Bronchial responsiveness to inhaled histamine in both adults with intrinsic and extrinsic asthma: the importance of prechallenge forced expiratory volume in 1 second.

Background: Recent evidence suggests that both nonspecific bronchial hyperresponsiveness and degree of airflow obstruction may be involved in the deterioration of lung function observed in patients with bronchial asthma. To investigate to which degree the level of bronchial hyperresponsiveness reflects the size of the airways at the time of testing, we examined the relationship of nonspecific bronchial responsiveness to prechallenge pulmonary function in adult asthmatic patients.

Methods: Bronchial responsiveness to inhaled histamine was measured in 100 patients (age range, 28 to 79 years), of whom 62 had intrinsic and 38 had extrinsic asthma. Histamine responsiveness was analyzed by means of the dose-response slope (DRS).

Results: No significant difference in prechallenge forced expiratory volume expressed as a percentage of predicted value (FEV1%pred), duration of asthma, smoking habits (pack years), or bronchial responsiveness (DRS) was found between the patients with intrinsic and those with extrinsic asthma. The patients had, in general, reduced pulmonary function, because 80% had a prechallenge FEV1 less than 80%pred. The DRS displayed a significant inverse relationship to the prechallenge level of FEV1%pred in both patients with intrinsic asthma and those with extrinsic asthma (p < 0.000001); the initial FEV1%pred accounted for approximately 35% of the variance in measurements of histamine responsiveness. Excluding patients with abnormal prechallenge FEV1 (< 70%pred), or current and exsmokers (never smoked: n = 67) from the analysis did not change these findings.

Conclusions: Nonspecific bronchial responsiveness is to some extent determined by the prechallenge level of pulmonary function in both adults with intrinsic and extrinsic asthma.