Ebook: Basic Engineering for Medics and Biologists

Research and development in bioengineering and medical technology, conducted during recent decades, have led to spectacular progress in clinical medicine. These achievements have triggered an enormous increase in the number of courses offered in the areas of bioengineering, clinical technology and medical informatics; nowadays, most major universities offer curricula oriented towards these fields. The majority of participants however come from engineering backgrounds and so modules dealing with basic biological and medical sciences have been included. These have been facilitated by the ready availability of textbooks in this area, many of which were specifically written for nursing A & P (Anatomy & Physiology) programmes.

In contrast, relatively few participants from medicine and biology have taken up courses in biomedical engineering, to the detriment of scientific exchanges between engineers and medical doctors. The reasons for this imbalance are many and may vary from country to country, but a consistent finding is the difficulty (or courage) in taking the first step. ‘Introductory’ texts in bioengineering tend to involve vector algebra and calculus early in Chapter 1. While in most countries entry to medical school is very competitive and requires, among others, high grades in mathematics, little more than arithmetic is required during the course itself, so numeracy undergoes disuse atrophy.

Furthermore, to paraphrase George Bernard Shaw, medics and engineers are separated by a common language. To the medic, stress and strain are both symptoms of anxiety, while to the engineer they are defined by equations involving symbols such as σ and ε and are related to forces and deformations. To the average medic this is, literally, all Greek.

ESEM is a bridge between medicine and engineering. It promotes cultural and scientific exchanges between engineers and medics and training courses in biomedical engineering. What better way to achieve these objectives than to address this problem and help medics and biologists to take this first step.

To this end, we herewith present a series of First Step chapters in book form aimed at medics and biologists to help bring them to the level where they can begin an MSc in biomedical engineering, or at medics who “simply” wish to understand a particular medical technology. Written by engineers who are leaders in their field, with input from medical colleagues, they will cover the basic engineering principles underpinning biomechanics, bioelectronics, medical informatics, biomaterials, tissue engineering, bioimaging and rehabilitation engineering, and will include clinically relevant examples.

As Albert Einstein may have said ‘Everything should be made as simple as possible, but not simpler’.

Dublin & Zurich, December 2009

Clive Lee & Peter Niederer

The forces that act on an object determine its dynamic behaviour and defromation. Analysis of all forces and moments is essential. A free-body diagram summarizes all forces and moments that act on an object. To calculate the magnitude of the forces we can use the static equilibrium of forces and moments.

Mechanics of materials is the science of forces applied on a body and response of the body in terms of deformation. Different type of loadings on bodies with different geometries or made of different material give rise to different deformations. Last but not the least, this science allows to predict the failure of a body under certain loading condition hence makes it possible to optimize the design for that particular condition.

The part of (bio)mechanics that studies the interaction of forces on the human skeletal system and its effect on the resulting movement is called rigid body dynamics. Some basic concepts are presented: A mathematical formulation to describe human movement and how this relates on the mechanical loads acting on the skeletal system. These equations of motion depend on the mechanical properties of the skeletal system, such as dimensions and mass distribution. It is applied to describe and analyze human gait.

A fluid is a medium which deforms, or undergoes motion, continuously under the action of a shearing stress and includes liquids and gases. Applying biofluid mechanics to the cardiovascular system requires knowledge of anatomy and geometry, pressure data and blood flow, volume and velocity measurements. A good example is the assessment of the haemodynamics of biological and mechanical heart valves.

For simple constructions a mechanical analysis to determine internal stresses and deformation is possible using theoretical formulas. However, for complex constructions, like joint prostheses, this is not possible. Numerical simulation of internal stresses and deformations offers a solution for these constructions. The so-called Finite Element Analysis divides the complex structure in simple ones (elements), applies the mechanical formulas and adds the effect on each element to predict the behaviour of the complex contruction.

The paper describes the physical phenomena involved in the conduction of electricity, with particular reference to living tissue. The conduction of electricity depends on the flow of charge carriers in the material, while the dielectric properties are due to the rotation of dipoles that can align along an applied electric field. The relation between the electric variables in a conducting medium and their physical meanings are explained. The phenomena responsible for the electric and dielectric properties of living tissues are described. The presence of cells limits the flow of charge carriers, in particular at low frequency, and the membranes are responsible for dielectric relaxation. The passive response of cell membranes to weak applied signals enables bioelectrical tissue characterisation. Practical tools for electrical impedance spectroscopy are given with an overview of the most recent applications.

