The Electrical Impedance of Pulsatile Blood Flowing Through Rigid Tubes: A Theoretical Investigation

The electrical impedance of blood is used in biomedical applications such as impedance cardiography for monitoring blood flow. Impedance cardiography assumes a constant value for the conductivity of blood. However, this assumption has been shown to be invalid for the case of flowing blood since the conductivity is affected by flow induced changes in the orientation of red blood cells. A number of previous studies have modeled the conductivity of blood in constant flow. This study investigates the conductivity changes due to pulsatile flow as experienced during the cardiac cycle. This is achieved through the development of a theoretical model of the conductivity of pulsatile blood flowing through rigid tubes. Conductivity waveforms of pulsatile blood were generated by incorporating realistic physiological flow and cell orientation dynamics into previously reported steady flow conductivity models. Results show that conductivity correlates with the spatial average blood velocity and that features of the velocity waveform are reproduced in the conductivity signal. Conductivity was also shown to be dependent on the shape of the velocity profile. The modeled conductivity change is comparable with previously published experimental results for pulsatile blood flow, supporting the reliability of the model.