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1869 results in Biomedical engineering

Page 21 of 94

Biomechanics
  • Concepts and Computation
  • 2nd edition
  • Cees Oomens, Marcel Brekelmans, Sandra Loerakker, Frank Baaijens
  • Published online:
    02 February 2018
    Print publication:
    08 February 2018
  • Thoroughly revised and updated for the second edition, this comprehensive textbook integrates basic and advanced concepts of mechanics with numerical methods and biomedical applications. Coverage is expanded to include a complete introduction to vector and tensor calculus, and new or fully updated chapters on biological materials and continuum mechanics, motion, deformation and rotation, and constitutive modelling of solids and fluids. Topics such as kinematics, equilibrium, and stresses and strains are also included, as well as the mechanical behaviour of fibres and the analysis of one-dimensional continuous elastic media. Numerical solution procedures based on the Finite Element Method are presented, with accompanying MATLAB-based software and dozens of new biomedical engineering examples and exercises allowing readers to practise and improve their skills. Solutions for instructors are also available online. This is the definitive guide for both undergraduate and graduate students taking courses in biomechanics.

  • Preface

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp xi-xv

  • Summary

    The main aim of this textbook is to provide the tools to understand the function and design of different biomedical instruments and devices, and for the reader to be able to use these tools to envision new and improved future technology and designs. Throughout the book the terms medical and biomedical are used interchangeably, and similarly with the terms device and instrument. With several thousand instruments and devices on the market it is clearly impossible to consider more than a handful in detail. Instead, this book concentrates on the following general approach.

  • (i) What is the clinically relevant measurement that needs to be made?

  • (ii) What are the pathophysiological mechanisms that give rise to the clinical condition?

  • (iii) What are the characteristics (e.g. magnitude, frequency, bandwidth) of the signal to be measured? How accurate and reproducible does the measurement have to be? What are the interfering signals that have to be suppressed?

  • (iv) What are the recommended instrumental specifications for the particular device? How does one design the device to meet these specifications?

  • (v) How does one test the biocompatibility and electrical safety of such a device, whether it is external or implanted, so that it can operate safely for a number of years?

    • Traditionally, most of these instruments and devices have been located in a hospital, and patients travel to the clinics for the measurements to be performed by trained personnel. However, this model is changing and nowadays there is an increasing role for what is termed mobile health (m-health), which involves a much greater degree of healthcare being performed by the patients themselves at home. This means that a biomedical device must operate in the patient's home environment without specialized training, as well as transmit the data wirelessly and securely to the physician. This model of continuous patient monitoring not only provides a much more complete assessment of the patient's health, but also reduces the number of visits that a patient has to make to the hospital.

    The main areas of technological development that have enabled the rapid incorporation of m-health into the healthcare infrastructure are wearable and implantable devices that can transmit data to the physician via mobile phone networks.

  • 9 - Safety of Biomedical Instruments and Devices

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 271-307

  • Summary

    Introduction

    Every year many thousands of patients receive some form of electrical shock from medical devices and instruments. These are typically not fatal and do not cause serious injury, but rather result in significant discomfort to the patient and may cause effects such as ventricular fibrillation. There are many incidents of physicians and nurses also receiving electric shocks. These events occur despite strict regulations to ensure the electrical safety of all medical devices. Although some events occur due to a design flaw in a particular device, the most common situation in which electrical shocks occur is one in which a patient is hooked up to many different devices in the operating room (OR), as shown in Figure 9.1. These devices might include defibrillators, pacemakers, ultrasound scanning equipment, cardiac catheters and EEG equipment to monitor anaesthesia. In addition, there are a number of ancillary devices such as high intensity lights and intravenous lines, which are attached to, or close to, the patient. Conductive body fluids also result in unintended conduction paths close to the patient or in the medical device itself if these fluids come into contact with the equipment. In general, medical equipment, and particularly the power cords and power cables feeding the equipment, see many years of use, and it is estimated that over 70% of electrical ‘incidents’ occur due to wear and tear on the power cords, which are regularly run over or mechanically stressed. The electrical insulation around equipment also becomes damaged over time during normal operation. In order to govern the design of medical equipment, regulatory bodies have produced documents to safeguard patients, and the IEC has produced a standard, the IEC 60601 Medical Electrical Equipment – Part 1: General Requirements for Safety and Essential Performance. A brief description of the tests that must be performed before installation, and for regular maintenance, is covered in section 9.5 of this chapter.

