Signals derived from the human cardiovascular system are well known to exhibit highly complex, nearly periodic, oscillatory behaviour whose nature is something of an enigma. It has, for example, been variously described as chaotic, fractal, stochastic, and subject to 1/f fluctuations — and its true nature is still the subject of vigorous debate. We review and describe some recent experiments that illuminate the problem and discuss a combination of noise and almost periodic frequency modulation as a signature of the system dynamics.
This is the author’s version of a work that was accepted for publication in Physica A. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in PHYSICA A, 314, 1-4, 2002 DOI: 10.1016/S0378-4371(02)01165-2