Stronger correlation of peak oxygen uptake with distance of incremental shuttle walk test than 6-min walk test in patients with COPD: a systematic review and meta-analysis

Background The 6-min walk test (6MWT) and incremental shuttle walk test (ISWT) are valid and reliable measures to assess exercise capacity of patients with chronic obstructive pulmonary disease (COPD). However, the comparison of correlation between peak oxygen uptake (peak VO2) and 6MWT or ISWT distance has not been investigated. We aimed to investigate the correlation between peak VO2 and 6MWT and ISWT distances in COPD patients through a meta-analysis. Methods We systematically searched MEDLINE, Scopus, Embase, and the Cochrane Library up to June, 2020 for studies comparing the correlation of peak VO2 with either 6MWT or ISWT in COPD patients. Meta-analysis was performed with R software using a fixed-effect model. We compared the correlation coefficient and measured the heterogeneity using I-2 statistics. Results We identified 12 studies involving 746 patients. Meta-analysis showed a significant correlation between peak VO2 and 6MWT and ISWT distances (6MWT: r = 0.65, 95% CI 0.61-0.70; ISWT: r = 0.81, 95% CI 0.74-0.85; p < 0.0001). The heterogeneity was lower in ISWT than in 6MWT (6MWT: I-2 = 56%, p = 0.02; ISWT: I-2 = 0%, p = 0.71). Subgroup analysis showed a higher correlation coefficient in the low exercise capacity group than in the high exercise capacity group in both field tests. Conclusions 6MWT and ISWT significantly correlated with peak VO2. Our findings suggest that ISWT has a stronger correlation with peak VO2 than 6MWT. The exercise capacity in COPD patients may affect the strength of the relationship between peak VO2 and walking distance in both field tests, suggesting the importance of using various exercise tests. Trial registration CRD 42020200139 at crd.york.ac.uk/prospero/