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← Theoretical A

Q49 — Esophageal Doppler Monitoring

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Cardiovascular Physiology

Esophageal Doppler Monitoring (EDM) is a minimally invasive method to measure blood flow in the aorta and assess cardiac output. A Doppler probe is inserted into the esophagus near the aorta. The principle behind the measurement is the detection of changes in frequency (Doppler shift) of ultrasound waves reflected by moving red blood cells. Using the Doppler effect, the probe calculates blood flow velocity from the equation Δf = 2vf₀cos(θ)/cₛ, where cos(θ) = √2/2, cₛ = 1540 m/s, and f₀ = 4 MHz.

The resulting waveform provides important data on heart function, such as stroke volume and cardiac output, which helps guide clinical decisions in real-time.

Diagram of Doppler probe placement in the esophagus near the aorta, and a velocity-time waveform showing a peak systolic velocity of 100 cm/s over a repeating cardiac cycle. Figure 1. A Placement of the Doppler probe in the esophagus near the aorta to measure blood flow velocity (red arrow). B Doppler waveform showing linear blood velocity (cm/s) over time (s), with a peak systolic velocity of 100 cm/s. The area under the curve shows the distance traveled by blood.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Tachycardia decreases the intervals between waveforms on the velocity-time graph.
B. Without any compensation from the heart, high arterial resistance increases peak velocity.
C. If the largest frequency shift observed for a patient was 4.4 kHz, their peak velocity is around 120 cm/s.
D. According to Figure 1B and 1A, a person's heart ejects 4.9 L of blood per minute.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)