Biopotentials and Electrophysiology Measurement
This chapter reviews the origins, principles, and designs of instrumentation used in biopotential measurements, in particular for the electrocardiogram (ECG), the electroencephalogram (EEG), the electromyogram (EMG), and the electrooculogram (EOG). These biopotentials represent the activity of the respective organs: the heart, brain, muscle, and eyes. The biopotentials are acquired with the help of specialized electrodes that interface to the organ or the body and transduce low-noise, artifact-free signals. The basic design of a biopotential amplifier consists of an instrumentation amplifier. The amplifier should possess several characteristics, including high amplification, input impedance, and the ability to reject electrical interference, all of which are needed for the measurement of these biopotentials. Ancillary useful circuits are filters for attenuating electric interference, electrical isolation, and defibrillation shock protection. Practical considerations in biopotential measurement involve electrode placement and skin preparation, shielding from interference, and other good measurement practices.