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Biosignals: Acquisition and General Properties Amine Na¨ıt-Ali and Patrick Karasinski

Abstract The aim of this chapter is to provide the reader with some basic and general information related to the most common biosignals, in particular biopotentials, encountered in clinical routines. For this purpose, the chapter will be divided into two main sections. In Sect. 1.1, we will consider the basis of bipotential recording (i.e., electrodes, artifact rejection and safety). In the second section, some general properties of a set of biosignals, will be introduced briefly. This will concern essentially, ECG, EEG, EPs and EMG. This restriction is required to ensure an appropriate coherency over the subsequent chapters which will deal primarily with these signals.

1.1 Biopotential Recording As mentioned previously in the introduction to this book, biosignals are intensively employed in various biomedical engineering applications. From unicellular action potential to polysomnogram, they concern both research and clinical routines. Since this book deals specifically with biopotentials (i.e. bioelectrical signals), a special focus on their acquisition is provided in this section. As is the case in any common instrumentation system, biopotential recording schemes include an observed process, a sensor and an amplifier. In our case, the observed process is recorded from a human body which requires particular precautions to be taken into account. Consequently, the following three most important aspects will be underlined in this section: 1. The sensor: electrode description and its modeling will be given in Sect. 1.1.1. 2. The power supply artifact: this point will be discussed in Sect. 1.1.2, in which we provide a description of some common schemes, 3. Safety: constraints and solutions are presented in Sect. 1.1.3.

A. Na¨ıt-Ali (B) Universit´e Paris 12, Laboratoire, Image, Signaux et Syst`emes Intelligents, LiSSi, EA. 3956. 61, avenue du G´en´eral de Gaulle, 94010, Cr´eteil, France e-mail: [email protected] A. Na¨ıt-Ali (ed.), Advanced Biosignal Processing, C Springer-Verlag Berlin Heidelberg 2009 DOI 10.1007/978-3-540-89506-0 1, 

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A. Na¨ıt-Ali and P. Karasinski

1.1.1 Biopotentials Recording Electrodes Generally speaking, to ensure an appropriate interface between living tissue and a conductor, specific sensors are required to transform ionic concentrations to electronic conductions. This sensor is, actually, an electrode in which a chemical reaction produces this transformation. The biopotentials are produced from cell activity that changes the ionic concentration in intra and extra cellular environment. In electrical devices, electron activity produces tensions and currents. Both of them are electrical phenomenon but charge carriers are different. A current in an electronic circuit results from an electron movement and from the displacement ions in living tissue. As mentioned above, electrodes ensure the transformation from ionic conduction to electronic conduction through a chemical reaction. Biopotential elec