Morphologic and functional features of cyclic alternating pattern (CAP) sequences in normal NREM sleep.

The Cyclic Alternating Pattern (CAP) is an EEG biphasic periodic activity of normal NREM sleep, generally organized in sequences of two or more cycles and correlated to long-lasting fluctuations in the level of arousal. The remaining NREM sleep is characterized by prolonged stationary activities or non-CAP (NCAP). Criteria for the detection of morphology and reactivity of CAP and NCAP segments are defined in the sleep recordings of 10 healthy young adults. Standard sleep variables and CAP rates, referred to the ratio of CAP time to Total NREM sleep time (CAPR/NREM) and to each NREM sleep stage, were scored for statistical inferences and correlations. CAPR/NREM may be considered an additional non-redundant sleep variable which determines the measure of arousal instability during NREM sleep. The relationship between CAP and the biphasic behavior of microarousals is discussed.