Gary L. Hansen

Temperature-modulated pressure ulcers: A porcine model

OBJECTIVE A reliable porcine model was developed to facilitate investigations of pressure ulcer formation, healing, and prevention. In the present study, it was specifically used to study the relationship between applied temperature, applied pressure, and time of application in the formation of cutaneous and deep tissue injuries. DESIGN An apparatus and procedure were created to simultaneously apply 12 metal discs (each with a diameter of 51mm) on the dorsal aspect of the swine, all at an equal pressure of 100mmHg, for a 5-hour period, while servo-controlling disc temperatures at either 25, 35, 40, or 45 degrees C. RESULTS The severity of the resultant tissue injuries correlated with an increase in applied temperature. No damage was observed in the superficial or deep tissues underlying the sites of the 25 degrees C pressure applicators. In general, only deep tissue damage resulted from the application of a 35 degrees C temperature, whereas the application of higher temperatures caused both cutaneous and subdermal damage (the extent of necrosis being greater at the 45 degrees C sites). There was a high degree of reproducibility of these results among a large population of sites per temperature (n = 64) and number of animals investigated (n = 16). Furthermore, subsequent healing (monitored up to 4 weeks) was uniform for the degree of induced damage. Insights into pressure ulcer formation were also sought via systematic examination of histological sides and postmortem visual assessment over the 4-week period. CONCLUSION It was concluded that this animal model of temperature-modulated pressure ulcers has the potential for significant use in all major areas of this field, ie, wound formation, healing, and prevention.

Wound status evaluation using color image processing

An accurate diagnosis of burns and pressure ulcers in the early stages can be made by computerized image processing. This study describes a critical assessment of potential methodologies for noninvasive wound evaluation using a color imaging system. The authors also developed a method for quantifying histological readings and applied these techniques to a porcine animal model of wound formation. Differences in calibrated hue between injured and noninjured skin provided a repeatable differentiation of wound severity for situations when the time of injury was known. This color analysis allowed statistically significant differentiation of mild, moderate, and severe injuries within 30 minutes after the application of the injury. It was more difficult to distinguish wound severity one to four days later, however the correlation re-emerged when the wounds were five to seven days old. This technique could be adapted for assessing and tracking wound severity in humans in a clinical setting.

Assessing wound severity with color and infrared imaging of reactive hyperemia

This study examined the use of cutaneous reactive hyperemia as a means for noninvasive assessment of wound severity of newly formed temperature‐modulated pressure injuries in a porcine model. Two methods to quantify the extent of the reactive hyperemic reflex were developed. First, color image analysis was used to measure the hue of injured tissue. The specific hue of the skin surface of the wounded site was found to provide an indication of the severity of the wounds. Second, infrared imaging, coupled with computer image processing, was used to detect differences in skin temperature. The relative surface temperature of the wounds showed a strong correlation with the presence or absence of deep tissue injury. Both techniques correlated with the severity of the injuries as determined by a histologic assessment of biopsied tissue, but infrared imaging provided the better means to assess wound depth.