Biomedical Engineering Reference
In-Depth Information
before bioelectricity was well understood, much was al-
ready known about the electrical activity of nerves and
muscles. Plato (427-347
BC
) mentioned electric rays
(torpedinidae) found in the Mediterranean Sea. Aristotle
(384-322
BC
) also wrote about these marine creatures.
He mentioned that touching these rays could cause
deafness. In the eighteenth century, Aloisius Luigi
Galvani (1737-1798), a professor at the University of
Bologna, performed experiments on frog nerve-muscle
preparations. He stimulated with electrical charges the
nerve that led to the frog's femur and found that during
stimulation the femur muscle contracted. In one of his
experiments, he demonstrated the cell membrane po-
tential, the polarizing potential of cells in rest. For his
achievements, Galvani was named the father of electro-
physiology. From that time onward, an increasing num-
ber of scientists started to study the action potentials
generated in living organisms.
These electrical signals are primarily the cell mem-
brane potentials, action potentials of heart and muscles,
and the action potentials of the brain. Studying action
potentials requires sensitive equipment and thorough
knowledge in measuring technique. Depending on the
source of their origin, the amplitude and frequency do-
mains of these signals are significantly different. From the
point of view of measurement technique, the heart
action potentials, the ECG waves, can be considered as
the easiest to measure. Voltage potentials of these signals
are in the millivolt (mV) range, their useful frequency
domain is 0.1-100 Hz. Brain action potentials are on the
order of microvolt (
m
V) and the frequency domain is
0.1-10,000 Hz. Evoked potentials are even lower with
a frequency range of approximately 10-10,000 Hz.
Around 1856, electrocardiographic signals of a frog's
heart were measured for the first time. In 1903, Willem
Einthoven (1860-1927) introduced his string-galvanometer
and recorded ECG signals. Hans Berger started to study
the electrical signals of the brain by electroencephalo-
graph measurements in 1924. However, his first good-
quality electroencephalogramwas not ready until 1929. In
1943, Weddel succeeded in registering muscle action
potentials with an electron beam oscilloscope. But the
first commercial electromyograph did not enter the
market until around 1960.
definition of the blood pressure. There was no simple,
bloodless way of measuring the instantaneous value of
blood pressure until the introduction of the systolic-
diastolic measurement. Still accepted in daily routine,
this detection technique is based on the Korotkoff
sounds. Digital technology made small blood pressure
meters possible with a concomitant surge in their use in
the home as well as the hospital.
Anesthesia and the relief of pain
Horace Wells, an American dentist, performed the first
painless dental operation in 1844. He used nitrous oxide,
known also as ''laughing gas.'' Therefore, he is considered
the inventor of narcosis. Anesthesia, resulting in a pain-
less operation on patients, was an immense development
in surgery. It gave enormous push to the development of
surgical instruments and apparatuses used in operating
rooms and beyond.
It is also interesting to draw attention to a different
medical advance, acupuncture anesthesia. Western
medicine is learning more and more about this practice of
traditional Chinese medicine. While its mechanism is
still not completely known, it does prove useful in certain
areas of anesthesia.
X-ray and nuclear medicine
The desire of physicians for centuries to be able to look
into the human body was finally realized in 1895 with
Conrad Roentgen's discovery of X-rays. In the following
century, the application of X-rays to diagnosis and ther-
apy gave strong momentum to the advance of medicine.
In hospitals and clinics, the medical applications of
X-rays became a separate professional field. With the
development of the engineering sciences and, later, infor-
matics and computer techniques, application of the
images generated by X-ray increased. Of course, this
went along with the construction of more sophisticated
equipment. Therefore, the demand for experts who are
familiar with the operation and maintenance of these
devices increased.
Blood pressure
Imaging and image processing
Aware of the importance of blood circulation, studying
blood pressure was a natural requirement. In one of the
first experiments, a tube was inserted into the neck
artery of a horse, and the pressure variation generated
by the heart was measured. For human application, the
bloodless measurement of blood pressure was a neces-
sity. However, one had to give a measurable, practical
X-ray images, with their increasingly fine details, pro-
vided increasingly more information. Image intensifiers
and video monitors rendered possible the manifold ap-
plicability of X-ray equipment. High-power and fine-
resolution X-ray tubes expanded further the application
possibilities. X-ray equipment, such as the tomograph,
angiograph, angio-cardiograph, and the urograph, was
