The Doppler effect is used in hospitals for measure the direction and speed of blood flow in arteries and veins. This is used in echo - cardiograms and medical ultrasonography and it is an effective tool in diagnosis of vascular problems.
The Doppler effect is an observed change in frequency of a wave ( for example sound or light ,) as the source and the observer move toward or away from each other.
This phenomenon was named after the Austrian doctor, Christian Doppler, in 1842.