Wheatstone Bridge Application — FRCA Primary MCQ

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HardPhysics & Clinical MeasurementWheatstone Bridge ApplicationFRCA Primary

An arterial transducer is correctly zeroed but is positioned 20 cm below the right atrial reference level. Approximately how will the displayed pressure differ from the pressure at heart level?

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Correct answer: B — It will read 15 mmHg higher

The best answer is “It will read 15 mmHg higher”. A transducer below the reference level experiences an additional hydrostatic column and reads high. Twenty centimetres of water corresponds to about 14.7 mmHg because 1 mmHg is approximately 1.36 cmH2O. Zeroing removes atmospheric offset but does not correct an error in vertical levelling.

Reference: Saugel et al., How to measure blood pressure using an arterial catheter: a systematic 5-step approach: https://pmc.ncbi.nlm.nih.gov/articles/PMC7183114/