MODELING OF CARDIAC-RELATED CHANGES IN LUNG RESISTIVITY MEASURED WITHEITS

Resistivity data from 9.6 kHz to 1.2 MHz were recorded from eight norm al subjects using an electrical impedance tomographic spectroscopy (EI TS) system and then averaged to a mean cardiac cycle using the ECG gat ing technique. The Cole-Cole model, that is, extracellular resistance R connected in parallel with intracellular resistance S and membrane c apacitance C in series, with a distribution parameter a, was applied t o model the frequency characteristics and to produce parametric images . During systole, SC and RC were found to decrease and FR increase. Th e changes in R/S were not consistent among the subjects. We estimated the peak changes in R, S and C to be -2.5%, -3.3% and -7.6% respective ly. The results can be explained by considering the brood vessels as s pheres of different sizes with blood inside them. The decrease in R du ring systole might be caused by the increased blood content in relativ ely large vessels, whereas that in S by the increased blood volume in relatively small vessels. The capacitance of blood is normally smaller than that of lung tissue, whereas FR of blood is higher than that of lung tissue. Hence, as blood content increases, C should decrease and FR increase.