    One can analyze the different potential danger points in terms of the possibility that multiples of these are present, and can cause a potential electrical shock to the patient or physician, as shown in Figure 9.2.

  • 8 - Mobile Health, Wearable Health Technology and Wireless Implanted Devices

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 235-270

  • Summary

    Introduction

    The standard model of healthcare is that a patient with disease symptoms visits a general practitioner, who refers the case to a specialized physician at a hospital. The patient then visits the specialist who orders a battery of tests and scans. Some time later, when the results of the tests and scans have been interpreted, the patient revisits the hospital and the appropriate therapeutic course is prescribed. At regular periods the patient may be asked to revisit the hospital, whereupon updated tests are performed, progress assessed and any necessary changes to the medication are implemented.

    There are several obvious inefficiencies in this process. First is the lack of any prior information that can be transmitted to the general practitioner before the patient's initial visit. Second is the requirement for the patient to visit the hospital multiple times. Perhaps the most important limitation is the lack of continuous monitoring of the patient's situation after therapy has started. Infrequent visits to the hospital provide only a snapshot of the entire treatment process. While the process may merely be inconvenient in the developed world, the entire concept breaks down in many developing countries.

    This chapter considers the design of software and hardware that can be used to provide continuous information from a patient to a physician and vice versa, as well as from a device to the patient and the physician, all without the patient being required to be physically present at the hospital. Figure 8.1 schematically represents different ways in which information transfer can be achieved. In order of increasing complexity, the general areas covered are:

  • (i) the use of mobile/smartphone utilities for information dissemination and patient reminders: this comes under the general description of mobile health

  • (ii) the design of wearable activity monitors that can wirelessly upload data to the patient and physician

  • (iii) the application of physical patches that can be attached to the skin and record heart rate, blood pressure, sweat, temperature etc. and can wirelessly send data to the hospital

  • (iv) the design and operation of implanted monitoring devices such as continuous glucose monitors, which can wirelessly transmit data through the body to a recording device that provides feedback to the patient and the physician, and

  • 19 - Cancer versus Regeneration: The Wrong versus Right Response to the Microenvironment

  • from Part III - Coordination of complex functions
  • Michael Sheetz, Columbia University, New York, Hanry Yu, National University of Singapore
  • Book:
    The Cell as a Machine
    Published online:
    06 August 2018
    Print publication:
    11 January 2018, pp 402-421

  • Summary

    Due to the presence of mechanisms that regenerate portions of tissue after disease or damage, it is possible that excessive or inappropriate growth may occur. In humans, when a portion of tissue grows excessively, it is often described as a cancer; however, there are many forms of excessive growth that are limited and not life-threatening. At the heart of a cancerous growth is the inappropriate response of the cell to its microenvironment. Sensory modules that determine mechanical aspects of the microenvironment contribute to cancerous growth. In particular, the depletion of rigidity-sensing modules enables cells to grow on soft surfaces, much in the way that loss of sensing in self-driving cars causes inappropriate movement. There are common features of inappropriate growth that are considered in the rubric of cancer biology and many books are written on the details. Here we consider growth in the context of cell states and the response of the cell to its microenvironment. By definition, cells in cancers have ignored normal growth controls and have grown excessively. Because tissue growths need vascularization to grow rapidly beyond millimeter dimensions, they are normally self-limiting. Further, telomere shortening will limit the number of divisions of cells. Thus, these two factors act as safeguards to keep most tumors small in size and benign. When cells move to states that continue growth, elongate telomeres and promote vascularization, they can be life-threatening. Even then, surgeons can remove the growths and the normal cells can often heal the area and restore function. What is life-threatening is the ability of inappropriately proliferating cells to disseminate to other parts of the body and to differentiate and grow in many different environments. Then, the surgeon cannot remove all of the tumors and the multiple, differentiated cells will not be killed by a single therapy. Furthermore, the act of killing the tumor cells often elicits a general repair response in the body that will promote further growth of tumors. The lessons of Cancer Biology can tell us a lot about biology in general.

    In the previous chapter, we discussed normal development and the process of differentiation. When a loss of cells occurs during normal development, neighboring cells typically divide to fill the gaps. This is important, because with the loss of cells in a tissue, both physical mass and functional performance are lost.

