Effects of intravenous histamine on pulmonary mechanics in nonasthmatic and asthmatic subjects

Histamine is thought to be one of the primary mediators of the airways response in allergic asthma. We have studied in detail in nonasthmatic and asthmatic volunteers the effects of its intravenous infusion on pulmonary mechanics. The doses used were similar in both groups and limited by vascular rather than pulmonary effects. Measurements were made of lung resistance, the subdivisions of lung volume, maximal flow, density dependence, lung elastic recoil and dynamic compliance. The only mean group changes were a decrease in dynamic compliance and increase in frequency dependence of compliance in the nonasthmatics. Although in nonasthmatic individuals, statistically significant changes occasionally occurred in some parameters, the response was variable on repeated studies and sufficiently small to be of questionable physiological significance. Some of the asthmatics developed larger changes, but these only occurred in those individuals whose preinfusion pulmonary function was abnormal. Our results suggest the possibility that altered prechallenge pulmonary function rather than an unusual sensitivity to histamine may determine the greater responses observed in asthmatics.