• Naoki Ijiri, Hiroshi Kanazawa, Takahiro Yoshikawa, and Kazuto Hirata.
• Department of Respiratory Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan.
• Int J Chron Obstruct Pulmon Dis. 2014 Jan 1;9:1235-40.

BackgroundNew 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.MethodsA 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).ResultsThe 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.ConclusionThe 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.

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