Six minute walk test Z score: correlations with cystic fibrosis severity markers

Abstract

Background: The six-minute-walk-test (6MWT) has been increasingly used in cystic fibrosis (CF) patients. However, few studies in children have correlated 6MWT with current parameters used to evaluate CF severity. Moreover, no study transformed the values of distance walked from meters into Z scores to avoid bias like age and gender, which are sources of 6MWT variability.

Methods: A cross-sectional descriptive study was performed to analyze the correlations (Spearman) among forced expiratory volume in one second (FEV(1)), body mass index (BMI), chest radiography (CXR), chest tomography (CT), and 6MWT Z score (Z-6MWT). Clinically stable CF patients, aged 6-21 years, were included.

Results: 34 patients, 14F/20M, mean age 12.1±4.0 years were studied. The mean Z-6MWT was -1.1±1.106. The following correlations versus Z-6MWT were found: FEV(1) (r=0.59, r(2)=0.32, p=0.0002), BMI Z score (r=0.42, r(2)=0.17, p=0.013), CXR (r=0.34, r(2)=0.15, p=0.0472) and CT (r=-0.45, r(2)=0.23, p=0.0073).

Conclusions: In conclusion there was a significant, but poor, correlation between the six minute walk test Z score and the cystic fibrosis severity markers currently in use.