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Preface to the Second Edition xvi Perhaps the three major impacts on biomedical engineering in recent years are the tremendous expansion of non-invasive techniques. Because intensive care equipment and computers have also changed. Introduction to Biomedical Instrumentation Science has progressed through since Archimedes and scientific discoveries.

Since there have been a number of overlapping technological ages. Each of these fields reached a peak of activity and then settled down to a routine. Nuclear engineering and aerospace engineering are good examples. It is a long time Greek contemporaries started down the path of but a technological historian could easily trace the trends through the centuries.

Engineering has emerged out of the roots of science. The time for the age of biomedical engineering has now arrived. These problems include air and water pollution. One school of thought subfects are — for example. These categories usually indicate the use of that area of engineering applied to living rather than to physical components.

This Medicine. Many purists have stated that technology is an evil. A few years ago an engineering committee was formed to define biowas Subcommittee B Instrumentation of the Engineers Joint Council Committee on Engineering Interactions with Biology and engineering.

Bioinstrumentation implies measurement of biological variables. Their recommendation was that bioengineering be defined as application of the knowledge gained by a cross fertilization of engineering and the biological sciences so that both will be of man.

The prefix bio-. Yet these side ef- minor compared to the benefits that mankind can derive from it. Introduction to Biomedical Instrumentation 2 The age of computer engineering.

The probability is known great that the s will be was made as the decade in important field.

In addition. A biomedical equipment technician BMET is an individual who is knowledgeable about the theory of operation. In late The Age of Biomedical Engineering More 3 new applications have emerged.

This association consists of both engineers and physicians. Most go into the profession through the engineering out as physicists or physiologists.

His capabilities related technical ment equipment as well as operation or supervision of equipand maintenance programs and systems. In one hospital the title biomedical engineers. This person is not to be confused with the medical technologist. The latter is usually used in an operative sense.

The level of sophistication of the BMET is usually higher than This was also an years of training at a that of the technologist in terms of equipment. Another new term. They must have at least a B.

A clinical engineer is a professional who brings to health care facilities a of education. The result is that the engineer. Improved communication among engineers. To help acquaint the reader with this special aspect of biomedical engineering. In some cases. These definitions are all noteworthy. Introduction to Biomedical Instrumentation 4 It is now possible to become professionally registered as a clinical two different agencies who certify and the requirements have not been standardized.

Although it is important for the physician to understand enough engineering terminology to allow him to discuss problems with the engineer. The language and jargon of the physician are quite different from those of the engineer. Some engineer. Another major problem of biomedical engineering involves communication between the engineer and the medical profession. In addition to the language problem. With this point in mind. This appendix is in two parts: Appendix A.

Since the physician whereas the engineer is usually concept of the fiscal approach exists. Many instruments were developed as early as the nineteenth century— for example. Development of Biomedical Instrumentation 5 Since the development and use of biomedical instrumentation must be a joint effort of the engineer or technician and the physician or nurse.

Although it is true that many of the same components were used. At was rather slow equipment. During the next decade many instrument manufacturers entered the field of medical instrumentation. The aerospace medicine programs were expanded considerably. The use of adjunct fields. Many developments with excellent potential seemed to have become lost causes. They also encountered a severe communication problem with the medical profession. A large measure of help was provided by the U.

Some of the concepts and features of patient-monitoring systems presently used in hospitals throughout the world evolved from the base of astronaut monitoring. Progress of electronic available. This process occurred primarily during the s and the results were often disappointing. By being aware of their possible existence. It was during this period that some progressive companies decided that rather than modify existing hardware. The ticular Mercury. Biomedical instrumentation provides the tools by which these measurements can be achieved.

When principles are the same. A thermistor. Another example is the strain gage. Some forms of biomedical instrumentation are unique to the field of medicine but many are adaptations of widely used physical measurements. The of this device. When suitably excited by a source of constant voltage. Since pressure can be translated into strain by various means. Introduction to Biomedical Instrumentation g and techniAlso. In later chapters each of the major forms of biomedical instrumentacovered in detail.

It operates on the principle that electrical resistance is changed by the stretching of a wire or a piece of semiconductor material. In the design or specification of medical instrumentation systems.

