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Respir Care. 2014 Mar;59(3):353-62. doi: 10.4187/respcare.02494. Epub 2013 Aug 13.

Kinetics of changes in oxyhemoglobin saturation during walking and cycling tests in COPD.

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Division of Pulmonary Medicine, Department of Critical Care Medicine, Chung Shan Medical University Hosptial, and School of Medicine, Chung Shan Medical University, Taichung, Taiwan.



The patterns and kinetics of changes in SpO2 in the 6-min walk test (6MWT) and cycling test have not been addressed in patients with COPD.


We studied 60 COPD subjects, with a mean ± SD FEV1 of 54 ± 18% of predicted. We compared the changes in SpO2 (ΔSpO2) within and between the 2 tests, and the differences between the desaturators and non-desaturators.


In the 6MWT there were 4 patterns of SpO2. Desaturation then resaturation was the most common (46%). ΔSpO2 ≥ 3% occurred at approximately 1.2 min, and the nadir was at 3.5 min where resaturation occurred thereafter. The ΔSpO2 between the start and the nadir (start-vs-nadir ΔSpO2) was greater than the start-vs-end ΔSpO2 (P < .001). The desaturators had less inspiratory muscle strength, worse dyspnea, and shorter 6-min walk distance, whereas the resaturators had greater FEV1/FVC and less functional residual capacity (all P < .05). In the cycling test there were 3 patterns of SpO2. Desaturation was the most common (57%). The ΔSpO2 ≥ 3% and nadir SpO2 occurred at 4.6 min and 6.6 min, respectively, of the 6.8-min cycling exercise duration. The desaturators had lower body mass index, lower oxygen-cost diagram score, less post-exercise inspiratory muscle strength, lower diffusing capacity, lower SpO2, lower work during 6MWT, and lower peak exercise performance (all P < .05). In both tests, the start-vs-nadir ΔSpO2 during the 6MWT was greater (P = .02) but the start-vs-end ΔSpO2 was similar (P = .79). The desaturators in both tests had lower oxygen-cost-diagram scores (P < .01) and poorer peak exercise performance.


Measurement of start-vs-nadir ΔSpO2 rather than start-vs-end ΔSpO2 during the 6MWT is recommended, because start-vs-nadir ΔSpO2 is greater, and the nadir SpO2 is earlier. In both the 6MWT and the cycling exercise test, desaturation can be predicted with the oxygen-cost-diagram score, which has more capability to predict peak exercise performance than the 6MWT.


6-min walk test; COPD; desaturation; hypoxemia; incremental cardiopulmonary exercise test

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