Dyspnea

Mechanisms, Measurement, and Management, Third Edition

Donald A. Mahler, Denis E. O'Donnell, Donald A. Mahler, Denis E. O'Donnell

• Publisher: CRC Press
• Year: 2014
• ISBN:
  9780429585869
• Edition: 3
• Topic: Medicina
• Subtopic: Teoria, pratica e riferimenti medici

With the high prevalence of chronic pulmonary diseases, including asthma, COPD, and interstitial lung disease, physicians need to recognize the cause of dyspnea and know how to treat it so that patients can cope effectively with this distressing symptom. Detailing recent developments and treatment methods, this revised and updated third edition of

Section II

Measurement and Assessment

7 Domains of Dyspnea Measurement

Mark B. Parshall and Richard M. Schwartzstein

CONTENTS

7.1 Historical Overview

7.2 Classifying Dyspnea-Related Measures

7.2.1 Psychometric and Conceptual Approaches

7.2.2 Factor Analytic Approach

7.3 Domain Framework for Dyspnea Measures

7.4 Applying the Dyspnea Domains: Illustrative Examples

7.4.1 Case 1: Clinical Dyspnea

7.4.2 Case 2: Laboratory Dyspnea

7.5 Future Directions for Dyspnea Measurement

References

In recent years, there has been explosive growth in the number of instruments (questionnaires, rating scales, etc.) designed to measure various aspects of dyspnea. Much of that growth has been haphazard, and reports on dyspnea measurement have often been vague with respect to which aspects of the symptom are being measured. Indeed, prior to the 1960s, the dogma was that dyspnea could not be measured, at least not directly. By the 1990s, there was greater acceptance that dyspnea was both a sensory experience and a symptom^1,2 and that at least some aspects of it could be measured,³ but there was little agreement over how dyspnea should be defined.¹

In 1999, the American Thoracic Society (ATS) published a consensus statement with a “suggest[ed]” definition that referred to “qualitatively distinct sensations that vary in intensity,” interactions with “physiological, psychological, social, and environmental factors,” and “secondary physiological and behavioral responses.”⁴ This definition was reaffirmed in an update of the consensus statement in 2012.⁵ Key to this definition is that dyspnea consists of “sensations,” which implies that it can be assessed and reported only by the experiencing individual. Although an observer may infer discomfort based on physical findings, such as changes in vital signs or use of accessory muscles of ventilation, only the patient can confirm the presence or absence and intensity or quality of the dyspnea.

Even with that consensus definition, clinicians and researchers could continue using existing measures or develop new measures pertaining to any (or several) of those sensations, factors, or responses and lay legitimate claim to be measuring dyspnea. The heterogeneity of instruments and measurement approaches contributed to a lack of clarity about what aspects of the symptom were being measured. As a consequence, there have been persistent difficulties in communicating or comparing findings across research studies or clinical settings using different dyspnea-related measures.⁵

In this chapter, we provide a brief, historical overview of dyspnea measurement and discuss various ways of evaluating and classifying dyspnea-related questionnaires and rating scales. We also summarize recent efforts to bring some order to the field of dyspnea measurement through a proposed domain framework,⁵ which attempts to categorize dyspnea measures in a manner congruent with the conceptual definition of dyspnea.^4,5 To illustrate the application of this framework to real-world measurement issues, we provide two case studies, one clinical and one laboratory, in which we apply the measurement domains to the problem presented. We conclude with some thoughts on future directions in dyspnea measurement.

