To validate bioimpedance spectroscopy (BIS) as a field method for measuring small, acute changes in extracellular water (ECW) during a fluid fast/rehydration manipulation.
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 (ΔECW), measured by bioimpedance spectroscopy (BIS-ΔECW), was compared with ΔECW, measured by bromide dilution (Br-ΔECW), and change in body weight (ΔBW).
Regardless of hydration status, BIS-ΔECW and Br-ΔECW 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 ΔECW = ΔBW, ΔECW as estimated from ΔBW differed significantly from Br-ΔECW, but not from BIS-ΔECW. In addition, BIS-ΔECW correlated significantly with ΔBW (r = 0.57 and 0.65 during dehydration and rehydration, respectively). However, the magnitude of ΔECW impacted the accuracy of BIS-ΔECW because BIS measures tended to overestimate ΔECW at values between 0.0 and 1.0 kg and to underestimate changes at values above 1.0 kg.
These findings suggest that BIS provides an accurate estimate of ΔECW compared with bromide dilution during short-term changes in hydration.
1Department of Nutritional Sciences, The University of Arizona, Tucson, AZ; and 2Tucson Area Indian Health Service, U.S. Department of Health and Human Services, Tucson, AZ
Address for correspondence: Wanda H. Howell, The University of Arizona, Department of Nutritional Sciences, PO Box 210038, Tucson, AZ 85721-0038; E-mail: firstname.lastname@example.org.
Submitted for publication July 2006.
Accepted for publication January 2007.