As shown in Figure 4 , estimated VD physiol /V T systematically underestimated measured VD physiol /V T , with a poor concordance correlation coefficient of 0.19 (95% confidence interval (95% CI) 0.091 to 0.28), a bias of 0.16 and an agreement between -0.05 and 0.37. Concerning changes in VD physiol /V T during PP, estimated VD physiol /V T had a concordance correlation coefficient of 0.51 (95% CI 0.32 to 0.66) (Figure 4 ).