Cyclic Alternating Pattern And Noncyclic Alternating Pattern

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CAP is organized in sequences of two or more CAP cycles. Each CAP cycle consists of a phase A and a phase B, each lasting between 2 and 60 s. All CAP sequences begin with a phase A and end with a phase B. In NREM sleep, the phase A patterns are composed of the single or clustered arousal-related phasic events peculiar to the single sleep stages:

• Intermittent alpha rhythms and sequences of vertex sharp waves, in stage 1

• Sequences of two or more K-complexes with or without alphalike components and beta rhythms, in stage 2

• Delta bursts that exceed by at least one-third the amplitude of the background activity, in stages 3 and 4

• Transient activation phases (Schieber et al., 1971) or EEG arousals (ASDA, 1992), in all the stages

Sleep spindles are generally excluded from the CAP scoring criteria, especially when they appear at the beginning or at the end of a phase A pattern.

CAP appears as a synchronous and widely diffused EEG activity on both hemispheres with minor differences in morphology and amplitude across the various leads. Bipolar longitudinal montages warrant the most clear cut detection of CAP.

In NREM sleep, the CAP sequences may extend across successive sleep stages and thus the A phases may present different patterns within the same CAP sequence. In REM sleep, due to the lack of EEG synchronization, the A phases consist exclusively of desynchronized patterns (transient activation phases or arousals). Under physiological conditions, the 3-4-min interval between these A phases in REM sleep (Schieber et al., 1971) does not meet the temporal requirements for the scoring of CAP in this sleep stage. The period of sleep between two successive A phases separated by an interval >60 s is scored as NCAP.

Phase A Subtypes

Variations during CAP involve to different degrees muscle tone, heart rate, and respiratory activity, which increase during phase A and decrease during phase B (Lugaresi et al., 1972; Terzano et al., 1985, 1988; Evans, 1992; Terzano and Parrino, 1993). On the basis of the information derived from EEG activities, muscle tone, and neurovegetative responses, three subtypes of A phases (Fig. 8.3) corresponding to different levels of neurophysiological activation can be distinguished.

Subtypes Al

These A phases have synchronized EEG patterns (intermittent alpha rhythm in stage 1; sequences of K-complexes or delta bursts in the other NREM stages), associated with mild or trivial polygraphic variations.

Subtypes A2

These A phases have desynchronized EEG patterns preceded by or mixed with slow high-voltage waves (K-complexes with alpha and beta activities, K-alpha, arousals with slow wave synchronization), linked with a moderate increase of muscle tone and/or cardiorespiratory rate.

Subtypes A3

These A phases have desynchronized EEG patterns alone (transient activation phases or arousals) or exceeding | of the phase A length, coupled with a remarkable enhancement of muscle tone and/or cardiorespiratory rate.

EMG— . > L-"" " 11 * 11 ""■ "

FIGURE 8.3 Specimens of phase A subtypes in NREM sleep. Top left, A1 subtype in stage 2: brief cluster of syncronized EEG patterns (sequence of K-complexes). Top right, A1 subtype in slow wave sleep: delta burst lasting about 7 s with an amplitude that exceeds the background EEG activities by at least 5. Muscle tone and heart rate show irrelevant modifications. Middle, A2 subtype in stage 2: phase A that starts with a dominant EEG synchronization (mainly K-complexes) and continues with a prevailing desynchronized EEG pattern. The synchronized and desynchronized portions of the A2 subtypes are equivalent in duration. Notice the moderate reinforcement of muscle tone and increase of heart rate concomitant to the onset of EEG desynchrony. Bottom, A3 subtype in stage 2: phase A introduced by a short EEG synchronization, but occupied extensively by a sustained desynchronized EEG pattern, associated with a robust increase of muscle tone and irregular heart rate acceleration. The A3 phases are characteristically longer than the A1 and A2 subtypes.

The EEG criteria for the identification of subtypes A3 and partially of subtypes A2 show extensive similarities with the ones proposed for arousals by the American Sleep Disorders Association (ASDA, 1992).

In the physiological architecture of sleep, the A1 subtypes prevail in the buildup and maintenance of deep NREM sleep (Ferrillo et al., 1997), while the A2 and A3 subtypes dominate in light sleep that precedes the onset of desynchronized REM sleep (Terzano et al., 2000).

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