Reference Equation for Six Minute Walk Test in Healthy Western India Population

Introduction: The Six Minute Walk Test (6MWT) is used to assess disease progression and survival in chronic cardiopulmonary disorders. However, variability is noted in the six minute walk test distance (6MWD) in different populations. Aim: We aimed to develop a reference equation for 6MWD in healthy Western India population and compare the results with previously published Indian and Caucasian reference equations. Materials and Methods: Total 174 healthy subjects between 25 to 75 years performed the 6MWT. Variables assessed were age, height, weight, body mass index and sex. Predicted equations were derived using multiple linear regression and compared with the equations for North Indian male, South Indian and Caucasian population using Bland - Altman method. Results: The 6MWD mean (SD) was 512.38 (67.84) m for men and 457.27 (56.75) m for women with p=0.001. The 6MWD correlated with age (r=-0.44), height (r=0.43), weight (r=0.21) in univariate analysis. Stepwise multiple regression analysis showed age and sex to be independent predictors of 6MWD, R-2 = 0.307. The reference equation for healthy Western India population is 553.289 + (-2.11 x age) + (45.323 x sex; men= 1 and women = 0). Bland Altman analysis showed that the mean bias was 50.87m (95% limits of agreement 134.77 to 33.0) for North Indian male equation, 50.75m (95% limits of agreement 105.72 to -4.22) for South Indian equation and 122.72m (95% limits of agreement 254.11 to -8.67) for Enright and Sherrill's equation. Conclusions: The North Indian male, South Indian and Caucasian equations significantly over-estimated the predicted walk distance for our healthy population. Hence, there is a need to develop subgroup population specific reference equations.