Effects of the magnitude of pressure on the severity of injury and capillary closure in rat experimental pressure ulcers.

Experimental pressure ulcers were successfully produced in the rat abdominal wall at 100 mmHg in our previous study. We hypothesized that injury is less severe when pressures are lower than 100 mmHg and explored a critical pressure in the production of pressure ulcers. At 70 and 60 mmHg, repeated compressions for 4 h daily for 5 consecutive days resulted in partial skin necrosis and eschar formation in the majority of rats, whereas skin injuries were absent or very mild in most of the rats at 50 mmHg. The extent of ischemia was also examined by visualization of capillary blood flow using intravascular infusion of Lycopersicon esculentum lectin. Rat abdominal walls were compressed in the range from 0 (control) to 100 mmHg. The percentages of open capillaries were 62.8 ± 10.1% at 0 mmHg and 34.7 ± 18.5% at 10 mmHg. The ratio of open capillaries was further decreased with increasing pressure, but not pressure dependently. In conclusion, the severity of injury at 50 mmHg was drastically milder than that at 60 mmHg or higher, whereas the extent of ischemia (capillary closure) was not significantly different. The pressure is vitally important; however, other factor(s) besides ischemia is likely to promote the development of pressure ulcers.