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ΔSpO2/distance ratio from the six-minute walk test in evaluation of patients with chronic obstructive pulmonary disease.

INTRODUCTION
The six-minute walk test (6MWT) contains two independent components: walk distance (6MWD) and oxygen saturation (SpO₂). 6MWD does not give detailed data on numerous COPD associated disorders. As oxygen desaturation plays a key role in exercise limita-tions, a few new parameters integrating oxygen desaturation during exercise along with walk distance are necessary. So, this study was conducted to assess the relationships between ΔSpO₂/distance ratio and pulmonary function test in addition to extent of pulmonary emphysema in COPD patients.


MATERIAL AND METHODS
57 stable COPD patients who attended the outpatient clinic of chest medicine department. Mansoura university. were enrolled. Included patients were classified according to GOLD airflow limitation. Age, sex, and modified Medical Research Council dyspnea score (mMRC) were recorded. furthermore, every patient completed the 6MWT and underwent a pulmonary function test and a CT scan to evaluate the degree of pulmonary emphysema.


RESULTS
ΔSpO₂/distance ratio was moderately correlated with DLCO%, FVC % and GOLD classification. However, strong correlation was found with FEV1% and RV%. mMRC was weakly correlated with ΔSpO₂/distance ratio. In addition, weak nonsignificant correlation was found between ΔSpO₂/distance ratio and extent of pulmonary emphysema as measured by HRCT volumetry. A significant moderate cor-relation was noticed between the ΔSpO₂/distance ratio and 6MWD (r = -0.5, P < 0.001). a significant strong cor-relation was observed between the ΔSpO₂/distance ratio and ΔSpO₂ (r = 0.87, P < 0.001).


CONCLUSION
ΔSpO₂/distance ratio could be a simple and valuable index for the evaluation of exercise capacity in COPD individuals and might be utilized to predict severity of airway obstruction, pulmonary diffusing capacity disorder and severe hyperinflation.