title: Simultaneous comparison of helium and nitrogen expiratory "closing volumes".
mesh_terms: D000328:Adult; D000368:Aged; D006371:Helium; D006801:Humans; D008722:Methods; D008875:Middle Aged; D009584:Nitrogen; D012119:Respiration; D012129:Respiratory Function Tests; D014797:Vital Capacity
chemical_list: D006371:Helium; D009584:Nitrogen