A 34-year-old woman presents in the emergency department with tachypnea and shortness of breath of acute onset. The history reveals that she has been taking oral contraceptives for 9 years. A lung scan demonstrates a perfusion defect in the left lower lobe. Which of the following occurs if the blood flow to alveolar units is totally obstructed by a pulmonary thromboembolism?
a. The ratio of the alveolus equals zero.
b. The PO₂ of the alveolus will be equal to that in the inspired air.
c. The PO₂ of the alveolus will be equal to the mixed venous PO₂.
d. There will be an increase in shunting (venous admixture) in the lung.
e. There will be a decrease in alveolar dead space.