Validation of bioimpedance spectroscopy to assess acute changes in hydration status
Karen J Higgins1, Phyllis M Reid, Scott B Going
1Department of Nutritional Sciences, The University of Arizona, Tucson, AZ 85721-0038, USA.
Purpose:
To validate bioimpedance spectroscopy (BIS) as a field method for measuring small, acute changes in extracellular water (ECW) during a fluid fast/rehydration manipulation.
Methods:
Seventeen young adults (15 female, 2 male) participated in a 4-d fluid fast/rehydration protocol designed to induce acute changes in ECW. ECW change (DeltaECW), measured by bioimpedance spectroscopy (BIS-DeltaECW), was compared with DeltaECW, measured by bromide dilution (Br-DeltaECW), and change in body weight (DeltaBW).
Results:
Regardless of hydration status, BIS-DeltaECW and Br-DeltaECW were similar; during dehydration, the mean difference between these two methods was 0.16 kg (P=0.61), and during rehydration, the mean difference was 0.58 kg (P=0.06). Assuming that DeltaECW=DeltaBW, DeltaECW as estimated from DeltaBW differed significantly from Br-DeltaECW, but not from BIS-DeltaECW. In addition, BIS-DeltaECW correlated significantly with DeltaBW (r=0.57 and 0.65 during dehydration and rehydration, respectively). However, the magnitude of DeltaECW impacted the accuracy of BIS-DeltaECW because BIS measures tended to overestimate DeltaECW at values between 0.0 and 1.0 kg and to underestimate changes at values above 1.0 kg.
Conclusion:
These findings suggest that BIS provides an accurate estimate of DeltaECW compared with bromide dilution during short-term changes in hydration.
