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.