A decrease in carbon dioxide (CO2) concentration in the blood will lead to:

Correct answer: D. Increased tidal volume as the body compensates

• A. Decreased CO2 would NOT increase oxygen demand — oxygen demand is related to tissue metabolism.
• B. Decreased CO2 causes respiratory ALKALOSIS, not acidosis.
• C. Decreased CO2 causes alkalosis (not acidosis) and typically leads to decreased (not increased) respiratory drive.
• D. Correct. Decreased blood CO2 (hypocapnia) causes respiratory alkalosis. The body compensates by reducing the respiratory drive (decreasing rate and depth of breathing) to allow CO2 to accumulate back to normal. If CO2 is already low, the body may paradoxically need to increase tidal volume to compensate — but the most common board answer relates to respiratory rate decrease.

Note: ⚑ Contested across the series. A FALL in CO2 removes the main respiratory drive, so respiration SLOWS (apnea/hypopnea). Increased tidal volume is the response to a RISE in CO2. | The source describes 'decreased CO2 leads to increased tidal volume' — this interpretation is clinically specific to hypoxic drive situations. Standard physiology: decreased CO2 = reduced respiratory drive. Flag for study group discussion.