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Original Research: Signs and Symptoms of Chest Diseases |

The Effect of Placebo Conditioning on Capsaicin-Evoked Urge to CoughPlacebo Suppression of Urge to Cough

Jennifer Leech, BSc Hons; Stuart B. Mazzone, PhD; Michael J. Farrell, PhD
Author and Funding Information

From the School of Biomedical Sciences (Ms Leech and Dr Mazzone), University of Queensland, St. Lucia, QLD; and Florey Neuroscience Institutes (Ms Leech and Dr Farrell), University of Melbourne, VIC, Australia.

Correspondence to: Stuart B. Mazzone, PhD, School of Biomedical Sciences, University of Queensland, St. Lucia, QLD, Australia 4072; e-mail: s.mazzone@uq.edu.au


Funding/Support: This research was supported by grants to Drs Mazzone and Farrell from the National Health and Medical Research Council (NHMRC) of Australia [566734, 454776, 1025589].

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2012;142(4):951-957. doi:10.1378/chest.12-0362
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Background:  The urge to cough is a clinical symptom of respiratory disease that precedes the motor act of coughing. Although previous studies have shown that cough is particularly susceptible to placebo suppression, it is unclear whether the perception of an urge to cough is also modifiable by placebo. Therefore, we tested the hypothesis that capsaicin-evoked urge to cough could be suppressed by placebo conditioning.

Methods:  Eleven healthy participants were unknowingly conditioned to believe that an inert inhaler temporarily suppressed capsaicin-induced urge to cough by deceptively modifying the challenge concentration of capsaicin. In subsequent testing, capsaicin-evoked urge-to-cough subjective ratings were assessed in four challenges with a single dose of inhaled capsaicin following no treatment or the placebo metered-dose inhaler. An additional 10 participants were informed that the inhaler therapy was inert prior to receiving capsaicin challenges with and without inhaler treatment.

Results:  There was a significant decrease in mean urge-to-cough ratings to capsaicin challenge following placebo compared with no treatment followed by capsaicin challenge (P < .001), with a peak decrease of 45%. The placebo inhaler alone had no effect on urge-to-cough subjective ratings when participants were aware that it contained no active medication.

Conclusions:  These data confirm that the urge to cough is susceptible to placebo inhibition. This provides further evidence that higher brain networks are involved in the processing of respiratory sensations related to airway irritation.

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