A patient has a V/Q ratio of 0 in a region of the lung. This region is described as:

• A Dead space ventilation: ventilated but not perfused
• B Normal ventilation with low perfusion
• C Optimal gas exchange zone with maximum efficiency
• D Intrapulmonary shunt: perfused but not ventilated ✓

Explanation

V/Q ratio represents the relationship between alveolar ventilation (V) and perfusion (Q). V/Q = 0 means no ventilation but perfusion continues — this is an intrapulmonary shunt (e.g., complete atelectasis, lobar consolidation). Blood passes through without being oxygenated, contributing to hypoxaemia that cannot be corrected by supplemental O2 alone (shunt refractory hypoxaemia). V/Q → infinity means ventilation without perfusion (dead space, as in pulmonary embolism). Normal V/Q is approximately 0.8.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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