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GLOSSARY OF TERMS USED IN TIME SERIES ANALYSIS OF CARDIOVASCULAR DATA

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Object with self-similar structure across scales, so that resembling structures appear as one zoomes in and out.

Since such self-similar structures are composed by subunits similar to the larger ones, which in turn are composed by yet smaller similar subunits and so on, fractals do not have a single length scale. Because of their intrinsic irregularity, the size of fractal objects is not measureable in terms of classic euclidean geometry. Rather, their size can be characterized by defining a noninteger dimension (fractal dimension).
The concept of self-similar structures can be also applied to time-series: a fractal time series is a process in which self-similar fluctuations appear at different temporal scales.

Goldberger AL (1992) Fractal mechanisms in the electrophysiology of the heart. IEEE Engineering in medicine and biology, 11,2, 47-52
Butler GC et al. (1994) Fractal nature of short-term systolic BP and HR variability during lower body negative pressure. Am J Physiol.

useful links: Dynamical Systems and Fractals Lecture Notes by D.J. Wright