Why is the change in sound made by a passing train's whistle similar to the reason the pitch rises quickly in systole and drops quickly in early diastole when measuring arterial sounds?

Question

Quizplus · Accepted Answer

The Doppler Effect is the change in the frequency of echo signals that occurs whenever there is a change in the distance between the sources of a sound and the receiving object.The probe,or transducer,is aimed toward the blood vessel at an angle of 45 to 60 degrees.This directs an ultrasound beam that is reflected to the probe by moving red blood cells (RBCs).The velocity of the flow of cells is converted into an audible signal heard through a speaker.The signal is described as a swishing sound.The sound is called a signal,not a pulse.

Why Is the Change in Sound Made by a Passing