Compare the effect on arterial blood carbon dioxide and oxygen levels of ventilation / perfusion inequalities.

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College Answer

The main points expected for a pass were:
· Range, regional pulmonary differences and gradients of V/Q ratios.
· Definitions of shunt (V/Q = 0) and dead space (V/Q = ).
· Explanation of why and how V/Q mismatch lowers arterial PaO2 (majority of pulmonary
blood flow being from basal regions, shape of haemoglobin disassociation curve).
· Explanation of why and how V/Q mismatch lowers arterial PaCO2 (majority of
pulmonary blood flow being from basal regions, predominately linear shape of CO2
disassociation curve within the physiological range of PaCO2 values).
Again, the use of illustrations would be very useful aids as part of a good answer.
Candidates often failed to frame their answer to the question that was asked and deviated to
areas not directly sought after by the question. This resulted in wasted time and opportunities
for marks.
Syllabus B1g
Reference Nunn 4th edition page 165-187