Handbook of ThirdEdition Handbook of Third Edition R.S. Khandpur Director General Pushpa Gujral Science City, Kapurthala, Punjab Formerly, Director Centre for Electronics Design and Technology of India (CEDTI) Now, Centre for Development of Advanced Computing (C-DAC) Mohali (Chandigarh), Punjab Director General CEDTI, New Delhi Head, Medical Electronics Instruments Division Chandigarh McGraw Hill Education (India) Private Limited NEW DELHI New Delhi New York St Louis San Francisco Auckland Bogotá Caracas Kuala Lumpur Lisbon London Madrid Mexico City Milan Montreal SanJuan Santiago Singapore Sydney Tokyo Toronto Published by McGraw Hill Education (India) Private Limited, P-24, Green Park Extension, New Delhi 110 016. Handbook of Biomedical Instrumentation, 3| Ed. Copyright © 2014, 2003, 1987, McGraw Hill Education (India) Private Limited. 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Road, Shahdara, Delhi 110095 Cover Designer: Kapil Gupta Cover Printer: Preface to the Third Edition I am delighted to place before you the third and enlarged edition of my popular book ‘Handbook of Biomedical Instrumentation’. This edition is totally revised and updated based on the tremendous technological advances which have penetrated in the field of health care technology during the last decade. Changes have been made in every chapter so that you can get the best. The technologies driving the medical equipment industry today include micro-electronics, micro-electromechanical systems, advanced signal processing, wireless communication and new energy sources for portable and implantable devices. The circuit design activity, which earlier used to be with the equipment designers is now shifted to the chip designers and manufacturers. For example, various texts on medical instrumentation have been discussing special features of bio-potential amplifiers for equipment circuit designers and maintenance engineers. Now you can have single chips for the entire analog front end along with A/D converter for an ECG/EEG monitor. Such is the power of micro-electronics that the task of equipment designer is much simplified. Reference to such integrated circuits is given wherever these have become available. Several new topics have been included in the revised text. These include gamma knife, cyber knife, multislice CT Scanner, new sensors, digital radiography, PET scanner, laser lithotripter, peritoneal dialysis machine and new implantable devices. The existing material has been thoroughly revised, updated and better illustrated. Information and communication technologies have made significant contribution in better diagnosis and treatment of patients and management of health facilities. With increased use of electronic medical records (EMR), telehealth services and mobile technologies like tablets and smart phones, physicians and patients are both witnessing the benefits that the new technologies are bringing in their lives. These developments have been included in this edition as a separate chapter on ‘Telemedicine Technology’. As some technologies become easier to use, less expensive and equipment becomes more transportable, even complex technologies can diffuse out of hospitals and institutional settings into outpatient facilities and patients homes. Such equipment, especially those designed for home care have special features such as efficient power management and wireless connectivity. These features are appropriately addressed wherever relevant while revising the contents of the existing text. Similarly, more and more implantable devices are preferred to treat numerous conditions, particularly in neurological stimulation to treat pain management, epilepsy and bladder control vi Preface to the Third Edition etc. The implantable medical devices technology has been well established and these devices have been around for decades now. Such devices have been included wherever appropriate. One of the distinctive features of the text is its visual impact by including good graphs and photographs of latest commercial equipment. The list of references has been expanded to include latest research material in the text. These will be useful for those who wish to pursue research career in this field. I thank the readers once again for sending me the feedback and suggestions, which I have tried to incorporate in the revised edition. I do hope that the book would be found even more useful to students and professionals working in the field of bio-medical instrumentation. The book continues to enjoy an enviable position in the field of biomedical instrumentation, both in India and abroad, for which I feel obliged to the students and the teachers for patronizing the book. I, on my part, has endeavoured to make the text more lucid and illustrations more meaningful wherever they required such an indulgence. I am thankful to my wife Ramesh Khandpur, who has always been a source of encouragement and strength and in assisting me in my writing pursuits. My children are settled in their lives in their own way and now planning careers for their children who have all entered the teens. Their occasional visits to our house peps up my mood and vigour to undertake and complete such a task which I consider could be helpful to the society in some way. Thanks are also due to McGraw Hill Education for bringing out an excellent publication. R.S. K HANDPUR Preface to the First Edition During the last two decades, there has been a tremendous increase in the use of electronic equipment in the medical field for clinical and research purposes. However, it is difficult to find a book which describes the physiological basis as well as the engineering principles underlying the working of a wide variety of medical instruments. The present volume has been written to fill this gap. The book has been designed to cater to a wide variety of readers. The users of medical instruments would find the text useful, as they would be able to appreciate the principle of operation, and the basic building blocks of the instruments they work on everyday. An attempt has been made to present the highly technical details of the instruments with descriptive and lucid explanations of the necessary information. It thus provides a useful reference for medical or paramedical persons