Impedance devices and methods of using the same in connection with a mammalian vasculature. In an embodiment of a method for determining vessel compliance, the method comprises the steps of introducing at least part of an impedance device into a site within a vessel, the impedance device comprising an elongated body having a distal body end, and a first electrode located along the elongated body at or near the distal body end, providing electrical current to the first electrode and a first external electrode not coupled to the elongated body to generate the electric field, the first external electrode positioned upon or within a mammalian body having the vessel therein, operating the impedance device to obtain two or more conductance values within the electric field, and calculating vessel compliance based upon the relationship between a change in vessel parameter and a change in pressure during a cardiac cycle.
