Equação de referência para o teste do degrau de seis minutos baseado em um estudo multicêntrico brasileiro

Abstract

Introduction: The six-minute step test (6MST) has been highlighted in recent years for a simple functional test that requires minimal physical space and is easily applicable in clinical practice. It has already been validated for patients with chronic obstructive pulmonary disease and has been increasingly used in other deseases. However, an interpretation of their results is limited due to the absence of reference values involving a large sample and several regions of Brazil. Objective: To establish a reference equation to estimate the number of steps in the 6MST and to validate it prospectively, and to test the reproducibility of the 6MST in the multicenter sample. Methods: This is a multicenter cross-sectional study with a sample of healthy individuals recruited from six Brazilian cities in different regions. We evaluated 476 healthy individuals, subdivided into age groups: 18-28, 29-39, 40-49, 50-59, 60-69 and 70-79 years. The volunteers participated in only one day of following evaluations: anthropometric assessment, spirometry, levels of physical activity by a questionnaire and two free-cadence 6MST, with a 20 cm step and a 30-minute interval between them. After establishing the reference equation, a new sample of 46 individuals (24 women) performed the 6MST to test the prediction equation proposed by this study and compare it with the existing previous equation. Results: Multiple linear regression analysis showed an equation model with age, sex and heart rate variation (ΔHR) as variables, explaining 55% of the variability in the 6MST, which resulted in the following equation: Steps = 166.9 - age + (0.7 × ΔHR) + (20.7 × sex). It was shown from a posteriori sample analysis that the predicted value was not different from the actual performance of the 6MST (164 ± 24 vs. 167 ± 28 steps respectively, p = 0.462), presenting the accuracy of the performance prediction equation. The reliability between the tests was excellent, with ICC of 0.96 (0.95-0.97, p <0.001). Conclusion: The 6MST was highly reproducible and the equation proposed in this study was accurate to predict the 6MST for Brazilians.