Estimation of intra and extra-cellular segmental volumes using electrical impedance measurements

Authors:Rosell, J. Casas, O. Bragós, R. Riu P.J. and Adersen L.J

Journal: Medical & Biological Engineering & Computing Volume 35 Supplement Part 1, p.333

Conf. title:World Congress on Medical Physics and Biomedical Engineering, Nice, France, September 14-19,1997

Abstract: Introduction Estimates of body composition and body fluids from electrical impedance measurements are usually based on the right side impedance at a single frequency. In this work we estimate intra- and extra-cellular water volumes for different body segments using measurements of their impedance from 10 kHz to 1 MHz. Materials and Methods Specific equipment and software were designed to measure seven body segments (head + neck, both arms, both legs, abdomen and thorax) using 11 electrodes. The system is able to measure at 8 selected frequencies in the range of 10 kHz to 1 MHz. For this experiment we selected 8 male subjects (23-29 years, 74-84 kg, 179-194 cm). Total body water (TBW) was estimated from 40K measurements, extracellular water (ECW) using 51Cr-EDTA and segmental volumes using a DEXA scan. We measured the impedance of each subject twice, for a basal state and after ingestion of water (3.5% of TBW), at 10, 20, 50, 100, 500 and 1000 kHz. New estimation equations for TBW and ECW were produced for each segment where is an equivalent electrical length for each segment, H is the height, KTBW and KECW are gain constants and KoTBW and KoECW residual volumes. All parameters were adjusted using a least squares method. Results Correlation between TBW estimation using DEXA and segmental impedance is 0.72, between DEXA and 40K is 0.73. Using the right side impedance correlation against DEXA is 0.66. TBW changes due to water loading were estimated with a SD of 0.54 l and ECW changes estimation had a SD of 0.25 l, both compared to expected values. Correlation for segmental volumes range from 0.12 for the head to 0.63 for the arms. Conclusion The estimation of segmental water volumes using impedance is a convenient method and we show that the results correlate with DEXA scan measurements. Also, the addition of segmental volumes gives better estimates for TBW and ECW than the right side impedance method. Acknowledgment This work was supported by Nuevas Tecnologías del Espacio S.A. and the European Space Agency.