Correct use of medical equipment within the clinical environment is of prime importance. This includes awareness of the safety issues regarding equipment, particular when it is an electrically powered device. Incidents can occur in the clinic in which a medical device is suspected of contributing to patient or staff injury. It is important that one can identify in advance any potential hazards which may arise with electrical equipment due to technical or environmental factors. This paper gives an overview of electrical safety.

There is a constant need in medicine to obtain objective measurements of physical and cognitive function as the basis for diagnosis and monitoring of health. The body can be considered as a chemical and electrical system supported by a mechanical structure. Measuring and quantifying such electrical activity provides a means for objective examination of heath status. The term electrogram, from the Greek electro meaning electricity and gram meaning write or record, is the broad definition given to the recording of electrical signal from the body. In order that comparisons of electrical activity can be made against normative data, certain methods and procedures have been defined for different electrograms. This paper reviews these methods and procedures for the more typical electrograms associated with some of the major organs in the body, providing a first point of reference for the reader.

The ability to accurately measure physiological and chemical changes in the body is fundamental to the development of new diagnostic and therapeutic methods. This chapter provides an introduction to biosensors, devices which convert a biological response into an electrical signal. The interface between the biosensor and the biological system being measured is of critical importance. Awareness of the components and characteristics of a biosensors, allows correct selection of the most appropriate for clinical application. The basic components of a biosensor include a biological element and the physiochemical transducer. The transducer is a device that converts one form of energy to another. The signal produced by the transducer requires amplification and processing to correctly interpret the measurement data. This chapter also provides examples of the application of biosensors in clinical engineering, focusing on direct and indirect blood pressure measurements and also assessing lung function through spirometry. Biosensors have an enormous clinical impact both in diagnosis and therapy, as well for being critical for data collection for biomedical research.

Medical Informatics comprises the theoretical and practical aspects of information processing and communication, based on knowledge and experience derived from processes in medicine and healthcare. The processing takes place within computers ranging from large supercomputers for research, high performance work stations for image processing and retrieval to smart phones which support mobility and pervasive health applications. A variety of Operating Systems are used, dominated by Microsoft and Linux. The latter promotes an ‘open source’ approach, which is favoured by many in health. In today's ‘connected health’ paradigm, end-user devices are linked to hospital servers, each other and the Internet. This requires knowledge and understanding of security considerations which are important in this disciple, due to the ethical dimension of healthcare. In this section we study the use of a web based system to facilitate rehabilitation of people with Stroke. This can be classified as an eHealth application, and is an exemplar of the self management paradigm, which is set to become more important due to the ageing society and associated prevalence of chronic disease.

Medical interventions produce a broad range of data types: text-based data, for example a physician's notes describing the patient encounter; physiological signals such as the well known electrocardiogram (ECG), but also recordings from brain (electroencephalogram, EEG) and muscle activity (electromyogram, EMG); and images such as Compute Tomography (CT) scans, Magnetic Resonance Images (MRI) or ultrasound images. In addition, recent progress in medical science and technology has led to the accumulation of a tremendous amount of genomic data in support of individualised healthcare and personalised therapies. In this section, the characteristics of typical clinical data are introduced, followed by a brief introduction to genomic data. Coding of data is important for summarising data in computer systems. Well known examples are Read Codes and SNOMED-CT. These assist in promoting a shared understanding for the healthcare professionals and facilitate the use of software tools for medical audit, classification and research. Interoperability, which allows computer systems to communicate, is an important concept. Unambiguous description and standards are important. Web standards based on XML, facilitate WEB2.0 participation, with a view to producing a semantic web. For health, we provide an example based on a markup language to describe the electrocardiogram (ecgML).

