Practice Questions: Answers -- Blood Gas Transport


1. E. Cyanosis is due to a blood concentration of reduced Hb of greater than 6-8 gm Hb/dl blood.

2. D. As blood passes through systemic capillaries, the CO2 and H+ added to the blood by the metabolizing tissue decrease the affinity of Hb for O2, thus shifting the Hb-O2 dissociation curve to the right.

3. E. Pa-O2 would be normal as it depends only upon PA-O2 and alveolar-arterial equilibration and not on the type or amount of hemoglobin in blood. However, fetal Hb would have a higher O2 saturation because of its greater affinity for oxygen.

4. C. Pulmonary arterial blood has the same composition as systemic venous blood.

5. A. Carbonic anhydrase catalyzes the reaction CO2 + H2O <=> H2CO3.

6. C. Fully saturated Hb in a normal person contains 20 ml O2 / dl blood. When breathing pure O2 another 2 ml O2 / dl blood is added as dissolved oxygen (0.3 ml O2 / dl blood / 100 mmHg PO2), for a total of 22 ml O2 / dl blood. Note that choice "E" is not correct as it requires a number of hours of breathing pure O2 to induce lung oxygen toxicity.

7. B. For  a person at rest, normal hemoglobin oxygen saturation is 75%, so the value of 25% is much below normal.

8. A. Normal hemoglobin concentration in young adult males 1s 16 gm/dl and for young adult females is 14 gm/dl;  the "physiological" value is 15 gm/dl.  Thus, a value of 20 gm/dl is significantly above normal; this person would be classified as polycythemic.