It is quite possible that inflation of an intra-aortic balloon during intraaortic balloon pumping (IABP) results in a marked increase in electrical impedance in the aorta and, therefore, an increase in transthoracic electrical impedance. No remarkable change in electrical impedance of the thoracic organs and tissues excepting the aorta results from IABP, as compared with various types of assisted circulation with ventricular bypass technique. Therefore, the difference of transthoracie (total) electrical impedance, ΔZB, defined by the following equation, must be due to inflation of an intra-aortic balloon.
where
ΔZB: total impedance during IABP-ON, and Zo: total impedance during IABP-OFF.
Assuming that the aorta is compatible with a Windkessel model (time constant=, R/K), and that the aorta is oceluded. by an intra-aortie balloon at the time (α) after closure of the aortic valve, ΔZB is related to the balloon volume ( ΔV) by the following equations (Fig. 6.):
Experiments were performed using Minnesota Impedance Cardiograph MDL-304A, AVCO IABP Model-7, animal balloons (10ml and 20ml), a human balloon (30ml), etc., in mongrel dogs.
As a result, there was convincing evidence to support the conception that there existed a quantitative relation between ΔZB and ΔV, The actual volume of a balloon inflated during IABP was obtainable using calibration curves, and prompt detention of malfunctioning of the balloon was possible.
It may be concluded that impedance cardiography is an useful method to monitor cardiac output, intrathoracic fluid volume, and the performance of an intra-aortic balloon continuously.
