M12.1 Overview

Physiological systems are composed of a large number of feedback control loops. Examples include the baroreceptor reflex that regulates blood pressure, and the synthesis of insulin and glucagon by the pancreas to regulate blood glucose. The focus of the examples presented in this module is on exogenous feedback regulation using devices external to the human body.

There is a rich history of automated control applications in biomedicine. Initial studies on feedback control of anesthesia were performed by Bickford at the Mayo Clinic in the 1950s. Several different anesthetics were studied as the manipulated input, while the measured variable was the integrated rectified amplitude of the EEG. The control strategy did not gain acceptance because it was not clear what feature of the EEG signal should be used as an indicator of the depth of anesthesia.

Modeling biomedical processes can be quite challenging. For physiological systems, drug material balances can be written based on a compartmental model; that is the body or tissues are "lumped" into "volumes" in the same fashion that stirred tanks are used to represent chemical process behavior.