This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 1, Subject name: Physiology
A 49-year-old man has a pulmonary embolism that completely blocks blood flow to his left lung. As a result, which of the following will occur? 
Select and explain. 
A. Ventilation/perfusion (V/Q) ratio in the left lung will be zero, B. Systemic aerial PO2 will be elevated, C. V/Q ratio in the left lung will be lower than in the right lung, D. Alveolar PO2 in the left lung will be approximately equal to the PO2 in inspired air
D: Alveolar PO2 in the left lung will be approximately equal to the PO2 in inspired air
Answer: D: Alveolar PO2 in the left lung will be approximately equal to the PO2 in inspired air 
Explanation: Alveolar PO2 in the left lung will equal the PO2 in inspired air-No blood flow to the left lung- No gas exchange between the alveolar air and the pulmonary capillary blood-Consequently, O2 is not added to the capillary blood. The ventilation/perfusion (V/Q) ratio in the left lung will be infinite (not zero or lower than that in the normal right lung) because Q (the denominator) is zero. Systemic aerial PO2 will, of course, be decreased because the left lung has no gas exchange. Alveolar PO2 in the right lung is unaffected.