Question
Which point on the V/Q (ventilation/perfusion) graph indicates the effect of pulmonary embolism?
Show Answer
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Correct Answer � D
Explanation
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– Pulmonary embolism causes obstruction to perfusion while ventilation continues. This → a V/Q (ventilation/perfusion) ratio = ∞, called dead space ventilation.
– Point D on the graph illustrates this scenario, showing ventilation without perfusion.
– Results in ↑ alveolar PO₂ (close to inspired O₂ ~150 mmHg) & ↓/absent alveolar PCO₂.
– This situation signifies a lung unit ventilated but not involved in gas exchange, characteristic of a pulmonary embolism.
Incorrect Options:
– A: V/Q = 0 (true shunt). Perfusion present, ventilation absent—seen in airway obstruction, not PE.
– B: Low V/Q ratio, seen in COPD/asthma, not PE.
– C: Near-normal V/Q matching, not PE-related.
