Reference Equations for the Six-Minute Walk Distance in Healthy North-East Indian Population Aged 18-60 Years


Silpa Kshetrimayum, Asoka Wangkheimayum, Lalfakzuala Renthlei, Sujas Datta, Nuthan Vallapudasu, Balaji Munuswamy, Noklangkumla Sangtam

BACKGROUND Six-minute walk test is a simple and objective tool for functional assessment of patients with cardiopulmonary disease. Healthy population-based reference equations to predict 6MWD show wide variations from region to region. Our study derives reference equations for the north-eastern population of India. METHODS 150 healthy, non-smoker subjects aged 18-60 years were enrolled. Spirometry and 6MWT was done for all subjects according to the American Thoracic Society prescribed protocol. Pearson correlation and subsequently stepwise multiple regression analysis was used to develop the reference equations. RESULTS The mean six-minute walk distance (6MWD) for males was 503.39 ± 31.95 meters which was significantly more than that for females which was 454.19 ± 36.46 meters (p= 0.001). The regression equation derived in our study shows age, height and weight as the most important predictors of the 6MWD. The predictive equations derived are- Males: 6MWD= 377.18-[1.235 x Age (yr.)] + [1.006 x Height (cm)]; r2= 0.427, p<0.001 Females: 6MWD= 129.75-[0.510 x Age (yr.)] + [2.186 x Height (cm)]; r2= 0.375, p= 0.028. Alternative equations derivedMales: 6MWD= 381.52 - [1.235 x Age (yr.)] + [0.963 x Height (cm)] + [0.062 x Weight (Kg)]; r 2=0.427, p<0.001; Females: 6MWD= 107.255 - [0.430 x Age (yr.)] + [2.451 x Height (cm)] - [0.421 x Weight (Kg)]; r 2=0.38, p= 0.064. Reference equations from other regions of the world over-predicted the 6MWD for our population probably due to anthropometric and demographic variations. CONCLUSIONS The 6MWD shows considerable variability according to anthropometric, cultural and social characteristics of the population studied. The regression equation derived in our study shows age and height as the most important predictors of the 6MWD. There is over prediction of 6MWD by equations from Western and other Asian studies. The gender specific equations derived in our study from this region may thus help in the assessment of patients with chronic cardiorespiratory diseases by providing correct reference values of normal.