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Excerpt
Bioelectrical impedance can theoretically detect changes in fluid compartments. The influence of the ionic composition of the compartment being measured or perturbed has not been studied. The aim of this study was to measure with multi-frequency bioelectrical spectroscopy (BIS) changes during infusion of equal volumes of different solutions, namely 0.9% NaCl, 3.3%glucose with 0.3% NaCl, and 5% glucose. In four healthy volunteers (2M, 2F, age 33 ± 5 yr) BIS was measured using a Xitron PC-4000 analyzer. Each volunteer received 1000 ml of each solution over 1 hour through an intravenous line. BIS was recorded at frequencies varying from 5 to 500 kHz every 5 min during the infusion and 15 min thereafter. With the infusion of 0.9% NaCl there was a significant decrease in resistance (p<0.03), which was expected as a result of the expansion of total body water volume. Resistance increased significantly with the infusion of 5% glucose(p<0.001) and of 3.3% glucose and 0.3% NaCl (p<0.04). Repeated measures ANOVA showed a significant difference in resistance among the three solutions(p<0.01). No relationship was found between changes in resistance and calculated changes in total body water or extracellular water initially, measured by dilution techniques, but there was a significant correlation between changes in resistance and changes in plasma osmolarity(r2=-0.64, p<0.001). We conclude that BIS might be able to detect changes in the composition of the body fluids rather than measuring the volume of total body water.
