Provides in-depth information about Biomedical Engineering with Big Data and Internet of Things Includes technical approaches for solving real-time healthcare problems and practical solutions through case studies in Big Data and Internet of Things Discusses big data applications for healthcare management, such as predictive analytics and forecasting, big data integration for medical data, algorithms and techniques to speed up the analysis of big medical data, and more.
The handbook describes the use of instruments and techniques for practical measurements required in medicine. It covers sensors, techniques, hardware, and software as well as information on processing systems, automatic data acquisition, reduction and analysis, and their incorporation for diagnosis.
Suitable for both instrumentation designers and users, the handbook enables biomedical engineers, scientists, researchers, students, health care personnel, and those in the medical device industry to explore the different methods available for measuring a particular physiological variable. It helps readers select the most suitable method by comparing alternative methods and their advantages and disadvantages.
In addition, the book provides equations for readers focused on discovering applications and solving diagnostic problems arising in medical fields not necessarily in their specialty. It also includes specialized information needed by readers who want to learn advanced applications of the subject, evaluative opinions, and possible areas for future study. Popular Books. The Summer Proposal by Vi Keeland. End of Days by Brad Taylor.
It Ends with Us by Colleen Hoover. In order for a medical instrument to be used in the performance of therapy, it must feed back a signal or force to the biological system, as in- dicated by the position of the feedback transform in Figure 1.
Therapy is applied by a crutch, for example, allowing a leg to heal while the patient remains ambulatory. More complex therapy may be applied by a biofeed- back instrument such as a speech therapy device capable of deriving the information-bearing elements from speech and applying them to another sense such as sight or touch. Other therapeutic instrumentation may operate independently of physiological parameters in the system to which the ther- apy is applied.
An example is an ultrasonic massager operated by a physi- cal therapist. This is closely related to another category of instruments used in surgery and surgical procedures, namely invasive-units, which penetrate the skin of the patient. These include electrosurgical knives, hypodermic needles, and lasers. The medical instruments illustrated in Figure 1. Another category is assigned to labo- ratory instruments used to investigate and assess biological fluids and tis- sue.
The measurement of pH is fundamental to the operation of many of these instruments, as are techniques for investigating particles in fluids. Throughout history, as technology was developed, the number of human functions extended by the use of tools increased. Most recently, the introduction of computers has extended even our ability to think, particularly in calculating, analyzing, and storing large amounts of information.
Consider, for example, the sense of touch. Modern instruments that extend the sense of touch include devices - for massage, such as electrical current stimulators, automatic vibrators, and ultrasonic therapy equipment. In this function, the thermometer ex- tends the sense of touch, serving to quantify a measurement that had previously been only approximate.
The Invention of the Thermometer In , the Italian scientist Galileo showed that a closed glass tube inserted in a container of water could be arranged so that the height of the water sucked into the tube by a partial vacuum varied with the temperature. In , Santorio Santonio, a Slavic physician, constructed a similar device, which he used to measure the temperature in the human body. The prob- Jem with the instrument Figure 1. This problem was solved a quar- ter of a century later when Ferdinand II, Grand Duke of Tuscany, sealed the water in a closed vessel to eliminate the effect of atmospheric pressure.
Microwave diathermy Wednesday, March 30, 23 Anatomy and Physiology Physiology which relates to the normal function of the organs of the body. Wednesday, March 30, 26 Major Subsystems of the body 1. Wednesday, March 30, 28 The Heart 1 2 3 5 6 7 8 94 1 Major vessel from upper body to heart 2 Vessels from lung to heart 5 The. Pathways of Blood Wednesday, March 30, Wednesday, March 30, 31 These impulses make the heart contract and pump blood. Wednesday, March 30, 33 Major Subsystems of the body 2.
