Clinical relevance of constant power exercise duration changes in COPD.

The endurance time during constant high work-rate exercise (t(LIM)) is used to assess exercise capacity in patients with chronic obstructive pulmonary disease and as an outcome measure for pulmonary rehabilitation. Our study was designed to establish the minimum clinically important difference for the t(LIM). t(LIM) was measured in 105 patients (86 males) before and after an 8-week outpatient pulmonary rehabilitation programme. Subjects were asked to identify, from a five-point Likert scale, the perceived change in their exercise performance immediately upon completion of the exercise tests. The scale ranged from "better" to "worse". The mean+/-sd age was 64+/-5 yrs, forced expiratory volume in 1 s (FEV(1)) 47+/-10% and FEV(1)/forced vital capacity 54.7+/-16.3%. Baseline t(LIM) at 75% of the peak work rate was 397+/-184 s, which increased by 62+/-63% after rehabilitation. In subjects who felt their exercise tolerance was "slightly better", the mean improvement was 34% in the relative improvement over the baseline value (95% CI 29-39)% or 101 (86-116) s compared with 121 (109-134)% in those who reported that their exercise tolerance was "better" and 8 (2-14)% in those who felt their exercise tolerance was "about the same". Minimum clinically important improvement for t(LIM) averaged approximately 33% of baseline. Patients were able to distinguish at least one further additional level of benefit at 120% of baseline.