Fig. 5. Variables affecting central venous pressure. AbdP = intraabdominal pressure; CPF = cardiac pump function; CVP = central venous pressure; Fio 2= inspired fraction of oxygen; PcdP = pericardial pressure; PulmArtR = pulmonary arterial resistance; ThorP = intrathoracic pressure; VenR = venous resistance; VR = venous return; Vs = stressed volume; Vu = unstressed volume. Thickness of the arrow reflects the importance and/or relative frequency of influences in clinical practice. Up and down arrows represent increase or decrease of value of a function of a variable, respectively. The main factors that tend to decrease intramural and transmural CVP include venodilation (increase in Vu) and hypovolemia: Both may decrease CVP via a decrease in Vs and VR. Less important factors include an increase in VenR, an increase in CPF, and a decrease in ThorP. The main factors causing an increase in CVP include a decrease in CPF, a decrease in Vu, an increase in Vs, and an increase in ThorP and/or PcdP. Other factors include an increase in PulmArtR secondary to hypoxic hypoxia (decrease in Fio2) or controlled ventilation. Controlled ventilation increases intramural (but not transmural) CVP via an increase in ThorP. An increase in AbdP may increase intramural and transmural CVP directly via a shift of blood volume from the splanchnic vasculature through inferior caval vein to the right heart and indirectly (only intramural CVP) via a shift of the diaphragm upward and associated increase in ThorP.