Alphabet Soup: Assessment of Dyspnea

VAS, UCSD SOB, SGRQ, CRDQ, TDI/BDI and now SAC BDI/TDI! What is one to make of this alphabet soup of these acronyms for the multiple different tools to measure shortness of breath? Are they important for me to understand?

Dyspnea is the principal symptom of patients with chronic obstructive pulmonary disease. Measurement of this key symptom is paramount to the evaluation of outcomes of a host of pharmacologic agents (such as bronchodilators) and other therapies (including pulmonary rehabilitation and surgical approaches). The fundamental importance of shortness of breath is underscored by its use as a guide to the management of patients with COPD as recommended by international clinical practice guidelines [[1]][[2]]. Thus, tools to evaluate dyspnea are of paramount importance in clinical research and clinical practice in COPD.

Two types of approaches have been employed to assess shortness of breath—measurement during activity and measurement by questionnaire. Dyspnea can be measured during a standardized activity or more commonly during a formal exercise test such as a six‐minute walk, shuttle test, submaximal exercise or maximal exercise. During activity, the most commonly utilized tools are the visual analogue scale (wherein a patient identifies the degree of dyspnea along a 10 cm scale) and the modified Borg scale (wherein a patient indicates a number ranging from 1 to 10 corresponding to the degree of dyspnea; phrases to identify severity are placed along the scale) [[3]]. One example of the usefulness of the Borg scale for dyspnea measurement can be seen in a recent study of the effects of a long‐acting anticholinergic bronchodilator compared to placebo [[4]]. Although dyspnea at the end of a steady state exercise endurance test was similar as measured by the Borg scale, exercise duration was longer, and dyspnea at a submaximal degree of exercise was less with the bronchodilator.

Dyspnea is more easily assessed by questionnaire. Questionnaires obviate the need for an exercise test but are subject to recall of the patient since they query the type of activity causing shortness of breath and the degree of dyspnea with activity. Some of the most commonly used questionnaires to assess changes in dyspnea in response to interventions in COPD are the University of California Shortness of Breath Questionnaire (UCD SOB) [[5]] and the Baseline/Transitional Dyspnea Index (BDI/TDI). However, because of the importance of dyspnea, it is also one of the factors assessed by measures of health status in patients with COPD. Dyspnea subscales are components of two commonly used respiratory disease‐specific quality of life instruments—the St. George's Respiratory Questionnaire (SGRQ) [[6]] and the Chronic Respiratory Disease Questionnaire (CRDQ) [[7]]. However, the dyspnea subscales of these health status instruments were not developed as stand‐alone measures of shortness of breath and have not been validated as dyspnea assessments.

In this issue of the Journal of COPD, Mahler et al. describe initial efforts to develop a modified version of the BDI/TDI, the SAC BDI/TDI [[8]]. Why is development of a revised dyspnea measure necessary? The most pressing needs are for a tool which is easier to administer and is not subject to potential interpretation by an interviewer. The current version of the BDI/TDI is interviewer‐administered and a standardized interview method for its administration has not been developed. Indeed, the authors note at least four different videos have been developed in an attempt to standardize the use of the BDI/TDI. The article by Mahler et al. begins to address this need with the development of a computerized self‐administered tool. The rationale for change of some of the items appears reasonable, particularly since patient and expert input was used to help assure the current revisions optimally identify the issues of most importance to patients with COPD. However, the SAC TDI still requires patients to compare current dyspnea to previous ratings. The computerized version provides reminders about patients' prior level of shortness of breath. Alternative approaches might be explored in future studies; for example, re‐administration of the BDI to assess change may eliminate the need for patient recall or patient prompts about their previous responses. The SAC version also modified the range of available scores; however, the tool does not appear to take advantage of the full range of potential intermediate responses available with a visual analogue scale. Use of a computer to administer the SAC version provides advantages but raises other potential resource issues. Computers may not be readily available in all research and clinical practice settings.

The SAC BDI/TDI may prove useful not just as a tool for clinical investigation, but possibly also as a measure to be used in clinical practice. However, as with all evaluative tools and as noted by the authors, the SAC BDI/TDI must be validated to assure it truly identifies the symptom under investigation, is reproducible, is sensitive to change, and is useful in different settings. In addition, studies to determine the minimal clinically important difference are required to guide researchers and clinicians about the significance of responses achieved by various therapeutic interventions.