DLCO testing requires specific demand valves and high-quality bacterial filters with low resistance, typically less than 1.5 cmH2O/L/s. You also need specialised gas mixtures containing exactly 0.3% Carbon Monoxide and 0.3% Methane or Helium as a tracer gas. Using the wrong filter can increase dead space by 50ml or more, which significantly alters the calculated diffusion capacity and leads to inaccurate clinical interpretations for your patients.