Anesthesia, Evidence and Experience

Description of the Entropy algorithm as applied in the Datex-Ohmeda S/5 Entropy Module

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Acta Anaesthesiol Scand. 2004 Feb;48(2):154-61. (PDF: 418KB)

Introduction

There are a number of concepts and analytical techniques directed to quantifying the irregularity of stochastic signals, such as the EEG. One such concept is entropy. Entropy, when considered as a physical concept, is proportional to the logarithm of the number of microstates available to a thermodynamic system, and is thus related to the amount of 'disorder' in the system. For information theory, entropy was first defined by Shannon and Weaver in 1949 (1), and further applied to a power spectrum of a signal by Johnson and Shore in 1984 (2). In this context, entropy describes the irregularity, complexity, or unpredictability characteristics of a signal. In a simple example, a signal in which sequential values are alternately of one fixed magnitude and then of another fixed magnitude has an entropy value of zero, i.e. the signal is completely regular and totally predictable. A signal in which sequential values are generated by a random number generator has greater complexity and higher entropy.

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This is an electronic version of articles published in Acta Anaesthesiologica Scandinavica VOLUME: 48, Issue 2 PAGE NUMBERS 154 - 161, which is published by Blackwell Publishing Ltd. To access the journal on-line, please visit www.blackwell-synergy.com

Last updated: 9 July 2004 Created
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