What is Admittance and conductance in cardiac performance?

There is an established practice of using the electrical conductance of blood in heart ventricles to determine the instantaneous volume of the ventricle. This technique involves inserting a tetra-polar catheter into the ventricle and measuring conductance. This measured conductance is a combination of blood and muscle and various techniques are used to identify the blood conductance from the total measured conductance. Blood conductance can then be converted to volume using a linear or a non-linear relationship that relates conductance to volume.