Results of classification and regression tree analysis in patients with pulmonary hypertension-sickle cell disease. Results of classification and regression tree analysis in patients with pulmonary hypertension-sickle cell disease. TRV: tricuspid regurgitant velocity; 6MWT: 6-min walk test; NT-proBNP: N-terminal pro-brain natriuretic peptide; RHC: right heart catheterisation; PH: pulmonary hypertension; 6MWD: 6-min walk distance. Reproduced from [18] with permission from the publisher. Marc Humbert et al. Eur Respir Rev 2012;21:306-312 ©2012 by European Respiratory Society