Temporal fluctuations in regional red blood cell flux in the rat brain cortex is a fractal process.

Temporal fluctuations ever since it was observed and recognized as an elementary feature of blood flow in the microcirculation by Krogh in 1929 (Krogh, 1929) became the essence of concepts termed “vasomotion” and “flow motion”. Such fluctuations in flow are common in various microcirculatory beds including that of the brain and can be continuously monitored by laser-Doppler flowmetry (Stern, 1975; Nilsson et al., 1980; Rosenblum et al., 1987; Fasano et al., 1988; Hudetz et al., 1992; Morita-Tsuzuki et al., 1992). When challenged, they often show slow (6–12 cycles/minute) oscillatory pattern, which allow for a relatively simple characterization if the higher frequencies are eliminated from the signal (Hudetz et al., 1992; Morita-Tsuzuki et al., 1992). Temporal variation in microcirculatory flow is however multifactorial and the interactions among these factors can manifest in a complex structuring of the time series recorded by high-resolution laserDoppler flowmetry (LDF). With no apparent dominating frequency present (Fig. 3), they are much too complex to be analyzed in specific terms by conventional descriptive statistics, amplitude and frequency measures. Thus we have used fractal methods genuinely holistic in nature to gain statistical insight into random signals of this kind and to determine if under unchallenged control conditions they represent disorganized behavior or show long-range correlations (West and Goldberger, 1987; Bassingthwaighte, 1988; West and Shlesinger, 1990; Weibel, 1991; Bassingthwaighte et al., 1994).