The cyclic alternating pattern plays a gate-control on periodic limb movements during non-rapid eye movement sleep

Spike-wave discharge and the microstructure of sleep-wake continuum in idiopathic generalised epilepsy

This review summarises all the evidences about the influence of different vigilance states on the occurrence of spike wave discharge (SWD) in idiopathic generalised epilepsy (IGE) patients. Numerous converging observations showed that full REM-sleep and alert wakefulness exert strong inhibition. A critical zone of vigilance which is a transitional state between waking and non-REM (NREM) sleep, and NREM sleep and REM sleep, has a promoting effect on the absence type spike wave discharge. Spike wave discharges are associated with phasic arousals without awakening and are attached to oscillation son the microstructural level of sleep, perpetuated by cyclic arousal events known as 'cyclic alternating pattern' (CAP), especially within the critical zone, but also along the whole sleep process. More specifically SWD seems to be attached to the 'A-phase' of CAP which is a reactive one and reflects synchronised NREM sleep EEG elements, like K-complexes, spindles and delta groups. The more slow wave elements are found in phase A--like in subtype A1--the more the coincidence with SWD occurs, and the more it is characterised by fast rhythms--as in subtype A2 and A3--the less the association with SWD could be observed. Since subtype A1 is associated with the first sleep cycle and with the descending branches of cycles, it is concluded that SWD appear in those dynamic moments of vigilance level oscillations which were characterised by strong sleep-like answers to arousal influences in high sleep pressure periods of sleep cyclicity. These data harmonize with another line of evidence suggesting that SWD represent the epileptic variant of the complex thalamocortical system function which is the substrate of NREM sleep EEG phenomena. In idiopathic generalised epilepsy there is a growing body of evidence that--as it was assumed by Gloor--spindles transform to SWD pattern. These data explain why those dynamic changes which evoke sleep responses are promoting for the occurrence of SWD. Adapting these data we offer a new interpretation to explain the strong activation effect of sleep deprivation in this kind of epilepsy. We assume that it is mainly due to the forced vigilance level oscillations, especially in morning, when elevated sleep pressure and circadian wake promoting forces, representing opposite tendencies, increase the amount of oscillations.

Unilateral periodic limb movements during sleep in corticobasal degeneration

Periodic limb movements in sleep (PLM) have been associated with several degenerative disorders and other focal or diffuse diseases. We present a patient with clinical diagnosis of corticobasal degeneration and sleep complaints, in whom video recording and polygraphic study confirmed the presence of right PLM. The unilaterality of the movements and the positron emission tomography findings (hypometabolism in the left frontoparietal, basal ganglia, and thalamic areas) suggest that the loss of inhibitory descending central pathways, with origin in the cortex or basal ganglia, may be involved in the pathogenesis of PLM.

Periodic leg movements and sleepiness in patients evaluated for sleep-disordered breathing

Most polysomnograms are performed because sleep-disordered breathing (SDB) is suspected, but periodic leg movements during sleep (PLMS) are frequent incidental findings, and their significance is not well understood. In a clinical series of 1,124 adult patients with suspected or confirmed SDB, we tested for an association between the rate of periodic leg movements and one important outcome, the severity of daytime sleepiness. Objective sleepiness was assessed by the Multiple Sleep Latency Test in all subjects, problem sleepiness by self-rating in 873, and subjective sleep propensity by the Epworth Sleepiness Scale in 201. Increased leg movements were associated with decreased objective sleepiness (p = 0.03) but explained less than 1% of the variance. When nocturnal arousals were scored (n = 321 subjects), rates of leg movements associated with arousals predicted less objective sleepiness (p = 0.008); rates of leg movements without arousals predicted nothing. The rates of leg movements showed no association with subjective problem sleepiness or sleep propensity. We conclude that incidental periodic leg movements during sleep are not associated with excessive daytime sleepiness, and therefore appear unlikely to contribute to this problem. Increased sleepiness may reduce the likelihood of arousal with each leg movement.

EEG arousals and awakenings in relation with periodic leg movements during sleep

It is known that periodic leg movements are frequently accompanied by full awakenings or by signs of EEG arousals. The time relationship of these EEG arousals with leg movements varies from patient to patient. They may precede or follow leg movements or occur simultaneously. It is not clear whether these arousals trigger leg movements or, alternatively, whether both EEG arousals and leg movements are separate expressions of a common pathophysiological mechanism. We investigated the temporal relationship of five EEG arousals, such as alpha activity, K-complexes, spindles, K-alpha, K-spindle activities and awakenings, with leg movements in 10 periodic leg movement patients. These EEG arousals were considered to be associated with leg movements if they occurred 10 s before/after or simultaneously with the onset of right or left tibialis muscle EMG potentials. It was found that 49.19% of EEG arousals occurred before leg movements, 30.61% occurred simultaneously and 23.18% occurred just after leg movements. The number of EEG arousals was significantly higher in the 10 s preceding leg movement than simultaneously or in the 10 s following. Alpha activity was the phenomenon associated most frequently with leg movements, irrespective of its temporal organization and was significantly higher during the 10 s preceding movement. Spindle and K-spindle activities were significantly higher before leg movement, whereas K-complex activity was significantly more frequent during leg movements. The number of awakenings was significantly higher after leg movements than simultaneously. These results indicated that leg movements are not primary, but rather are a phenomenon associated with an underlying arousal disorder.

