The six-minute walk test – a reliable test for detection of exercise-related desaturation in patients with chronic obstructive pulmonary disease

Abstract

Introduction: Exercise-induced desaturation is common in patients with moderate to severe chronic obstructive pulmonary disease (COPD). It provides additional information about physical capacity and disease evolution, and it is an important predictor of mortality. Aim: To compare the six-minute walk test (6MWT) and the cardio-pulmonary exercise test (CPET) as methods for detection of desaturation in COPD patients. To explore the relationship between exercise-related desaturation, symptom questionnaires (mMRC, CAT, and SGRQ), pulmonary function testing (PFT), and blood-gas analysis. Patients and methods: Forty adult male COPD patients, mean age 67.2±8.4 years (mean ± SD) underwent 6MWT, CPET, PFT, blood-gas analysis, and scored their symptoms (mMRC, CAT, and SGRQ). Oxygen desaturation was monitored during exercise. Desaturation was defined as a decrease in SpO2 of ≥4% and values ≤88% held for ≥3 minutes. Results: The studied patients had COPD stage 2A – 4D (GOLD 2011). The patients were categorized into two groups – with desaturation (A, n=19) and without desaturation (B, n=21). CPET elicited 21 individuals who experienced desaturation, 19 of them desaturated during 6MWT as well. In the whole group, the percentage of desaturation during CPET was 6.6±4.9% compared to 6.0±4.9% during 6MWT (p<0.001). There was a significant difference in the maximal oxygen consumption reached by the patients in group A – 16.2±4.5 and group B – 19.9±4.7 (p=0.016). Desaturation during 6MWT correlated significantly with that during CPET (r=0.75, p<0.001). Conclusions: Exercise-related desaturation in patients with moderate to severe COPD could easily and reliably be detected by 6MWT.