Vascular function curve: confusion, clarification and new insights.

The vascular function curve (VFC) in cardiovascular physiology describes the relationship between the steady state venous return (VR in L/min, in the Y-axis) and the steady state right atrial pressure (RAP in mmHg, in the X-axis). However, in some literature, the RAP is considered the independent variable (IV) and the VR the dependent variable (DV), whereas in other literature, the VR is the IV and the RAP the DV. Because of this confusion, when the VFC is combined with the cardiac function curve (CFC), which describes the relationship between the steady state cardiac output and the RAP, it is not strange that the interpretations of the combination are problematic. Hence, in this article, we will trace the origin of the inconsistency, differentiate the VFC into two types based on who created them, and differentiate the RAP into RAP as the IV and DV respectively. Through these in-depth analyses, the confusion will be clarified and new insights into the combination of a VFC with the CFC will develop.