Wednesday, March 30, 35 Major Subsystems of the body 3. Wednesday, March 30, 39 your nervous system is divided into the central nervous system CNS and the peripheral nervous system PNS which is the brain and spinal cord which connects everything to the brain and spinal cord Peripheral Nervous System Wednesday, March 30, 42 Nerves : visible bundles of axons and dendrites that entend from the brain and spinal cord to all other parts of the body - Motory Nerves - Sensory Nerves What do you think can change neurons and their connections?
Drugs and alcohol bind important receptors on neurons Alcohol damages dendrites - can repair after abstinence Alcohol blocks receptors and slows down transmission SIDS What if neurons die here? The mechanical device converts the physical quantity to be measured into a mechanical signal. Such mechanical device are called as the primary transducers. Such electrical device are known as secondary transducers A variable associated with the physiological processes of the body is known as a physiological variable.
Bio-Electric Potential Wednesday, March 30, 62 Of muscles These electrodes are used to obtain bioelectric potentials from the surface of the body. Electrical Activity Measurement cont. Net current flow is zero but there exists a potential difference depends upon the position of equilibrium and concentration of ions. That p. ECG Wednesday, March 30, 67 EEG Wednesday, March 30, 68 Electrode Placement Wednesday, March 30, 69 Microphones for Phonocardiography Brain Wave Classification Wednesday, March 30, 79 EEG rhythms correlate with patterns of behavior level of attentiveness, sleeping, waking, seizures, coma.
Lower frequencies: strongly synchronized activity nondreaming sleep, coma. Blood Pressure Wednesday, March 30, 85 Blood Pressure Risks BMTS 88 Cont. Auscultatory Method cont. Oscillometric Method cont. Ultrasonic Method A transcutaneous through the skin Doppler sensor is applied here. The motion of blood-vessel walls in various states of occlusion is measured.
The frequency difference between transmitted 8 MHz and received signal is Hz and it is proportional to velocities of the wall motion and the blood. Ultrasonic Method cont. Direct Methods in Blood Pressure Measurements Extravascular Sensor The sensor is located behind the catheter and the vascular pressure is transmitted via this liquid-filled catheter. Extravascular Sensor cont. The hydraylic link is the major source of errors. Normally the interesting frequency range is 0 — Hz.
Intravascular Sensor The sensor is located in the tip of the catheter. No time delay. Blood Pressure Blood pressure is an important signal in determining the functional integrity of the cardiovascular system. Scientists and physicians have been interested in blood pressure measurement for a long time. Transducers for Blood Pressure Measurement cont.
So, capacitance becomes function of pressure and that pressure can be measured by using bridge ckt. It can be used for blood pressure measurent. In parts a, the thin sensor diaphragm remains parallel to the fixed electrode and in part b, the diaphragm deflects under applied pressure resulting in capacitance change The other pressure sensing approach, characterized by a diaphragm in front of the fibre optic link, is based on the light intensity modulation of the reflected light caused by the pressure-induced position of the diaphragm.
In late , they developed a definition that is widely accepted:. A clinical engineer is a professional who brings to health care facilities a of education, experience, and accomplishment which.
They must have at least a B. Another new term, also coined in recent years, the 'biomedical equipclinical engineers. AAMI definition. Typically, the BMET has two community college. This person is not to be confused with the medical technologist. The latter is usually used in an operative sense, for example in blood chemistry and in the taking of electrocardiograms.
These definitions are all noteworthy, but whatever the name, this age of the marriage of engineering to medicine and biology is destined to benefit all concerned. Improved communication among engineers, technicians, and doctors, better and more accurate instrumentation to measure vital physiological parameters, and the development of interdisciplinary tools to help fight the effects of body malfunctions and diseases are all a part of this new field.
With this point in mind, the authors of this book use the term biomedical engineering for the field in general and the term biomedical instrumentation for the methods of measurement within the field. Another major problem of biomedical engineering involves communication between the engineer and the medical profession.
The language and jargon of the physician are quite different from those of the engineer. In some cases, the same word is used by both disciplines, but with entirely different meanings. Although it is important for the physician to understand enough engineering terminology to allow him to discuss problems with the engineer, the burden of bridging the communication gap usually falls on the latter.
