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In which of the following area of the lung the ventilation perfusion ratio is maximum:

A Apex of lung
B Base of lung

C Equal in all areas
D Right posterior lobe

Ans. A Apex of lung

In an upright person, pulmonary arterial flow and alveolar ventilation of APEX OF LUNG are much less than the lower part. However, the blood flow is much less in comparison to ventilation. Here the VENTILATION/PERFUSION RATIO IS 2.5 TIMES MORE THAN THE IDEAL VALUE. (Physiological dead space).

PHYSIOLOGICAL SHUNT On the other extreme the ventilation perfusion ratio is 0.6 times the ideal value at the base of lung and represents a physiological shunt.