Remote physiological sensing: historical perspective, theories and preliminary developments.

Many physiological processes are characterized by the generation and propagation of multiple, dynamic, infinitely variable, and often transient electrical phenomena in the respective tissues and organs where they originate. The purpose of physiological recording is to obtain a record that is an exact facsimile or analog of the events under investigation. However, since it is seldom feasible to attach pickup elements directly to the tissues or organs being investigated, some method of sensing the reflections and projections of the phenomena from the surface of the body must usually be employed. Such methods always introduce measurement errors that result in a distorted picture of the processes being recorded. In spite of this limitation, these techniques have proven highly useful for the medical and allied professions. As a result of the transition of medicine from a descriptive to an analytical science, a wide variety of pickup elements of various sophistication have been developed and are presently available for recording many important phenomena associated with various physiological functions from different anatomical sites. With the exception of the electrocardiogram (ECG), electroencephalogram (EEG), and electromyogram (EMG), other forms of biomonitoring have not yet achieved the acceptance necessary to allow their full development. It would seem that the development of the ECG, EEG, and EMG are reaching toward a plateau, and other forms of biomonitoring techniques are required to interpret physiological changes and parameters.