Final answer:
The PCO2 and PO2 membranes facilitate gas exchange and should be changed regularly to maintain efficiency and reduce health risks associated with accumulations and plasticizer migration.
Step-by-step explanation:
The PCO2 (Teflon) and the PO2 (polypropylene) membranes should be changed often because these membranes are critical in the process of gas exchange, removing oxygen from and adding carbon dioxide to alveolar air. Over time, the membranes can accumulate deposits or sustain damage, which can impede their efficiency and effectiveness in gas exchange. Additionally, the presence of plasticizers in materials like polyvinyl chloride can lead to health concerns as they may migrate into the environment. Frequent replacement ensures optimal functionality and minimizes potential health hazards.