

Specialty Tests - MSLT & MWT

• Multiple Sleep Latency Test (MSLT):

  • Objectively measures sleepiness; the primary test for narcolepsy.
  • Involves 4-5 nap opportunities every 2 hours.
  • Narcolepsy criteria: Mean sleep latency ≤ 8 minutes AND ≥ 2 SOREMPs (Sleep-Onset REM Periods).

• Maintenance of Wakefulness Test (MWT):

  • Assesses the ability to remain awake.
  • Evaluates treatment efficacy and fitness-for-duty (e.g., pilots).

⭐ An overnight PSG must precede the MSLT to ensure ≥ 6 hours of sleep and rule out other sleep disorders.

High-Yield Points - ⚡ Biggest Takeaways

• Polysomnography (PSG) is the gold standard for diagnosing sleep-related breathing disorders like obstructive sleep apnea (OSA).
• It records EEG (sleep staging), EOG (eye movements for REM), and EMG (muscle atonia).
• The Apnea-Hypopnea Index (AHI) is the key metric for OSA severity.
• Look for shortened REM latency in narcolepsy; confirm with a Multiple Sleep Latency Test (MSLT).
• REM sleep behavior disorder is diagnosed by identifying REM sleep without atonia.