Effect of body orientation and joint movement on local bioimpedance measurements

Abstract

The purpose of this pilot study was to determine if body orientation, skin treatment, joint angle, and shoulder arch movements affect localized bioimpedance spectroscopy (BIS) measurement. Nowadays, there are various wearable and portable impedance measurement tools in different shapes and sizes. Therefore, the body position and orientation of the subject during measurement may be of great importance for the comparability of the results. Ultrasound machine was used to measure the thickness of the skin layers and then bioimpedance measurements were performed for ten young men (age=23 ± 5) at room temperature (22°C) for different body orientations, skin treatments, joint angle, and shoulder arch movements. The results were analyzed using statistical methods and graphical presentation using Python and MatLab. Our observations indicate that there is a significant difference between standing straight up, supine and sitting positions. The results show that there is a significant difference between the two skin treatments (alcohol vs tape stripping). Moreover, joint angle and shoulder arch movements also have an impact on the impedance data. Therefore, to be able to control these factors can potentially improve the quality and comparability of the measured impedance data.

Keywords: Bioimpedance; Body position; Skin layer characterization; Ultrasound.

Figure 1:

The electrode placement during the measurements.

Figure 2:

The mean of the bioimpedance measurement results of all volunteers for the first three body postures, i.e., standing straight up, lying down in supine position, and sitting with arm down and relaxed.

Figure 3:

The mean of the bioimpedance measurement results of all subjects for each body posture. The 6 green legends “Sitting” refers to the measurement made after each movement (shoulder joint and shoulder arch movements), the subjects were asked to return to the starting position (Sitting and arms straight down and relaxed).

Figure 4:

The correlation coefficient between the impedance measurement result and the two skin layer thickness. Pearson correlation was performed between 8 different joint angles and shoulder arch positions and the two skin layer thicknesses.

Figure 5:

The correlation coefficient between the phase angle measurement result and the two skin layer thickness. Pearson correlation was performed between 8 different joint angles and shoulder arch positions and the two skin layer thicknesses.

Figure 6:

The comparison between the impedance measurements of the two skin treatments. The shaded area is the 95% confidence interval, the solid line in the middle represents the mean value of each group.

Figure 7:

The comparison between the phase angle measurements of the two skin treatments. The shaded area is the 95% confidence interval, the solid line in the middle represents the mean value of each group.

Figure 8:

The comparison between the impedance measurements of the two skin treatments. The Wilcoxon rank sum test was performed between 8 different joint angles and shoulder arch positions of the two skin treatments before the attachment of the electrode.

Figure 9:

The comparison between the phase angle measurement of the two skin treatments. The Wilcoxon rank sum test was performed between 8 different body positions, joint angles, and shoulder arch positions of the two skin treatments before the attachment of the electrode. In the y-axis, the number represents: 1-Standing straight up; 2-supine; 3-sitting; 4-Arms straight forward; 5-Arms behind the back; 6-Arms straight out to the side; 7-Arms straight back; 8-Arms straight up.