For a thermistor. In a linear system the sensitivity would be the same for all absolute levels of input. Indications sen- of sensitivity are frequently expressed in terms of scale length per quantity to be measured — for example. Hysteresis Hysteresis from the Greek. The sensitivity of an instrument determines how small a variation of a variable or parameter can be reliably measured.

The objective should be to provide an instrument that will give a usable reading from the smallest expected value of the variable or parameter being measured to the largest. This factor differs the instrument's range in that sensitivity levels from not concerned with the absolute of the parameter but rather with the minute changes that can be The detected. Sensitivity 1.

Too high a sen- optimum sitivity often results in nonlinearities or instability. In form of nonlinearity whereas in others it is is some instruments a certain purposely introduced to create a desired effect.

Linearity should be obtained over the most important segments.

Biomedical instrumentation and measurements

Biometrics 7 Range 1. In most measurements. Accuracy 1. Errors can occur in a multitude of ways. It is bridge or a similar device. In certain types of instruments.

Component 3. This condition is referred to as a ''flat response'' over a given range of fre- reproduce all quencies. The first concerns correct instrument zeroing. This is especially true in further discussed later in this chapter. Mechanical friction in a meter. Two additional sources of error should not be overlooked. Although not always present simultaneously.

An instrument system should be able to respond rapidly enough to frequency components of the waveform with equal sensitivity.

Signal-to-Noise Ratio It is important that the signal-to-noise ratio be as high as possible. The frequency response of an instrument is its variation in sensitivity over the frequency range of the measurement.

Errors due to poor frequency response. Errors due to tolerances of electronic components. In the hospital environment. Accuracy is a measure of systemic error. Introduction to Biomedical Instrumentation g reached in a descending directhe movement tion.

It is important to display a waveshape that is a faithful reproduction of the original physiological signal. Mechanical errors in meter movements. Another source of on the parameter to be measured. Reading errors due to parallax. Frequency Response 1. It is also important to know and control the signal-to-noise ratio in the actual environment in which the measurements are to be 1.

Telemetry is also used where movement of the person or animal to be measured is essential. This point discussed in later chapters.

Simplicity All systems and instruments should be as simple as possible to eliminate the chance of component or human error. Isolation 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. 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. This is than be driven a factor that varies with the amount of amplification. Baseline stability is the maintenance of a constant baseline value without drift.

This requirement is often necessary for reasons of electrical safety see Chapter 16 or to avoid interference between different instruments used simultaneously. The overall system must be sufficiently stable over the useful range. Electrical isolation can be achieved by using magnetic or optical coupling techniques.

Calibration should always is organism or in situ connected to or within the. Although thermal noise is often the limiting factor in the detection of signals in other fields of electronics.

Stability In control engineering. This step can be done external to the living body. 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. It also contains a powerful computer. In fact. An example would be that of a complicated. The living black box presents other problems.

To further complicate the situation. Many of the important variables to be measured are not readily accessible to measuring devices. Within this box can be found electrical. These functions may be relatively simple or extremely complex. The situation is made even worse by the application of the measuring device itself.

The object is to learn the nature and characteristics of the A classic exercise in engineering analysis unknown system. This involves the system. That is. The result is that some key relationships cannot be determined or that less accurate substitute measures must be used.

Still other problems are associated with such measurements: Information gathering: The basic objectives of any instrumentation system generally one of the following major categories: As indicated earher. Instrument System is 11 the very problem facing those in the medical field who attempt to measure and understand the internal relationships of the human body.

Because special problems are encountered in obtaining data from living organisms. The function of medical instrumentation is to aid the medical chnician and researcher in devising ways of obtaining reliable and meaningful measurements from a living human being. There may also be some mechanism for automatic control of certain processes within the system. An instrumentation system is defined as the set of instruments and equipment utilized in the measurement of one or more characteristics or phenomena.

Additional factors that add to the difficulty of obtaining valid measurements are 1 safety considerations. Introduction to the engineers. In other words. This means that many of the measurement techniques normally employed in the instrumentation of nonliving systems cannot be applied in the instrumentation of humans.