  • 11 - Microenvironment Controls Life, Death, and Regeneration

  • from Part II - Design and operation of complex functions
  • Michael Sheetz, Columbia University, New York, Hanry Yu, National University of Singapore
  • Book:
    The Cell as a Machine
    Published online:
    06 August 2018
    Print publication:
    11 January 2018, pp 243-264

  • Summary

    In the adult organism, the cellular microenvironment is critical in controlling cell growth, death, or regeneration. Although the fluid microenvironment includes several factors that influence cells, such as nutrients, salts, and hormones, we will focus here on the extracellular matrix and neighboring cells. The cellular microenvironment must support the tissue functions in the organism and should enable cell turnover and repair. Repair necessitates controlled growth to the proper cell density relative to matrix; however, safeguards are then needed to avoid uncontrolled growth, which can result in cancer. In this chapter, we will discuss the organizing principles in (1) cell–matrix interactions, (2) cell–cell interactions, and (3) the interplay between the two. In the case of the extracellular matrix (ECM), the composition of the ECM and its architecture sets the program for the adjacent cells through both the chemical nature of the ECM molecules and the shape of the crosslinked matrices in the adult. The detergent-resistant matrix of a tissue contains a lot of information that can direct the regeneration of stem cells when added to the matrix. In addition, the ECM will direct the cellular repair process following the loss of individual or small numbers of cells and the mechanical characteristics are critical. Matrix provides mechanical support through basement membranes, ECM fibrous networks, or linear fibers. The number of cells in the given matrix will be set by the physical aspects of the cell–cell contacts and the amount of ECM available. In the case of cell–cell junctions, there is a more limited set of components in adhesions, but some of the same cytoskeletal elements are important. Again, mechanical signals derived from the reciprocal communication between neighboring cells as well as the matrix are critical for directing the growth of the organism and controlling repair processes. Most importantly, the cell must only grow in an environment that is defined by a combination of cell neighbors, the matrix as well as nutrients and hormones. If the cell doesn't respond properly to the local cell and matrix cues, then it is likely that dysfunction will result. Major trauma and damage in the adult is usually bandaided with collagen fibers that cover the damage site (scar tissue) but do little to restore normal function in that region.

  • 5 - Electrocardiography

  • Andrew G. Webb
  • Book:
    Principles of Biomedical Instrumentation
    Published online:
    11 August 2019
    Print publication:
    11 January 2018, pp 140-168

  • Summary

    Introduction

    An ECG, also sometimes referred to as an EKG from the original German word ‘electrokardiogram’, measures the electrical activity of the heart [1]. This electrical activity produces the contractions and relaxations of the cardiac muscles required to pump blood around the body. An ECG is recorded over a series of cardiac cycles (heartbeats) and shows the different phases of the cardiac cycle. The ECG indirectly measures transmembrane voltages in myocardial cells that depolarize and repolarize within each cardiac cycle. These depolarization and repolarization events produce ionic currents within the body, and these are transduced into voltages by electrodes (described in Chapter 2) placed on the surface of the chest and thorax, as shown in Figures 5.1(a) and (b). Up to twelve different lead voltages are recorded, with the magnitude of the voltages being in the low mV range, Figure 5.1(c), and a frequency spectrum between 0 and 30 Hz, as shown in Figure 5.1(d). The ECG signal has many distinct features, such as the P-wave, QRS-complex and T-wave, illustrated in Figure 5.1(c). The amplitude, shape and relative timing of these features can be used to diagnose different clinical conditions.

    An ECG is an essential part of diagnosing and treating patients with acute coronary syndromes and is the most accurate method of diagnosing ventricular conduction disturbances and cardiac arrhythmias. It is also used to diagnose heart conditions such as myocardial infarcts, atrial enlargements, ventricular hypertrophies and blocks of the various bundle branches. An ECG is universally used to monitor a patient's cardiac activity during surgery.

    Most ECG machines are now digital and automated, meaning that the data is analyzed automatically. Software algorithms measure different aspects (such as delays, durations and slopes) of the ECG waveform and provide a set of keyword interpretations of the scan such as ‘abnormal ECG’ or more specific suggested diagnoses such as ‘possible sinoatrial malfunction’. The most common software package is the University of Glasgow algorithm, which is outlined in detail in section 5.4.1. The major interference signals are caused by electromagnetic coupling from external sources such as power lines, which must be removed by appropriate filtering.

