The following is a summary of “Minimal important difference of the constant work rate cycle test in severe COPD,” published in the AUGUST 2023 issue of Pulmonology by Molen, et al.

A widely used and accurate test to determine if a patient with COPD is responding to treatment is the Constant Work Rate Cycle Test (CWRT). 

Before this, a well-conducted study assessed the Minimal Important Difference (MID) of the CWRT to be 101 s (or a 34% change from baseline). For a study, researchers sought to determine the MID of the CWRT in patients with severe Chronic Obstructive Pulmonary Disease (COPD), as previous estimates were based on a population with mild-to-moderate COPD.

The study included 141 patients with severe COPD who underwent different treatments, including pulmonary rehabilitation, bronchoscopic lung volume reduction with endobronchial valves, or a sham bronchoscopy as a control group. An incremental cycle test determined The CWRT workload at 75% of the peak work capacity. To calculate the MID, we used the change in 6-minute walking test (6-MWT), forced expiratory volume in 1 second (FEV1), residual volume (RV), and St. George’s Respiratory Questionnaire (SGRQ) total score as anchors.

All anchor measures showed a significant association of ≥0.41 with the change in CWRT performance. The MID estimates based on the different anchors were as follows: 6-MWT 278 seconds (95% CI), FEV1 273 seconds (90% CI), RV 240 seconds (84% CI), and SGRQ 208 seconds (71% CI). Taking the average of these four MID estimates, the resulting MID for CWRT in patients with severe COPD was 250 seconds (or 85% change from baseline).

In patients with severe COPD, they determined the MID for CWRT to be a 250-second (or 85% change from baseline) performance improvement. These findings contribute to the understanding of treatment success and clinical significance in the management of severe COPD, particularly in interventions such as pulmonary rehabilitation or bronchoscopic lung volume reduction.


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