Prediction of peak oxygen uptake from 6-minute walk test in pulmonary hypertension

Maximal oxygen consumption (VO 2max ) assessed by cardiopulmonary exercise training (CPET), is an important parameter for risk assessment in patients with pulmonary hypertension (PH). However, CPET may not be available for all PH-patients. Thus, we aimed to test previously published predictive models of VO 2max from the 6-min walk distance (6 MWD) for their accuracy and to create a new model. We tested four models (Ross (2010), Miyamoto (2000) and Zapico et al . (2019)). To derive a new model, data was split into a training and testing dataset (70:30) and step-wise linear regression was performed. To compare the different models standard error of estimate (SEE) was calculated and the models have been graphically compared by Bland-Altman plots. Sensitivity and specificity for correct prediction into low risk classification (VO 2max >15 mL min kg −1 ) was calculated for all models. 276 observations were included in the analysis (194/82 training/ testing dataset). 6 MWD and VO 2max significantly correlated (r=0.65, p<0.001). Linear regression showed significant correlation of 6 MWD, weight and heart rate response (HRR) with VO 2max and the best fitting prediction equation was: VO 2max =1.83+0.031×6 MWD(m)–0.023×weight(kg)–0.015×HRR(bpm). SEE for the different models were 3.03, 3.22, 4.36 and 3.08 mL min kg −1 for Ross, Miyamoto, Zapico et al . and the new model respectively. Predicted mean VO 2max was 16.5 mL min kg −1 ( versus observed 16.1 mL min kg −1 ). 6 MWD and VO 2max reveal good correlation in all models. However, the accuracy of all models is inadequate for clinical use. Thus, CPET and 6 MWD measures both remain valuable risk assessment tools in the management of PH.