A Portable Sensor for Skin Bioimpedance Measurements

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.

Ulcerated skin evaluation by electrical impedance measurements

“…The use of electrical parameters in order to evaluate the condition of the skin seems to be effective in view of the results presented above as well as the measurements conducted in other centers. Measurements using portable devices for the assessment of skin electrical parameters were conducted by Harvey et al 4 They found that the measurements of electrical parameters could be applicable to both animal and human studies aimed at assessing ulcer formation. 4 The electrical parameters were also used in the studies of skin parameters around the lesions and in other distant tissues.…”

“…Measurements using portable devices for the assessment of skin electrical parameters were conducted by Harvey et al 4 They found that the measurements of electrical parameters could be applicable to both animal and human studies aimed at assessing ulcer formation. 4 The electrical parameters were also used in the studies of skin parameters around the lesions and in other distant tissues. For the purpose of the research, the impedance measurements were performed at the frequency ranging from 30 Hz to 10 MHz.…”

“…The presented results encourage the introduction of bioimpedance as a method of management in patients with lower leg ulcers, as was also demonstrated in the aforementioned studies. 4,9,22…”

“…Interestingly, in the course of one of the studies, skin measurements were conducted 27 times per hour. 4 Skin discontinuity often accompanies the development of pressure ulcers, and in this case, electrical impedance testing may also be applied. The tests were performed at the early stage of bedsores formation in elderly patients who were not fully mobile or were disabled.…”

“…The electrical properties of biological tissues, which include the electrical impedance, depend on the structure of the tissue and on the frequency of the current conducted 1,2 . The most commonly analysed electrical parameter in terms of the skin is impedance, 3,4 which was discussed in publications as early as around 1920 5 . Impedance varies depending on the thickness and hydration level of the skin, sweat gland activity, trauma, age, and environmental conditions, including temperature and humidity 1,2 .…”