What causes a cyclic alternating pattern (CAP)?

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Causes of Cyclic Alternating Pattern (CAP)

The cyclic alternating pattern (CAP) is the EEG marker of unstable sleep, representing periodic EEG activity during NREM sleep that reflects fluctuations in the level of arousal. 1

Definition and Physiological Basis

  • CAP is a long-lasting periodic activity consisting of two alternating EEG patterns that corresponds to fluctuations in arousal levels during NREM sleep 2
  • It represents a physiological component of normal NREM sleep, functionally correlated with long-lasting arousal oscillations 3
  • CAP can be identified in both adult and children's sleep, making it a sensitive tool for investigating sleep disorders across the lifespan 1

Primary Causes of CAP

Normal Sleep Physiology

  • CAP corresponds to a periodic succession of spontaneous phasic phenomena recurring within every NREM sleep stage (intermittent alpha rhythm, K-complex sequences, reactive slow wave sequences) 2
  • It is the EEG translation of the brain's reorganization when challenged by modifications in environmental conditions 2
  • CAP sequences are closely linked to sleep onset and sleep recoveries after nocturnal awakenings 3

Sleep State Transitions

  • Almost 50% of all NREM stage changes are accompanied by CAP sequences 3
  • CAP indicates a functional linkage between cyclic fluctuations of arousal and the beginning of any sleep behavioral state 3
  • The transitions between wakefulness and sleep appear as symmetrical events in the organization of arousal based on their temporal relationship with CAP sequences 3

Factors That Increase CAP

Sleep Disorders

  • CAP is known to increase in many conditions of sleep disruption including obstructive sleep apnea syndrome and periodic limb movements in sleep (PLMS) 4
  • It serves as a marker of sleep instability in various sleep disorders 1

Environmental Factors

  • CAP is sensitive to environmental influences on sleep, as demonstrated by significant differences in CAP rates between first and second nights in sleep laboratories (first-night effect) 5
  • The first night in a sleep laboratory shows significantly higher CAP rates (33.29%) compared to the second night (26.34%) 5

Arousal Control Mechanisms

  • CAP reflects two different functional states in the arousal control mechanism 2
  • The organization of sleep and preservation of ultradian rhythms may determine the manifestation of CAP 4
  • CAP may arise from the activation of higher cortical areas as part of a central generator mechanism 4

Clinical Significance

  • CAP analysis provides insight into sleep quality beyond traditional macrostructural measures 5
  • It can be used to investigate the underlying pathophysiology of sleep disorders 4
  • CAP subtypes (A1, A2, A3) have different clinical implications and may represent different underlying pathophysiological mechanisms 4
  • The dimension of sleep instability as measured by CAP has provided new insights into the pathophysiology and management of sleep disorders 1

Measurement and Analysis

  • CAP is measured by analyzing EEG patterns during NREM sleep 2
  • Each EEG specific alternating pattern (defined as a cycle) can be subdivided into phases depending on the arousal response to stimulation 2
  • CAP rate is calculated as CAP time divided by sleep time, and can be determined for total sleep time, NREM sleep, or individual NREM sleep stages 2
  • Microstructural analysis of sleep using CAP can detect subtle differences in sleep quality that may not be apparent through traditional macrostructural analysis 5

References

3
Research

The cyclic alternating pattern sequences in the dynamic organization of sleep.

Electroencephalography and clinical neurophysiology, 1988

4
Research

Cyclic Alternating Pattern Analysis in Periodic Leg Movements in Sleep in Patients With Obstructive Sleep Apnea Syndrome Before and After Positive Airway Pressure Treatment.

Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society, 2021

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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