Chen TX, et al. - This study was designed to test the hypothesis that the “sex-specific” chronic thromboembolic pulmonary hypertension (CTEPH) indices could estimate the severity of inoperable CTEPH. A variance was noted in the correlation of different cardiopulmonary exercise testing (CPET) measurements of gas exchange efficiency with pulmonary vascular resistance (PVR) between male and female patients, even after confounding for age and body mass index. This potentially could be used to estimate the severity of CTEPH.