Can subjective asthma symptoms be learned?

OBJECTIVE: We investigated whether perception of subjective asthma symptoms can be brought under control of biomedically irrelevant cues in the environment, i.e., whether subjective asthma symptoms can be learned in response to harmless stimuli.
METHODS: Twenty patients with asthma and 20 healthy participants were presented with two placebo-inhalers presented as new chemicals for diagnosing asthma. One inhaler was coupled three times with rebreathing 5% CO2 in oxygen, the other inhaler was coupled three times with rebreathing oxygen. In the subsequent test phase, both inhalers were coupled once with oxygen. We assessed airway resistance and subjective symptoms throughout the study.
RESULTS: Both groups expected and reported more symptoms with the inhaler that was previously associated with the CO2 trials compared with trials with the inhaler that was used on trials without CO2 without concomitant effects on respiratory resistance. The learning effects were most pronounced in a subgroup of patients reporting symptoms of hyperventilation during asthma exacerbations in daily life.
CONCLUSIONS: Subjective respiratory symptoms can be learned in response to harmless stimuli and a substantial proportion of patients with asthma might be especially vulnerable to this phenomenon. Because asthma patients rely mainly on perceived symptoms for their medication use, it is likely that they will take reliever medication based on expected symptoms instead of real exacerbations of respiratory dysfunction.