Modifications of sleep structure induced by increasing levels of acoustic perturbation in normal subjects.

In each non-REM (NREM) sleep stage, the aggregation of the arousal-related phasic events permits identification of periods of arousal fluctuation (cyclic alternating pattern or CAP) and periods of long-lasting arousal stability (non-CAP or NCAP). As the ratio CAP time to NREM sleep time (CAP/NREM) measures the instability of arousal during sleep, any perturbing event determines an increase of CAP/NREM. On the basis of these premises, 6 healthy volunteers underwent 5 sleep recordings at increasing intensities of sound pressure level (basal condition followed by continuous white noise at 45 dBA, 55 dBA, 65 dBA and 75 dBA, respectively). Besides a remarkable enhancement of CAP/NREM (P less than 0.00001), acoustic perturbation induced a significant linear increase of waking time after sleep onset, stage 2, NREM sleep, stage shifts and a significant linear decrease of stage 4, deep sleep, REM sleep and total sleep time. At each step of environmental disturbance, the values of the CAP ratio were consistent with the gradual changes of sleep organization. Although the Multiple Sleep Latency Test was unremarkable during the day following the sleep recording, CAP/NREM was significantly correlated with the personal evaluation of sleep quality (P less than 0.01). Through this model of transient situational insomnia it was possible to outline different degrees of subjective complaint depending on 3 ranges of CAP/NREM. A crucial role of CAP in the pathophysiological mechanisms of clinical insomnia is hypothesized.

[Cyclic alternating pattern. A new approach to the pharmacology of sleep disorders]. / Les tracés alternants cycliques. Une nouvelle approche en pharmacologie du sommeil.

The Cyclic Alternating Pattern (CAP) is an intrinsic component of normal NREM sleep. This periodic activity is organized in biphasic 40-sec cycles clustered in sequences. CAP sequences are functionally correlated to long lasting arousal instability. CAP is induced by endogenous stimuli (change in sleep stage, body movements) but it is considerably increased by exogenous impulses (noise). CAP rate (CAPR) is a novel polysomnographic variable that measures the amount of CAP during sleep, and it may be calculated for total sleep time and total NREM sleep. We demonstrated that all-night exposure to a 45 dB(A) white noise induced a significant CAPR increase, correlated with impaired sleep quality, even without changes in sleep architecture. We hypothesized that administration of an hypnotic should attenuate this CAPR rise. This hypothesis was verified in a double-blind placebo study, in which 12 healthy young adults received zolpidem, a new imidazopyridine hypnotic. During the noise perturbed nights, zolpidem clearly demonstrated a protective effect on CAPR (mainly during slow wave sleep) and on sleep quality. CAPR appears to be a sensitive indicator of sleep quality, and the cumulative distribution of CAPR throughout the night represents a new method to evaluate the effects of an hypnotic in sleep.

Variations of cyclic alternating pattern rate and homeostasis of sleep organization: a controlled study on the effects of white noise and zolpidem.

The Cyclic Alternating Pattern (CAP) is a physiologic structure of normal non-REM (NREM) sleep, functionally correlated to long-lasting arousal instability. In 12 healthy volunteers, a continuous 45 dB (A) white noise induced no remarkable changes on the standard sleep parameters. However, compared to the baseline conditions, the acoustic perturbation determined a significant increase of the Cyclic Alternating Pattern Rate (CAPR), that measures the amount of CAP during sleep. Ten mg of zolpidem, a novel imidazopyridine hypnotic compound, did not modify the structure of unperturbed sleep, but induced a highly significant reduction of the increased values of CAP Rate due to white noise. The homeostatic function of CAP is stressed. CAPR appears to be a highly sensitive indicator of environmental modification during sleep.

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.