Doppler echocardiography
is a method for detecting the direction and velocity of moving blood
within the heart. As will be seen in this program, the technique
may be used for detection of cardiac valvular insufficiency and
stenosis as well as a large number of other abnormal flows. The
current interest in Doppler echocardiography has reached a remarkable
level in just the past few years. Doppler methods extend the use
of cardiac ultrasound into the evaluation of normal and abnormal
flow states and provide quantitative data that are essential in
the clinical decision making process concerning patients with heart
disease.
Understanding Doppler echocardiography begins with an understanding
of the Doppler principle. All readers are familiar with the Doppler
effect in every day life. For example, an observer stationed on
a highway overpass readily notices that the pitch of the sound made
from the engine of a passing automobile changes from high to low
as the car approaches and then travels into the distance. The engine
is emitting the same sound as it passes beneath, but the observer
notices a change in pitch dependent upon the speed of the auto and
its direction. Figure 1.1 demonstrates the changes in the frequency
from an approaching and departing sound source (the moving automobile)
relative to a stationary sound source.
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| Fig.1.1 |
The first description of the physical principles used in Doppler
echocardiography is attributed to Johann Christian Doppler, an Austrian
mathematician and scientist who lived in the first half of the 19th
century. Doppler's initial descriptions referred to changes in the
wavelength of light as applied to astronomical events. In 1842,
he presented a paper entitled "On the Coloured Light of Double Stars
and Some Other Heavenly Bodies" where he postulated that certain
properties of light emitted from stars depend upon the relative
motion of the observer and the wave source. He suggested that the
colored appearance of some stars was caused by their motion relative
to the earth, the blue ones moving toward earth and the red ones
moving away.
He drew an analogy of a ship moving to meet, or retreat from, incoming
waves. The ship moving out to sea would meet the waves with more
frequency than a ship moving toward the shoreline. Interestingly,
Doppler never extrapolated his postulations to sound waves.
The Doppler principle is now used in many complex technologies.
It is the fundamental principle upon which complex radar weather
systems detect the severity of approaching storms and tracks its
speed. It is also used by police to determine the speed of fast
moving automobiles.
2004
