Comparison of in vivo and in vitro responses to histamine in human airways.

The study was designed to compare in vivo responses to histamine in 14 patients prior to thoracotomy with in vitro responses to histamine of both parenchymal and bronchial tissue. Although a wide range of responsiveness occurred in vivo, as measured by the histamine inhalation test, the variation in the in vitro dose-response curves was negligible. There was no correlation between the dose of histamine that resulted in a 20% reduction in forced expiratory volume in one second and the concentration of histamine producing 50% of the maximal response in vitro. These findings raise the possibility that airway hyperresponsiveness may not result from an intrinsic abnormality of airway smooth muscle.