Question
Which point on the V/Q (ventilation/perfusion) graph indicates the effect of pulmonary embolism?
| A. |
A |
| B. |
B |
| C. |
C |
| D. |
D |
|
Correct Answer � D Explanation |
 |
– 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.