Venous congestion from a vascular waterfall perspective: reframing congestion as a dynamic Starling resistor phenomenon

The vascular waterfall phenomenon, rooted in Starling resistor principles, describes how blood flow becomes independent of downstream pressure when intraluminal pressure falls below a critical closing pressure (Pcrit). This review first introduces the classic arterial vascular waterfall, where local Pcrit enables organ-specific autoregulation of blood flow despite varying metabolic demands. Building on this framework, we extend the concept to the venous side, where similar mechanisms govern venous return and protect against congestion. The pulmonary vascular waterfall serves as a prototype, illustrating how alveolar pressures redefine downstream limits, shaping the effects of mechanical ventilation and positive end-expiratory pressure (PEEP). In valveless venous beds such as the hepatic veins, a reverse vascular waterfall may occur when elevated downstream pressure, typically right atrial pressure, causes brief, localized backflow buffered by vessel collapse and the emergence of a new Pcrit. These mechanisms explain organ-specific vulnerabilities to venous congestion: organs with effective venous waterfalls, such as the liver and intestine, can partially buffer overload, whereas the kidney, lacking such protection, is highly susceptible to venous pressure-dependent injury. Clinical implications include refined approaches to PEEP titration, fluid management balancing responsiveness with tolerance, and congestion assessment through Doppler ultrasound. Reframing congestion as a dynamic Starling resistor process explains why similar CVP elevations produce heterogeneous organ effects and provides a mechanistic basis for individualized, physiology-guided critical care.