BME 305 Biological Systems And Control Lecture Notes PDF

BME 305 – BIOLOGICAL SYSTEMS AND CONTROL Weeks 1: Introduction to Biological Systems 1.0 Introduction Since biomedical engineering is an interdisciplinary field based in both engineering and the life sciences, it is important for biomedical engineers to have knowledge about and be able to c...

BME 305 – BIOLOGICAL SYSTEMS AND CONTROL Weeks 1: Introduction to Biological Systems 1.0 Introduction Since biomedical engineering is an interdisciplinary field based in both engineering and the life sciences, it is important for biomedical engineers to have knowledge about and be able to communicate in both areas. Biomedical engineers must understand the basic elements of the body and how they function well enough to exchange ideas and information with physicians and life scientists. Two of the most basic terms and areas of study in the life sciences are anatomy and physiology. Anatomy refers to the internal and external structures of the body and their physical relationships, whereas physiology refers to the study of the functions of those structures. 1.1 General Definition of System A system is a representation of a situation. It is an assembly of elements interrelated by relation R in an organized whole. The behavior of one element in the relation R is different from its behavior in another relation S. A system can be a closed system or an open system. A closed system is a type of system where no relationships are found or made between elements of the system and things external to it, while an open system exchanges material, information and/or energy with its environment across a boundary. Boundary identification is usually not evident. An open system maintains itself in continuous inflow and outflow, a building up and breaking down of elements, never being, as long as it is alive, in a state of chemical or thermodynamically equilibrium, but is maintained in a so-called steady-state. This is the essence of metabolism in living cells. 1 Element is the representation of some phenomena of the natural or social world. It has some significant attributes that may change in time through its own behavior. There exists a relationship between the elements E1 and E2 if the behavior of either is influenced or controlled by the other. The relationship or communication between the elements may be flows of materials, information, or energy. A biological system (or organ system or body system) is a group of organs that work together to perform a certain task. Common systems, such as those present in mammals and other animals, seen in human anatomy, are those such as the circulatory system, the respiratory system, the nervous system, etc. The human body consists of a number of these biological systems and each carries out specific functions necessary for everyday living. The study of biological system can be related to the conservative system which has three basic implications: i. A system is designed to achieve a predetermined objective ii. Interrelationship and interdependence iii. The objective of the system organization as a whole has a higher priority than the objective of the subsystem, e.g the priority of the biological system is to sustain life 1.2 General Characteristics of a System Biological Systems are systems, in the normal sense. If they have some special characteristics, the general properties of systems are also applied to them. A system is characterized by the following; 1. Organisation: This is the structure and order of arrangement of elements that helps to achieve the objective of a system 2. Interaction: this refers to the manner in which each of the elements in the system functions and communicates with one another 2  3. Interdependence: This means that part of the elements in the system organization depends on one another. They are mutually coordinated and linked together according to plan in such a way that one subsystem depends on the output of another subsystem for proper functioning 4. Integration: This refers to the holism of system, it is concerned with the interconnectivity of the elements in the system 5. Central Objective: A system has a central objective which could be real or stated 1.3 Elements of a System: 1. Outputs and inputs: A major objective of a system is to produce an output that has value to its user. In order to get a good output, inputs to system must be appropriate. It is important to point out here that determining the output is a first step in specifying the nature, amount and regularity of the input needed to operate a system. 2. Processors: It is the element of a system that involves the actual transformation of input into output. It is the operational component of a system. Processors may modify the input totally or partially, depending on the specifications of the output. In some cases, input is also modified to enable the processor to handle the transformation. 3. Control: The control elements guide the system. It is the decision-making subsystem that controls the pattern of activities governing input, processing, and output. 3 4. Feedback: Feedback measures output against a standard in some form of cybernetic procedure that includes communication and control. Feedback may be positive or negative, routine or informational. Positive feedback reinforces the performance of the system. It is routine in nature. Negative feedback generally provides the controller with information for action. Example: the dynamics of predator-prey pair. Let us assume that due to an increase in vegetation the population of a small herbivore explodes. This enables the population of a carnivore species that eat this herbivore to explode. Consequently the herbivore population decreases. The increase in the herbivore population feeds back on itself through its relationship with the carnivore population. 5. Environment: The environment is the “supra-system” within which an organization operates. It is the source of external elements that impinge on the system. In fact, it often determines how a system must function. A system and the relationships between its elements, including feedback, can be distinguished from its environment, with which the system shares only input and output relationships. Defining a boundary around the system makes the demarcation between the system and its environment. This distinction is absolute in the theoretical construct of a closed system where no relationships are found or made between elements of the system and things external to it. For example physical chemistry treats the reactions, their rates, and the chemical equilibrium established in a closed vessel where reactants are brought together. The laws of thermodynamics apply only to closed systems. 4 Figure 1: Definition of system a) a set of elements without relationships is not a system; b) a set of elements with few relationships is not a system; c) a system (with many relationships between elements, its boundary, its input and its output: d) S is a system, S1, S2 and S3 are subsystems; e) system and environment. 6. Boundaries and Interfaces: A system should be defined by its boundaries- the limits that identify its elements, processes and interrelationships when it interfaces with another system. 5  READING LIST Dourado António, Biological Systems Theory: An Inroduction, Center for Informatics and Systems of the University of Coimbra, Department of Informatics Engineering John Endele, Susan Blanchard, Joseph Bronzino, Introduction to Biomedical Engineering, Second Edition, 2005, Chapter 3 Joseph D. Bronzino, The Biomedical Engineering HandBook, Second Edition, Boca Raton: CRC Press LLC, 2000 6