Increased bronchial responsiveness as assessed with a bronchoconstrictor agent clearly is central to the criteria for asthma specified in the ATS definition of this disorder. It is generally recognized that airway responsiveness is log normally distributed (Fig 1 and 2). What is less frequently appreciated is that airway responsiveness and level of lung function are correlated. Studies in which level of lung function is used as a criterion for challenge testing or patient selection result in a truncation of the more responsive end of the distribution of responsiveness. For this reason, and others that will be enumerated, the number of subjects in population studies who respond to a bronchoconstrictor agonist (methacholine or histamine) at concentrations less than 2 mg/ml is small. An additional issue that changes the sensitivity and specificity of bronchial challenge testing are the criteria used to define a positive test. buy antibiotics online
Recently, Rijcken et al examined the effect of these different factors on the distribution of bronchial responsiveness to histamine in a random population sample. They studied 339 subjects in Vlaardingen, The Netherlands, using the DeVries histamine protocol, which involves doubling concentrations of histamine biphosphate inhaled during 30 s of tidal breathing. Concentrations of 1, 2, 4, 8, 16, or 32 mg/ml of histamine were used. A variety of different indices of bronchial responsiveness were computed, including PC10, PC*, PDio, and PDW and continuous indices using the slope of all points or the first and the last point.
Figure 1. (Modified from Rijcken et al. Am Rev Respir Dis 1989; 140:615-23)
Figure 2. (Modified from Rijcken et al. Am Rev Respir Dis 1989; 140:615-23)
Tags: Airway responsiveness, Asthma, bronchial responsiveness, lung function, smoking