Voluntary suppression of cough induced by inhalation of capsaicin in healthy volunteers

Abstract

The aim of the present study was to investigate the voluntary suppression of cough in response to capsaicin inhalation in healthy volunteers, and to determine if the dose-response curve to capsaicin was significantly altered when volunteers were asked to suppress their cough response. The quantification of the degree of voluntary suppression of induced cough could provide a new methodology for screening antitussive agents as antitussives may act by influencing voluntary control of cough. Cough was induced by inhalation of capsaicin. Two challenges were given 5 min apart, each comprising five ascending concentrations of capsaicin (1 x 10(-5) M-3.33 x 10(-4) M). During one of these challenges the volunteer was allowed to cough when required, and during the other they were asked to suppress cough. These two conditions were given in random order. The cough response was recorded by means of a microphone with the integrated sound trace displayed on a chart recorder. A dose-response relationship was obtained on administration of ascending concentrations of capsaicin. In the non-suppressed challenge 23/24 subjects coughed on inhalation of capsaicin (3.33 x 10(-4) M) with a mean number of coughs of 2.92 +/- 0.34, whereas in the suppressed challenge only 3/24 subjects coughed with a mean number of coughs of 0.29 +/- 0.18 (P < 0.001). These results demonstrate that cough induced by inhalation of capsaicin can be voluntarily suppressed. The mechanism of voluntary suppression of cough is discussed in relation to capsaicin challenge and the screening of antitussive medications.

Investigation of the Neural Control of Cough and Cough Suppression in Humans Using Functional Brain Imaging

“…The utility of this stimulus is that, when inhaled, capsaicin evokes both coughing and the associated urge to cough (Davenport et al, 2002;Mazzone et al, 2007). Furthermore, capsaicin-evoked coughing can be consciously suppressed (Hutchings et al, 1993;Mazzone et al, 2007). Our present data extend our previous fMRI analysis of capsaicin-evoked urge to cough (Mazzone et al, 2007(Mazzone et al, , 2009b, confirming activations associated with capsaicin challenge that encompass sensory, motor, and limbic structures, some of which overlap with those activated during cough.…”

Cough and ventilatory adjustments evoked by aerosolised capsaicin and distilled water (fog) in man

“…Therefore, it has been proposed that C-fibre activation results in the conscious perception of airway irritation and in respiratory sensations ultimately leading to cough . Accordingly, human subjects can voluntarily suppress capsaicin-induced cough at least up to a certain stimulus intensity (Hutchings et al, 1993). Nevertheless, we are confident that the observed cough responses and differences in cough frequency do not entirely depend upon supramedullary influences, since prior to each trial subjects were carefully instructed to avoid any attempt to facilitate or inhibit cough, that is, they were recommended to cough freely when they could not abstain from doing so.…”

Measuring voluntary and reflexive cough strength in healthy individuals

“…However, Hutchings, Morris, Eccles, & Jawad (1993) have demonstrated that reflexive coughing to capsaicin can be voluntarily suppressed. This indicates that either cortical inhibition of RC is possible, or alternatively, that a true RC has not been initiated at all.…”