Errors in prolonged electrical impedance measurements due to electrode repositioning and postural changes

Abstract

Long-term electrical impedance measurements are affected by specific errors. Electrode failure, changes in its impedance due to aging, and postural changes are among the most important. We analyse errors due to electrode replacement and body postural changes. Electrode replacement errors can cause impedance changes up to 5% of basal value. This is one of the most important factors in data reproducibility. Body postural changes also contribute to impedance variations. We have proposed the use of a reference position to carry out impedance measurements as the one that shows the smallest impedance sensitivity to postural changes. In general, we observed that this is achieved with arms and legs slightly separated from the body. We propose the use of a ratio of impedance at two different frequencies to discern the origin of impedance changes, whether from physiological phenomena or postural errors.

Assessing abdominal fatness with local bioimpedance analysis: basics and experimental findings

“…In our two subjects we observed similar impedance changes as reported in Lozano et al 30 where electrode dislocations by up to 1 cm caused a DZ rel,disp of up to 4.4% on arms and legs. The main reason for the displacement error is probably the change of the geometrical boundary conditions for the current ®eld.…”

“…Experiments were carried out in only two persons (one male, one female, 23 and 25 y, 68 and 83 kg, 172 and 192 cm, respectively) because similar data were published previously for whole-body and segmental arrangements. 30 So it was just checked whether the data range was comparable. In addition to the con®guration in Figure 1 electrodes were placed 2 cm right from the original positions in order to simulate a transversal displacement.…”

Electrical impedance tomography system based on active electrodes

“…First, EIT is very sensitive to issues associated with the patient interface (i.e. electrodes Soleimani et al (2006); Lozano et al (1995) and cables Hong et al (2007)). The electrode contact to the body tends to have relatively high contact impedance, Z c , which also varies with time due to body movement, moisture on the contact surface and electrode replacement.…”

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