Medical control systems

(medicine) Physiological and artificial systems that control one or more physiological variables or functions of the human body.

Physiological and artificial systems that control one or more physiological variables or functions of the human body. Regulation, control processes, and system stability are at the heart of the survival of living organisms, both unicellular and multicellular. In the nineteenth century, C. Bernard concluded that the higher animals, far from being indifferent to their surroundings, must be in close and intimate relation to them. The equilibrium they maintain is the result of compensation established as continually and exactly as if by a very sensitive balance. W. B. Cannon (1929) differentiated the stability properties of biological systems from those of physical systems, and introduced the term homeostasis to describe the steady states in the body that are maintained by complex, coordinated physiological reactions. The condition of homeostasis is achieved either by regulation of supplies (for example, control of blood sugar level) or by regulation of processes (for example, control of body temperature and control of voluntary movements). See also Homeostasis.

Medical control systems may be classified into two groups: (1) the physiological control systems in normal or pathological conditions (for example, control of electrolytes, arterial pressure, respiration, body temperature, blood sugar, endocrinal functions, neuromuscular and motor activity, and sensory functions), and (2) the external (artificial) control systems that interface with physiological systems (for example, artificial kidneys or hemodialyzers, blood oxygenators or heart-lung machines used during open-heart surgery, external prosthetics and orthotics, cardiac pacemakers, ventilators, implantable defibrillators, and implantable pumps for drug delivery). For the development and proper functioning of artificial devices, the underlying control mechanisms of the normal and of the disabled physiological systems with which the external devices must interface must be adequately understood. Thus, in its broadest sense, the area of medical control systems encompasses all branches of engineering, mathematical biology, biophysics, physiology, and medicine. See also Biomechanics; Biomedical chemical engineering; Biomedical engineering; Control systems; Mathematical biology.

The importance of control systems engineering in medical applications has grown because of the inherent complexity of medical control systems. H. A. Simon's concept of complexity is very appropriate for medical control systems: complex systems are composed of subsystems that in turn have their own subsystems, and so on; and the large number of parts interact in a complicated way so that it is sometimes impossible to infer the properties of the whole from the properties of the parts and their laws of interaction. Indeed, the analytical models developed, using control systems engineering, of the components of a medical system have had limited success in predicting the behavior of the overall system.

Examples of medical control systems include myoelectric prostheses, which are replacement devices for lost limbs; external orthoses, which are used for rehabilitation of patients with acquired disabilities; and implantable devices such as defibrillators and pumps for drug delivery. Numerous other devices,such as cardiac pacemakers, artificial kidneys, heart-lung machines, andartificial ventilators, have been in routine clinical use for many years.