Cough, pain and dyspnoea: Similarities and differences

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Abstract

The three common symptoms, pain, dyspnoea and cough, share some important features. We felt that the analogies to be made among them could be instructive, possibly suggesting new avenues of research. Each of these symptoms can be profoundly uncomfortable, and can profoundly degrade quality of life. The sign, cough, is often given more prominence than the symptom, urge to cough, but both are important to the patient (the former may be of more concern to nearby people). Advances in pain research over the last several decades have pointed the way to new studies of dyspnoea; they may serve as a model for the psychophysical study of the perception of urge to cough, as well as providing models for understanding both central and peripheral sensitization of the afferent pathway. We briefly review here the afferent and central pathways and psychophysics of pain, dyspnoea and urge to cough.

Introduction

Pain, dyspnoea and cough are very common and troubling symptoms. There are a number of important analogies to be made among these three common symptoms (internal sensations). Each of these symptoms can be profoundly uncomfortable. All three of these symptoms also produce externally observable signs—this is most prominent in the case of cough, where the sign, cough, is often given more prominence than the symptom, urge to cough. This may be true because cough is more easily quantified than urge to cough, or because cough is more disturbing to surrounding people (e.g. in a concert hall) than are withdrawal from pain or laboured breathing. In all cases, we must ask what is it we wish to treat, sign or symptom—what is important to the patient? In all cases, treatment to the extent of eliminating the symptom entirely may put the patient at risk, while inadequate treatment may allow a profound decrease in quality of life and ability to work.

The rapid, near explosive growth in pain research serves as both a scientific and political model for future advances in cough and dyspnoea. The advances in pain research are the result of tireless efforts from a number of individuals, exemplified by the late John Bonica, who worked vigorously at all levels of scientific organization, business, government and the press to advance the quality and quantity of pain research and treatment. As a result, our knowledge of pain has grown dramatically. In the early 1970s, the entire field of pain, like the current fields of cough and dyspnoea, received only a brief mention, if any, in typical medical textbooks. The field of pain research has grown so rapidly that now no one person can grasp all of it; the latest Textbook of Pain condenses it into 1214 pages! This advance in pain research serves as an excellent social–political model, and also as an excellent scientific model that may share many features with cough and dyspnoea. We describe here the physical and experiential similarities of these three disorders with the view to suggesting future research directions.

Section snippets

Afferent inputs

Pain, cough and dyspnoea share a common feature: they originate in afferent nervous systems that detect and signal real or impending threats to the organism.

Psychophysics

Studies of perception of urge to cough, pain, and dyspnoea share problems of measurement [26]. While mediated by a protective neural system that can be partly assessed through focussed and more generalized methods, all three of these methods are ultimately ‘internal feeling’ states that are most appropriately assessed by an individual's verbal description of their own experience. The experience is characterized by both sensory qualities and by affective/emotional properties that motivate

Summary

The field of pain science is clearly ahead of both dyspnoea and cough sciences. The field of dyspnoea science has shown that it is possible to apply some of the concepts and methods used by pain scientists to a complex respiratory event. It is our hope that the neurophysiological and psychophysical approaches used to understand pain and dyspnoea can be modified to help discoveries about the perception of urge to cough, and the function of afferent and central pathways of cough.

Acknowledgements

Supported in part by DAMD 17-00200018 (Gracely), HL46690 (Banzett) and HL62296 (Undem).

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