Monitoring of Hypohydration Caused by Physical Exercise Using a System-on-Chip-Based Bioimpedance Meter

• Published in: Sensors & transducers Vol. 237; no. 9/10; pp. 8 - 16
• Main Authors: Leonov, Vladimir, Konijnenburg, Mario, Grundlehner, Bernard, Van Helleputte, Nick
• Format: Journal Article
• Language: English
• Published: Toronto IFSA Publishing, S.L 01.09.2019
• Subjects: Accuracy; Body fluids; Dehydration; Diet; Dilution; Fluids; Hydration; Impedance; Methods; Monitoring; Physical exercise; Population; Standard deviation; System on chip; Water intakes; Weight measurement
• ISSN: 2306-8515; 1726-5479

This paper describes accurate monitoring of hydration using impedance variation in a human being, which accompanies extracellular fluid loss or gain. A prototype of a precision multifrequency bioimpedance meter built around advanced biomedical S°C (System on Chip) MUSEIC v.2 was used in this study. Calibration of the bioimpedance board was conducted on an RC-model of the volunteer selected for the experiments. The model was built using the averaged results of multiple impedance measurements on the subject within the 1 Hz - 100 kHz, which were repeated on different days on near-euhydrated volunteer. The sources of observed variability in bioimpedance have been studied. Several factors were spotted that affect hydration assessment but were not reported in the literature before. The specific protocols for reaching fluid shift were developed in this study. They enabled minimization of errors in altered hydration state. The bioimpedance method is shown in this research to correctly reflect hydration variation in a single person, so that there is no need for averaging over large population to observe the trend. For demonstration of sensitivity of the developed device to fluid shift, it was tested on the volunteer undergoing repeated mild dehydration and rehydration using light-effort exercise (outdoor cycling). The bioimpedance results were compared with the reference hydration. The latter was obtained using the subject weight measurement and precise counting of caloric intake, the weight of food, and also with the aid of established weight baseline prior to any planned experiment. Special attention has been paid to sodium balance, and several diets have been developed for its regulation. The predictable body fluid loss and gain was supported by measured sweating rate, and also by dehydration and rehydration diets designed for precise control of ion and water intake. The accuracy of fluid shift measurement down to a standard deviation of 200 ml is demonstrated, which essentially exceeds capabilities of known methods and devices, including 'gold standards' like isotope dilution for hydration assessment. Such accuracy satisfies requirements of healthcare and sport. The device has not yet been validated on population.