The result is that the engineer, or technician, must learn the doctor's language, as well as some anatomy and physiology, in order that the two disciplines can work effectively together. To help acquaint the reader with this special aspect of biomedical engineering, a basic introduction to medical terminology is presented in Appendix A. This appendix is in two parts: Appendix A.
In addition to the language problem, other differences. Since the physician. Also, engineers,. Since the development and use of biomedical instrumentation must be a joint effort of the engineer or technician and the physician or nurse ,. By being aware of their possible existence, the engineer or technician can take steps to avert these pitfalls by adequate preparation and care in establishing his relationship with the medical profession.
The field of medical instrumentation is by no means new. Many instruments were developed as early as the nineteenth century for example, the electrocardiograph, first used by Einthoven at the end of that century. This process occurred primarily during the s and the results were often disappointing, for the experimenters soon learned that physiological parameters are not. They also encountered a severe communication problem with the medical profession.
Many developments with excellent potential seemed to have become lost causes. It was during this period that some progressive companies decided that rather than modify existing hardware, they would design instrumentation specifically for medical use.
Although it is true that many of the same components were used, the philosophy was changed; equipment analysis and design were applied directly to medical problems. A large measure of help was provided by the U. Mercury, Gemini, and Apollo programs needed accurate physiological monitoring for the astronauts; consequently, much research and development money went into this area. The aerospace medicine programs were expanded considerably, both within NASA facilities, and through grants to universities and hospital research units.
Some of the concepts and features of patient-monitoring systems presently used in hospitals throughout the. The use of adjunct fields, such as biotelemetry, also finds some basis in the NASA programs.
Along with the medical research programs at the universities, a need developed for courses and curricula in biomedical engineering, and today almost every major university or college has some type of biomedical engineering program. However, much of this effort biomedical instrumentation per se. Biomedical instrumentation provides the tools by which these measurements can be achieved. In later chapters each of the major forms of biomedical instrumentacovered in detail, along with the physiological basis for the measureis tion The physiological measurements themselves are summarized involved.
Some forms of biomedical instrumentation are unique to the field of medicine but many are adaptations of widely used physical measurements. A thermistor, for example, changes its electrical resistance with is that of an engine or Only the shape and size of the device might be different.
Another example is the strain gage, which is commonly used to measure the stress in structural components. It operates on the principle that electrical resistance is changed by the stretching of a wire or a piece of semiconductor material.
When suitably excited by a source of constant voltage, an electrical output can be obtained that is proportional to the amount of the strain. Since pressure can be translated into strain by various means, blood pressure can be measured by an adaptation.
In the design or specification of medical instrumentation systems, each of the following factors should be considered. The objective should be to provide an instrument that will give a usable reading from the smallest expected value of the variable or parameter. Linearity should be obtained over the most important segments, even if it is impossible to achieve it over the entire range. Mechanical friction in a meter, for example, can cause of the indicating needle to lag behind corresponding changes in the ing direction.
It is important to display a waveshape that is a faithful reproduction of the original physiological signal. An instrument system should be able to respond rapidly enough to.
This condition is referred to as a ''flat response'' over a given range of fre-. Accuracy is a measure of systemic error. Errors can occur in a multitude of ways. Although not always present simultaneously, the following errors should be considered: Errors due to tolerances of electronic components.
Mechanical errors in meter movements. Errors due to poor frequency response. Reading errors due to parallax, inadequate illumination, or excessively wide ink traces on a pen recording. Two additional sources of error should not be overlooked. The first concerns correct instrument zeroing. In most measurements, a zero, or a baseline,. Another source of on the parameter to be measured, and measurements in living organisms and is.
It is important that the signal-to-noise ratio be as high as possible. In the hospital environment, power-line frequency noise or interference is common and is usually picked up in long leads. Also, interference due to elec-. Although thermal noise. Often measurements must be made on patients or experimental animals in such a way that the instrument does not produce a direct electrical connection between the subject and ground.
