Abstract
The costs of pressure injury treatments continue to rise with a steadily aging population and consistent pressure injury incidence rates. Evidence suggests that the bioimpedance of living tissues changes in response to continuous pressure loading and may be useful as an indicator for the onset of pressure injuries. Therefore, the development of a low-cost, accurate, and portable sensor capable of measuring the bioimpedance of human skin has practical significance in the development of pressure injury prevention devices. This paper reports the design and characterization of a system for measuring skin impedance based on the AD5933 impedance analyzer. The sensor was tested for accuracy via measurements of a simplified electrical equivalent skin model. Long duration measurement stability was assessed over 24 hours and skin measurement repeatability was performed on the volar forearm. The power consumption was measured both during idle and when transmitting data for each major component. The sensor demonstrated accuracies similar to those reported for other AFE’s used in conjunction with the AD5933. Additionally, the sensor shows good stability over long measurement durations as well as good repeatability when measuring the skin bioimpedance on the volar forearm. Power consumption was as expected and future suggestions for lowering the overall circuit power consumption and size are presented.
Highlights
In an aging population, the number of individuals at risk of developing pressure-induced injuries is steadily increasing
Bioimpedance (Z) is a complex quantity composed of the real resistance component (R), which is primarily attributed to total body water and the imaginary reactance component (Xc), which is attributed to the lumped capacitance of cell membranes [19]
Studies have shown that damaged tissues exhibit lower overall impedance, reactance, and phase angle [8, 20, 21]. This has been described as a disturbance of biological structures, the destruction of healthy cell membranes which leads to increased ion flow and reduced capacitance
Summary
The number of individuals at risk of developing pressure-induced injuries is steadily increasing. Pressure injuries ( known as pressure ulcers, decubitus ulcers, bed sores) are localized damage to the skin and underlying soft tissues caused by excessive pressure, shear, or a combination of the two for a prolonged duration. These injuries typically form over a boney prominence such as the sacrum, heels, and occipital bone. Visual inspection by trained nursing staff is the gold standard for pressure injury detection, which can lag the pressure loading event by several days to weeks This delay, as well as the subjective nature of visual inspections, has led researchers to investigate various alternative non-invasive monitoring techniques such as ultrasound, thermography, photography, and sub-epidermal moisture (SEM) [3,4,5,6]. No system currently exists that can continuously monitor an individual and alert them or a clinician before tissue damage may result in a pressure injury
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