  • 8 - Signaling and Cell Volume Control through Ion Transport and Volume Regulators

  • from Part II - Design and operation of complex functions
  • Michael Sheetz, Columbia University, New York, Hanry Yu, National University of Singapore
  • Book:
    The Cell as a Machine
    Published online:
    06 August 2018
    Print publication:
    11 January 2018, pp 166-189

  • Summary

    Many cellular functions depend heavily upon the ionic environment within cells and upon the gradients of ions across membranes. In terms of robust devices, the transmembrane potential and ion movements provide a simple means of coordinately regulating multiple functions. Not only are the levels of calcium, magnesium and protons critical, but trace ions like zinc and iron are also needed for many specialized reactions. Gradients of protons and ions across membranes drive neuronal and muscular signaling, ATP production, and even cell death signals. Because ions cannot freely pass through membranes, there are a large number of proteins that have been created with specialized functions to move ions under the right conditions. In general, the cytoplasm of mammalian cells is high in potassium and low in sodium with several millimolar of magnesium, submicromolar of free calcium, and a pH of about 7.0. Outside of the cell, the fluid is high in sodium and low in potassium with several millimolar of both magnesium and calcium (pH 7.4). Total solute concentrations (designated as osmolality or the sum of the concentrations of negative ions, positive ions, proteins and small molecules) are matched inside and out in resting cells. During most cell functions, proteins act as pores, ion-selective channels, or exchangers to control ion movements. Due to the small volume in cells, only a small number of ions need to cross the membrane to produce major changes in concentration, pH, and particularly transmembrane voltage. These parameters control chemical- and electrical-based signal transduction and, therefore, rapid ion movements across membranes must be carefully orchestrated in a robust system. Neuronal signaling and muscle contractility, for example, are controlled by rapid and reliable electrical signaling, which occurs through cell depolarization. Imbalances or mistiming of ion movements in these and other physiological cases are linked to cell damage and disease.

    To respond to changes in ionic strength due to dehydration, or rapid intake of large amounts of water, cells possess intrinsic mechanisms that regulate their volume. These rely heavily upon osmosensing, whereby the movement of water out of or in to the cell changes the cell volume, causing the compression of the membrane onto the cytoskeleton or pulling of the membrane away from the cytoskeleton, respectively. In response, the cell will open channels that will allow the entry of salt or the exit of metabolites like taurine.

  • 5 - Life at Low Reynolds Number and the Mesoscale Leads to Stochastic Phenomena

  • from Part I - Principles of complex functions in robust machines
  • Michael Sheetz, Columbia University, New York, Hanry Yu, National University of Singapore
  • Book:
    The Cell as a Machine
    Published online:
    06 August 2018
    Print publication:
    11 January 2018, pp 95-116

  • Summary

    As noted earlier, cellular functions are always driven by the diffusion of molecular components at a basic level. Thus, it is important to understand why the low Reynolds number of cellular systems demands that basic movements of proteins occur by diffusion. We will go through the physical basis of the cellular systems and the implications of diffusion for cellular functions. In addition, cells of all sizes need to concentrate components in subcellular regions and organize their proteins and membranous organelles by transporting them from one place to another in the cytoplasm. Because diffusion basically limits the speed of transport of materials in the absence of energy-dependent active transport, it is important to remember that slow as well as very small life forms can rely upon diffusion for life processes. There is an active debate about when transport is best accomplished by diffusion or by a motor-dependent system. Both diffusive transport and active transport have been observed and we will consider the mechanism of both in this chapter. Physical constraints of diffusion in cell systems limit the size of life forms, but can be circumvented by reducing dimensionality as well as by active transport systems. As cellular dimensions reach beyond 100 μm, diffusive transport times become very long and animal cells typically utilize active transport systems supported by linear filaments to move materials rapidly. Membrane depolarization and pressure waves can move much faster than diffusion and are often used for signaling when actual material transport is not needed.

    Thermal Energy versus Momentum at Low Reynolds Number

    To understand cellular functions, it is necessary to understand the fundamental physics of molecules (proteins, lipids, and carbohydrates) at the nanometer level. As particles get smaller, their mass scales roughly as the cube of their size, and the velocities of particle movement also tend to decrease. Because the energy of a moving particle is one-half of the mass multiplied by the velocity squared, the energy in a moving small particle is much less than the energy of macroscopic particles. At some point, the particle size will be small enough such that the typical kinetic energy of particle movement will be less than its thermal energy or kT. At that point, the dominant factor in particle movements will be diffusive. In water, that point is larger than bacteria and smaller than fleas.

Page 21 of 94