Discontinuous incremental threshold loading test - Measure of respiratory muscle endurance in patients with COPD

Study objective: To assess the discontinuous incremental threshold lending (DC-ITL) test as a measure of respiratory muscle endurance for patients wit h COPD in terms of perceived breathing difficulty, reliability, and validit y. Design: The DC-ITL test was repeated three times at weekly intervals under identical test conditions. Setting: Clinical research laboratory. Patients: Forty-eight patients with moderate to severe COPD, Measurements and results: Rating of perceived breathing difficulty (RPBD) w as measured at the end of each stage of the DC-ITL test with a Borg categor y-ratio scale, The maximal inspiratory pressure (Pimax) was measured before and after the DC-ITL test. Breathing patterns were measured during the DC- ITL test. The mean (+/- SD) for RPBD at the maximal load was 6.3 (3.1), 6.6 (2.8), and 6.7 (2.7) for visits one, two, and three, respectively (not sig nificant). The mean relative maximal load for the DC-ITL test (peak mouth p ressure as a percent of Pimax) at the last completed stage was 59 +/- 23%, 62 +/- 20%, and 63 +/- 19% for visits one, two, and three, respectively (no t significant). Test-retest reliability was r(1,2) = 0.82 and r(2,3) = 0.69 for relative maximal load and r(1,2) = 0.90 and r(2,3) = 0.90 for absolute maximal load (peak mouth pressure). Tidal volume decreased (p < 0.01) and respiratory rate increased (p < 0.01) from the next-to-the-last to the last completed stage. Pimax decreased after the DC-ITL test (p < 0.01). Conclusions: Moderate breathing difficulty was experienced during the DC-IT L test. The test was reliable and the results of this study support its val idity as a measure of respiratory muscle endurance.