Application of bioelectrical impedance phase angle in mice: Comparison between young and old mice

Introduction

Phase angle is an important parameter for assessing tissue quality. Bioelectrical impedance analysis (BIA) is used to assess phase angle in human subjects, but its application in mice is scarcely reported.

Methods

A commercially available BIA device (InBody M20, InBody, Korea) was used in this study. Needles were inserted subcutaneously for measurements under inhaled anesthesia. The phase angle at 50 kH was used for comparison. First, the measurements were conducted in different electrode positions (proximal or distal) and different time series during anesthesia or after euthanasia. Second, we compared the phase angle, body weight, grip strength, and tibialis anterior muscle cross-sectional area between young (12 weeks) and old (approximately 2 years) male C57BL/6J mice.

Result

The phase angle was different in the proximal or distal position of the electrode (p = 0.02). Although the phase angle changed after euthanasia, it was not different during anesthesia (p = 0.39–84). Under distal electrode position and anesthesia, the body weight and cross-sectional area of the right anterior muscle were higher in old mice than in young mice (young vs. old, body weight: 24.4 ± 1.0 g vs. 33.2 ± 3.4 g, p < 0.01; cross-sectional area: 723 ± 365 μm² vs. 977 ± 398 μm², p < 0.01), but grip strength was lower in old mice (14.6 ± 1.3 g vs. 12.7 ± 1.8 g, p = 0.02). The phase angle was lower in old mice than in young mice (11.5 ± 0.9 vs. 10.2 ± 1.2, p < 0.02).

Conclusion

BIA measurement in mice was feasible and reproducible, and the low phase angle was associated with reduced muscle strength.