Which statement best describes why hyperventilation causes respiratory alkalosis?

• A. CO2 retention
• B. Bicarbonate accumulation
• C. Excessive loss of CO2
• D. Hydrogen ion loss

Answer: (C)

Hyperventilation causes respiratory alkalosis because it blows off more carbon dioxide than the body produces. In the blood, carbon dioxide forms carbonic acid, which dissociates into hydrogen ions and bicarbonate. When you exhale too much CO2, the amount of carbonic acid drops, so fewer hydrogen ions are released. With fewer hydrogen ions, the pH rises and the blood becomes more alkaline. The essential point is that the disturbance comes from CO2 loss in the lungs, not from retaining CO2 or from changes in bicarbonate alone. Retaining CO2 would acidify the blood; accumulating bicarbonate would cause a metabolic (not respiratory) alkalosis; hydrogen ion loss can accompany alkalosis but is a consequence here of the CO2 drop, not the primary cause.