Kinetics of Changes in Oxyhemoglobin Saturation during Walking and Cycling Tests in Chronic Obstructive Pulmonary Disease

BACKGROUND AND OBJECTIVE: The patterns and kinetics of changes in oxyhemoglobin saturation measured with pulse oximetry (ΔSpO₂) in six-minute walking test (6MWT) and cycling test has not been addressed in patients with chronic obstructive pulmonary disease (COPD).

METHODS: Sixty COPD patients with FEV₁ 54±18%pred were evaluated for anthropometrics, oxygen-cost diagram (OCD) score, lung function tests, and the 6MWT and cycling test with SpO₂ measurements. The ΔSpO₂ were compared within individual tests and between both tests. The differences in the variables between desaturators and non-desaturators were compared.

RESULTS: In the 6MWT, four patterns of SpO₂ developed. Desaturation-re-saturation was the most common (46%). ΔSpO₂ ≥3% occurred approximately at 1.2 minutes and the nadir re-saturated at 3.5 min. The ΔSpO₂ between the start and the nadir (ΔSpO_2SN) was greater than that between the start and the end (ΔSpO_2SE) (p<0.0001). The desaturators had less inspiratory muscle strength (IMS), more dyspnea, and shorter distance on the 6MWT, while the re-saturators had greater FEV1/FVC and less functional residual capacity (all p<0.05). In the cycling test, three patterns of SpO₂ developed. Desaturation was the most common (57%). The ΔSpO₂ ≥3% and SpO_2nadir occurred at 4.6 min and 6.6 min, respectively, of the 6.8-minute exercise duration. The desaturators had less body mass index, OCD score, IMS post-exercise, diffusing capacity, SpO₂ and work on walking, and peak exercise performance (all p<0.05). In both tests, the ΔSpO_2SN during the 6MWT was greater (p<0.05) but the ΔSpO_2SE was similar (p=0.79). The desaturators in both tests had lower OCD scores (p<0.01) and poorer peak exercise performance.

CONCLUSIONS: Measurement of ΔSpO_2SN rather than ΔSpO_2SE during the 6MWT is recommended because ΔSpO_2SN is greater and the SpO_2nadir is earlier. In both exercise tests, exertional desaturation can be predicted with the OCD scores and has more capability to predict peak exercise performance than the 6MWT.