A Comparison of Bronchial Hyper-Responsiveness and Diurnal Variation in Peak Expiratory Flow Rate in Children With Asthma

Bronchial hyper-responsiveness and diurnal variability in airways function are thought to be important features of asthma. We have investigated the relationship between bronchial hyper-responsiveness measured by non-specific challenge tests and diurnal variability measured by cosinor analysis in children of varying severities of asthma. Forty asthmatic children and ten normal control children were both tested with a histamine challenge test and standardised treadmill exercise before and after a week long period of home peak flow rate recording. A further 35 normal children (age range 7-14 yrs) underwent only the week long measurement of peak flow at home. For both histamine challenge test and exercise tests there was evidence of a significant difference in reactivity between normals and asthmatic children on inhaled prophylactic medication. However, the range in the asthmatic subjects was wide and overlapped with the normal subjects. The mean diurnal variation in PEF measured as the peak to trough amplitude by cosinor analysis was 13.2% (SD 10.4%; range 0.9% to 45.2%) of the mean PEF in the asthmatic children compared to 6.8% (3.6%; 0.7% - 19.5%) less than has been reported in adult asthmatics. The correlation between the two measurements of bronchial reactivity and the measurements of diurnal variability (Pc2o, percent fall in peak flow after exercise and the amplitude of peak flow variability derived from cosinor analysis) was weak (Spearman's Rank correlation: PC20 vs. the cosinor derived peak to trough amplitude r = -0.483 (P<0.02); per cent fall in peak flow after exercise vs. cosinor peak to trough amplitude r = 0.481 (P