Development of a Novel Device for Non-Invasive Body Composition Measurements

Cole, Thomas 1, 2 ;  Gavrilovic, Bojan 2 ;  Popovic, Milos 1, 2 ;  Yadollahi, Azadeh 1, 2

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 2. Toronto Rehabilitation Institute, University Health Network

Background: Bioimpedance Analysis (BIA) is a simple and non-invasive method to assess fluid volumes and tissue composition. This includes muscle mass, fat mass, total body water, and intra- and extra-cellular fluid volume. Current methods of assessing tissue composition are limited to X-rays and MRI measurements, which are expensive and impractical in many settings. Furthermore, current BIA devices on the market are limited to performing single-frequency or whole-body analysis. Where, single-frequency analysis lacks the ability to differentiate between intracellular and extracellular fluid volumes and whole-body analysis cannot determine regional edema or abnormalities in tissue composition. Furthermore, the ability to measure fluid volume both regionally and simultaneously, gives the added ability to monitor fluid shifts. Our objective is to develop a practical clinical tool which utilizes Multi-Frequency BIA to accurately monitor and assess the tissue composition and fluid volume of multiple body segments simultaneously.

Methods: Tissue composition is calculated using the electrical impedance (resistance and reactance) measurements of the tissue along with anthropometric measures such as segmental length and circumference. By injecting a low amplitude alternating current into the tissue we can measure the resulting impedance. It is known that the resistance is proportional to the length and inversely proportional to the width of a conducting medium. Furthermore, resistivity of the tissue is inversely proportional to the hydration level. Using these properties we can estimate the tissue composition.

The proposed device will measure the tissue composition of the neck, thorax, abdomen, and leg simultaneously, and will be validated against an established bioimpedance device currently on the market (SFB7, ImpediMed, CA). While recording tissue composition of the above segments with the device, subjects will be asked to change positions from supine to sitting up to determine whether fluid shifts are observable.

Expected Results: We expect that our proposed device will have comparable accuracy to the existing device. Furthermore, we expect to be able to observe fluid shift between body segments during position changes.

Significance: The proposed device will fill the need for a practical clinical tool that is portable and easy to use for continuous monitoring of tissue composition and fluid volume of various body segments. The device is a multifaceted tool that can be used to assess and monitor tissue composition such as: fluid levels and edema in patients with fluid retaining disorders including heart failure and renal failure, muscle mass in the elderly and frail population, fat mass in the obese, hydration level of patients undergoing hemodialysis, and fluid shift in patients with sleep apnea.