Rationale: Dyspnoea is a debilitating and distressing symptom that is reflected in different verbal descriptors. It is usually measured using single item scales or indirectly through report of activity limitation or quality of life. Our objective was to develop an instrument that measures overall dyspnoea severity using descriptors that reflect its different aspects.
Methods: Eighty-one 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 was 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 unidimensional model (n=22), 12 were retained. The ‘Dyspnoea-12’ had good internal-reliability (Cronbach’s alpha=0.9) and fit to the Rasch model (x2 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 Hospital Anxiety and Depression Scale (anxiety r=0.51; depression r=0.44, p<0.001, respectively), six-minute walk distance (r=-0.38, p<0.01), MRC Grade (r=0.48, p<0.01), and had good stability over time (ICCC=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.