title: Twelve- or 24-hour oxygen therapy: why a clinical trial?
mesh_terms: D002986:Clinical Trials as Topic; D003365:Costs and Cost Analysis; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000628:therapy; D010102:Oxygen Inhalation Therapy / Q000191:economics / Q000379:methods* / Q000523:psychology; D011660:Pulmonary Heart Disease / Q000628:therapy; D013997:Time Factors