In 1957 Shigeo Satomura of the Institute of Scientific and Industrial Research, Osaka University, demonstrated the application of the Doppler shift in the frequency of ultrasound backscattered by moving cardiac structures.
This was the beginning of doppler ultrasound for evaluating blood flow and pressure by bouncing high-frequency sound waves (ultrasound) off red blood cells.
S. Satomura, "Ultrasonic Doppler Method for the Inspection of Cardiac Functions," J. Accoust. Soc. Amer. 29 (1957) 1181-85.