ABSTRACT
Before describing and analyzing the electronic circuits, amplifiers, and filters required to condition the signals found in clinical medicine and biomedical research, it is appropriate to describe the sources and properties of these signals (i.e., their bandwidths, distribution of amplitudes, and noisiness). Broadly speaking, biomedical signals can be subdivided into two major classes: (1) endogenous signals that arise from natural physiological processes and are measured within or on living creatures (e.g., ECG; EEG; respiratory rate; temperature; blood glucose; etc.) and (2) exogenous signals applied from without (generally noninvasively) to measure internal structures and parameters. These include but are not limited to ultrasound (imaging and Doppler); x-rays; monochromatic light (e.g., two wave lengths used in transcutaneous pulse oximeters); fluorescence from fluorophore-tagged cells and molecules stimulated with blue or near UV light; optical coherence tomography (OCT); laser Doppler velocimetry (LDV) used to measure blood velocity; and applied magnetic fields used in NMR). Other examples of exogenous signals can be found in the text by Northrop (2002).
