Minimal clinically important difference in 30 second sit-to-stand test after pulmonary rehabilitation in patients with COPD

Abstract

The sit-to-stand test (STST) is a feasible alternative for measuring peripheral muscle strength of the lower limbs. Our aim was to evaluate, in Chronic Obstructive Pulmonary Disease (COPD) patients, the minimal clinically important difference (MCID) of 30-second STST (30-STST) after pulmonary rehabilitation (PR).

Stable COPD inpatients undergoing 30-STST and 6-minute walk test (6MWT) before and after PR were included. Responsiveness to PR was determined by pre-to-post PR (∆) evaluation of 30-STST. The MCID was evaluated using an anchor-based method.

96 moderate-to-severe COPD patients were included. At baseline, 30-STST was significantly related to distance at 6MWT (6MWD) (r=0.65; p<0.0001), FVC (r=0.46; p<0.0001), PaCO2 (r=-0.42; p<0.0001), FEV1 (r=0.39; p<0.0001) and age (r=-0.31; p<0.01). After PR a significant improvement in 30-STST was observed (mean difference +2 repetitions; p<0.0001). ∆30-STST was positively related to ∆6MWD (r=0.61, p<0.0001), TDI (r=0.61, p<0.0001) and baseline RV (r=0.27, p<0.01). Receiver operating characteristic curves identified a ∆30-STST cut-off of 2 repetitions as the best discriminating value (area under curve: 0.892; p<0.001) to identify the MCID for ∆6MWD (30 meters).

In a multivariate logistic regression model, baseline MRC (Odds ratio 2.27; p=0.003) and RV/TLC (OR 1.05; p=0.040) predict the risk to have a value >2 repetitions ∆30-STST.

In COPD patients 30-STST is a sensitive tool to assess PR efficacy. A ∆30-STST of at least 2 repetitions represents the MCID, that may be predicted by dyspnea and lung hyperinflation.