whose knowledge of instrumentation is limited. The field of biomedical engineering is fast developing and new departments are being established in universities, technical colleges, medical institutes and hospitals all over the world. In addition to graduate engineers involved in developing biomedical instrumentation techniques, the book will find readership in the increasing number of students taking courses in physiological measurements in technical colleges. With the widespread use and requirements of medical electronic instruments, it is essential to have knowledgeable service and maintenance engineers. Besides having a basic knowledge of the principles of operation, it is important for them to know the details of commercial instruments from different manufacturers. A concise description of typical instruments from leading manufacturers is provided wherever deemed necessary for elucidation of the subject matter. The book has been divided into four parts. The first part deals with recording and monitoring instruments. This part has 11 chapters. The first chapter begins with the explanation that the human body is a source of numerous signals, highly significant for diagnosis and therapy. These signals are picked up from the surface of the body or from within. This requires electrodes of different sizes, shapes and types. Also, there are some parameters like temperature, blood flow, blood pressure, respiratory functions etc., which are to be routinely monitored. These parameters, which are basically non- electrical in nature, are converted into corresponding electrical signals by various transducers. Electrodes and transducers constitute the first building blocks of most of the diagnostic medical instruments and are, therefore, described in the first part of this book. viii Preface to the First Edition After picking up the signals of interest from the body, they are processed and presented in a form most convenient for interpretation. Display is generally on a picture tube for quick and visual observation or a record on graph paper. Such records facilitate a detailed study by specialists at a later convenient time. Display and recording systems, and the most commonly used biomedical recorders are covered in the subsequent three chapters. Next is a presentation of the various types of patient monitors. The systems aid the nurses and the medical personnel to quickly gather information about the vital physiological parameters of the patient before, during and after operation, and in the intensive care ward where the patient’s condition is kept under constant surveillance. Apart from the description of conventional equipment for monitoring heart rate, blood pressure, respiration rate and temperature, a separate chapter has been included on arrhythmia monitoring instruments. This class of instruments constantly scan ECG rhythm patterns and issue alarms to events that may be premonitory or life-threatening. The chapter also includes a description of ambulatory monitoring instruments. Foetal monitoring instrumentation is another area where considerable progress has been reported in the last few years. Instruments for foetal heart rate monitoring based on the Doppler shift have become more reliable because of better signal processing circuitry and the use of microprocessors. Intelligence is now incorporated in the cardiotocographs to provide data processing for making correlation studies of the foetal heart rate and labour activity. Wireless telemetry permits examination of the physiological data of subjects in normal conditions and in natural surroundings without discomfort or obstruction to the person or animal under investigation. Telemetric surveillance is the most convenient method for assessing the condition of the patient during transportation within the hospital for making stress studies before discharge from the cardiac wards. The chapter on biomedical telemetry explains the techniques and instrumentation for monitoring physiological data by telemetry in a variety of situations. It also includes transmission of biomedical signals over the telephone lines for their study and analysis at a distant place. An extensive use of computers and microprocessors is now being made in medical instruments designed to perform routine clinical measurements, particularly in those situations where data computing and processing could be considered as part of the measurement and diagnostic procedure. The use of microprocessors in various instruments and systems has been explained not only at various places in the text, but a full chapter gives a comprehensive view of computer and microcomputer applications in the medical field. With the increasing use of monitoring and therapeutic instruments, the patient has been included as a part of an electrical circuit and thus exposed to the possibility of providing a pathway to the potentially fatal leakage currents. Such a situation particularly arises when he carries indwelling catheters. A full chapter on patient safety describes various situations requiring attention to avoid the occurrence of avoidable accidents. Precautions to be taken while designing electromedical equipment from the point of view of patient safety is also discussed. The next part details the various measurement and analysis techniques in medicine and comprises seven chapters. The first two chapters concern the measurement of blood flow and volume. Blood flow is one of the most important physiological parameters and is also one of the most difficult to measure. This has given rise to a variety of techniques in an effort to meet the requirements of an ideal flow metering system. Both invasive as well as non-invasive techniques Preface to the First Edition ix have been developed. The ultrasonic Doppler technique has proved to be particularly useful in blood flow measurement. A detailed description of the modern methods of blood flow measurement including those making use of the laser Doppler technique has been given in Chapter 12. A separate chapter on cardiac output measurement details out the present state of art in this important area. Pulmonary function testing equipment act as the additional means in automated clinical procedures and analysis techniques for carrying out a complete study of the lung