Which equations to estimate peak work rate from six minute walk test in patients with cystic fibrosis post lung transplantation?

The maximum work rate (Wmax) advisable during exercise training early after lung transplantation (Ltx) have not been studied so far ( Ruud H. Knols et al. Systematic Review Front. Physiol.2018 9:946; Langer D. Respiration. 2015;89(5):353-62.). The aim of this study was to investigate the performance of predictive model for Wmax as function of 6MWD in adults with cystic fibrosis (CF) hospitalized after Ltx. Consecutive adults (>=18 years with CF) who underwent bilateral Ltx have been enrolled from August 2017 to December 2019. 6MWD and Wmax achieved during a symptom-limited incremental cycle ergometry test were recorded 20±5 days after LTx. Multivariable linear regression and bootstrap interval validation were performed to develop predictive model using height, weight, gender, FVC, FEV1 and 6MWD as dependent variables. 37 CF adults [mean (SD) age: 30.5 (8.2) yrs; 38% female; mean (SD) FEV1: 59% (31.8%)] were included. The shrinkage adjusted equation derived to estimate Wmax was: Wmax (W)= - 41.73 + 0.12 * 6MWD(m) + 0.97 * weight (kg) + 9.98 * Sex (male sex=1); internal validated adjusted R2 was 0.58; residual standard error of the estimate was 14.47. Calibration intercept and slope were 1.16 and 0.98, respectively. There was no association between Wmax and FEV1 or FVC (p-value>0.1). In our study population Wmax could be estimated from an equation based on 6MWD, weight and sex. Further data are needed to better assess the performance of the model, to evaluate the role of additional variables and to investigate external validation.