Impact of Dyspnea: From Validity Indices to the Clinical Utility of the French-canadian Version of the Modified Dyspnea Index

Introduction: Dyspnea is a cardinal symptom among patients with respiratory and cardiovascular diseases. Its underlying mechanisms are complex, including pathophysiological as well as psychological and environmental factors. There is no gold standard to its evaluation and it has been recognized that multidimensional tools could provide a more comprehensive evaluation of the symptom. Hypothesis: The purpose of this study was to examine the validation of the scores of the French-Canadian version of the Modified Dyspnea Index(MDI), a multidimensional measure of dyspnea, among chronic cardiovascular and pulmonary patients. Methods: This study includes 137 patients: 79 with pulmonary arterial hypertension and 58 with interstitial lung disease. The cross-cultural adaptation and reliability of the MDI were already reported. The hypothesis guiding the test of convergent validity were that the final score of MDI, which reflects the intensity of dyspnea and its functional impact, would have correlations with: pulmonary function (forced vital capacity-FVC and FVC%), physical capacity (6 Minutes Walk Test-6MWT and Veterans Specific Activity Questionnaire-VSAQ), the practice of physical activity (Godin-Shephard Leisure-Time Physical Activity Questionnaire - GSLTPAQ) and quality of life (SF-12). Partial correlations were performed controlling theses variables: diagnosis, age, sex, BMI, and schooling. Results: The following correlations were observed between the total score of MDI and the reference variables: FVC 0.36 ( p<0.001 ); FVC% 0.29 ( p=0.008 ); 6MWT 0.58 ( p<0.001 ); VSAQ 0.77 ( p<0.001 ); GSLTPAQ 0.50 ( p<0.001 ); SF12-Physical Component 0.73 ( p<0.001 ); SF12-Mental Comp. 0.31 ( p<0.001 ). Conclusions: The results confirmed the associations hypothesized. The total score of the MDI explained much more the variance of the quality of life and perceived physical capacity, than lung function explained the MDI score. It is aligned with the described impact of the symptom in the daily life of the patient and the complexity of the factors underlying its triggering and perception. The use of the MDI can be very helpful in the clinical follow-up, guiding the choice of the best therapeutic approach and evaluation the outcomes of the interventions implemented.