SVR is representative of the force that the left heart must pump against in order to deliver the stroke volume into the periphery.
VI is the maximum rate of impedance change, and is representative of aortic blood velocity.
ACI is the maximum rate of change of blood velocity and representative of aortic blood acceleration. TFC is calculated as the inverse of the baseline impedance measurement. Outside of direct measurement with a Pulmonary Artery Catheter, a default value of 12 mm Hg can be used because of PAOP's minimal effect on LCW determination.