CAP and arousals in the structural development of sleep: an integrative perspective

It is known that the number of arousals per hour of sleep increases linearly across life, while the amount of cyclic alternating pattern (CAP) undergoes a u-shaped evolution. The present study aimed at investigating the differences, overlaps and age-related distribution of arousals and CAP components, i.e. subtypes A1, A2, A3. The relationship between the phase A subtypes and the structural organization of sleep was also evaluated.

Forty healthy subjects were examined. Polysomnographic analysis was performed according to the scoring rules for sleep stages, CAP and American Sleep Disorders Association arousals.

Arousals occurred more frequently during CAP (40 events per hour) than in total sleep time (18 events per hour), non-rapid eye movement (NREM) sleep (20 events per hour), and rapid eye movement (REM) sleep (12 events per hour). Within CAP, arousals always coincided with a subtype A2 or A3. Both arousals and subtypes A2 and A3 showed a similar evolution with relation to age (linear positive), and to the amounts of light NREM sleep (linear positive) and deep NREM sleep (linear negative). In contrast, subtypes A1 showed a u-shaped profile across the life span and appeared closely related (linear positive) to the time spent in stages 3 and 4. Almost 90% of arousals occurring in NREM sleep were preceded in the previous 3s by a K-complex or a delta burst, indicating a topical involvement of slow electroencephalographic (EEG) components in the arousal build-up.

Arousals show only one side of the multi-faceted activation complexes, whereas the three subtypes of CAP provide a graded picture of arousal features from the strongest A3 subtypes, showing a prevalence of EEG desynchrony, to the weakest A1 phases, which are dominated by EEG synchrony and represent the prevalent components of CAP (60% of all the phase A subtypes).