Bioimpedance Spectroscopy for the Estimation of Body Fluid Volumes in Mice

Abstract

Conventional indicator dilution techniques for measuring body fluid volume (BFV) are time‐consuming, expensive and require bulky equipment. Bioimpedance spectroscopy (BIS) may be a useful alternative for BFV determination due to being rapid, minimally invasive and allowing repeated measurements. BIS has not been reported in mice; such analysis would be helpful particularly in rare transgenic or knockout mouse lines. Hence, we examined how well BIS estimates BFV in mice. Using C57/Bl6 wildtype mice, the BIS system demonstrated <5% inter‐mouse variation in total body water (TBW), extracellular (ECV) and intracellular fluid volume (ICV) between animals of similar body weight (BW). TBW, ECV and ICV differed between heavier male and lighter female mice, however, the ratio of TBW, ECV and ICV to BW did not differ within mice and corresponded closely to values in literature. Default resistance coefficients used by the BIS system defined for rats produced body composition values for TBW that exceeded BW in mice. Therefore, body composition was measured in mice using a range of resistance coefficients. Resistance values at 10% of those defined for rats provided TBW, ECV and ICV ratios to BW that were similar to those published in literature. Further evaluation of the sensitivity of the BIS system was determined by its ability to detect volume changes after saline infusion. One mL saline provided the predicted increases in compartmental fluid volumes in mice. In summary, BIS is a sufficiently sensitive and accurate method for the estimation of body composition in mice. The ability to perform serial measurements will be a useful tool for future studies.