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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

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