INVESTIGATING THE EFFECTS OF OPIOID DRUGS ON ELECTROCORTICAL ACTIVITYUSING WAVELET TRANSFORM

Fetal electrocortical activity (ECoG) is characterized by two distinct patterns: HVSA (high voltage, slow activity) and LVFA (low voltage, f ast activity). Using the wavelet transform (WT), we recently reported that the frequency characteristics of these two ECoG patterns undergo significant maturational changes prior to birth (Akay et al. 1994a). W e now report that fetal ECoG can also be significantly affected by pha rmacological agents. In this paper, we compared the effects of two opi oid drugs (morphine and [D-Pen(2), D-Pen(5)]-enkephalin, DPDPE) on fet al ECoG, using the chronically instrumented fetal lamb model. Morphine was infused intravenously (i.v.) at 2.5 mg/h, while DPDPE was infused into the lateral cerebroventricle (i.c.v.) at 30 mu g/h. The ECoG was analyzed using WT. We performed multiresolution decomposition for fou r sets of parameters D-2j where -1 < j < -4. The four series WTs repre sent the detail signal bandwidths: (1) 16-32 Hz, (2) 8-16 Hz, (3) 4-8 Hz, (4) 2-4 Hz. The data were subjected to statistical analysis using the Kolmogorov-Smirnov (KS) test. Both morphine and DPDPE resulted in a significant increase in power in the first wavelet band, while power was reduced in the second, third and fourth wavelet bands. In additio n, both drugs resulted in a disruption of the normal cyclic pattern be tween the two ECoG patterns. There was a difference in the time course of action between morphine and DPDPE. This is the first occasion in w hich continuous ECoG has been subjected to rigorous statistical analys is. The results suggest that the WT-KS method is most suitable for qua ntitating changes in the ECoG induced by pharmacological agents.