Wk 1 Lecture 2, Sleep Stages and Polysomnography

Sleep Stages & Polysomnography

• Introduction

  • Importance of understanding sleep.

  • Polysomnography as the gold standard in sleep measurement.

Key Personnel

• Kath Maddison, PhD

  • Director, Centre for Sleep Science, UWA.

  • Research Fellow at West Australian Sleep Disorders Research Institute, SCGH.

  • Faculty member involved in teaching and research.

Learning Outcomes

• Describe normal sleep, sleep stages & sleep architecture in humans

• Recall major physiological processes during sleep

• Summarise advantages & disadvantages of in-laboratory polysomnography

• Recount physiological signals recorded during a polysomnogram

Overview of Sleep Architecture

1. Polysomnography: Gold Standard Measure of Sleep

2. Types of Human Sleep

3. Advantages & Disadvantages of Polysomnography

Historical Context

• Historical Insights

  • Interest in sleep and dreaming spans millennia, but sleep medicine has emerged since the 1970s.

  • J Allan Hobson (1989): "Sleep is a dynamic behaviour... controlled by elaborate and precise mechanisms."

Sleep States and Stages

• Sleep is divided into two states:

  • NREM (Non-Rapid Eye Movement) Sleep

    • Stages Include:

      • Stage N1

      • Stage N2

      • Stage N3

  • REM (Rapid Eye Movement) Sleep

    • Stage R

Levels of Consciousness in Sleep Stages

• Deep Sleep vs. Light Sleep vs. Awake

  • Stage N1: Transition from wake to sleep.

  • Stage N2: Light sleep, easily interrupted.

  • Stage N3: Deep sleep, restorative processes.

  • REM: Associated with vivid dreaming.

Sleep Cycle Overview

• Typical Duration: Each sleep cycle lasts about 90 minutes.

  • Varies across different cycles throughout the night.

  • Includes stages N1, N2, N3, and REM.

Sleep Architecture Across Cycles

1. First Sleep Cycle: 70-100 mins of N3

2. Subsequent Cycles: 90-120 mins, with variations in stage durations.

• REM Sleep increases in later cycles.

• Stage N3 generally decreases in subsequent cycles while Stage N2 increases.

Physiological Consequences of Sleep Stages

1. Wakefulness

2. Stage N1

• Light sleep, presence of slow rolling eye movements, hypnic jerks.

• Approx. 1-7 mins in the first sleep cycle.

3. Stage N2

• Majority of time spent in this stage, further decreased awareness, memory transfer.

• Approx. 20 mins in the first sleep cycle.

4. Stage N3

• Deepest sleep with growth hormone release and memory consolidation.

• Approx. 35 mins in the first sleep cycle.

5. REM Sleep

• Characterized by vivid dreams, increased heart rate, and respiratory rate.

• Approx. 5 mins in the first sleep cycle.

Measuring Sleep

• Techniques

  • Electroencephalography (EEG) to monitor brain activity.

  • EEG characterizes sleep stages based on frequency and amplitude.

In-Laboratory Polysomnography (PSG)

• Definition: The reference standard for sleep recording, important for diagnosing sleep disorders.

• Parameters Recorded:

  • EEG (brain), EOG (eye movements), EMG (muscle), ECG (heart).

  • Additional signals include airflow, respiratory effort, and oximetry.

Additional Sleep Studies

1. Type 1: Attended, comprehensive PSG in the lab.

2. Type 2: Unattended home PSG.

3. Type 3: Limited channels monitoring breathing parameters only.

4. Type 4: Minimal channel monitoring.

Advantages & Disadvantages of Sleep Studies

• Type 1: Highly standardized, but requires significant resources.

• Types 2-4: Variations in depth of monitoring, lower costs but less comprehensive.

Conclusion

• Key Takeaways:

  • Sleep architecture consists of uniquely characterized sleep stages.

  • Polysomnography remains the gold standard in sleep measurements.

  • Understanding various sleep studies helps inform appropriate diagnostic choices.

Further Reading and References

• The American Academy of Sleep Medicine 2023.

• Kapur et al. (2017), guidelines on sleep apnea.

• Douglas et al. (2017), clinical practice guidelines for sleep studies.