In this setting. Instrumentation The general tent. Introduction to Biomedical Instrumentation -2 variables to aid man in his quest for knowledge about himself and the universe in which he lives. Although some instruments can be used in both areas. Biomedical instrumentation can generally be classified into two major and research.

Similar instrumen- gathering instrumentation. Clinical instruments are used by the physician or nurse. Measurements are used to determine the ability of a 4.

Measurements are made to help hopefully. In some applications. Instrumentation to aid the physician in the diagnosis of disease and other disorders also has widespread 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 types: In- strumentation for biomedical research can generally be viewed as informationit sometimes includes some monitoring and control devices.

Clinical instrumentation is basically devoted to and treatment of patients. An example would be a device inserted into the bloodstream to measure the pH of the blood directly. 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. The only real difference having a living being as the subject. Although the man-instrument system described here applies mainly to in vivo measurements. An in vivo measurement is one that is made on or within the living organism itself.

Components of the Man-Instrument System 1. The system components are given below. The Transducer In general.

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An in vitro measurement is one performed outside the body. A block diagram of the man-instrument system The basic components of this is shown in Figure 1. In the man-instrument system.. The stimulus may be tactile e. Its output is some form of In the man-instrumentaequipment may include a graphic pen recorder that visual.

Display Equipment To be meaningful. In essence. It should be noted that the term tion for possible later use or to transmit recorder is used in two different contexts in biomedical instrumentation. Equipment for these functions is often a vital part of the man-instrument system. The transducer may measure temperature.

It is Recording. Signal-conditioning equipment more is also used to combine or relate the outputs of two or transducers. The input to the display device is the modified electric signal from the signal-conditioning equipment. The found always an electric signal. As indicated in Figure part of the instrumentation system that amphfies. By means of a multilevel control system and communications network. Through the integrated operation of all these systems.

Most are readily accessible for measurement. Just as the these whole person communicates with his environment. Next to the whole being in the hierarchy of organization are the major functional systems of the body. Measurements can be made organization.

This system usually consists of a feedback loop in which part of the output from the signal-conditioning or display equipment system is is used to control the operation of the system in some way. Within the human body can be found electrical. These organization communicates with his environment in methods of communicating could be regarded as the inputs and outputs of the black box and are illustrated in Figure 1.

Each major system is discussed later in this chapter. For example. The process can continue down to the cellular level and perhaps even to the molecular level. The problem is. The major goal of biomedical instrumentation is to make possible the measurement of information communicated by these various elements.

If all the variables at be measured. Although each of the systems is treated in much more chapters. Communication of man with his environment. The interrelationships among elements are sometimes so complex the and involve so many systems that the "laws" and relationships thus far derived are inadequate to define them completely.

These functional systems can be broken down into subsystems and organs. The four-chamber pump acts as two synchronized but functionally isolated two-stage pumps. To an it incorporates an efficient waste disposal system. The Cardiovascular System engineer. 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 also contains mechanisms for repairing small system punctures and for rejecting foreign elements from the system platelets and white blood cells. Carriers red blood cells of fuel suppHes and waste all materials are transported to predetermined destinations by the fluid.

Biomedical Instrumentation and Measurements

In system arteries. Reservoirs in the system veins acteristics to satisfy certain control change its some parts of the diameter to control their volume and char- requirements. 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. 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 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. The fluid blood. Sensors provided to detect changes in the need for supplies.

The Respiratory System Whereas the cardiovascular system body. 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.

Automatic control will return. The bags connected to the outside environment through a passageway nasal are cavities. Physiological Systems of the Body 19 the buildup of waste materials. In the tiny air spaces of the bags is a membrane interface with the body's hydraulic system through which certain gases can diffuse. This system also has a number of relatively fixed volumes and capacities. System variables of primary importance are respiratory rate.

An air pump dia- phragm. Oxygen is taken into the fluid blood from the incoming air. Manual control can take over at any time either to accelerate or to inhibit the operation of the pump.

The pump operates with a two-way override. The variables of prime importance in this system are the pump cardiac output and the pressure. 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. The passageway divides to carry air into each of the bags. Feedback regarding every action controlled by the system is provided to the computer through appropriate sensors. Almost as fascinating as the central computer are the millions of communication lines afferent and efferent nerves that bring sensory information into.

