THE PHYSIOLOGICAL AND CLINICAL-SIGNIFICANCE OF NONLINEAR TCD WAVE-FORM ANALYSIS IN OCCLUSIVE CEREBROVASCULAR-DISEASE

In order to compare the results of nonlinear analysis of hemodynamical ly compromised and noncompromised cerebral circulations we measured co nsecutive transcranial Doppler (TCD) waveforms of fourteen patients wi th a unilateral or bilateral occlusion of the internal carotid artery. The cerebral vasomotor reactivity (VMR) to acetazolamide in both midd le cerebral artery (MCA) territories was established by using TCD. Con ventional TCD data and nonlinear TCD analysis of data were compared. N onlinear analysis of the TCD rime series suggested dynamical chaos bas ed on the fractal dimension of the TCD curve and the positive Lyapunov exponents in the compromised and noncompromised MCA territories. In t he areas with the compromised circulation the positive Lyapunov expone nts were significantly lower compared to the noncompromised side and i n some cases with a negative VMR, the Lyapunov exponent was almost zer o. The latter is suggestive for periodic behavior of the impaired cere bral circulation instead of the dynamical chaos which is found under n ormal conditions. The TCD time series of a hemodynamic compromised cer ebral territory not only shows phenomena related to a decreased perfus ion pressure (such as a 'damped waveform') but also phenomena which ar e related to a more prominent periodicity. We speculate that conventio nal and nonlinear TCD analysis could be used to determine the VMR.