[Agreement between tracheal auscultation and pulmonary function in methacholine bronchial inhalation challenge in asthmatic children]. / Medida de la respuesta bronquial a la metacolina en niños asmáticos mediante la auscultación traqueal.

BACKGROUND: PC wheezing (PCw) is defined as the concentration of methacholine at which wheeze is detected on auscultation of the trachea. PCw has been suggested as a measure of bronchial hyperresponsiveness in methacholine challenge testing (MCT). OBJECTIVE: The aim of this study was to determine the agreement between the concentration of methacholine that produces a 20 % decrease in forced expiratory volume in 1 second (FEV1) (PC20) and PCw in MCT in asthmatic children. PATIENTS AND METHODS: Eighteen asthmatic children with a mean age of 11.5 years (range: 6-16 years) were studied. Fifteen of the children were under treatment with inhaled glucocorticoids. MCT was performed according to the guidelines of the American Thoracic Society (1999) using a Hudson nebulizer calibrated to obtain a mean output of 0.14 ml/min. After each nebulization, two independent observers registered FEV1 and tracheal auscultation. FEV1 was determined by forced spirometry 30 and 90 seconds after the end of nebulization and PC20 was registered (exponential model). Respiratory rate and transcutaneous oxygen saturation were continuously monitored. Tracheal auscultation was performed at 0, 60 and 120 seconds after the end of nebulization. The end point was defined as the appearance of wheezing over the trachea. The values of PC20 and PCw, as well as the concentration of methacholine corresponding to a decrease in FEV1 equal to or higher than 20 %, were compared using Student's matched pairs-test and Wilcoxon's test. The degree of agreement between variables was compared by using Bland-Altman's test. RESULTS: MCT was positive in 17 of 18 patients. No differences were found between PC20 and PCw (p 0.15). Both variables showed agreement in 12 of 17. A clear association was found between both measures (log PCw, log PC20): R: 0.92; p < 0.001. The mean decrease in FEV1 on reaching PCw was 24.8 % (range: 10-41). No adverse effects were observed. CONCLUSION: The agreement between PC20 and PCw in MCT in asthmatic children is excellent. PCw could be helpful in determining bronchial hyperresponsiveness in young asthmatic children in whom spirometry is not feasible.