Define venous admixture and list its causes. (50% of marks)

How is it diagnosed and how is it quantified? (50% of marks)

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College Answer

This question related to an area of basic respiratory physiology. A good answer necessitated
the precise meaning of venous admixture, being that amount of mixed venous blood which
would have to be added to ideal pulmonary end-capillary blood to explain the observed
pulmonary end-capillary to arterial PO2 difference. Diagnosis required the candidate to
mention, a demonstrated increased in the Aa-DO2, what are normal values. For quantification
mention and description of the shunt equation was required. Candidates lacked a definition
for venous admixture, were inaccurate with their description of the shunt equation and often
overlooked mentioning calculation of arterial and mixed venous blood oxygen content.
Syllabus - B1a
Reference: Nunn’s Applied Respiratory Physiology 6th Ed p122