Pulmonary vascular resistance index: Getting the units right and why it matters.

Pulmonary vascular resistance (PVR) and PVR index (PVRI) are key variables in a broad range of contexts, including prediction of outcomes in heart and liver transplantation, determining candidacy for closure of atrial or ventricular septal defects, and guiding treatment of pulmonary hypertension. Significant variability exists among the units used to report PVRI in current literature, making the interpretation of data and translation into clinical practice difficult. Here, we will review the measurement and derivation of PVR and PVRI and demonstrate the extent of confusion in the literature. We conducted a literature search of all published articles in PubMed using the term "PVRI." This yielded 218 sources with defined units for PVRI, including 33 unique variants. Among all reviewed literature, 45.4% of sources reported PVRI with units ending in m2 (meters squared), which we defined as correct, whereas 54.6% reported PVRI with units not ending in m2 , which we defined as incorrect. This lack of uniformity has led to considerable confusion among researchers and clinicians, with potentially life-altering consequences.