Modified BODE Index to Predict Mortality in Individuals With COPD: The Role of 4-Min Step Test

Respir Care. 2020 Jul;65(7):977-983. doi: 10.4187/respcare.06991. Epub 2020 Jan 28.

Abstract

Background: The BODE (body mass index, air-flow obstruction, dyspnea, exercise capacity) index is a composite prognostic marker that predicts mortality in COPD. It includes body mass index, air-flow obstruction, dyspnea score, and exercise capacity by using the 6-min walk distance. However, a 30-m-long corridor is necessary to perform the test and this limits its use in clinical practice. Step tests may elicit distinct physiologic responses compared with the 6-min walk test but are easy to perform in the office setting. We sought to investigate whether a 4-min step test would be a suitable surrogate of the 6-min walk test, in a modified BODE step index (simplified BODE index), to predict mortality in COPD.

Methods: Individuals with COPD performed a self-paced 4-min step test, and the simplified BODE index was calculated by replacing the 6-min walk distance by the number of steps climbed. Cutoff values were determined by receiver operating characteristic curve analysis as follows: score 0 for >60 steps; score 1 for 50-60 steps; score 2 for 40-49 steps; and score 3 for <40 steps.

Results: A total of 186 individuals with COPD were enrolled from 2011 to 2016 (60% males; mean ± SD age, 65 ± 9 y; mean ± SD FEV1, 50 ± 17 L). There were 36 deaths among the study cohort. The simplified BODE index was a prognostic marker, independent of cardiovascular comorbidities and oxygen desaturation (HR 1.12, confidence interval (CI) [1.03-1.22]). Individuals with simplified BODE index scores ≥ 7 were at higher risk of death from any cause (P < .001, log-rank test).

Conclusions: This was the first study, to our knowledge, to show that the 4-min step test as a surrogate of exercise capacity in the BODE index (simplified BODE index) is an independent predictor of mortality in COPD and may help to spread its use among practicing physicians.

Keywords: 6-min walk test; 6-min walking distance; BODE index; COPD; exercise capacity; step test.

MeSH terms

  • Aged
  • Body Mass Index*
  • Dyspnea / etiology
  • Dyspnea / mortality
  • Exercise Test
  • Exercise Tolerance*
  • Female
  • Forced Expiratory Volume
  • Humans
  • Male
  • Middle Aged
  • Predictive Value of Tests
  • Pulmonary Disease, Chronic Obstructive* / complications
  • Pulmonary Disease, Chronic Obstructive* / mortality
  • Severity of Illness Index