In many together in the cases. The computer is self adapting in that if a certain section is damaged. In addition to the central computer. The Nervous System is the communication network for the body. Both serial and parallel coding are used. By use of this solve complex problems. Information is usually coded in the system by means of electrochemical pulses nerve action potentials that travel along the needs of the system.

Introduction to Biomedical Instrumentation 20 volume the additional amount of air that can be forced out of the lungs after normal expiration. In general. The pulses can be transferred from one element of a network to another in one direction only.

Action by some elements tends to inhibit transfer the signal lines nerves. A number of feedback loops are accomplished by this method. Its center a self-adapting central information processor or computer the brain The nervous system is with memory.

Although ethical restrictions sometimes are not as severe with animal subjects. One of system some the greatest problems in attempting measurements is from a living the difficulty in gaining access to the variable being measured.

This process involves the measurement of some other related variable that makes possible a usable estimate of the inaccessible variable under certain conditions. 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.

In using indirect measurements. Sometimes the problem stems physical size of the transducer as compared from the required to the space available for the measurement. Where a variable is inaccessible for measurement. Variability of the Few of Data the variables that can be measured in the human body are truly deterministic variables.

Most of these problems were introduced in earher sections of the chapter. A stochastic process is a time variable related to other variables in a nondeterministic way. Physiological variables can never be viewed as strictly deterministic values but must be represented by some kind of statistical or probabilistic distribution. In cases. Another problem arises from the interaction discussed earlier. This penetration can easily kill the cell or damage it so that it can no longer function normally.

Introduction to Biomedical Instrumentation 22 time. In many situations the physical presence of the transducer changes the reading significantly.

Often the presence of. Lack of Knowledge About Interrelationships The foregoing variability in measured values could be better explained if more were known and understood about the interrelationships within the body. The of one part of a given system generally affects in some way sometimes in all result is that stimulation other parts of that system an unpredictable fashion and often affects other systems as well. The again. Effect of the Transducer on the Measurement Almost any kind of measurement the measuring transducer.

For this reason. This situation is especially true in the brain and other parts of the nervous system. 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 substitutes for inaccessible effective use of indirect job of coupling the instrumentation to the physiological system.

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. 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.

Magnetic induction also plays an important role at the output of many biomedical instrumentation systems. Analog meters using d'Arsonval movements, light-beam galvanometers in photographic recorders, and pen motors in ink or thermal recorders are all based on the principle of magnetic induction and closely resemble the basic transducer configuration shown in. These microphones use an electret to create an electrostatic field between two capacitor plates.

Electrets which are the electrostatic equivalent of magnets are normally in the form of foils of a special plastic material that have been heat-treated while being exposed to a strong electric field. It is conceivable that the principle of the electret microphone could also be applied advantageously to biomedical transducers.

The natural materials in which this piezoelectric effect can be. When the authors and publishers decided that a second edition should be prepared much soul searching was necessary to decide on what changes should be made to improve the work.

Obviously everything had to be updated. Also there were the constructive criticisms of our colleagues around the world to consider. Preface to the Second Edition xvi Perhaps the three major impacts on biomedical engineering in recent years are the tremendous expansion of non-invasive techniques, the sophistication buih up in special care units and, along with other fields, the greater use of computers and the advent of microprocessors.

Taking all these facts together, the authors re-studied the book and and decided on the direction for the new edition. With respect to criticism, it was obvious, even after early adoptions, that the concept and principles of transducers should be presented earlier in the work.

The original Chapters 1 and 2 were combined into a new introductory chapter and a new Chapter 2 was written on basic transducers, including some material drawn from the old Chapter 9.Even same material may produce a small electrode offset voltage. When operated into a small load maximum cell is resist- ance the current delivered by either cell is proportional to the intensity of The voltage of these cells cannot exceed a certain value the incident light.

There is depth where needed. The living black box presents other problems. According to one theory. The computer is self adapting in that if a certain section is damaged. The photomultiplier consists of a photoemissive cathode of the type used in photoemissive cells.

EEG is a large phenomenon has not been shown con- the closed eyelids.