Spontaneous oscillations in cerebral blood flow velocities in middle cerebral arteries in control subjects and patients with epilepsy

Background and Purpose Cardiac arrhythmias mediated by the sympathetic nervous system have been implicated in sudden, unexplained deaths in patients with epilepsy. Cerebral blood flow velocities (CBFV) as measured by transcranial Doppler are characterized by slow spontaneous oscillations in part attributed to changes in sympathetic activity (M waves, 3 to 9 cycles per minute) and to discharges of monoaminergic neurons in the brain stem (B waves, 0.5 to 2 cycles per minute). This study was designed to compare spontaneous fluctuations of CBFV in patients with epilepsy with those in normal control subjects. Methods Simultaneous registrations of scalp electroencephalograms, with electrodes placed according to the 10-20 System, and transcranial Doppler recordings of both middle cerebral arteries were performed in 27 patients (9 with primary generalized epilepsy, 18 with focal epilepsy). Data analysis of CBFV was based on the envelope curves of the Doppler spectrum. A fast Fourier transformation over the 20-minute CBFV curve was performed, and the amplitudes of B and M waves were calculated and compared with those in 20 normal, age-matched control subjects. Results While the amplitudes of the B waves in both groups were similar, patients with epilepsy showed significantly in creased M waves. Patients with focal epilepsy did not present asymmetries between the normal hemisphere and the side of the epileptic focus with respect to both M and B waves. Conclusions Enhanced M waves in epileptic patients may reflect increased sympathetic activity even in the absence of seizures. This study provides further evidence for an autonomic dysfunction as a possible mechanism for sudden unexplained death in patients with epilepsy.