Electrode Placement for Calf Bioimpedance Measurements During Hemodialysis

Congestive Heart Failure (CHF) is a chronic medical condition that causes reduced exercise tolerance, shortness of breath, and fluid buildup in the lungs, legs, and abdomen. Monitoring patient fluid status using non-invasive techniques such as bioimpedance may help reduce CHF related read- mission rates. Bioimpedance measurements were performed in a controlled environment (hemodialysis) at two locations on the calf (side and back) to determine ideal electrode placement for monitoring changes in fluid status. Changes in calf bioimpedance were heterogeneous. Three out of seven patients had higher changes at the back of the calf compared with the side of the calf for the bioimpedance parameter $R_{0}$ (the resistance measured at low frequency that is related to extracellular water). These data suggest there are differences in resistivity within the calf. Simulations showed that the use of point electrodes weights tissue nearest the electrodes more heavily, but that this dependence can be eliminated through the use of ring electrodes, effectively averaging resistivity around the calf.