Comparison between a weight compression and a magnet compression for experimental pressure ulcers in the rat. Histological studies and effects of anesthesia.

To develop an experimental model and evaluate the effects of the magnitude and duration of pressure, the rat abdominal wall (25x20 mm) was subjected to compression either by a weight or by two magnets. In the weight compression tests, a steel plate was inserted under anesthesia into the rat peritoneal cavity, and the abdominal wall was compressed in situ between the underlying steel plate and a weight placed on the abdominal wall. This method resulted in moderate changes in the subcutaneous connective tissue and muscle at 100 mmHg (13.3 kPa) for 4 h, while some muscle damage was observed at 50 mmHg (6.7 kPa) for 4 h and at 100 mmHg for 2 or 3 h. In the magnet pinching tests, a magnet was inserted into the peritoneal cavity, and another magnet overlaid on the skin. Then the abdominal wall was compressed by the two magnets with or without anesthesia. The compression without anesthesia produced significant edema and injuries of the abdominal wall at 50 mmHg for 4 h and at 100 mmHg for 3 or 4 h, while the injuries incurred at 100 mmHg for 2 h were mild. Susceptibility to pressure was high in the muscle, moderate in the subcutaneous connective tissue, and low in the skin. The compression with anesthesia produced significantly milder injuries than those under anesthesia. These findings indicate that the difference in the extent of injuries between the weight compression and magnet compression models are clearly attributable to the pentobarbital anesthesia induced during the compression. Results therefore show that experimental pressure ulcers should be examined in a waking condition and that magnet compression is a useful model for studying the pathogenesis of pressure ulcers.