The clinical application of Doppler echocardiography is based on the Doppler shift principle by which sound waves increase or decrease their frequency as the object that produces or reflects them approximates or moves away from a given point. A transducer that acts as a transmitter and receiver is placed so that ultrasound waves are sent parallel to cardiac flow, the red cells reflect these waves and alter the frequency of the ultrasound wave proportionally to the velocity in which they are moving.
By knowing the velocity of ultrasound through cardiac tissue, the frequency of the transmitted and received sound waves and the angle of incidence, it is possible to calculate the velocity of the blood flow. Volume measurements can be calculated by measuring with echocardiography, the diameter or area of a given vessel or chamber and multiplying this by the Doppler derived velocity through them.
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