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Table 2 Physiologic terminology

From: Perioperative Quality Initiative (POQI) consensus statement on fundamental concepts in perioperative fluid management: fluid responsiveness and venous capacitance

Arterial elastanceThe ratio of left ventricular end-systolic pressure and stroke volume
Intravascular volumeThe blood volume within the vascular system (arteries, capillaries, veins)
Mean systemic filling pressureThe pressure of venous return when cardiac activity is absent
PreloadVolume defined by the distending pressure it generates. In the heart, preload is LV wall stress at end of diastole (= EDV)
Stressed volumeThe (theoretically measurable) volume of blood that exerts distending pressure against the vascular wall
Total body waterThe amount of sodium-free water in the whole body, commonly divided into the extracellular fluid space and the intracellular fluid space
Unstressed volumeThe volume of blood just to the point of filling the blood vessels but without exerting any pressure on the vessel walls
Vascular capacitanceThe change in volume divided by the change in pressure (i.e., the inverse of elastance)