Background: New parameters in the 6-minute walk test (6 MWT) are required for comprehensive analysis of exercise capacity in patients with chronic obstructive pulmonary disease (COPD). The aim of the present study was to apply a novel index, the desaturation distance ratio (DDR), to clinical research on COPD as an estimate of exercise capacity and to examine whether DDR is a potential parameter for manifold analysis of exercise capacity in patients with COPD.
Methods: A total of 41 patients with COPD (median age [interquartile range] =75 [68-79] years; and body mass index [BMI] =22.3 [19.4-23.8] kg/m(2)) participated in the study. The 6 MWT was performed along with anthropometric measurements and a pulmonary function test. The "desaturation area" was measured as the total area above the curve created using peripheral oxygen saturation (SpO2) values observed at each minute during the 6 MWT. Then the DDR was calculated as the ratio of the desaturation area to the 6-minute walk distance (6 MWD).
Results: The 6 MWD was 370 (328-445) m, and the decline in SpO2 values (ΔSpO2) was -5.0% (-8.0% to -1.5%). The DDR correlated modestly with baseline pulmonary function in patients with COPD (forced expiratory volume in 1 second [% of predicted value]: r=-0.658, P<0.001; and diffusing capacity of the lung for carbon monoxide [DL(CO)]: r=-0.470, P=0.002), comparable with the findings of the 6 MWD. The DDR correlated well with ΔSpO2 (r=-0.656, P<0.001) and with the increase in subjective sense of dyspnea during the 6 MWT, as assessed by Borg scale scores (ΔBorg) (r=0.486, P=0.001), in contrast with the 6 MWD, which was not significantly correlated with ΔSpO2 and ΔBorg scale scores.
Conclusion: The DDR is more informative for manifold analysis of exercise capacity associated with oxygen desaturation and subsequent sense of dyspnea by exercise in patients with COPD.
Keywords: 6MWD; DDR; chronic obstructive pulmonary disease; six-minute walk distance.