ABSTRACT
Before describing and analyzing the electronic circuits, amplifiers, and filters required to condition the signals found in clinical medicine, biomedical research, and physiology, it is appropriate to describe the sources and properties of these signals (i.e., their bandwidths, amplitude distributions, and noisiness). Broadly speaking, biomedical signals can be subdivided into two major classes: (1) Endogenous signals, which arise from natural physiological processes and which are measured within or on the surface of living creatures (examples include electrocardiogram (ECG), electroencephalogram (EEG), respiratory rate, temperature, blood pressure, blood glucose). (2) Exogenous signals that are applied from without (generally noninvasively) to measure internal structures and physiological parameters. These include, but are not limited to, ultrasound (imaging and Doppler), X-rays (CAT scans), and monochromatic light (such as the two wavelengths used in transcutaneous pulse oximeters, excitation of fluorescence from fluorophoretagged cells and molecules stimulated with blue or near UV light, optical coherence tomography (OCT), laser Doppler velocimetry (LDV) used to measure blood velocity, and the strong magnetic fields used in magnetic resonance imaging (MRI)). For many other examples of exogenous signals refer to Northrop (2002).
