Practice Questions: Alveolar-Arterial Equilibration


1. Which of the following represents a "right-to-left shunt"?

A. pulmonary blood flow through a region of lung atelectasis (alveolar collapse
B. blood flow from the left ventricle to the right ventricle through a hole in the interventricular septum
C. blood flow from skin arteries to skin veins which does not pass through skin capillaries
D. blood flow from the aorta into the pulmonary artery through the ductus arteriosis
E. all of the above

2. A patient has an alveolar PA-O2 of 60 mmHg and a systemic arterial Pa-O2 of 56 mmHg. The most likely explanation for these values is

A. hypoventilation
B. diffusion limitation
C. right-to-left shunt
D. ventilation-to-perfusion nonuniformity
E. either B, C, or D above

3. All of the following are possible causes of a higher than normal AaDO2 except

A. pulmonary edema
B. mismatching of alveolar ventilation and pulmonary perfusion
C. chronic bronchitis
D. a cardiac septal defect that allows blood to flow from the right atrium to the left atrium
E. none of the above; that is, none are exceptions, since all could lead to a high AaDO2

4. Lack of oxygen equilibration due to diffusion limitation ("alveolar-capillary block") can be evaluated by measuring the

A. distribution of an inhaled gas mixture containing a radioactive marker
B. diffusing capacity of CO (carbon monoxide)
C. diffusing capacity of CO2 (carbon dioxide)
D. diffusing capacity of N2 (nitrogen) when inhaling air
E. FEV-1/VC when inhaling pure oxygen

5. Blood gas measurements in an hypoxic patient indicates that the patient’s systemic arterial oxygen content is normal but his systemic venous oxygen content is low. This is characteristic of

A. diffusion limitation
B. right-to-left shunt
C. pulmonary ventilation/perfusion nonuniformity
D. anemic hypoxia (low Hb concentration)
E. stagnant hypoxia (low cardiac output)

6. A patient has a normal oxygen partial pressure and content in pulmonary venous blood but his systemic arterial blood shows a significantly lower than normal oxygen partial pressure and content. This is diagnostic of

A. diffusion limitation
B. right-to-left shunt
C. pulmonary ventilation/perfusion nonuniformity
D. stagnant hypoxia (low cardiac output)
E. A, B. or C above