Cyclic alternating pattern (CAP) and epilepsy during sleep: how a physiological rhythm modulates a pathological event

OBJECTIVES

Epileptic susceptibility is triggered by the sleeping condition. However, both ictal and interictal events are not equally affected by the different sleep states. Besides the well-known dichotomy between non-REM sleep (high activation) and REM sleep (low activation), epileptic phenomena are deeply sensitive to the ongoing level of arousal.

METHODS

During non-REM sleep the arousal level can be either unstable, as expressed by the repetitive sequences of the cyclic alternating pattern (CAP), or stable, as reflected by non-CAP. Phase A (arousal complex) and phase B (post-arousal rebound response) are the two basic components of the CAP cycle, which presents a 20-40 s periodicity. Three subtypes of A phases can be recognized: the A1 subtypes, which are thoroughly composed of K-complexes and delta bursts, and subtypes A2 and A3 dominated by moderate (A2) or prominent (A3) EEG desynchrony.

RESULTS

As a manifestation of unstable sleep, CAP offers a favorable background for the occurrence of nocturnal motor seizures that in most cases arise in concomitance with a phase A. In primary generalized epilepsy (PGE) and in lesional epilepsies with fronto-temporal focus, activation of interictal discharges is high during CAP reaching the climax during phase A and the strongest inhibition during phase B. A lack of modulation is observed instead in epilepsy with benign rolandic spikes. In PGE, the interictal bursts are mostly associated with the highly synchronized phase A1 subtypes.

CONCLUSIONS

The analysis of sleep microstructure based on CAP parameters offers a sensitive framework for exploring the linkage between dynamic EEG events and epileptic phenomena.

Origin and Significance of the Cyclic Alternating Pattern (CAP). REVIEW ARTICLE

This article reviews the 15 years of studies conducted on the cyclic alternating pattern (CAP), the electro- encephalogram (EEG) marker of arousal instability during sleep. Starting from the limits and drawbacks of conventional sleep parameters (macrostructure), investigation of the underground world (microstructure) is extensively carried out with particular attention to K-complexes and other arousal-related phasic events of non-rapid eye movement (NREM) sleep. The continuity between conventional and non-conventional arousals is stressed in the light of autonomic function and motor activity evidence. The similarities and differences between CAP and arousals are thoroughly illustrated as well as the putative biological bases of these phenomena. The oscillatory nature of CAP, the involvement of CAP in the modulation of EEG synchrony, the sleep-maintenance properties of CAP in response to arousing stimuli, the clinical applications of CAP parameters and the promising availability of automatic scoring systems are highlighted.

The impact of cyclic alternating pattern on heart rate variability during sleep in healthy young adults

OBJECTIVE

Cyclic alternating pattern (CAP) consists of arousal-related phasic events while the complementary condition, non-CAP (NCAP), is characterized by a rhythmic background activity, reflecting a condition of stable arousal, during non-REM sleep. The arousal swings that accompany the appearance of CAP on the EEG are associated with transient variations of muscle tone and autonomic activities, including heart rate (HR). The aim of our study was to evaluate HR variability in relation to CAP during non-REM sleep in healthy adults.

METHODS

Ten healthy subjects (mean age = 28.1 years) underwent 8 h polysomnography. HR variations were measured by power spectrum analysis. The ECG signals were segmented in correspondence of the different sleep stages and different CAP conditions.

RESULTS

A significant difference between CAP and NCAP conditions was found in low frequency (LF) component (increased in CAP) and high frequency (HF) component (decreased in CAP). LF/HF ratio was increased in CAP.

CONCLUSION

Physiological fluctuations of the EEG arousal level influence cardiac autonomic activity in normal subjects. The studies on nocturnal variation in sympathetic and vagal tone should take in account the microstructural sleep changes, other than the conventional polysomnographic parameters.

The influence of sex, age and sleep/wake state on characteristics of periodic leg movements in restless legs syndrome patients

Restless legs syndrome (RLS) patients experience periodic stereotyped leg movements while awake and during sleep. The aim of the present study was to measure the effects of sex, age and the sleep/wake state on several characteristics (frequency, duration and periodicity) of these periodic leg movements (PLM). One hundred unrelated patients diagnosed with primary RLS were studied. During wakefulness, frequency of PLM increased and the mean inter-movement interval decreased with advancing age. The modal value of inter-movement interval distribution was also altered suggesting that aging influences rhythm-generation mechanisms. Sleep/wake states had a profound effect on leg movement characteristics. Movements of longer duration were seen during wakefulness, while REM sleep was characterized by the shorter duration and the lowest frequency of PLM, due most likely to the inhibition of spinal motoneurons that prevails in REM sleep. States of vigilance also modulated the periodicity of PLM. Intervals were shorter during wakefulness and increased progressively from stage 1 to stage 2 sleep, and to slow wave sleep (SWS). During REM, the duration of sleep intervals returned to values obtained in stage 1 sleep; these two stages sharing similar patterns of EEG activity. These results indicate that a single state dependent mechanism may be responsible for the periodicity of PLM noted both during sleep and wakefulness.

