A 68-year-old woman with chronic heart failure is admitted with dyspnea and fluid overload. Arterial blood gas shows respiratory alkalosis (pH 7.47, PCO₂ 32 mmHg), suggesting increased CO₂ elimination in the lungs. The physician explains that hemoglobin plays a major role in CO₂ release in the lungs via the Haldane effect. Which of the following best explains the Haldane effect?
