The Electroencephalogram, Blood Flow, and Oxygen Uptake in Rabbit Cerebrum

In the present study, the relationships among electroencephalographic (EEG) amplitude shifts, cerebral blood flow (CBF), and cerebral oxygen uptake (CMRO 2 ) have been characterized in halothane-anesthetized rabbits. CBF was measured by timed collection of venous effluent from the superior sagittal sinus. CMRO 2 was calculated as the product of CBF and the arteriovenous difference in oxygen content. The depth of anesthesia in the first series of experiments was maintained at a constant level that was characterized by spontaneous EEG shifts from high- to low-voltage states (HV-LV shifts). These shifts were associated with transient decreases in mean arterial pressure (MAP), which averaged 23 ± 2 mm Hg ( n = 17). Ninety seconds after spontaneous HV-LV shifts, MAP had returned to its original value, CBF had increased by 26 ± 7% ( n = 8), and CMRO 2 had increased 22 ± 4% ( n = 7). In a second series of experiments, HV-LV shifts were induced by a 90-s application of a standardized nociceptive stimulus ( n = 13). Following these stimulation-induced HV-LV shifts, CBF increased 28 ± 5% and CMRO 2 increased 27 ± 4%. Under scopolamine (0.35 mg/kg, i.v., n = 8), no change in CBF was observed following HV-LV shifts induced by 90-s of stimulation, although CMRO 2 increased significantly by 14 ± 3%. After 300 s of post-scopolamine stimulation, however, both CBF and CMRO 2 had significantly increased by 12 ± 3 and 15 ± 3% ( n = 8) of control, respectively. These results demonstrate that HV-LV shifts, whether spontaneous or stimulation-induced, are associated with significant increases in both CBF and CMRO 2 . Because the early (90-s) increases in CBF but not those in CMRO 2 could be blocked by scopolamine, we suggest that the cerebral vasodilatation that occurs during the early phase of HV-LV shifts involves cholinergic mechanisms. Because scopolamine could not block the increase in CBF observed after 300 s of stimulation, we suggest that the final value of CBF obtained after an HV-LV shift is determined by a combination of both cholinergic and noncholinergic factors.