Development of the i-BODE: validation of the incremental shuttle walking test within the BODE index.

Background: The BODE index has been shown to predict mortality in COPD. The index includes the 6 min walking test as the measure of exercise capacity. The incremental shuttle walking test (ISWT) is an alternative measure of exercise capacity which can be used to prescribe exercise and has been found to correlate well with peak VO2. The objective of the study was to evaluate the incorporation of the ISWT within the BODE index (named the i-BODE) to predict mortality in COPD.

Methods: Data was analysed from 633 patients with COPD attending pulmonary rehabilitation over an 11 year period, and mortality determined a minimum of one year on from initial assessment. An i-BODE score was calculated using ISWT(m) then Cox regression analysis evaluated the capacity of the index to predict risk of death.

Results: BMI, ISWT (m), MRC dyspnoea score, pack years and age were all significantly associated with mortality. Cox regression revealed the i-BODE index was an independent and significant predictor of mortality (hazard ratio 1.27 (CI 1.17-1.35), p < 0.001) and Kaplan Meier survival analysis showed each quartile increase in severity in i-BODE score was significantly associated with increased mortality (p < 0.001 by log rank test).

Conclusion: We have found the i-BODE index to be an independent predictor of mortality in COPD, even when other strong predictors such as age and pack years are adjusted for. We conclude that the ISWT can be successfully substituted for the 6MWT as an alternative measure of exercise capacity within the BODE index.