Cough induced by mechanical stimulation of the upper airway in humans

Objectives - Cough has previously been induced in animals by means of mechanical stimulation of the upper airway but this method has not previously been applied to humans. The aims of this study were to determine if cough could be induced in humans on mechanical stimulation of the upper airway and to see if this mechanically induced cough was reproducible. We also wished to investigate if there was any difference in cough sensitivity between healthy subjects and those with acute upper respiratory tract infection (URTI). Material and Methods - In the first investigation, 2 groups were studied: 15 healthy subjects and 30 subjects with URTI with a mean age of 20 years. Cough was induced by vibration of the airway at the level of the trachea using a modified men's shaver. In the second investigation to determine the reproducibility of this mechanically induced cough, two groups from a different population were studied: 15 healthy subjects and 29 subjects with URTI with a mean age of 20.3 years. Cough was induced by airway vibration before and after a 90-min rest period. Results - In the first investigation it was demonstrated that cough can be induced within 2 s of vibration; subjects with URTI are more sensitive to cough induction and cough approximately five times more than healthy subjects; cough increases with repeated stimulation and reaches a maximum after three periods of vibration; the cough response may be mediated by rapidly adapting airway sensory receptors. In the second investigation there was no significant difference in mean cough counts before and after a 90-min rest period in both groups, which demonstrates that the mechanically induced cough is reproducible. Conclusion - This is the first study to elicit cough in humans by mechanical stimulation of the upper airway. This new method of inducing cough in subjects with URTI may be useful for studying both the mechanism of cough and the effects of antitussive medicines.