function from the respiratory process. Besides the conventional pneumotachometry, several new techniques like the ultrasound spirometer and microprocessor based analysers are under development. The measurement of gases is also important for respiratory studies. Chapter 14 gives a detailed description of various instruments and systems for assessing pulmonary function. The measurement of gases like oxygen and carbon dioxide in the blood, along with blood pH form important test parameters for studying the acid-base balance in the body. Blood gas analysers have greatly developed in the last few years. The modern microprocessor controlled instruments include automatic sample dilution and data processing. A separate chapter on blood gas analysers gives details of modern instruments and their use in clinical practice. Oximeters are covered in Chapter 16, which describes various techniques of assessing the oxygen saturation level of blood both by invasive and non-invasive techniques. A chapter on blood cell counters touches upon electronic methods of blood cell counting and microprocessor based system for making calculations important in haematology. The third part contains four chapters on medical imaging systems. The last decade saw an unprecedented progress in this area and resulted in the evolution and development of ultrasonic, computerised tomography and NMR scanners. Ultrasound has proved a useful imaging modality because of its non-invasive character and ability to distinguish interfaces between soft tissues. Ultrasonic imaging systems are now applied to obtain images of almost the entire range of internal organs in the abdomen. The chapter on ultrasound covers extensive information on this technology and includes the physics of ultrasound, pulse echo systems including M-mode echocardiography and a variety of scanning systems and techniques. CT scanners are considered as the most significant development since the discovery of X-rays. In spite of their inherent high cost, several thousands of these are now installed in hospitals around the world. Keeping in view the impact on medical diagnostics, a detailed description of the various scanning techniques in CT systems has been given in Chapter 19. The chapter also carries information on the basic X-ray machine and image intensifiers. Thermography—the science of visualizing and interpreting the skin temperature pattern—is another technique, which stands alongside X-ray, ultrasonic and clinical examination as an aid to medical diagnostics. Keeping in view its usefulness and recognizing the non-availability of information on this topic in most of the medical electronic instrumentation books, a separate chapter has been included in this text. The last part with six chapters is devoted to therapeutic instruments. Two types of instruments are commonly employed to meet cardiac emergencies. These are the pacemakers and the defibrillators. The technology of implantable pacemakers has considerably developed in the past few years, resulting in the availability of pacemakers with life long guarantee of their activity. This has become possible due to improvements in power sources, low drain current circuits and better encapsulation techniques. The availability of programmable pacemakers has further helped to individualise the pacemaker treatment. Similarly, microprocessor based defibrillators have appeared in the market to give the possibility of more efficiently delivering x Preface to the First Edition the defibrillating discharge by appropriately adjusting the output on the basis of patient- electrode impedance. These two topics are covered in two separate chapters. The use of high frequency in electro-surgical procedures is well established. There has not been very many changes in the basic design except for the availability of solid state versions with better safety provisions for the patients and operators. Application of lasers for bloodless surgery and for coagulation of fine structures in the small and sensitive organs of the body is now routinely practiced in many centres in the world. Separate chapters cover the high frequency electro-surgical machines and laser applications in medicine respectively. The maintenance of renal function in acute and chronic renal failure through dialysis is a routinely practiced technique. Haemodialysis machines for use in hospitals contain a variety of monitoring and control facilities, and some of these functions have also been computerised. There have also been attempts to bring out a wearable artificial kidney so that patients suffering from this disease could enjoy a near normal life during their stay away from the dialysis centre. The chapter on haemodialysis machines includes a description of the well established machines with an indication of the efforts on the development of portable systems. Physiotherapy instruments like the short-wave diathermy machine, microwave diathermy machine and ultrasonic therapy units have acquired an established role in the hospitals. Similarly, the technique of electro-diagnosis and electrotherapy are now routinely employed in the physiotherapy departments. An extension of this technique has been the development of small stimulators for a variety of applications like pain relief, control of micturition, epilepsy, etc. The information on these techniques is usually not available in the books on the subject. The inclusion of a full chapter on these techniques fulfils this gap. A large number of references have been included at the end. This is to help the more interested readers to conveniently look for extra material on the subject of their interest. I am thankful to the Director, Central Scientific Instruments Organization, Chandigarh for kind permission to publish this book. I am also grateful to various manufacturers of medical electronic instruments who supplied valuable information on the products along with some interesting photographs. Finally, I am extremely grateful to my wife Ramesh Khandpur who helped me in correcting and comparing the typed script. I also acknowledge the assistance provided to me in this work by my children Vimal, Gurdial and Popila. All of them bore the brunt of uncalled for neglect over a long period during the preparation of the manuscript. R.S. KHANDPUR