The cerebral hemodynamic response to electrically induced seizures in man

Abstract

The hemodynamic response to seizure has long been a topic for discussion in association with the neuronal damage resulting from convulsion. Electroconvulsive therapy (ECT) is an appropriate clinical model for the investigation of the cerebral physiology of seizure. In this study, we monitored the oxygenation state of brain tissue using near infrared (NIR) spectrophotometry, and flow velocity at the middle cerebral artery (MCA) using transcranial Doppler ultrasonography (tc-Doppler) in ninety cases where ECT was prescribed to patients suffering from endogenous depression. Under general anesthesia with thiopental and succinyl choline, an electrical current was applied bilaterally at the minimal energy level. Throughout the therapy, end-tidal CO 2 tension was maintained at 30–35 mmHg, and the SpO 2 value was maintained above 98% by manual ventilation assistance. The total- and oxy-hemoglobin contents in the brain were reduced during the electrical shock, and then recovered to the pre-shock value (total-hemoglobin; 44.13 ± 12.88 s after the shock, oxy-hemoglobin; 88.62 ± 11.69 s after the shock). Subsequently, these values further increased beyond the preshock value. On the other hand, the deoxy-hemoglobin content increased for 90.73 ± 15.88 s during and after the electrical shock, and decreased afterward. Reduction of cytochrome aa3 began 3.04 ± 0.51 s after the electrical shock, and this was reoxygenated at 171.88 ± 12.95 s after the shock. The flow velocity at MCA was drastically increased (mean flow velocity; from 44.8 ± 1.2 cm/s to 106.4 ± 7.5 cm/s) 1 min after the shock and returned to the pre-shock level after 10 min. From these observations, it was suggested that electrical shock provoked a contraction of arterial wall smooth muscle, and depolarized the synaptic terminal, which triggered neurotransmitter release and sympathetic activation. This depolarization also caused an abrupt increase in the energy consumption of neurons and the cytochrome aa3 was temporarily reduced. However, this imbalance in energy supply and consumption was improved by the subsequent hyperdynamic blood circulation and by suppression of neuronal activity at the postictal phase. It was concluded that electrically induced seizure provokes a temporary imbalance in energy consumption and supply, and that these new non-invasive monitors are useful in the study of the physiological events that occur in the nervous system in man.