Abstract
It is reasonable to deduce that the subtraction of transthoracic electrical impedance, ΔZB(t), defined by the following equation, is due to inflation of an intra-aortic balloon: ΔZB(t)=Z2(t)-Z1(t), where Z2 and Z1 are the impedance during inflation of the balloon and during the preceding diastolic phase without balloon inflation respectively. Assuming that the aorta is compatible with a Windkessel model and that the shape of the inflated balloon is cylindrical, the balloon volume (VB(t)) can be expressed approximately as the following equation: VB(t)≅(Ls/L){C(t)·ΔP(t)+ρ(L/Z0)2·ΔZB(t)}, where Ls is the length of the intra-aortic balloon, L is the distance between two inner electrodes, ρ is the electrical resistivity of blood, Z0 is the mean transthoracic impedance, C (t) is compliance of the aorta, and ΔP (t) is the increase in aortic pressure induced by balloon inflation respectively. Based on this theory, the authors developed a new device, “IABP MONITOR MODEL-1”, which had the function for the prompt and precise measurement of ΔZB (t) and ΔP (t). As a result, the change with time in actual balloon volume could be shown, and the difference of balloon performance between 2 types of IABP devices could be detected.
