A ventilation/perfusion (V/Q) ratio mismatch occurs when:

• A. A disruption in blood flow inhibits the exchange of oxygen and carbon dioxide in the lungs, even though the alveoli are filled with fresh oxygen.
• B. Ventilation is compromised, resulting in CO2 buildup in the bloodstream, alveoli, and the tissues and cells of the body.
• C. Ventilation is inadequate due to a traumatic injury or medical condition, which results in an impairment in pulmonary gas exchange.
• D. A traumatic injury or medical condition impairs the body's ability to effectively bring oxygen into the lungs and remove carbon dioxide from the body.

Answer: (A)

V/Q mismatch arises when ventilation and perfusion in the lungs are not matched. In this scenario, the alveoli are ventilated and filled with fresh oxygen, but blood flow through the surrounding pulmonary capillaries is disrupted. Without adequate perfusion, oxygen cannot diffuse into the blood and carbon dioxide cannot be efficiently removed from the blood, so gas exchange is impaired even though the air reaching the alveoli is oxygen-rich. This specific situation—normal ventilation with reduced perfusion—best illustrates a V/Q mismatch.