Association of the 6-minute walking test ratio and difference with pulmonary function in patients with interstitial lung disease

Methods: The present retrospective study included patients hospitalized in Beijing Hospital of Traditional Chinese Medicine, Capital Medical University between September 2018 and December 2019. The outcomes included the difference between the actual and predicted 6MWT values (6MWT difference) and the ratio of the actual to predicted 6MWT value (6MWT ratio). Results: This study included 137 patients. The predicted 6MWT value was 519 +/- 61 m and the actual 6MWT value was 449 (196.5,694)m. The 6MWT ratio was 84.7 +/- 177.6 and 6MWT difference was 73.9 +/- 95.1 m. Fractional exhaled nitric oxide (FeNO) (3=-2.157, standard error [SE]=0.836, p=0.014) and diffusing capacity of the lungs for carbon monoxide (DLCO) (3=-22.528, SE=7.48, p=0.004) had independent associations with 6MWT difference. The FeNO (3=0.403, SE=0.163,p=0.018) and DLCO (3=4.355, SE=1.458, p=0.005) had independent associations with 6MWT ratio. Conclusion: In ILD, 6MWT difference and 6MWT ratio were associated with FeNO and DLCO. The 6MWT value was not associated with hospital stay. Therefore, the 6MWT might be a surrogate marker of pulmonary function in clinical ILD.