DYNAMICAL CHAOS DETERMINES THE VARIABILITY OF TRANSCRANIAL DOPPLER SIGNALS

In order to estimate whether or not the variability of a timeseries of transcranial Doppler (TCD) waveforms is the result of a random or a d eterministic process the following study was designed. From eight norm al volunteers the middle cerebral artery blood flow velocities were me asured for 50 sec and the maximum blood flow velocities (or waveforms) were analysed. From these waveforms socalled attractors were reconstr ucted and shown in a two dimensional phase portrait. The attractor oi the TCD timeseries shows the entire range of states the cardiovascular system can display. The geometric structure of the attractor can be e stimated by calculation of the correlation dimension D2. The correlati on dimension D2 shows that the time evolution of the TCD timeseries is essentially nonperiodic and can be characterized by low dimensional c haos. It has been shown that the D2 value during hypocapnia has a sign ificant higher value compared to the D2 values during normocapnia. The biological and clinical significance of these observations are outlin ed.