101.

[Cover] [Abbreviated Contents] [Contents] [Index]

Page 196

		2.5.3— Example of the Fractal Dimension of the Phase Space Set: The Heart

		The electrical activity of the heart can be recorded from electrodes placed on the chest. These recordings are called the electrocardiogram, which is abbreviated as ECG or EKG. Each heartbeat generates an electrical pulse. Thus the ECG can be used to measure the time between heartbeats.

		Many people are now using "chaos" methods to characterize the normal working of the heart, to differentiate normal and life threatening ECG signals that could be used in automatic clinical monitors, and to find new parameters to predict the future course of heart disease in each person.

		A small sample of this work includes constructing phase space sets from either: (1) the ECG voltage as a function of time recorded from the heart, or (2) the intervals of time between consecutive heartbeats.

		All the studies have found that there is a considerable variability in the beating of the normal human heart.

		However, other results from these studies are less clear. Different groups have found different fractal dimensions from ECG recordings of the same type of heart condition.

		For example, if it is electrically excited, each small piece of the heart will beat on its own. Normally, a wave of electrical activity sweeps across the heart, organizing these separate pieces into a coherent contraction that pumps the blood out of the heart. This organization fails in a condition called fibrillation. In fibrillation each piece of the heart beats separately, blood is not pumped, and death follows shortly. Some groups have found that fibrillation is high dimensional, which means that each piece of the heart is beating independently of the other pieces. Other groups have found that fibrillation is low dimensional, which means that the beating of each piece of the heart is actually linked together.

 

[Cover] [Abbreviated Contents] [Contents] [Index]