This requirement is often necessary for reasons of electrical safety see Chapter 16 or to avoid interference between different instruments used simultaneously. Electrical isolation can be achieved by using magnetic or optical coupling techniques, or radio telemetry. Telemetry is also used where movement of the person or animal to be measured is essential, and thus the encumbrance of connecting leads should be avoided see Chapter Most instrumentation systems require calibration before they are actually used.
Each component of a measurement system is usually calibrated individually at the factory against a standard. An example would be that of a complicated, remote blood-pressure monitoring system, which is calibrated against a simple mercury manometer. The object is to learn the nature and characteristics of the. The end product of such an exercise is usually a set of input-output equations intended to define the internal functions of the box.
One of the most complex black boxes conceivable is a living organism, especially the living human being. Within this box can be found electrical, mechanical, acoustical, thermal, chemical, optical, hydraulic, pneumatic,.
To further complicate the situation, upon attempting to measure the inputs and outputs, an engineer would soon learn that none of the input-output relationships is deterministic. That is, repeated application of a given set of input values will not always produce the same output values. In fact, many of the outputs seem to show a wide range of responses to a given set of inputs, depending on some seemingly relevant conditions, whereas others appear to be completely random and totally unrelated to any of the inputs.
The living black box presents other problems, too. Many of the important variables to be measured are not readily accessible to measuring devices. The result is that some key relationships cannot be determined or that less accurate substitute measures must be used.
Furthermore, there is a high degree of interaction among the variables in this box. Thus, it is often impossible to hold one variable constant while measuring the relationship between two others. In fact, it is sometimes difficult to determine which are the inputs and which are the outputs, for they are never labeled and almost inevitably include one or more feedback paths.
The situation is made even worse by the application of the measuring device itself, which often affects the measurements to the extent that they may not represent normal conditions reliably. The function of medical instrumentation is to aid the medical chnician and researcher in devising ways of obtaining reliable and meaningful.
Still other problems are associated with such measurements: the process of measuring must not in any way endanger the life of the person on whom the measurements are being made, and it should not require the subject to endure undue pain, discomfort, or any other undesirable conditions.
This means that many of the measurement techniques normally employed in the instrumentation of nonliving systems cannot be applied in the instrumentation of humans.
Additional factors that add to the difficulty of obtaining valid measurements are 1 safety considerations, 2 the environment of the hospital in which these measurements are performed, 3 the medical personnel usually involved in the measurements, and 4 occasionally even ethical and legal considerations.
Because special problems are encountered in obtaining data from living organisms, especially human beings, and because of the large amount of interaction between the instrumentation system and the subject being measured, it is essential that the person on whom measurements are made be considered an integral part of the instrumentation system.
In other words, in order to make sense out of the data to be obtained from the black box the human organism , the internal characteristics of the black box must be considered in the design and application of any measuring instruments.
Consequently, the overall system, which includes both the human organism and the intrumentation required for measurement of the human is called the man-instrument system. An instrumentation system is defined as the set of instruments and equipment utilized in the measurement of one or more characteristics or phenomena, plus the presentation of information obtained from those measurements in a form that can be read and interpreted by man.
In some cases, the instrumentation system includes components that provide a stimulus or drive to one or more of the inputs to the device being measured. There may also be some mechanism for automatic control of certain processes within the system, or of the entire system. In some applications, this type of instrumentation may be classed as 'troubleshooting equipment. Monitoring: Instrumentation is used to monitor some process or. Instrumentation to aid the physician in the diagnosis of disease and other disorders also has widespread use.
Similar instrumen-. Biomedical instrumentation can generally be classified into two major. Clinical instrumentation is basically devoted to and treatment of patients, whereas research instrumentation is used primarily in the search for new knowledge pertaining to the various systems that compose the human organism.
Although some instruments can be used in both areas, clinical instruments are generally designed to be more rugged and easier to use.
