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Haldane effect — FRCA Primary MCQ

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ModeratePhysiologyHaldane effectFRCA Primary

After ventilation is improved in a hypercapnic patient, oxygenation rises and CO2 elimination improves. Which haemoglobin-related effect helps unload CO2 in the lungs?

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Correct answer: C — Oxygenation of haemoglobin reduces CO2 carriage

The Haldane effect describes reduced CO2 carriage by haemoglobin when haemoglobin becomes oxygenated in the lungs, aiding CO2 unloading. Deoxygenated haemoglobin actually buffers hydrogen ions and carries CO2 better. Acidosis decreases oxygen affinity through the Bohr effect. This effect explains why oxygenation and ventilation are physiologically linked beyond simple gas diffusion.

Reference: West Respiratory Physiology; Ganong Review of Medical Physiology