Fractal rigidity in migraine

We study the middle cerebral artery blood flow velocity in humans using transcranial Doppler ultrasonography. Scaling properties of time series of the axial flow velocity averaged over a cardiac beat interval may be characterized by two exponents. The short-time scaling exponent (STSE) determines the statistical properties of fluctuations of blood flow velocities in short-time intervals while the Hurst exponent describes the long-term fractal properties. In many migraineurs the value of the STSE is significantly reduced and may approach that of the Hurst exponent. This change in dynamical properties reflects the significant loss of short-term adaptability and the overall hyperexcitability of underlying cerebral blood flow control system. We call this effect fractal rigidity.