Cortical activation states in sleep and anesthesia. I: Cardio-respiratory effects

Under light urethane anesthesia, animals cycle through patterns of EEG activity which superficially appear like waking, light sleep and slow-wave sleep patterns (States I, II and III, respectively) in unanesthetized animals. The present study questioned whether similar cortical activity patterns in anesthetized and unanesthetized golden mantled ground squirrels represented analogous states in terms of cardiorespiratory function. Sleep exerted a strong negative influence on breathing frequency and ventilation, but had less consistent effects on tidal volume. Urethane-anesthetized animals demonstrated exactly the same alterations in respiratory variables when switching between states with similar cortical activity. Cardiovascular function was also affected by arousal state; heart rate decreased and variation increased significantly as animals moved from wake into sleep. Although urethane anesthesia greatly increased heart rate and abolished respiratory sinus arrhythmia, state-dependent changes in heart rate were still evident. Overall, the states observed under urethane anesthesia mimicked sleep/wake in terms of their effect on cardio-respiratory function. (C) 1998 Elsevier Science B.V. All rights reserved.