Clinical Correlates of pH Levels
Problem Set

Problem 7: Chronic compensation for collapsed lung

Correct!

Suppose a patient has a collapsed lung and cannot expel CO₂ at a normal rate. Chronic compensation would involve:

A.	increased activity of carbonic anhydrase. Carbonic anhydrase cannot help because it will not alter the equilibrium of the reaction. Because the primary defect is respiratory, compensation must involve the kidney.
B.	kidney retention of H+. This would make things worse, only adding to the acidosis caused by the buildup of CO2.
C.	kidney retention of HCO3-. Decreased renal resorption of bicarbonate will increase the blood levels of this species. This will effectively match the increased CO2 caused by the pneumothorax and maintain the ratio of bicarbonate to CO2, thus maintaining a normalized pH.
D.	kidney expulsion of HCO3-. Lowering HCO3- would pull the reaction to the right, causing H+ to go up and make the respiratory acidosis worse.
E.	switching to anaerobic metabolism. Except for skeletal muscle during strenuous exercise, humans do not have the ability to switch to anaerobic metabolism.