Final answer:
The contribution of the chest wall to ventilation decreases when transitioning from standing to supine position due to the diaphragm's impaired ability to move, leading to less efficient expansion of the chest cavity and ventilation.
Step-by-step explanation:
The contribution of the chest wall to ventilation changes when a person transitions from standing to supine position. In the supine position, the weight of the abdominal contents presses against the diaphragm, which can decrease the efficiency of the chest wall muscles, leading to a reduction in the contribution of the chest wall to ventilation. Therefore, the answer is B. Decreases. In this context, the decrease is due to the diaphragm's impaired ability to move downward as efficiently as it does when standing, reducing the chest cavity's volume expansion and leading to less efficient ventilation.