Decision support systems (DSS) are software entities that assist the physician in the decision making process. They have found application in medicine due to the large amounts of data (e.g. laboratory measurements such as blood pressure, heart rate, body-mass index) and information (e.g. patient history, population statistics based on age and sex) that must be considered before diagnosing any disease or recommending a therapy. A well known example is the embedded software in defibrillators which allows a ‘shock’ to be delivered, by analyzing the electrocardiogram for known conditions (heart attack). The shock can restart the heart and timely delivery can resuscitate the patient. As well as assisting in primary diagnosis, a DSS can reduce medical error, assist compliance with clinical guidelines, improve efficiency of care delivery and improve quality of care. Decision support still has significant acceptance issues in clinical routine, but can achieve more prominence, as systems are demonstrated to provide effective knowledge based support. Data mining is often used to provide some insight to a data set and update our accepted knowledge. In this section, we discuss a study which examines where electrocardiographic information should be recorded from a patient's torso in order to increase diagnostic yield.

Remote healthcare monitoring is the process of assessing the well-being of a patient when the patient and their healthcare professional are not located together. Advances in technology, specifically medical devices, sensors and high speed fixed and wireless communication networks have made it possible to bring the assessment process to the patient, as opposed to limiting the assessment to the constraints of hospitals and doctors' surgeries. It is also possible for patients to benefit from expert consultants anywhere in the world and receive their advice, without a face-to-face meeting. We discuss these issues in the context of home based medication management and propose a technical solution using emerging technologies. This uses a base station acting as a reservoir of medication and a means to connect the patient to an Internet based care model. The following details of the system are presented; an Internet portal in the form of a web based interface to support the prescribing of medication; an interface for the pharmacist to support the filling of medication containers; a caregiver's interface that provides a means to assess the patient's adherence to their medication regimen.

As the field of regenerative medicine progresses, one of the key challenges is to try to mimic the structure and role of the natural extracellular matrix (ECM) more accurately in synthetic substitutes. In particular, the field of biomaterials has played a crucial role in the development of tissue engineered products. Scaffold design is central in the field of biomaterials, and involves investigating and controlling important characteristics such as biocompatibility, degradability, pore architecture and mechanical properties. Undoubtedly, we will move closer towards reducing the number of patients awaiting donor tissues, as more advanced biomaterials continue to be developed in this field. This chapter discusses scaffold requirements for tissue engineering applications and the current state of the art with a specific focus on collagen-based scaffolds.

Many cells are capable of responding to mechanical stimuli in their environment, such as fluid flow, compression, pressure and stretch. By means of mechanosensors, cells may detect and respond rapidly to stimuli (e.g. touch, sound waves, limb position) or they may begin a structural response to chronic events. For example, in limbs that are constantly exercised, cells will produce bigger muscles, stronger ligaments and denser bone. This may involve the recruitment, proliferation, differentiation and stimulation of a variety of cells. Investigations are aimed at discovering the cell components responsible for these responses and understanding the process that links receptors to signal transduction to the cell response. This chapter discusses each of these areas.

A bioreactor can be defined as a device that uses mechanical means to influence biological processes. In tissue engineering bioreactors can be used to aid in the in vitro development of new tissue by providing biochemical and physical regulatory signals to cells and encouraging them to undergo differentiation and/or to produce extracellular matrix prior to in vivo implantation. This chapter discusses the necessity for bioreactors in tissue engineering, the numerous types of bioreactor that exist, the means by which they stimulate cells and how their functionality is governed by the requirements of the specific tissue being engineered and the cell type undergoing stimulation.

A proper knowledge of the mechanical and material properties of biomaterials is a necessity in all medical device technologies: from tissue engineering to prosthesis design. In many cases, the design of novel biomaterials is governed by the mechanical properties and their characterisation may become a crucial factor in determining the success of a product. This chapter discusses the basic concepts of the characterisation and testing of materials. Starting from the fundamental concepts of elastic, viscoelastic and plastic deformation, an introduction to experimental methods is given. The special limitations and requirements set by biomaterials are discussed.

High frequency ultrasound (2 – 8 MHz typically) has established itself as a major medical imaging method associated with a wide range of clinical applications. Advantages include real-time applicability, lower cost compared with other medical imaging technologies, possibility of measuring blood flow velocities and desk-top instrumentation. Disadvantage is associated with lower image quality than is obtained with x-ray or magnetic resonance methods.

X-ray projection imaging, introduced in the early 20^th century, was for a long time the only and still is a major routine diagnostic procedure that can be performed on the intact human body. With the advent of Computed Tomography in 1973, for the first time, a true 3D imaging of anatomical structures became feasible. Besides, digital recording and processing allowed further developments such as subtraction angiography in real-time or direct x-ray imaging without wet photographic methods.