Jon-Emile S. Kenny MD [@heart_lung] When we model the circulation at the bedside, we resort to generalizations. While these mechanistic heuristics don’t completely capture the complexity of hemodynamics, they do help us think quickly when confronted by clinical urgency. For example, distilling ‘venous return’ into an upstream pressure and downstream pressure separated by a single resistance, is certainly simplified [1-5]. As well, we often tie together the branching arterial tree into sequential ‘generations’ and assume each division to be completely characterized by a single compliance and resistance. Such an approach ignores the uniqueness of each organ and tissue bed; for example, we know that the skin, brain, kidneys and heart all behave differently at the level of pre-capillary arteriole [6-8]. As previously argued, ‘