POWER SPECTRAL-ANALYSIS OF ELECTROMYOGRAPHIC AND SYSTEMIC ARTERIAL-PRESSURE SIGNALS DURING FENTANYL-INDUCED MUSCULAR RIGIDITY IN THE RAT

We have measured electromyographic (EMG) and systemic arterial pressur e (SAP) signals during fentanyl-induced muscular rigidify in adult mal e Sprague-Dawley rats anaesthetized initially with ketamine 120 mg kg( -1) ip. during controlled ventilation. Fentanyl 100 mu g kg(-1) iv. in duced significant increase in EMG activity, recorded from the sacrococ cygeus dorsi lateralis muscle. Power spectral analysis revealed that t his was produced by an increase in the root mean square and a decrease in the mean power frequency values of the signals, signifying recruit ment and synchronous activation of motor units. Together with transien t hypotension and bradycardia, power spectral analysis of She SAP sign als demonstrated a reduced but maintained power density of the frequen cy components that represent respiratory, baroreceptor and vasomotor a ctivities. All these effects were only demonstrated unequivocally in r ats maintained by iv. infusion of ketamine until 10 min before the adm inistration of fentanyl. We conclude that analysis of the temporal alt erations in the spectral components of the EMG and SAP signals in rats during mechanical ventilation provides a sensitive method of measurin g fentanyl-induced muscular rigidify and the accompanying alterations in haemodynamic variables.