7.1 HISTORICAL OVERVIEW

The first formal rating for breathlessness was the Pneumoconiosis Research Unit (PRU) rating developed for evaluating disability due to pulmonary emphysema.^{6, 7, 8} According to Fletcher,⁶ the clinical diagnosis of emphysema was based on evaluation of dyspnea severity and the presence of physical signs. Although cough and sputum production were commonly present, Fletcher maintained that “so far as symptoms are concerned, dyspnea is really the only essential,” but he also observed that “such a subjective and comparative symptom cannot be assessed by any single, simple question, such as ‘How breathless are you on exertion?’” (p. 577). Therefore, the approach taken by the PRU was to assign one of five ordinal grades based on the degree of activity limitation due to breathlessness. The PRU rating subsequently evolved into the familiar Medical Research Council (MRC) scale,^{9, 10, 11} variants of which are still in use.^{10,12, 13, 14, 15, 16} Roughly contemporaneous with the original PRU rating, Wright and Branscomb¹⁷ reported that they could reliably produce intolerable air hunger by restricting the depth or rate of breathing together with either an exercise stimulus or hypoxia. At the same time, they noted that experimental production of dyspnea was “beset by many problems, not the least of which is the impossibility of recording either the quality or the quantity of the sensation.”¹⁷ They also noted that an experimental stimulus can be terminated at will, but if similar sensations developed “under circumstances beyond one’s control, they would be terrifying in the extreme….”¹⁷ This statement presaged work conducted decades later that would focus on the contribution of affective factors in the rating and assessment of dyspnea.

A decade later, Comroe observed that experimental approaches to studying dyspnea commonly involved “measurement of anything pertaining to the lungs, thorax, or respiration in man and correlating the values obtained with the absence, presence or severity of dyspnea.”¹⁸ For example, Campbell and colleagues pioneered the application of psychophysical methods in the study of mechanical and sensory responses to elastic¹⁹ and resistive²⁰ external breathing loads by inducing breathlessness. Any insights into mechanisms of breathlessness that were gained thereby were essentially a byproduct of a program of research in mechanisms of neuromuscular ventilatory control, and, for the most part, only the intensity of effort was measured.²¹ The application of psychophysical measurement methods to characterize a variety of respiratory sensations continued to mature throughout the 1970s.^{22, 23, 24}

In the late 1960s, Aitken²⁵ reported using a visual analog scale (VAS) to rate breathing discomfort for threshold detection of external airway resistance, but his overall purpose was validating use of the VAS to measure subjective “feelings” (i.e., sensations or sentiments), not the measurement of dyspnea, per se. The Oxygen Cost Diagram (OCD), which indexed activities to a VAS in relation to their relative oxygen requirements, was first used in the late 1970s.²⁶ In addition, efforts to capture the multidimensional nature of symptoms of respiratory disease by cluster analysis began in the 1970s and led to the development of affective and somatic symptom checklists for asthma^27,28 as well as emphysema and chronic bronchitis.^29,30 Other developments in the 1970s that had important influences on dyspnea measurement, despite not being directly concerned with dyspnea or respiratory sensation, include the original Borg Rating of Perceived Exertion (RPE)³¹ as well as initial attempts to catalog verbal descriptors of pain³² and subsequent development of the McGill Pain Questionnaire.^33,34

In the 1980s, Borg modified his original RPE scale to a 0–10 category-ratio scale,³⁵ which has been very widely used, as have various forms of VAS,^36,37 numerical rating scale (NRS),^24,38 and ordinal categorical ratings^39,40 in studies evaluating the intensity of dyspnea in response to exercise or changes in ventilatory parameters or partial pressures of inspired gases. Efforts to develop instruments intended to capture multiple aspects of dyspnea or the impact of dyspnea as part of a multidimensional conceptualization of health-related quality of life (HRQL) also began in earnest in the 1980s. In particular, the Baseline Dyspnea Index (BDI) and Transitional Dyspnea Index (TDI),^{13,41, 42, 43} as well as the Chronic Respiratory Disease Questionnaire (CRQ)⁴⁴ and Chronic Heart Failure Questionnaire (CHQ),⁴⁵ were initially developed as interviewer-administered instruments in the 1980s. The BDI and TDI include three scales for the degree of functional impairment in usual activities due to shortness of breath and the magnitudes of task and effort that typically ind...