June 4, 1999 Multifractal analysis uncovers differences between healthy and unhealthy hearts
(Boston, Mass.) - In a paper published in Nature this week, scientists from Boston University's Center for Polymer Studies describe a new technique derived from modern physics that can help doctors distinguish between a healthy heart and one that is headed for trouble.
Led by Research Associates Plamen Christov Ivanov and Luis Amaral, the team analyzed the timing of heartbeats of both healthy and sick hearts, looking for fractal patterns - self-similar patterns composed of smaller copies of themselves. They found that healthy hearts exhibited complex multifractal properties, while the beat patterns of unhealthy hearts were monofractal and less varied.
The discovery of the multifractality of the healthy heart is important because current medical practice is to prescribe medication to eliminate variability for patients with irregular heartbeats. "This could be doing as much harm as good," says Professor H. Eugene Stanley, director of the Center for Polymer Studies. Monofractals occur commonly in nature and have long been observed in physiological systems. A fern, for example, is fractal because each frond is composed of sub-fronds, each a miniature, but not necessarily identical copy, of the whole.
Other systems, like the healthy human heart, are much more complex, with dynamic changes occurring periodically over time. An individual jumps up as the alarm rings, pushes the snooze button and dozes for ten minutes, jumps out of bed, downs a cup of coffee and dashes for the bus, then settles in for a slow ride downtown. Each activity results in a different heart rate and the overall system is better described by multifractals - a more complex system of fractals within fractals.
"We presume that the healthy behavior is richer and more complex because it represents the body's ability to adapt to change," says Ivanov. "The ability of the body to adapt to changes in the environment is crucial to survival." The researchers are now working with Mitsubishi of Japan to develop a small monitoring device that would alert the wearer if the heartbeat changes from a multifractal to monofractal pattern. They are also planning to apply this technique to other physiological systems, such as the breathing patterns of people with sleep apnea.
Further information can be found at http://polymer.bu.edu/~amaral/Heart.html.
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