Reevaluation of the relationship between within-day bronchial variability and bronchial responsiveness in asthmatic children.

Earlier studies demonstrated a correlation between diurnal bronchial variability and bronchial responsiveness (BR) in asthmatic patients. However, since the most severe bronchial obstruction tends to occur from midnight to early morning, diurnal bronchial variability might underestimate within-day bronchial variability. This study was undertaken to reevaluate the correlation after assessing more precisely the within-day variability of bronchial caliber in 43 children with episodic asthma (23 boys, 20 girls), aged 8-12 years. Seven FEV1 measurements were made every 4 h between 10:00 and 10:00 for 2 consecutive days. The coefficient of variation (CV) of the last six FEV1 was defined as the amplitude. Just after measurement of FEV1 at 10:00 on day 2, measurements of BR to house-dust allergen, histamine, and 7-min free running were made in 14, 14, and 15 patients, respectively. The BR was expressed as the percent change in FEV1 from the baseline value in house-dust inhalation and running challenges, and as the provocative concentration causing a 20% fall in FEV1 (PC20), transformed into a logarithmic scale, in histamine challenge. There were significant correlations between CV [mean (SD), 8.1 (5.3)%] and BR to house-dust [mean (SD), -19.0 (11.8)%] (r = -0.663, p < 0.01), and between CV [mean (SD), 7.4 (5.5)%] and histamine PC20 (geometric mean, 0.38 mg/ml) (r = -0.661, p = 0.01). There was a marginally significant correlation between CV [mean (SD), 6.4 (3.7)%] and BR to running [mean (SD), 28.5 (16.6)%] (r = -0.496, 0.05 < p < 0.1). These results confirmed the reliability of earlier studies that suggested that the bronchial variability may be one of clinical indices of BR to various stimuli in asthmatic patients.