Emphasis is placed on obtaining a limited set of reliable measurements from a large group of patients and on providing the physician with enough information to permit him to. On the other hand, research instrumentation is normally more complex, more speciaUzed, and often designed to provide a much higher degree of accuracy, resolution, and so on.
Clinical instruments are used by the physician or nurse, whereas research instruments are clinical decisions. An in vivo measurement is one that is made on or within the living organism itself. An example would be a device inserted into the bloodstream to measure the pH of the blood directly. An in vitro measurement is one performed outside the body, even though it relates to the functions of the body. An example of an in vitro measurement would be the measurement of the pH of a sample of blood that has been drawn from a patient.
Although the man-instrument system described here applies mainly to in vivo measurements, problems are often encountered in obtaining appropriate samples for in vitro measurements and in relating these measurements to the living human being. The transducer may measure temperature, pressure, flow, or any of the other variables that can be. In essence, then, the purpose of the signal-conditioning equipment is to process the signals from the transducers in order to satisfy the functions of the system and to prepare signals suitable for operating the display or recording.
The input to the display device is the modified electric signal from the signal-conditioning equipment. Its output is some form of In the man-instrumentaequipment may include a graphic pen recorder that.
Equipment for these functions is often a vital part of the man-instrument system. Also, where automatic storage or processing of data is required, or where computer control is employed, an on-line analog or digital computer may be part of the instrumentation system.
It should be noted that the term. This system usually consists of a feedback loop in which part of the output from the signal-conditioning or display equipment. Within the human body can be found electrical, mechanical, thermal, hydraulic, pneumatic, chemical, and various other types of systems, each of which communicates with an external environment, and internally with the other systems of the body.
By means of a multilevel control system and communications network, these individual systems are organized to perform many complex functions. Through the integrated operation of all these systems, and their various subsystems, man is able to sustain Ufe, learn to perform useful tasks, acquire personality and behavioral traits, and even reproduce himself. In addition, these various inputs and outputs can be measured and analyzed in a variety of ways.
Most are readily accessible for measurement, but some, such as speech, behavior, and appearance, are difficult to analyze and interpret. Next to the whole being in the hierarchy of organization are the major functional systems of the body, including the nervous system, the cardiovascular system, the pulmonary system, and so on.
Each major system is discussed later in this chapter, and most are covered in greater detail in later chapters. Just as the these. These functional systems can be broken down into subsystems and organs, which can be further subdivided into smaller and smaller units.
The process can continue down to the cellular level and perhaps even to the molecular level. The major goal of biomedical instrumentation is to make possible the measurement of information communicated by these various elements. The problem is, of course, that many of the inputs at the various organizational levels are not accessible for measurement.
The interrelationships among elements are sometimes so complex. Thus, the models in use today contain so many assumptions and constraints that their application is often severely limited. All operations of this highly diversified and very efficient chemical factory are self-contained in that from a single point of intake for fuel food , water, and air, all the. Moreover, the chemical factory contains all the monitoring equipment needed to provide the degree of control necessary for each chemical operation, and.
The Cardiovascular System engineer, the cardiovascular system can be viewed as a complex, closed. Reservoirs in the system veins acteristics to satisfy certain control. The four-chamber pump acts as two synchronized but functionally isolated two-stage pumps. The first stage of each pump the atrium collects fluid blood from the system and pumps it into the second stage the ventricle. The action of the second stage is so timed that the fluid is pumped into the system immediately after it has been received from the first stage.
One of the two-stage pumps right side of the heart collects fluid from the main hydraulic system systemic circulation and pumps it through an oxygenation system the lungs. The other pump left side of the heart receives fluid blood from the oxygenation system and pumps it into the main hydraulic system.
The speed of the pump heart rate and its efficiency stroke volume are constantly changed to meet the overall requirements of the system.
The fluid blood , which flows in a laminar fashion, acts as a communication and supply network for parts of the system. Carriers red blood cells of fuel suppHes and waste. The fluid also contains mechanisms for repairing small system punctures and for rejecting foreign elements from the system platelets and white blood cells, respectively.
