Response of asthmatics to methacholine and suggestion

Effects of diluent, methacholine, and suggestion on pulmonary function were studied in 9 asthmatic subjects. On day 1, flavored diluent was given as a control preparation. On day 2, increasing concentrations of similarly flavored methacholine were administered. On day 3, the effect of flavored diluent plus suggestion was studied. Although all variables were affected, the dose-response relationships for methacholine were most pronounced for specific airway conductance and airway resistance, in contrast to maximal mid-expiratory flow, forced expiratory volume in 1 sec, and forced vital capacity. Suggestion toward bronchoconstriction significantly affected only the plethysmographic parameters, specific airway conductance, and airway resistance, and not the spirometric variables. Both airway resistance and 1-sec forced expiratory volume showed slight, but significant, changes as a result of bronchodilator suggestion, which was used to overcome the suggestion toward bronchoconstriction. Because suggestion had a greater effect on large airways than peripheral airways, a role for the vagus is implied. Thus, any protocol using body plethysmography must consider a possible effect of suggestion on results.