Impedance Cardiography at Higher Frequencies

Impedance cardiography is a non-invasive method to measure both stroke volume and cardiac output of the left ventricle. As a medical technique it is both cheap and simple to use, requiring little training. While there exists a fair amount of literature and documented experimentation on the subject, it still remains a lesser used technique in spite of its many pro’s. A major reason for this is the fact that there is still a large amount of uncertainty around the subject. Both regarding the source(s) of the measured signal, and the data that can be extracted from the different parts of the signal, their ratios and time intervals. This experiment will attempt to further our understanding of the sources of these signals. By using new equipment that allows us to not only measure with higher than normal current frequencies, but also with a sufficiently high sampling frequency, the goal is to get a better look at what parts of the signal are dependent on the frequency of the current, and which parts are not. More directly, we are attempting to look at the change, or lack thereof, in the amplitude of the differentiated impedance as current frequency rises. This will allow us to begin to categorize which bodily events may have an effect on the impedance cardiography, and to what extent relative to others.
The experiment will be conducted using a fairly standard ICG setup, including a tetrapolar electrode system, a commercial ICG product and a newer ICG product more angled towards lab work. The experiment itself will be conducted on a small number of test persons, all young and with no reported cardiac issues. Although a small sample size, every subject showed a reduced ICG amplitude at higher frequencies, however the signals did not completely disappear, rather dampen by around 50%. This implies that the sources of the ICG measurements are split between several bodily
effects. Some dependent on the current frequency and some not.