Because part of the system is required to work against gravity at times, special one-way valves are provided to prevent gravity from pulling fluid against the direction of flow between pump cycles.
The variables of prime. The passageway divides to carry air into each of the bags, wherein it again subdivides many times to carry air into and out of each of many tiny air spaces pulmonary alveoli within the bags.
The dual air input to the system nasal cavities has an alternate vent the mouth for use in the event of nasal blockage and for other special purposes. In the tiny air spaces of the bags is a membrane interface with the body's hydraulic system through which certain gases can diffuse.
Oxygen is taken into the fluid blood from the incoming air, and carbon dioxide is transferred from the fluid to the air, which is exhausted by the force of the pneumatic pump. The pump operates with a two-way override. An automatic control center respiratory center of the brain maintains pump operation at a speed that is adequate to supply oxygen and carry off carbon dioxide as required by the system.
Manual control can take over at any time either to accelerate or to inhibit the operation of the pump. Automatic control will return, however, if a condition is created that might endanger the system. System variables of primary importance are respiratory rate, respiratory airflow, respiratory volume, and concentration of CO2 in the expired air.
This system also has a number of relatively fixed volumes and capacities, such as tidal volume the volume inspired or expired during each normal breath , inspiratory reserve volume the additional volume that can be inspired after a normal inspiration , expiratory special valving.
Its center a self-adapting central information processor or computer the brain. The computer is self adapting in that if a certain section. Almost as fascinating as the central computer are the millions of communication lines afferent and efferent nerves that bring sensory information into, and transmit control information out of the create art, poetry,.
By means of the interconnection patterns, signals from a large number of sensory devices, which detect light, sound, pressure, heat, cold, and certain chemicals, are channeled to the appropriate parts of the computer, where they can be acted upon.
Similarly, output control signals are channeled to specific motor devices motor units of the muscles , which respond to the signals with some type of motion or force.
Feedback regarding every action controlled by the system is provided to the computer through appropriate sensors. Information is usually coded in the system by means of electrochemical pulses nerve action potentials that travel along.
The pulses can be transferred from one element of a network to another in one direction only, and frequently the transfer takes place only when there is the proper combination of elements acting on the next element in the chain. Action by some elements tends to inhibit transfer. Both serial and parallel coding are used, sometimes.
In addition to the central computer, a large number of simple decision-making devices spinal reflexes are present to control directly certain motor devices from certain sensory inputs. A number of feedback loops are accomplished by this method. In many. In some cases, however, animal subjects are substituted for humans in order to permit measurements or manipulations that cannot be performed without some risk. Although ethical restrictions sometimes are not as severe with animal subjects, the same basic problems can be expected in attempting measurements from any living system.
Most of these problems were introduced in earher sections of the chapter. However, they can be summarized as follows. In other situations the medical operation required to place a transducer in a position from which the variable can be measured makes the measurement impractical on human subjects, and sometimes even on animals. Where a variable is inaccessible for measurement, an attempt is often made to perform an indirect measurement.
This process involves the measurement of some other related variable that makes possible a usable estimate of the inaccessible variable under certain conditions. In using indirect measurements, however, one must be constantly aware of the limitations of the substitute variable and must be able to determine when the relationship.
In fact, such variables should be considered as stochastic processes. In other words, measurements taken under a fixed set of conditions at one time will not necessarily be the.
Here, methods must be employed in order to estimate relation-. The foregoing variability in measured values could be better explained if more were known and understood about the interrelationships within the body. Physiological measurements with large tolerances are often accepted by the physician because of a lack of this knowledge and the resultant inability to control variations.
Better understanding of physiological relationships. Because of the large number of feedback loops involved in the major physiological systems, a severe degree of interaction exists both within a given system and.
Even when attempts are collateral loops appear and some aspects of feedback loop are still present. Also, when one organ or ele-. In many situations the physical presence of the transducer changes the reading significantly. For example, a large flow. Similarly, an attempt to. This penetration can easily kill the cell or damage it so that it can no longer function normally.
