Full text: Available Index: LILACS (Americas) Main subject: Research Support as Topic / Respiratory Tract Diseases / Multicenter Studies as Topic / Biomedical Research Type of study: Controlled clinical trial Language: Spanish Journal: Rev. chil. enferm. respir Journal subject: Pulmonary Disease (Specialty) Year: 2004 Type: Article Affiliation country: Chile Institution/Affiliation country: Comisión Científica Sociedad Chilena de Enfermedades Respiratorias/CL