Abstract
BACKGROUND: The Modified Medical Research Council (MMRC) scale, baseline dyspnea index (BDI) and the oxygen cost diagram (OCD) are widely used tools for evaluation of limitation of activities due to dyspnea in patients with chronic obstructive pulmonary disease (COPD). There is, however, limited information on how these relate with each other and with multiple parameters of physiological impairment. OBJECTIVES: To study the interrelationships between MMRC, BDI and OCD scales of dyspnea and their correlation with multiple measures of physiological impairment. MATERIALS AND METHODS: A retrospective analysis of pooled data of 88 male patients with COPD (GOLD stages II, III and IV) was carried out. Dyspnea was evaluated using the MMRC, BDI and OCD scales. Physiological impairment was assessed by spirometry (FVC % predicted and FEV₁ % predicted), arterial blood gas (ABG) analysis and measurement of the 6-min walk distance (6MWD). RESULTS: The interrelationships between MMRC, BDI and OCD scales were moderately strong. The BDI and OCD scores had strong correlations with ABG abnormalities, weak correlations with spirometric parameters but none with 6MWD. MMRC grades were significantly associated with BDI and OCD scores but did not show clear associations with spirometric parameters, ABG abnormalities and 6MWD. CONCLUSIONS: The MMRC grades of dyspnea and the BDI and OCD scales are moderately interrelated. While the BDI and OCD scales have significant associations with parameters of physiological impairment, the MMRC scale does not.