title: A simple measurement of phase IV ("closing volume") using a critical orifice helium analyzer.
mesh_terms: D005069:Evaluation Studies as Topic; D006371:Helium; D006801:Humans; D008722:Methods; D011868:Radioisotopes; D012129:Respiratory Function Tests; D014978:Xenon
chemical_list: D011868:Radioisotopes; D006371:Helium; D014978:Xenon