What is cough and what should be measured?

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Abstract

Cough is usually defined as a three-phase event, although for convenience clinicians may prefer to define it as only the expiratory expulsive efforts. Cough may occur as a single event or as a cough ‘epoch’ (or ‘bout’ or ‘attack’) that includes several or many expiratory efforts in a single episode. The distinction between a single cough and a cough epoch is important, both in mechanistic and clinical implications, since the latter may include many ‘expiration reflexes’ (ERs), for which the functions and neural mechanisms are different from those of the cough reflex. We describe the various ways in which cough can be assessed. For simplicity in clinical work the main methods are patient scores or automated cough counters; these assess only one aspect of the complex changes in cough. For analytical and basic medical studies other facets of cough need to be included: expiratory EMGs, respiratory pressures, airflows and lung volume changes. Cough ‘intensity’, a much used expression, needs to be defined in terms of the facets of cough which are being measured.

Section snippets

What is cough?

Cough is defined in the dictionary as ‘A violent expulsion of air from the lungs with a characteristic sound’ [1], a description favoured by some clinicians [2]. However textbooks and reviews make it more complicated. They identify three phases: an initial inspiration (the inspiratory phase), followed by closure of the glottis and a forced expiratory effort (the compressive phase), followed by opening of the glottis and vigorous expiration (the expulsive phase), [(e.g.) 3]. Fig. 1 is a

What may be measured?

Since cough (and the ER) have many facets, there are many parameters that may be measured. In analytical studies of cough and its mechanisms, as many of these parameters as possible should be considered. In clinical studies it is usually appropriate and desirable, for reasons of simplicity, to measure only one or two of the parameters, usually including cough frequency assessed acoustically. The methods chosen should depend on the question being asked.

How and when may cough be measured?

As discussed elsewhere [19], the answer depends on the question being asked. The ‘simple’ question, ‘is the cough getting better or worse?’, 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. There is dispute as to whether the

Conclusions

Cough is a complex phenomenon, and different basic and clinical scientists may give different definitions of it. This does not matter very much provided the definition is clear. There are many methods for measuring and assessing cough. Each has advantages and disadvantages, and the choice of them, apart from practical and financial considerations, must depend on the question being asked.

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