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JOSEPH A. KISSLO, MD: Duke Center for Echo
DAVID B. ADAMS, RDCS: Duke Center for Echo
 
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Introduction

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.

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.

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