ABSTRACT
Cough is one of the most common respiratory symptoms (1). Epidemiolo-
gic studies estimate the prevalence of cough at between 3% and 40% (2-5). These figures derive from questionnaire surveys that assess mainly the pres-
ence or absence of cough and its characteristics, for example, productive or
nonproductive. In contrast, specifically designed cough questionnaires
allow measurement of the effects of cough on an individual’s quality of life
(6-9). Another way to quantify cough is using cough provocation tests.
These are of particular relevance when studying the pathophysiology of
the cough reflex and when assessing the effects of antitussive agents and
their mechanisms. The idea of inhalation cough challenge originated from the clinical
observation that during the administration of aerosols such as nebulized
bronchodilators, patients can experience a sense of irritation of the upper
airways resulting in cough. Cough is recognized to be a reflex action with
its sensory afferent mediated by the vagus nerve terminating in the airways
(10,11). The afferent nerve fibers transmit impulses to the cough center,
which is thought to be situated in the medulla and lower pons (12). The efferent limb of the cough reflex is via the phrenic and other spinal nerves
to the respiratory muscles. As aerosols can be delivered to the site of affer-
ent nerve endings, cough can be induced using a variety of chemical stimuli.
Inhalation of a tussigenic aerosol therefore forms the basis of cough
challenge testing.
