Longitudinal Determinants of Bronchial Responsiveness to Inhaled Histamine: Conclusion

Most of the subjects who ever had asthma had at least one positive histamine test result, but 64 subjects (16% of the sample) had asymptomatic BHR at either one or both of the surveys. A substantial proportion of hyperresponsive subjects therefore may seem to have transient BHR of probably only minor clinical significance. BHR in some asymptomatic and only temporary symptomatic subjects may be due to an acute inflammatory reaction in the airways with reversible hyperresponsiveness (that is, acute hyperresponsiveness), whereas BHR in persistent symptomatic subjects may reflect the combination of reversible airway inflammation and permanent damage to the airways (sequelae from long-standing inflammation) (that is, chronic hyperresponsiveness). In the present study, atopic subjects, especially subjects atopic to HDM, were more likely to be hyperresponsive, irrespective of asthmatic status, and, what may be of greater clinical significance, they were more likely to retain their hyperresponsiveness (data not shown). The former observation is supported by a recent Norwegian study showing that indoor allergic sensitization, especially presence of HDM antibodies, rather than allergic sensitization per se was related to increased BR. Furthermore, Peat and coworkers have recently published a study showing a dose-response relationship between exposure to HDM allergen and sensitization to HDM, BHR, and recent wheeze. These observations combined with the present findings suggest that subjects at greatest risk for development of chronic hyperresponsiveness and respiratoiy symptoms are those with both hyperresponsiveness and atopy, especially in the case of atopy to HDM. These observations might have significant implications for future intervention trials focused on primary asthma prevention. mycanadianpharmacy

In summary, our data have demonstrated substantial long-term variability in BR to inhaled histamine between childhood and early adulthood. The observed variability can at least partially be attributed to changes in airway caliber, as assessed by the FEVX %pred, and atopy, especially atopy to HDM, in both asthmatics and nonasthmatics. Future primary asthma prevention trials should possibly focus on subjects with both asymptomatic increased BR and atopy, not least subjects sensitized to HDM allergen.