Plethysmography Boyle's Law — FRCA Primary MCQ

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ModeratePhysiology - RespiratoryPlethysmography Boyle's LawFRCA Primary

Body plethysmography measures lung volume using which gas law?

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Correct answer: E — Boyle's law (P1V1 = P2V2)

Body plethysmography uses Boyle's law. The patient sits in an airtight box and breathes against a closed shutter. Changes in mouth pressure and box volume (or pressure) allow calculation of thoracic gas volume. It measures total thoracic gas volume including trapped gas (unlike helium dilution which only measures communicating gas).

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist