The effect of blood resistivity changes on impedance cardiography determined by 3D finite difference models of human thorax

The effect of blood resistivity changes in major vessels on the cardiogenic impedance signal was studied using three dimensional (3D) finite difference models of human thorax. The vessels studied included ascending aorta (AA), descending aorta (DA), common carotid artery (CA), superior vena cava (SVC), inferior vena cava (IVC) and internal jugular vein (JV). The end systolic data indicate that the impedance varies linearly with the percentage (%) change of blood resistivity in all vessels (R²>0.99). For a given blood resistivity change, the relative contributions are 34 % from 1)A, 27% from AA, 18% from SVC, 8% from CA, 7% from IVC and 6% from JV (the total is 69% from arteries and 31 % from veins). The results suggest that the blood resistivity change plays a major role in impedance cardiography to account for the negative impedance change (ΔZ) normally recorded from subjects.