UNIT-I INTRODUCTION TO BIOMEDICAL ENGINEERING
Definition Biomedical Engineering is defined as application of knowledge gained by a cross fertilization of engineering and biological sciences so that both will benefit the human being. Similarly, Biomedical Instrumentation is measurement of biological variables (Bioelectric Potentials). Development of Biomedical Engineering During 1951-60, many instrument manufacturers entered the field of medical instrumentation. But the development was slow due to high costs. Initial step was taken by US government in particularly by NASA. Many physiological parameters are needed to be monitored for the astronauts. Hence aerospace medicine programmes were expanded both within NASA facilities and other hospital research units. Some of the concepts and features of patient monitoring systems presently used in hospitals all over the world is based on astronaut monitoring system. Objectives of Biomedical Instrumentation The following are the objectives of Biomedical Instrumentation: A) Information Gathering: Instrumentation is used to measure natural phenomena and other variables to aid man in his search for knowledge about himself. B) Diagnosis: For the detection and correction of some incorrect behavior of the system being measured we require troubleshooting equipment. C) Evaluation: Measurements help to determine the ability of a system to meet its functional requirements. These could be classified as proof of performance tests. D) Monitoring: Instrumentation helps in monitoring some process or operation to obtain continuous or periodic information about the state of the system being measured. E) Control: Instrumentation may help control of the operation of a system based on changes in one or more parameters in the output of system. Man-Instrument System The overall system which includes both the organism and the instrumentation required for measurement of the human is called as Man Instrumentation system. A human being with his environment is shown below.
Subject: The patient upon which we take the measurement is called as Subject. Stimulus: The instrumentation used to generate and present this stimulus to the subject is an essential part of the man instrumentation system whenever responses are measured. e.g. flash of light, auditory tone, injection Transducer: A Transducer is defined as a device capable of converting one form of energy or signal to another form. In man instrumentation system, each transducer is used to produce an electrical signal. The transducer may measure temperature, pressure flow or any other variables in human body. Signal Conditioning Equipment: The instrumentation system part which amplifies, modifies, or in any other way changes the output of the transducer is called as signal conditioning equipment. The purpose of this equipment is to process the signals from the transducers to satisfy the functions of the system and prepare signals suitable for displays.
Display Equipment: The output of the signal conditioning equipment must be converted to some form of visual, audible information. The display equipment may include graphic pen recorder that produce a permanent record of the data. Recording Equipment: Recording of the information is done for possible future use or transmit it from one location to other whether within the hospital or around the world. The recording is used in two different contexts. A graphic pen recorder is used as a display device used to produce a paper recording. Sometimes we may use other recorders like cylindrical drum recorders and strip chart recorders. Control: It is necessary to have automatic control of the stimulus, transducers or any part of the man instrument system, a control is required. Such a system consists of a feedback loop in which part of the output is used to control the man instrumentation system. Problems encountered in measuring a living system The man instrumentation system describes the measurement on a human being. For measurement having risk to life some measurements are done on animal subjects. The measurement problems are given below. Inaccessibility of variables to measurement: Many times it is not possible to gain access to variable in living system. In some cases such as measurement of dynamic neurochemical activity in the brain it is impossible to place a suitable transducer to make measurement. Sometimes the variable is not approachable due to limitations. Variability of the data: Some of the variables measured in the human body are deterministic variables. In fact such variables should be considered as stochastic processes. The measurements taken under fixed set of conditions at one time may not be same under the same conditions at other time. Lack of knowledge about interrelationship The variability is measured values could be better explained if we know more about different physiological systems in the human body. Better understanding of relations among systems would help use of indirect measurement in place of inaccessible variables.