Application of a new parameter in the 6-minute walk test for manifold analysis of exercise capacity in patients with COPD.
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.


CONCLUSIONS
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.
Department of Respiratory Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan.
Naoki
N
Ijiri
Department of Respiratory Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan.
Hiroshi
H
Kanazawa
Department of Sports Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan.
Takahiro
T
Yoshikawa
Department of Respiratory Medicine, Graduate School of Medicine, Osaka City University, Osaka, Japan.
Kazuto
K
Hirata
D000368:Aged; D015415:Biomarkers / Q000097:blood; D004417:Dyspnea / Q000209:etiology / Q000503:physiopathology; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D011237:Predictive Value of Tests; D011379:Prognosis; D011653:Pulmonary Diffusing Capacity; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D012720:Severity of Illness Index; D013997:Time Factors; D014797:Vital Capacity; D016138:Walking
D015415:Biomarkers; D010100:Oxygen
6MWD; DDR; chronic obstructive pulmonary disease; six-minute walk distance