Final answer:
High partial pressure of CO2 causes the smooth muscles to dilate the airways, leading to an increase in air flow to correct V/Q mismatch and improve gas exchange.
Step-by-step explanation:
When there is small air flow (shunt-like), the high partial pressure of CO2 will act on smooth muscles to dilate the airway which will increase air flow. This is a compensatory mechanism of the lung to address the imbalance of ventilation and perfusion. In such a condition, the increase in the partial pressure of carbon dioxide in the alveoli causes the bronchioles to dilate in order to allow more carbon dioxide to be exhaled from the body, helping to correct the situation and restore proper gas exchange.