Another problem arises from the interaction discussed earlier. Often the presence of. For example, local cooling of the skin, to estimate the circulation in the area, causes feedback that changes the circulation pattern as a reaction to the.
The psychological effect of the measurement can also affect the Long-term recording techniques for measuring blood pressure have shown that some individuals who would otherwise have normal pressures show an elevated pressure reading whenever they are in the physician's of-. In designing a measurement system, the biomedical instrumentation engineer or technician must exert extreme care to ensure that the effect of the presence of the measuring device is minimal.
Because of the limited amount of energy available in the body for many physiological variables, care must also be taken to prevent the measuring system from loading'' the source of the measured variable. Since many transducers are sensitive to movement, the movement of the subject often produces measuring of a.
For example, resistance measurements require the flow of electric current. Some transducers generate a small amount of heat due to the current flow. In most cases, this energy level is so low that its effect is insignificant. However, in dealing with living cells,. Similarly, the measurement should not cause undue pain, trauma, or discomfort, unless it becomes necessary to endure these condi-.
Fortunately, however, new developments resulting in. In addition, greater knowledge of the physiology of the various systems of the gresses in his. When measurements are made on human beings, one further aspect must be considered. During its earlier days of development biomedical apparatus was designed, tested, and marketed with little specific governmental control.
True, there were the controls governing hospitals and a host of codes and regulations such as those described in Chapter 16, but today a number of new controls exist, some of which are quite controversial. On the other hand, there is little control on the effectiveness of devices or their side effects.
Food and drugs have long been subject to governmental control by a U. In a new addition, the Medical Devices Amendments Public Law , placed all medical devices from the simple to the complex under the jurisdiction of the FDA. Since then, panels and committees have been formed and symposia have been held by both physicians and engineers. They should always be fully conversant with what is going on and aware of issues and regulations that are brought about by technological, be economic and political realities.
Each of the major body systems is discussed by presenting physiobackground information. Then the variables to be measured are considered, followed by the principles of the instrumentation that could be used.
Finally, appUcations to typical medical, behavioral, and biological logical. The physiological systems from which these variables originate were introduced in Chapter 1. The principal physiological variables and their methods of measurement are summarized in Appendix B and discussed in detail in. As stated in Chapter a transducer is required to convert each variable into an electrical signal 1 which can be amplified or otherwise processed and then converted into Physiological variables occur in.
To conduct its function properly, one or more parameters of the electrical output signal say, its voltage, current, frequency, or pulse width must be a nonambiguous function of the nonelectrical variable at the input. Ideally, the relationship between output and input should be linear with, for example, the voltage at the output of a pressure transducer being proportional to the applied pressure.
A linear relationship is not always possible. For example, the relationship between input and output may follow a logarithmic funcversion. The two transducer types will nevertheless be described separately in the following sections. In theory active transducers can utilize every for converting nonelectrical energy. It is a characteristic of active transducers that frequently, but not always, the same transduction principle used to convert from a nonelectrical form of energy can also be used in the reverse direction.
For example, a magnetic loudspeaker can also be used in the opposite direction as a microphone. Sometimes different names are used to refer to essentially the same to convert. These principles with the exception of the Volta effect and electrical Chapter 4 are described in later. If an electrical conductor is moved in a magnetic field in such a way that the magnetic flux through the conductor is changed, a voltage is induced which is proportional to the rate of change of the magnetic flux.
Conversely, if a current is sent through the same conductor, a mechanical force is exerted. The result, which depends on the polarities of voltage and current on the electrical side or the directions of force and motion on the mechanical side, is a conversion from electrical to mechanical energy, or vice versa. All electrical motors and generators and a host of other devices, such as solenoids and loudit.
The output voUage in each case is propor-. The most important biomedical apsound microphones, pulse transducers, and electromagnetic blood-flow meters, all described in Chapter 6.
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