Which of the following would you expect to occur if ventilation to an area of the lung remained constant but perfusion to this same area decreased?

1. The PACO2 should fall.
2. The PAO2 should fall.
3. The ratio should rise.
a. 3 only
b. 1 and 2 only
c. 1 and 3 only
d. 1, 2, and 3

ANS: C
A decrease in pulmonary capillary blood flow will cause a fall in alveolar PCO2 and a rise in al-veolar PO2 assuming minute ventilation remains the same. This will result in an area of high .