Total Respiratory Compliance — FRCA Primary MCQ

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HardPhysiology - RespiratoryTotal Respiratory ComplianceFRCA Primary

A ventilated patient has lung compliance 50 mL/cmH2O and chest-wall compliance 100 mL/cmH2O. Assuming linear behaviour, what respiratory-system compliance is closest?

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Correct answer: C — 33 mL/cmH2O

The best answer is “33 mL/cmH2O”. Respiratory-system compliance is given by 1/Crs = 1/Clung + 1/Cchest wall. Therefore 1/Crs = 1/50 + 1/100 = 3/100, giving approximately 33 mL/cmH2O. Total compliance must be lower than either component; adding the two values or selecting one component ignores the series arrangement of lung and chest wall.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Respiratory mechanics in spontaneous and assisted ventilation: https://pmc.ncbi.nlm.nih.gov/articles/PMC1297597/