Introduction:Dynamic pulmonary hyperinflation(DH) is a common cause of dyspnea and exercise intolerance in patients with COPD.Direct comparisons on the ability to induce hyperinflation between 6minute walk test(6MWT) and 12MWT are rarely reported in literature.

Aim and objectives:To evaluate how two sub-maximal exercise tests (6MWT and 12MWT) induce DH in patients with COPD.

Methods:Twenty-eight patients diagnosed with COPD and CAT>10 were enrolled in a crossover study. Patients were evaluated over two separate randomized days for 6MWT and 12MWT by performing pulmonary function tests (PFR), including flow/volume curve and nitrogen washout at baseline and immediately after WT, without recovery time.Outcome of the study was the post 6 and 12MWT variation from baseline value of hyperinflation indices:forced vital capacity (FRC) primarily, and RV, RV/TLC, IC secondarily.

Results:Both the WTs showed an increase of FRC, RV, RV/TLC, and a decrease of IC from baseline values. In comparison of the two WTs, post-WT FRC (?FRC) increased 355±155mL and 729±524mL for 6 and 12MWT respectively,with a significant difference of +374mL between the two WTs. The results of the secondary indices are shown in the figure.In particular, IC was significantly reduced compared to baseline,but did not report a significant difference between the two WTs.

Conclusion:Six and 12MWT determined DH through a significant change in ?FRC measured with nitrogen washout, increasing proportionally to the minutes of the test.A greater FRC variability was observed among enrolled patients in the 12MWT than 6MWT,assuming a possible role of better differentiation in heterogeneous functional patterns of the COPD population.