Development of reference equations for the six-minute walk distance of school-aged Nigerian children

ABSTRACT Background The six-minute walk test ( 6MWT ), a simple, reliable and valid test that uses the distance walked in six minutes (six-minute walk distance, 6MWD ) to quantify functional capacity , is widely used in chronic cardiopulmonary and non-cardiopulmonary disorders. However, absence of reference standards for Nigerian school-age children limits its use in this age group. Objectives To develop normative values and equations for the 6MWT of school-aged Nigerian children. Methods In a cross-sectional study, healthy children aged 6-11 years in Lagos, Nigeria, completed 6MWT on 20-meter straight outdoor courses in their schools following standardized guidelines. Potential predictors : demographic (age, sex), anthropometric (height, weight, chest circumference, leg length) and physiologic data [pre-walk, immediate post-walk and 5 th minute-post-walk heart rate ( HR ), oxygen saturation ( SpO 2 ), systolic pressure ( SBP ), diastolic blood pressure ( DBP ) and rating of perceived exertion ( RPE )] and difference between pre-walk and post-walk HR (Δ HR) , SpO 2 ((Δ SpO 2 ), SBP (Δ SBP) , DBP (Δ DBP ) and RPE (Δ RPE ). Primary outcome : six-minute walk distance (6MWD) in metres. Results Overall, 627 pupils (52.1% girls) walked 504.6 ± 66.6 m (95% CI: 499.4, 509.8), ranging from 326.6 m to 673.0 m; 16 m longer in boys (p=0.002). Stepwise linear regression yielded: 6MWD (m) = 347.9 + 14 (Age) + 1.6 (ΔHR) + 17.6 (Sex) + 1.2 (ΔSBP); R 2 =0.25. Previously published reference equations over-estimated Nigerian children’s 6MWD. Conclusion The reference values and prediction equations, after validation in other Nigerian populations, may be useful for functional evaluation of Nigerian children aged 6-11 years with chronic childhood disorders.