title: Total body water measurements using resonant cavity perturbation techniques.
abstract: A recent paper proposed a novel technique for determining the total body water (TBW) of patients suffering with abnormal hydration levels, using a resonant cavity perturbation method. Current techniques to measure TBW are limited by resolution and technical constraints. However, this new method involves measuring the dielectric properties of the body, by placing a subject in a large cavity resonator and measuring the subsequent change in its resonant frequency, fres and its Q-factor. Utilizing the relationship that water content correlates to these dielectric properties, it has been shown that the measured response of these parameters enables determination of TBW. Results are presented for a preliminary study using data estimated from anthropometric measurements, where volunteers were asked to lie and stand in an electromagnetic screened room, before and after drinking between 1 and 2 l of water, and in some cases, after voiding the bladder. Notable changes in the parameters were observed; fres showed a negative shift and Q was reduced. Preliminary calibration curves using estimated values of water content have been developed from these results, showing that for each subject the measured resonant frequency is a linear function of TBW. Because the gradients of these calibration curves correlate to the mass-to-height-ratio of the volunteers, it has proved that a system in which TBW can be unequivocally obtained is possible. Measured values of TBW have been determined using this new pilot-technique, and the values obtained correlate well with theoretical values of body water (r = 0.87) and resolution is very good (750 ml). The results obtained are measurable, repeatable and statistically significant. This leads to confidence in the integrity of the proposed technique.
authors.affiliation: Physical Layer Group, Department of Electronics, University of York, Heslington, York YO10 5DD, UK. das125@ohm.york.ac.uk
authors.forename: Darren A
authors.initials: DA
authors.lastname: Stone
authors.forename: Martin P
authors.initials: MP
authors.lastname: Robinson
mesh_terms: D000886:Anthropometry / Q000379:methods*; D001834:Body Water / Q000378:metabolism / Q000502:physiology*; D002138:Calibration; D017097:Electric Impedance; D005110:Extracellular Space / Q000502:physiology; D005215:Fasting; D006801:Humans; D001743:Urinary Bladder / Q000502:physiology; D014867:Water / Q000737:chemistry / Q000502:physiology*
chemical_list: D014867:Water