Effective management of leg ulcer healing depends on accurate and reliable measurements of wound size. Current techniques usually rely on estimates of surface area or circumference which do not fully describe the healing process. A novel instrument has been developed that is capable of measuring the variations in the surface contours (topography) of a solid object. Its primary application is to measure the size of a leg ulcer by scanning a laser displacement sensor over the affected area. There is no contact with the wound and scanning takes approximately 2 minutes to perform. Volume is calculated by subtracting the measured topography from one calculated using an algorithm to reconstruct a healthy leg surface. A study was carried out where patients had their ulcers scanned during their visits to the leg ulcer clinic. Data are presented from two venous leg ulcers showing the calculated volume reducing over time.
The authors use photoelectric plethysmography to determine the external occlusion pressure for blood vessels in human tissue in vivo. Three wavelengths are employed; 950 nm (infra-red), 640 nm (red) and 583 nm (yellow). Each probe is applied in turn to one finger of each subject. Pressure is applied, using a neonatal blood pressure cuff, to the finger via the probe. This pressure is increased linearly to 20 kPa (150 mmHg) over 15 s and then decreased linearly to zero over 15 s. The pressure at which perfusion returns is obtained for four repeat measurements at each wavelength. The mean (+/-standard deviation) occlusion pressures for all 13 subjects investigated are 7.1 (+/-1.9) kPa for infra-red, 6.3 (+/-1.7) kPa for red and 5.8 (+/-1.8) kPa for yellow. The pressure is 0.79 (+/-0.83) kPa lower for red compared with infra-red (P < 0.01), 0.54 (+/-0.60) kPa lower for yellow compared with red (P < 0.002) and 1.3 (+/-1.0) kPa lower for yellow compared with infra-red (P < 0.005). The reduced penetration of shorter optical wavelengths can be used to detect the lower occlusion pressures of the smaller blood vessels nearer the skin surface.
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