Longitudinal Determinants of Bronchial Responsiveness to Inhaled Histamine: Discussion

The present study showed an overall decline in BR to inhaled histamine from childhood to early adulthood, possibly reflecting the growth-related increase in airway caliber, and furthermore, the level of FEV1 %pred, as an index of airway caliber, and atopy, especially to HDMs, are important determinants for changes over time in degree of histamine responsiveness in both asthmatic and nonasthmatic subjects. canadian family pharmacy online

The present population study not only confirmed that prechallenge airway caliber has a significant impact on degree of BR, but showed also that the level of FEVX in childhood has significant impact on the degree of histamine responsiveness in early adulthood, even when BR in early adulthood was adjusted for prechallenge FEVp These observations may have important implications. In epidemiologic studies focused on the prevalence of BHR, as an index of the proportion of individuals with airway abnormalities, it appears reasonable to standardize measurements of BR for airway caliber, not the least when comparing prevalences of BHR between different age groups, eg, children vs adults, and different populations, primarily due to hereditary differences in body size. BHR is a major risk factor for ongoing and subsequent development of respiratory symptoms, but a large proportion of subjects with BHR, especially when measured at only one point in time, are and will most likely remain asymptomatic. Adjustment for airway caliber might therefore be of importance for the identification of those hyperresponsive subjects with the highest risk for respiratory morbidity, in that some subjects with borderline hyperresponsiveness, for instance due to small stature, may be excluded from the group of subjects regarded as having “abnormal” airway function. In keeping with this, longitudinal studies of BR should probably be adjusted for airway caliber to assess true differences and changes in the studied subjects physiologic responses, not least in studies focused on predictors and clinical implications of increased BR. The latter not least because it has been suggested that those subjects with the greatest variability over time in physiologic airway responses might be the subjects at greatest risk for later development of chronic respiratory disease.