Orientation to Polysomnography (PSG)

Introduction

• Presenter: Tom Tolbert from the Sleep Medicine Department at Mount Sinai.
• Focus: Orientation for beginners on how to read sleep studies.
• Tools used: Compumetics or Minerva (examples provided in Minerva).

Overview of Sleep Study Interface

• Interface divided into three main panels, each with different time scales:
  1. Hypnogram: Represents the entire study showing sleep architecture.
     • Displays stages of sleep and wakefulness.
     • Includes stages such as wake, N1, N2, delta sleep (stage 3), REM, and sometimes position.
  2. Sleep Staging Panel: Typically 30 seconds per epoch.
     • Used to score sleep stages.
  3. Limb Movement and Respiratory Scoring Panel: Often 2 minutes.
     • Used for identifying limb movements and respiratory events.

Sleep Staging

• Key Elements for Sleep Staging:

  • EEG (Electroencephalography) for brain waves.
  • EOG (Electrooculography) for eye movements.
  • EMG (Electromyography) for muscle tone.

• EEG:

  • Uses the 10-20 system for electrode placement (F=frontal, C=central, O=occipital, M=mastoids).
  • Wave frequencies:
    • Delta: 0-4 Hz
    • Theta: 4-8 Hz
    • Alpha: 8-13 Hz
    • Beta: >13 Hz
  • Sleep spindles (11-16 Hz) and K-complexes are key for scoring.

• EOG:

  • Measures eye movements using dipole properties of the eye.
  • Important for identifying eye closure and movements.

• EMG:

  • Chin EMG used to assess muscle tone.

Sleep Stages

• Stage N1: Transition from wakefulness, characterized by low amplitude mixed frequency and slow rolling eye movements.
• Stage N2: Presence of sleep spindles and K-complexes.
• Stage N3: Delta waves dominate (slow wave or delta sleep).
• REM Sleep: Rapid eye movements, low chin tone, can appear similar to N1.

Limb and Respiratory Scoring

• Channels:

  • Nasal pressure channel (nasal cannula).
  • Oronasal thermistor for mouth breathing detection.
  • Respiratory inductance plethysmography (effort channels).

• Apneas:

  • Absence of airflow for at least 10 seconds.
  • Can be obstructive (effort present) or central (no effort).

• Hypopneas:

  • Reduction in airflow to 70% or less, lasting at least 10 seconds.
  • Must have a consequence: either desaturation of 3% or an associated arousal.

• Limb Movements:

  • Detected through EMG electrodes on the anterior tibialis.
  • Monitored for periodic limb movements.

Conclusion

• Understanding the basics of reading sleep studies involves recognizing different stages and events through EEG, EOG, and EMG readings.
• Practical application and interpretation are crucial for accurate scoring and diagnosis.