Figure 4.

Methods used to estimate right ventricle–pulmonary artery (RV–PA) coupling and diastolic stiffness. In both (A) the volume method, and (B) the pressure method, arterial elastance (Ea) is calculated from the ratio of end-systolic pressure (ESP) to stroke volume (SV). End-systolic elastance (Ees) as an approximation of maximum elastance in the volume method is estimated by the ratio of ESP to end-systolic volume (ESV), which results in a simplified Ees/Ea of SV/ESV. In the pressure method, Pmax is estimated from the nonlinear extrapolation of the early systolic and diastolic portions of the RV pressure curve. Ees is the ratio of (Pmax − mPAP) divided by SV, which results in a simplified Ees/Ea of (Pmax/mPAP − 1). (C) The single-beat method calculates Ees as a straight line drawn from Pmax tangent to RV pressure–relative change in volume relationship. The approach relies on an estimate of Pmax determined from the extrapolation of early and late isovolumic portions of an RV pressure curve and synchronized absolute or relative volume measurements. Ees is then defined by a tangent from Pmax to the pressure–volume relationship, and Ea is defined by a line drawn from the Ees point to end-diastolic volume (EDV) (at zero pressure). (D) Diastolic stiffness (β) is calculated by fitting the nonlinear exponential P = α(e^Vβ − 1) to pressure and volume measured at the beginning of diastole (BDP, ESV) and the end of diastole (EDP, EDV). Adapted by permission from Reference 184. BDP = beginning diastolic pressure; EDP = end-diastolic pressure; Evol = Ees estimated by the volume method; mPAP = mean pulmonary arterial pressure; Pmax = RV maximum pressure; sRVP = peak systolic RV pressure.