BACKGROUNDThe relationship between the 6-minute walk test (6MWT) and pulmonary function test in stable chronic obstructive pulmonary disease (COPD) remains unclear. We evaluate the correlation of 6MWT and spirometric parameters in stable COPD with different severities. 6MWT data assessed included three variables: the 6-minute walk distance (6MWD), 6-minute walk work (6MWORK), and pulse oxygen desaturation rate (SPO(2)%).

METHODS6MWT and pulmonary function test were assessed for 150 stable COPD patients with different severities. Means and standard deviations were calculated for the variables of interest. Analysis of variance was performed to compare means. Correlation coefficients were calculated for 6MWT data with the spirometric parameters and dyspnea Borg scale. Multiple stepwise regression analysis was used to screen pulmonary function-related predictors of 6MWT data.

RESULTSThe three variables of 6MWT all varied as the severities of the disease. The 6MWD and 6MWORK both correlated with some spirometric parameters (positive or negative correlation; the absolute value of r ranging from 0.34 to 0.67; P < 0.05) in severe and very severe patients, and the SPO2% correlated with the dyspnea Borg scale in four severities (r = -0.33, -0.34, -0.39, -0.53 respectively; P < 0.05). The 6MWD was correlated with the 6MWORK in four severities (r = 0.56, 0.57, 0.72, 0.81 respectively, P < 0.05), and neither of them correlated with the SPO(2)%. The percent of predicted forced expiratory volume in 1 second (FEV(1)% predicted) and residual volume to total lung capacity ratio (RV/TLC) were predictors of the 6MWD, and the maximum voluntary ventilation (MVV) was the predictor of the 6MWORK.

CONCLUSIONS6MWT correlated with the spirometric parameters in severe and very severe COPD patients. 6MWT may be used to monitor changes of pulmonary function in these patients.