title: Effect of volatile anesthetics on interhemispheric EEG cross-approximate entropy in the rat.
abstract: Dissimilarity of the electroencephalogram (EEG) between the two hemispheres was characterized by cross-approximate entropy (C-ApEn), an information statistical parameter applicable to nonlinear, aperiodic signals. EEGs were recorded bipolarly with pairs of epidural electrodes in the left and right frontal cortices. The signals were filtered for 1-100 Hz and digitized at 200 Hz. Inhaled anesthetic concentration was varied between 0.3 and 2.1% with 45-min equilibration periods while the rats were breathing spontaneously. Anesthetics produced concentration-dependent changes in C-ApEn. A greater dynamic range of C-ApEn was obtained by reducing the epoch length from 2 s to 100 ms. At a 0.4% inspired agent concentration halothane caused an increase of C-ApEn, whereas isoflurane did not. When the inspired concentrations of both agents were greater than 0.4%, C-ApEn dose-dependently decreased as agent concentrations increased. Isoflurane depressed C-ApEn more than did halothane at all equivalent minimum alveolar concentration levels, but the two agents became equipotent at 1.5% inspired concentration. C-ApEn fell below the awake baseline at 0.8% anesthetic concentration that also abolished the righting reflex. C-ApEn increased after high-pass filtering (>20 Hz) and decreased after-low pass filtering (<20 Hz) of the digitized EEG; the anesthetic dependence of C-ApEn was diminished by both filters. The results suggest that C-ApEn of bihemispheric EEG is a sensitive, agent-specific correlate of anesthetics' central effect.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. ahudetz@mcw.edu
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Hudetz
mesh_terms: D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D019277:Entropy; D005625:Frontal Lobe / Q000187:drug effects* / Q000502:physiology*; D007839:Functional Laterality; D006221:Halothane / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane; D006221:Halothane