What is the significance of (b) Dalton's law, to the process of respiration?

You and a friend are having a contest to see who can hold his or her breath the longest. Your friend hyperventilates before holding his breath, and subsequently wins the contest. Why did hyperventilation give him an advantage?

Fill in the blanks: When the alveolar Po₂ decreases, the pulmonary arterioles_____. When the arteriolar Pco₂ increases, the bronchioles_______.