IJCS | Volume 32, Nº2, March/April 2019

138 Morais and Rassi Six-minute walk test in heart failure Int J Cardiovasc Sci. 2019;32(2)134-142 Original Article 6MWD showed a moderate, significative correlation with age (r = -0.27; p = 0.01), MIP (r = 0.42; p < 0.01), MEP (r = 0.36; p < 0.01), HGS (r = 0.38, p < 0.01), Borg scale (-0.22, p = 0.04), Charlson index (r = -0.25; p = 0.02) and mMRC (r = -0.42, p < 0.01). Following the association tests and exclusion of variables by collinearity, the variables were selected in descending order of importance in the stepwise variable selection. Thereby, the following variables were included in the final model for the (dependent variable) 6MWD: mMRC (p < 0.01); sex (p < 0.01), age (p < 0.01) and FVC (p = 0.01). These variables explained 37% of the variance in the 6MWD in the study population (Table 4). In the hierarchical model, we found that clinical and physical functional variables were the ones with the best predictive value in the 6MWT (40% and 33%, respectively) (Table 5). Discussion Our findings suggested four potential variables with predictive value for a shorter 6MWD: female Table 4 - Predictors of the six-minute walk distance in heart failure patients Models Predictors R 2 Beta Standard error t p 1 mMRC 0.17 -0.41 11.51 -3.79 0.000 2 mMRC 0.24 -0.33 11.37 -3.14 0.002 Sex -0.29 20.66 -2.77 0.007 3 mMRC 0.31 -0.32 10.95 -3.13 0.003 Sex -0.31 19.89 -3.02 0.003 Age -0.26 0.76 -2.61 0.011 4 mMRC 0.37 -0.35 10.63 -3.48 0.001 Sex -0.36 19.68 -3.59 0.001 Age -0.29 0.74 -2.98 0.004 % FVC 0.25 0.51 2.46 0.016 mMRC: Medical Research Council modified dyspnea scale; %FVC: forced vital capacity. Table 3 - Comparison of the six-minute walk distance between sexes, New York Heart Association (NYHA) functional classes, physical activity level and dyspnea on activities of daily living (Medical Research Council modified dyspnea scale, mMRC) Variables 6MWD (mean ± SD) p %DTC6 (mean ± SD) p Male 467.7 ± 87.3* < 0.01 81.0 ± 14.4 0.96 Female 402.3 ± 82.8 77.2 ± 14.8 Functional class I 495.4 ± 86.8* 0.01 87.6 ± 12.1* 0.01 Functional class II and III 433.6 ± 88.3 77.9 ± 14.5 Sedentary 429.2 ± 95.8 0.07 77.1 ± 15.6 0.06 Active 465.9 ± 80.4 83.1 ± 12.4 mMRC (0 and 1) 472.4 ± 85.9* < 0.01 83.9 ± 14.0* < 0.01 mMRC (2, 3 and 4) 398.6 ± 80.4 72.7 ± 12.8 * p < 0.05;6MWD: distance covered during the six-minute walk test; DTC6: six-minute walk test.