Quantification of dyspnoea using descriptors: development and initial testing of the Dyspnoea-12

Abstract

Rationale: Dyspnoea is a debilitating and distressing symptom that is reflected in different verbal descriptors. Evidence suggests that dyspnoea, like pain perception, consists of sensory quality and affective components. The objective of this study was to develop an instrument that measures overall dyspnoea severity using descriptors that reflect its different aspects.

Methods: 81 dyspnoea descriptors were administered to 123 patients with chronic obstructive pulmonary disease (COPD), 129 with interstitial lung disease and 106 with chronic heart failure. These were reduced to 34 items using hierarchical methods. Rasch analysis informed decisions regarding further item removal and fit to the unidimensional model. Principal component analysis (PCA) explored the underlying structure of the final item set. Validity and reliability of the new instrument were further assessed in a separate group of 53 patients with COPD.

Results: After removal of items with hierarchical methods (n = 47) and items that failed to fit the Rasch model (n = 22), 12 were retained. The "Dyspnoea-12" had good internal reliability (Cronbach's alpha = 0.9) and fit to the Rasch model (chi(2) p = 0.08). Items patterned into two groups called "physical"(n = 7) and "affective"(n = 5). In the separate validation study, Dyspnoea-12 correlated with the Hospital Anxiety and Depression Scale (anxiety r = 0.51; depression r = 0.44, p<0.001, respectively), 6-minute walk distance (r = -0.38, p<0.01) and MRC (Medical Research Council) grade (r = 0.48, p<0.01), and had good stability over time (intraclass correlation coefficient = 0.9, p<0.001).

Conclusion: Dyspnoea-12 fulfills modern psychometric requirements for measurement. It provides a global score of breathlessness severity that incorporates both "physical" and "affective" aspects, and can measure dyspnoea in a variety of diseases.

Conflict of interest statement

None.

Figures

Figure 1

Illustration of logit (ie, severity) value for each item. *Indicates item loading onto the “physical” component identified with principal component analysis (PCA). †Indicates item loading onto the “affective” component identified with PCA. The value attached to each descriptor is the logit (ie, severity) associated with that descriptor (negative values indicate milder, positive values indicate more severe). By convention, in Rasch analysis the severity scale is centred on zero logits. Note: these logit values are not used to score the instrument; they are shown here to illustrate the different relative severity of the items.

Figure 2

Mean (+95%CI) of total Dyspnoea-12 scores (D12-TOTAL), Borg-intensity (Borg-INT) and Borg-distress scores (Borg-DIS) at each Medical Research Council (MRC) dyspnoea grade for all three conditions combined (n = 358). Ratings for all three measures increased progressively with similar gradients of between 8% and 10% of full scale per increment in MRC grade.