Autonomic correlates of orthostatic intolerance and seizures

We describe an integrated evaluation of central autonomic regulation, relating the simultaneously recorded electroencephalogram (EEG) and transcranial Doppler (TCD) to systemic cardiovascular indices. Signal analysis techniques included time-frequency analysis and nonlinear rescaled range analysis. The inhibition of centrally mediated autonomic rhythms can precede clinical manifestations e.g. syncope (increased slow EEG modulation, withdrawal of 0.05 Hz rhythms in BP and progressive decline in total peripheral resistance). We tested the hypothesis that partial complex seizures, which has a structural substrate with powerful autonomic manifestations, might also have autonomic alterations that precede EEG changes. We observed that sympathetic activation of slow rhythms in RRI preceded seizure onset, while parasympathetically mediated rhythms rapidly diminished at the beginning of the seizure. We used the Hurst exponent, based on the rescaled range analysis for evaluation of deterministic component in patients with orthostatic tachycardia. Data showed that the loss of variability in RRI was associated with increased values of Hurst exponent. Thus, the process become more deterministic.