An area of the lung has no blood flow but is normally ventilated. ...

[vHAUNG6011]

An area of the lung has no blood flow but is normally ventilated. Which of the following state-ments are true about this area?
 
  1. The alveolar gas is like air (PO2 = 150; PCO2 = 0).
  2. The area represents alveolar dead space.
  3. The / is elevated.
  a. 1 and 2 only
  b. 1 and 3 only
  c. 2 and 3 only
  d. 1, 2, and 3

Question 2

Which of the following would you expect to occur if perfusion to an area of the lung remained constant, but VA to this same area decreased?
 
  a. The PACO2 should fall.
  b. The HCO3 will fall.
  c. The PAO2 should fall.
  d. The ventilation/perfusion ratio () should rise.

[Perkypinki]

Answer to Question 1

ANS: D
At the extreme right of the graph, perfusion is 0 (/ = 0). Areas with ventilation but no blood flow represent alveolar dead space, as defined in Chapter 10. The makeup of gases in these areas is similar to that of inspired air (PO2 = 150 mm Hg; PCO2 = 0 mm Hg).

Answer to Question 2

ANS: C
A low / indicates that ventilation is less than normal, perfusion is greater than normal, or both. In areas with a low /, the alveolar PO2 is lower and the PCO2 is higher than normal.