Principles of Measurement and Transduction of Biomedical Variables

Vera Button

• Publisher: Academic Press
• Year: 2015
• ISBN:
  9780128011447
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie de la chimie et de la biochimie

Principles of Measurement and Transduction of Biomedical Variables is a comprehensive text on biomedical transducers covering the principles of functioning, application examples and new technology solutions. It presents technical and theoretical principles to measure biomedical variables, such as arterial blood pressure, blood flow, temperature and CO2 concentration in exhaled air and their transduction to an electrical variable, such as voltage, so they can be more easily quantified, processed and visualized as numerical values and graphics. The book includes the functioning principle, block diagram, modelling equations and basic application of different transducers, and is an ideal resource for teaching measurement and transduction of biomedical variables in undergraduate and postgraduate biomedical engineering programs.

• Will help you to understand the design and functioning of biomedical transducers through practical examples and applied information
• Covers MEMS and laser sensors
• Reviews the range of devices and techniques available plus the advantages and shortcomings for each transducer type

Chapter 1

Introduction to Biomedical Variables Transducing

This chapter presents a panorama of measurements usually made in the medical environment. Beyond characterizing the several kind of signals registered on biological systems, the transduction concept is discussed to show the reader the ways to achieve a particular signal or biomedical measurement. It also discusses the particular characteristics of a biomedical variable when compared to an electrical variable like the voltage difference measured across a resistor or the electric current flowing through a transistor. Basic concepts of measurement, useful to understand transducers operation, are presented as well.

Keywords

Medical environment; biological systems; biomedical variable; electrical variable; measurement; transducer

Contents

1.1 Introduction 1

1.2 Characteristics of Transducers 3

1.2.1 Static characteristics of transducers 4

1.2.1.1 Static sensitivity 4

1.2.1.2 Linearity 6

1.2.1.3 Input range 7

1.2.1.4 Accuracy, resolution, threshold, and precision 8

1.2.1.5 Repeatability and reproducibility 8

1.2.1.6 Hysteresis 9

1.2.1.7 Saturation 9

1.2.2 Dynamic characteristics of transducers 10

1.2.2.1 Dynamic variables 11

1.2.2.2 Linear ordinary time invariant system 13

1.2.2.3 Zero-order, first-order and second-order systems 16

1.2.2.4 Time delay 23

Recommended Readings 23

1.1 Introduction

When performing measurements on living organisms, it is necessary to understand the mechanisms involved in the generation of the signals to be measured, the effects of the devices involved in the measurement, and the best method to achieve the most possible reliable and accurate value of that variable or parameter. In this book, the functioning of the part of biomedical instrumentation required for the acquisition of biomedical variables, such as blood pressure, temperature, and blood flow, is studied: the transducers, which are responsible for transforming biomedical quantity into another physical quantity, usually electrical, more easily recorded, processed, and displayed by the instruments.

Biomedical equipment “see” the patients through transducers attached to their bodies. The biomedical variable is the quantity, condition, or physical property measured by the instrumentation system. Table 1.1 summarizes some of the biomedical variables, which are often obtained from patient body, for the purpose of either diagnosis, therapy, or monitoring.

Table 1.1

Biomedical variables measured by medical equipment

...

Biomedical variable	Description
ECG	Electrocardiogram
EEG	Electroencephalogram
HR	Heart rate (beats per minute)
CO	Cardiac output (liter per minute)
pH	H^+ concentration in blood plasma
paO2	Oxygen partial pressure in blood plasma
paCO2	Carbon dioxide partial pressure in blood plasma
SaO2	Percentage of hemoglobin cells O2 saturated
ETCO2	End tidal CO2
NIBP	Noninvasive blood pressure