No increase in walking distance on repeated tests in COPD patients with exercise-induced hypoxaemia

The aim of the study was to investigate the effect of retesting on the 12-min walking distance (12MWD) in patients with moderate or severe chronic obstructive pulmonary disease (COPD), with and without exercise-induced hypoxaemia (EIH) and to evaluate whether baseline characteristics derived before walking influence on variation of repeated tests. Fifty-seven COPD patients, mean age 66 (range 47 84) years, performed three 12-min walk tests within 1 week. Before and after each test, oxygen saturation (pulse oximetry, SpO₂), heart rate, breathing frequency, peak expiratory flow, and subjective ratings of exertion and dyspnoea were measured. EIH was defined as a fall in SpO₂ below 90% at the first walk test. The 12MWD did not increase on repeated testing in the EIH group. In the non-EIH group, the 12MWD increased by 12% (p<0.001) from test 1 to test 2 and by 4% (p<0.001) from test 2 to test 3. No day-to-day variation was observed in pre-walking characteristics. At least one training test is needed in non-EIH patients with COPD, as their effort and performance on the 12-min walk test increases on retesting (learning effects). In patients with EIH, the term "training test" is not relevant, as their walking distance did not homogeneously increase on repeated testing.