Cyclic alternating pattern (CAP) in normal sleep: polysomnographic parameters in different age groups

OBJECTIVES

The present study aimed at offering a standardized database for cyclic alternating pattern (CAP) parameters across representative ages of life.

METHODS

CAP parameters were quantified in 40 healthy sleepers and polygraphically investigated in a partially sound-proof recording chamber under a standard laboratory setting. Four age groups were investigated (teenagers: 10-19 years; young adults: 20-39 years; middle-aged: 40-59 years; elderly: 60 years). Each group included 10 subjects (5 males and 5 females). Nocturnal recordings were accomplished after adaptation to the sleep laboratory that also served to rule out the presence of sleep-related disorders. The study indicated that CAP is a natural phenomenon of NREM sleep, with specific age-related characteristics across the life cycle.

RESULTS

CAP rate in NREM sleep, defined as the percentage ratio of total CAP time to total NREM sleep time, showed a U-shape profile with minimum in young adults (31.9%), maximum in the elderly group (55.3%), and intermediate values in teenagers (43.4%) and in middle-aged subjects (37.5%). The longest duration of CAP cycles was found among the older subjects (31 s). The highest amounts of subtypes A1 were identified in teenagers (n = 261), while the highest amounts of A2 and A3 subtypes occurred in the elderly group (n = 183). Across the ages, the level of arousal mostly fluctuated in stages 1 and 3, whereas stage 4 emerged as the most stable NREM stage. Overall, stage 2 better reflected the CAP values referred to as total NREM sleep.

CONCLUSIONS

The periodic arousal fluctuations reflected by CAP are a natural phenomenon of NREM sleep with specific age-related variations across the life cycle.

Sleep bruxism is a disorder related to periodic arousals during sleep

There is evidence that sleep bruxism is an arousal-related phenomenon. In non-REM sleep, transient arousals recur at 20- to 40-second intervals and are organized according to a cyclic alternating pattern. Polysomnographic recordings from six subjects (two females and four males) affected by sleep bruxism (patients) and six healthy age-and gender-matched volunteers without complaints about sleep (controls) were analyzed to: (1) compare the sleep structure of bruxers with that of non-complaining subjects; and (2) investigate the relations between bruxism episodes and transient arousals. Patients and controls showed no significant differences in conventional sleep variables, but bruxers showed a significantly higher number of the transient arousals characterized by EEG desynchronization. Bruxism episodes were equally distributed between non-REM and REM sleep, but were more frequent in stages 1 and 2 (p < 0.0001) than in slow-wave sleep. The great majority of bruxism episodes detected in non-REM sleep (88%) were associated with the cyclic alternating pattern and always occurred during a transient arousal. Heart rate during the bruxism episodes (69.3+/-18.2) was significantly higher (p < 0.0001) than that during the pre-bruxing period (58.1+/-15.9). Almost 80% of all bruxism episodes were associated with jerks at the anterior tibial muscles. The framework of the cyclic alternating pattern offers a unified interpretation for sleep bruxism and arousal-related phenomena.

Cyclic alternating pattern as a provocative factor in nocturnal paroxysmal dystonia

PURPOSE

We made a polygraphic study of 6 patients with nocturnal paroxysmal dystonia (NPD) in which the cyclic alternating pattern (CAP) parameters were compared with those of a group of age- and sex-matched controls.

METHODS

All patients met the requirements for NPD diagnosis, characterized by generalized stereotyped movements (dystonic-dyskinetic), with a 1-min centered duration but with no clear evidence of epileptic abnormalities in the waking EEG and during nocturnal recordings.

RESULTS

Besides the major events, the NPD polysomnograms also showed shorter, repeated episodes of shorter duration (generally <20 s) consisting of abrupt movements involving one or more body segments. Overall, the motor events in patients with NPD were closely related to periods of unstable non-REM (NREM) sleep, as evidenced by the sequences of CAP, and began during an A phase. According to the conventional scoring parameters, NPD and controls differed only in sleep latency (+14 min in the NPD patients: p < 0.04). However, the architecture of sleep in the group with NPD was characterized by prolonged and irregular NREM/REM cycles. In addition, the NPD recordings showed significantly higher values of CAP rate (p < 0.0001). When major motor attacks were suppressed by medication, sleep was characterized by a decrease in the excessive amounts of CAP rate and by a more regular architecture.

CONCLUSIONS

The modulatory role of CAP on nocturnal motor events is reported.