You should prioritise supplies with ISO 13485 certification and a CE mark to ensure they meet European medical device regulations. These certifications prove the product has passed rigorous testing for 99.99% bacterial and viral filtration. We recommend checking for 2019 ATS/ERS compliance to guarantee that the filter resistance stays below 1.5 cmH2O/L/s, which is vital for accurate lung volume measurements and patient comfort during the testing process.