Abstract
Tissue dehydration is known to have adverse effects on health and is highly challenging to characterize in vitro due to the complexity of the cell/tissue organisation. There have been a large number of studies reporting the dielectric properties of animal and human tissue explants or bodily fluids such as urine or blood over a wide frequency range from 10 Hz to 100 GHz. However, variations in blood composition involving the cell type, haematocrit (HCT) protein levels, ionic conductivity, electrolyte or glucose concentration will affect the dielectric measurements. The present study examined the effects of physiological osmotic solutions with NaCl (280 mOsmol/kg to 300 mOsmol/kg), HCT (35% to 50%) and albumin (3.5 g/dl to 5.5 g/dl) isolated from bovine blood on the dielectric properties measured at frequencies spanning from 0.5 GHz to 20 GHz using an open-ended co-axial probe. Measurements demonstrated linear correlations between permittivity and loss factor of blood solutions with varying HCT levels, albumin or osmolality such that a high protein concentration reduced the dielectric response in a dose-dependent manner. Whilst the spectral trends for the permittivity response to HCT and albumin were similar in a concentration-dependent manner, the loss factor profile was influenced by osmolality of the solution. In summary, we characterized the dependence of the microwave dielectric properties of blood on HCT, albumin and osmolality. The dielectric measurement technique has the potential to determine hydration levels for future diagnostic and therapeutic devices.
Highlights
Dehydration is a continuing problem in malnutrition and healthcare resulting in critical patients who develop multiple organ failure with annual NHS costs estimated around £13 billion [1], [2]
A similar dielectric field pattern was found at 20 GHz, suggesting dielectric measurements could be performed in microliter sample volumes
The present study demonstrated linear relationships between broadband microwave dielectric properties of varying HCT and albumin concentrations in osmotic solutions measured between 0.5 GHz and 20 GHz
Summary
Dehydration is a continuing problem in malnutrition and healthcare resulting in critical patients who develop multiple organ failure with annual NHS costs estimated around £13 billion [1], [2]. The subject’s hydration levels are determined by urine, blood or plasma osmolality either with freeze-point or vapor pressure depression techniques to quantify electrolyte and fluid ration [3]. There have been a large number of studies reporting the dielectric properties of healthy or diseased tissues or bodily fluids from animals and humans over a wide frequency domain of 10 Hz to 100 GHz for medical diagnostics, therapeutics and wearable devices [4], [5]. Animal or human in vitro studies and numerical models have reported the tissue dielectric properties in dehydration, cancer, diabetes, inflammation, skin and lung disease [6]-[16]. The effects of changes in the cell membrane and the extracellular matrix composition will increase blood or plasma osmolality, haemoglobin and haematocrit (HCT) levels, a protein well known to represent red blood cell (RBC) or erythrocyte
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