Measurement of responsiveness to inhaled histamine using FEV1: Comparison of PC20 and threshold

Abstract

Two methods of interpreting histamine inhalation dose-response curves were compared in 27 normal and 41 asthmatic subjects. The histamine provocation concentration producing a 20% fall (PC20) in forced expiratory volume in one second (FEV1) was calculated on he basis of the lowest FEV, after inhalation of saline and the lowest value after inhalation of histamine. The histamine threshold was determined as the first histamine concentration causing he FEV1 to fall more than 2 SD below the mean of five pre-histamine (three pre-saline, two cost-saline) FEV1 determinations. The PC20 was on average one doubling concentration larger than the threshold. The PC20 provided better discrimination between asthmatic and normal subjects than did the histamine threshold and was significantly more reproducible. These findings suggest that the histamine threshold may prove useful for studies on populations, particularly hose with a low degree of responsiveness to histamine, because of the possibility of measuring a response at a lower histamine concentration. On the other hand, the PC20 is preferable for clinical se in individuals because of its better discriminating power and better reproducibility.