The influence of pulsatile flow on blood resistivity in impedance cardiography

The purpose of the study was to investigate the resistivity change over the cardiac cycle. This is important for the correct application of thoracic impedance cardiography (TIC). The ratio of spatial mean velocity over the vessel radius of the ascending and descending aorta of two female and eight male subjects (age ranging from 23 to 69 years) were measured in supine position using MRI. Based on Visser´s (1989) equation the relative resistivity change was calculated. In all subjects the authors found a change of less than 15%, which is smaller than rigid tube experiments predicted. However, the peak resistivity change occurs at the same time as the peak in the impedance signal. Thus, the effects of resistivity changes on stroke volume calculation in TIC needs further investigation