To evaluate the behavior of oxygen saturation curves throughout the six-minute walk test (6MWT) in patients with COPD.
We included 85 patients, all of whom underwent spirometry and were classified as having moderate COPD (modCOPD, n = 30) or severe COPD (sevCOPD, n = 55). All of the patients performed a 6MWT, in a 27-m corridor with continuous SpO 2 and HR monitoring by telemetry. We studied the SpO 2 curves in order to determine the time to a 4% decrease in SpO 2, the time to the minimum SpO 2 (Tmin), and the post-6MWT time to return to the initial SpO 2, the last designated recovery time (RT). For each of those curves, we calculated the slope.
The mean age in the modCOPD and sevCOPD groups was 66 ± 10 years and 62 ± 11 years, respectively. At baseline, SpO 2 was > 94% in all of the patients; none received supplemental oxygen during the 6MWT; and none of the tests were interrupted. The six-minute walk distance did not differ significantly between the groups. The SpO 2 values were lowest in the sevCOPD group. There was no difference between the groups regarding RT. In 71% and 63% of the sevCOPD and modCOPD group patients, respectively, a ≥ 4% decrease in SpO 2 occurred within the first minute. We found that FEV 1% correlated significantly with the ΔSpO 2 (r = −0.398; p < 0.001), Tmin (r = −0.449; p < 0.001), and minimum SpO 2 (r = 0.356; p < 0.005).