Systems Behavior, Feed-back Loops, and High Blood Pressure Research

A major challenge to those investigating the etiology and progress of hypertension, as well as of other diseases, results from the fact that the control and regulation of most bodily functions are comprised of multiple feedback loops involving many bodily "systems." Thus, mechanisms which seem to offer clues as to the etiology of an abnormality, when investigated as an isolated function, fail to explain the etiology when sought in the intact experimental animal or patient. Examples of simple closed-loop systems are described to illustrate the effects of feed-back. A simplified diagram of several factors known to play a role in the control and regulation of the characteristies of the blood vessel wall is described to illustrate the multiplicity of the feed-back pattern which probably occurs. Furthermore, it is evident that almost none of the factors which constitute the loops have been evaluated sufficiently to permit characterization of the system. It is not surprising that apparently promising clues turn out to be disappointing and to become lost in the system. The medical investigator must learn to deal with methods of analyzing systems containing multiple factors and functions as well as to characterize the properties and behavior of the parts of the system.