Exercise-induced desaturation in patients with chronic obstructive pulmonary disease on six-minute walk test

Exercise-induced desaturation (EID) is associated with increased mortality in chronic obstructive pulmonary disease (COPD). However, the relationship of EID with anthropometric and clinical parameters of resting pulmonary function test and six-minute walk test (6MWT) in COPD remains unclear. The study was designed to assess the correlate of EID and to identify various possible predictors of EID in stable normoxemic patients of COPD.

Sixty patients with stable COPD diagnosed and staged as per the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines underwent 6MWT. A drop in standard pulse oximetry (SpO2) of ≥4% or nadir up to ≤88% was defined as EID. Based on EID during 6MWT, two groups were formed: desaturators (DS) and nondesaturators (NDS). DS and NDS were compared for baseline and clinical characters by the Student's t-test while Pearson and Spearman rho correlation coefficient assessed strength of the association of anthropometric and clinical variables with EID. The predictors of EID were identified by logistic regression and receiver operator curve analysis.

Out of 60 patients with stable COPD, 33 patients desaturated on exercise (n = 33/60). DS had significantly lower values of FEV1 (P < 0.001), FVC (P < 0.01) FEV1/FVC (P < 0.01) compared to NDS. EID had significant negative correlation with FEV1 (r = 0.31, P < 0.01), resting oxygen saturation (r = 0.549, P < 0.001) and 6MWD (r = 0.511, P < 0.001). Resting SpO2 ≤93% was found to a predictor of EID with a sensitivity and specificity of 83% and 78%, respectively.

The 6MWT is a safe and sensitive test to recognize EID in normoxic stable COPD patients. Resting oxygen saturation is a good predictor of EID.