<prompt> If the alveolar oxygenation is halved, the PACO2 will beDoubled instantlyDoubled in a few minutesHalved instantlyHalved in a few minutes  <response>: Ans: d Halved in a few minutes Ref: Ganong 22nd ed p.675, 21st edp.680When the alveolar oxygenation is halved, the resulting hypoxia will increase the respiratory rate ventilation.This will lead to washing out of CO,. Since the effect on PACO, is due to increase in the respiratory rate, it will not occur immediately.There will be increase in respiratory rate only if the PO, drops from 100 to below 60 mm of Hg. 