Respiratory response to histamine- and methylcholine-induced bronchospasm in nonsmokers and asymptomatic smokers

The respiratory response to bronchospasms of the same magnitude induced by inhalation of histamine or methylcholine was measured non-invasively, using bellow pneumographs, in nonsmokers and asymptomatic smokers. In each subject, tidal volume (VT), breathing frequency (f) and inspiratory time (TI) were obtained on two different days, in a randomized crossover fashion, with the following sequence: basal conditions, after inhalation of buffered saline as a control and after histamine or methylcholine inhalation. Basal and control conditions did not differ from each other and were the same for both groups. The respiratory responses to both bronchoconstrictors did not differ from each other and were also the same in both groups: VT increased, f and TI remained unchanged. Thus, VT/TI, an index of respiratory drive, also increased. In nonsmokers the increased VT/TI and the associated increase in minute ventilation were both correlated to the decrease in FEV1. These correlations were not found in smokers. Although they have different effects on airway irritant receptors, inhaled histamine and methylcholine induce the same respiratory response in nonsmokers and smokers. Thus, the presumed smoking-related changes in airway mucosa permeability do not seem to influence the direct stimulating effect of histamine on these endings. The absence of correlation between FEV1 and VT/TI changes in smokers suggest that smoking might affect the respiratory drive in acute drug-induced bronchospasm.