Marchandise, B., Debruyne, B., Delaunois, L., & Kremer, R. (1987). Noninvasive Prediction of Pulmonary-hypertension in Chronic Obstructive Pulmonary-disease By Doppler Echocardiography. Chest : the cardiopulmonary and critical care journal, 91(3), 361-365. https://doi.org/10.1378/chest.91.3.361 (Original work published 1987)