Cough: what's in a name?

Abstract

The cough reflex (CR) and the expiration reflex (ER) are two defensive reflexes from the respiratory tract, the latter mainly from the larynx. Both are elicited by mechanical and chemical irritation of the airway mucosa, and are a characteristic of airway diseases, but they have different functions. The CR first draws air into the lungs, to accentuate the subsequent expulsive phase; the ER consists of a strong expiration, to prevent aspiration of material into the lungs. They have different sensory pathways, central nervous circuits, and physiological and pharmacological modulations. In practice, coughing often consists of a combination of the two reflexes, a cough bout, epoch or attack. Articles on cough usually do not distinguish between the two reflexes, or whether the coughs are single events or epochs; they usually only measure frequency of expiratory efforts, and neglect other aspects. Current methods for measuring and assessing cough are described, with indications of when the use of these methods may be important.

What is cough and what should be measured?

“…An initial reflex inspiration (cough) and an initial expiration (ER) must activate fundamentally different neural mechanisms, and this has been confirmed by Shannon and colleagues in extensive neurophysiological studies on the brainstem [22,23]. But, perhaps more important from a clinical viewpoint, the two reflexes have very different physiological and pharmacological properties [4,19].…”

“…These differences have been fully discussed elsewhere [4,19]. This consideration will be developed below.…”

“…In practice it often occurs as an epoch (or a bout or an attack), where an initial inspiration is followed by a series of glottal closures and expiratory efforts, sometimes with interspersed inspirations [4,19]. Whether an epoch should be described as a single cough or a series of cough has caused some contention, which will be discussed later.…”

“…Whether an epoch should be described as a single cough or a series of cough has caused some contention, which will be discussed later. The semantics probably do not matter very much, provided it is clear what is being measured and described [19]. However in terms of mechanisms the cough epoch has interesting features.…”

“…', may be answered by a cough questionnaire or by an automated audiometric device. More complicated questions, such as those that ask about the mechanisms of the cough, require more complicated methods [19]. To give one of many examples [see 19 for others]: gastro-oesophageal reflux is one of the commonest causes of cough.…”