Asthma and suggestion: psychological or physical?

The effect of suggestion on the airway response to ten inhalations of normal saline followed by doubling concentrations of isoprenaline was assessed in 12 normal and 30 asthmatic subjects. It was suggested that the first 5 saline solutions contained a bronchoconstrictor and the second 5 a bronchodilator, or vice-versa, and that the first four isoprenaline solutions were inert whilst the last was a bronchodilator. Nine asthmatic but no normal subjects bronchoconstricted after saline inhalation with a mean 40% fall in specific airway conductance (sGaw). This was dose-dependent and abolished when inhalations were carried out at 37 degrees C 100% relative humidity. Suggestion did not affect the airway response to saline or isoprenaline in either group. We conclude that bronchoconstriction following saline inhalation, previously attributed to the effect of suggestion, is caused by airway cooling.