On-line detection of sleep-wake states and application to produce intermittent hypoxia only in sleep in rats

Sleep-disordered breathing is associated with adverse clinical consequences such as daytime sleepiness and hypertension. The mechanisms behind these a ssociations have been studied in animal models, especially rats, but interm ittent stimuli such as hypoxia have been applied without reference to sleep -wake states. To determine mechanisms underlying the adverse physiological consequences of stimuli associated with sleep-disordered breathing requires criteria for detection of sleep-wake states on-line to trigger stimuli onl y in sleep. This study aimed to develop such a system for freely behaving r ats. Twelve rats with implanted electroencephalogram and neck electromyogra m electrodes were studied in the light and dark phases. Electroencephalogra m frequencies in the high (20-30 Hz) and low (2-4 Hz) frequency bands disti nguished non-rapid eye movement (REM) sleep, whereas neck electromyogram di stinguished REM. Using these parameters in a simple algorithm led to detect ion accuracies of 94.5 +/- 1.0 (SE) % for wakefulness, 96.2 +/- 0.8% for no n-REM sleep, and 92.3 +/- 1.6% for REM compared with blinded human judgment . The algorithm was then used to trigger hypoxic stimuli only in sleep. Bec ause frequency and amplitude analysis is readily performed using a variety of commercial systems, incorporation of these parameters into such an algor ithm will facilitate studies investigating mechanisms underlying the physio logical consequences of sleep-related respiratory stimuli in a fashion that more effectively models clinical disorders.