Sound Waves and the Doppler Effect (4D) Practice Test

A hospital Doppler device displays the reflected signal from blood as a higher frequency than the transmitted ultrasound. The technologist suspects the device is malfunctioning because “reflections can’t change frequency.” Which statement is most consistent with the Doppler Effect in this biologically relevant context?

During a fetal Doppler ultrasound exam, a clinician notes that the reflected sound returning from a moving heart wall is detected at a slightly higher frequency than the transmitted ultrasound. Assuming the speed of sound in tissue is approximately constant during the brief measurement, which frequency shift would be expected if the same heart wall were moving away from the transducer instead?

Which outcome is most consistent with the Doppler Effect?