Biomedical Engineering Reference
In-Depth Information
10.1 INTRODUCTION
Diagnostic bioinstrumentation is used routinely in clinical medicine and biological research
for measuring a wide range of physiological variables. Generally, the measurement is derived
from sensors or transducers and further processed by the instrument to provide valuable
diagnostic information. Biomedical sensors or transducers are the main building blocks of
diagnostic medical instrumentation found in many physician offices, clinical laboratories,
and hospitals. They are routinely used in vivo to perform continuous invasive and noninvasive
monitoring of critical physiological variables, as well as in vitro to help clinicians in various
diagnostic procedures. Similar devices are also used in nonmedical applications such as in
environmental monitoring, agriculture, bioprocessing, food processing, and the petrochemical
and pharmacological industries.
Increasing pressures to lower health care costs, optimize efficiency, and provide better
care in less expensive settings without compromising patient care are shaping the future
of clinical medicine. As part of this ongoing trend, clinical testing is rapidly being trans-
formed by the introduction of new tests that will revolutionize the way physicians will
diagnose and treat diseases in the future. Among these changes, patient self-testing and
physician office screening are the two most rapidly expanding areas. This trend is driven
by the desire of patients and physicians alike to have the ability to perform some types of
instantaneous diagnosis right next to the patient and to move the testing apparatus from
an outside central clinical laboratory closer to the point of care.
Generally, medical diagnostic instruments derive their information from sensors, elec-
trodes, or transducers. Medical instrumentation relies on analog electrical signals for an
input. These signals can be acquired directly by biopotential electrodes—for example, in
monitoring the electrical signals generated by the heart, muscles or brain, or indirectly by
transducers that convert a nonelectrical physical variable such as pressure, flow, or tempera-
ture, or biochemical variables, such as partial pressures of gases or ionic concentrations, to an
electrical signal. Since the process of measuring a biological variable is commonly referred to
as sensing, electrodes and transducers are often grouped together and are termed
.
Biomedical sensors play an important role in a wide range of diagnostic medical applica-
tions. Depending on the specific needs, some sensors are used primarily in clinical labora-
tories to measure in vitro physiological quantities such as electrolytes, enzymes, and other
biochemical metabolites in blood. Other biomedical sensors for measuring pressure, flow,
and the concentrations of gases, such as oxygen and carbon dioxide, are used in vivo to fol-
low continuously (monitor) the condition of a patient. For real-time continuous in vivo sens-
ing to be worthwhile, the target analytes must vary rapidly and, most often, unpredictably.
sensors
10.1.1 Sensor Classifications
Biomedical sensors are usually classified according to the quantity to be measured and are
typically categorized as physical, electrical, or chemical, depending on their specific applica-
tions. Biosensors, which can be considered a special subclassification of biomedical sensors,
are a group of sensors that have two distinct components: a biological recognition element,
such as a purified enzyme, antibody, or receptor, that functions as a mediator and provides
the selectivity that is needed to sense the chemical component (usually referred to as the
