Functional residual capacity (FRC) is the only static lung volume that can be measured routinely in infants. It is important for interpreting volume-dependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equipment, the plethysmographic method for measuring FRC is very simple to apply and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further advantage that with suitable adaptations to the equipment, simultaneous measurements of airway resistance can also be obtained.The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for plethysmographic measurements in infants. Implementation of these recommendations should help to ensure that such measurements are as accurate as possible and that meaningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects including terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus can be reached.
Background -Bronchial hyperreactivity to methacholine is present in children with asthma and other types of paediatric chronic obstructive pulmonary disease (COPD), while hyperreactivity to exercise is more specific for asthma. Adenosine 5'-monophosphate (AMP) is a potent bronchoconstrictor and, like exercise, may provoke asthma by activating mast cells. This study investigated the suitability of AMP as a specific challenge for asthma in children. Methods -Bronchial provocation challenges with methacholine and AMP were performed in a double blind fashion using tidal breathing in 51 children with asthma, 21 with paediatric COPD ofvarious types, and in 19 control children. Each subject also underwent a standardised exercise challenge after inhalation challenges were completed. Sensitivity and specificity curves were constructed and the intersection point of sensitivity and specificity for each type ofchallenge was determined. Results -When the asthmatic patients were compared with the children with COPD, the intersection points for AMP, exercise and methacholine were 90%, 85%, and 50%, respectively. When compared with the controls the same intersection points were 98%, 84%, and 92%, and when children with paediatric COPD were compared with controls they were 55%, 50%, and 82%. Conclusions -Methacholine distinguishes both asthma and paediatric COPD from controls with a sensitivity of 82-92%, but does not distinguish between asthma and paediatric COPD; exercise and AMP distinguish asthma from controls with a sensitivity and specificity of 84-98% but they also distinguish asthma from paediatric COPD with a sensitivity and specificity of 85-90%. AMP inhalation is a practical aid for diagnosing asthma and distinguishing it from COPD in children of all ages. (Thorax 1995;50:51 1-516)
An analysis was undertaken to determine the optimal cut-off separating an asthmatic from a normal response to a bronchial provocation challenge by exercise and the inhalation of methacholine or histamine in children and young adults. Data were extracted, after appropriate correction, from published studies available in Medline of large random populations that complied with preset criteria of suitability for analysis, and the distribution of bronchial reactivity in the healthy population for exercise and inhalation challenges were derived. Studies on the response to exercise and methacholine inhalation in 232 young asthmatics of varying severity were carried out by the authors and the distribution of bronchial reactivity of a young asthmatic population obtained. Comparisons of the sensitivity and specificity of the challenges were aided by the construction of receiver operating characteristic curves. The optimal cut-off point of the fall in forced expiratory volume in one second (FEV1) after exercise was 13%, with a sensitivity (power) of 63% and specificity of 94%. For inhalation challenges, the optimal cut-off point for the dose of methacholine or histamine causing a 20% fall in FEV1 was 6.6 micromol, with a sensitivity of 92% and a specificity of 89%. The cut-off values were not materially affected by the severity of the asthma and provide objective data with which to evaluate the results of bronchial provocation challenges in children and young adults.
Exhaled nitric oxide (eNO) has been used to diagnose asthma in adults and children using either the slow vital capacity method (SVCm) or, in younger children, the tidal breathing method (TBm). Adenosine 5'-monophosphate (AMP) challenge also has been found to be a sensitive and specific test for the diagnosis of asthma. In the present study, we used the AMP provocation concentration that caused wheezing (PCW) to confirm the diagnosis of asthma (PCW < or = 200 mg/mL). We studied 36 children (2-7 years) with mild intermittent asthma, 13 children (3-7 years) with moderate persistent asthma treated with inhaled steroids, 20 nonasthmatic children (2-7 years) with chronic cough and recurrent pneumonia, and 15 healthy children (4-6 years). Expired gas was collected in collection bags by the TBm, and eNO was measured. We evaluated the efficacy of eNO values in diagnosing asthma. The mean eNO level of the mild intermittent asthmatic children (5.6 +/- 0.4 ppb) not receiving inhaled corticosteroids was significantly higher (ANOVA P < 0.0001) than that of the moderate persistent asthmatics who were treated with inhaled steroids, the nonasthmatic children with chronic cough, and the group of healthy children (3.7 +/- 0.6 ppb, P < 0.05; 3.2 +/- 0.3 ppb, P < 0.001; 2.2 +/- 0.2 ppb, P < 0.001, respectively). The points of intersection for sensitivity and specificity curves of eNO to differentiate mild intermittent asthmatics from nonasthmatic children with chronic cough and from healthy children were 77% and 88% for eNO values of 3.8 ppb and 2.9 ppb, respectively. We conclude that eNO collected by the TBm can differentiate steroid-naive young children with intermittent asthma from healthy children, from nonasthmatic children with chronic cough, and from asthmatic children treated with inhaled steroids.
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