Author: Lui, Ka Him Michael
Title: Development of a near-infrared photometer for early detection of tissue distress at anatomical sites prone to pressure ulcer
Degree: M.Phil.
Year: 2012
Subject: Bedsores.
Bedsores -- Prevention.
Hong Kong Polytechnic University -- Dissertations
Department: Interdisciplinary Division of Biomedical Engineering
Pages: xvi, 122 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: Pressure ulcer increases the hospitalization time of non-ambulatory patients and induces heavy financial burden to health care institutions. To prevent the onset of pressure ulcer, clinicians rely on the measurements of skin blood flow and skin oxygenation to monitor the weight-bearing tissues. However, these assessment methods can only reveal the conditions of superficial tissues. Near infrared (NIR) spectroscopy has the potential to measure tissue oxygenation up to several centimeters below the skin surface. In this work, we developed a spatially resolved NIR photometer (λ = 690 and 830 nm) for tissue viability assessment. To ensure the applicability of the spatially resolved method, we examined the consistency of the linear relationship between the transport scattering coefficients (u's(λ)) and wavelengths λ among subjects at the greater trochanter region (a common site for pressure ulcer). Our result showed that the inter-subject variation was 8.3% in 11 subjects which was lower than other reported results at different anatomical sites. This confirmed the consistency of wavelength dependence of u's(λ) in the greater trochanter region among subjects and thus the spatially resolved method is suitable for use in tissue oxygenation measurements at the greater trochanter region. To validate our NIR photometer, a blood-Intralipid tissue phantom was developed. In vitro oxygen saturation measurements were conducted using this phantom and compared with results obtained from a commercially available blood gas analyzer. The result showed a high correlation (r² = 0.9718) between the measurements by the two systems. The average tissue oxygen saturation measured by using our NIR photometer in healthy subjects' forearm was 71.4 ± 14.0%. This value was comparable to those measured by other NIR spectroscopic systems under similar conditions (63.9% to 72.1%). During passive exercise of the forearm muscle by continuous electrical stimulation, tissue oxygenation in the targeted muscle was found to decrease by 10.5 ± 5.4% of its resting values. Due to the limited power output of the laser system, the penetration depth of our NIR photometer was estimated to be 3.4 mm, which was much less than other commercial NIR spectroscopic systems. Further improvements have to be made to increase the penetration depth of our NIR photometer before it can be applied to assess the oxygenation of deep tissues that are prone to pressure ulcer.
Access: open access

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