The influence of local heating on skin microcirculation in pressure ulcers, monitored by a combined laser Doppler and transcutaneous oxygen tension probe.

In a prospective, controlled study the skin microcirculation and transcutaneous oxygen tension were evaluated in 28 elderly patients (85 +/- 0.8 years) with grade 2 and 3 pressure ulcer. Laser Doppler fluxmetry and transcutaneous oxymetry techniques were used together in a combined probe to simultaneously evaluate the influence of heat stress at 44 degrees C, at the same time and in the same area of the ulcer edge. Total skin microcirculation was already increased at rest before heating, and increased even more during a fast and then a more gradually heat-induced hyperaemia response compared with undamaged skin. The increase showed a biphasic manner. On the other hand, the oxygen diffusibility from the capillaries to the skin surface was significantly reduced, compared with undamaged skin. One hypothesis may be that in ageing skin the main part of the increased skin microcirculation in a pressure ulcer were passing through thermoregulatory vessels in subpapillary tissue layers. Interactions between the increased blood flow and metabolic activity at the ulcer edge might be oxygen-consuming, leading to reduced oxygen content passing through the capillaries and contributing to tissue ischaemia. Disturbances of the local skin microcirculation and tissue oxygenation will influence the ulcer healing rate and may affect the healing progress.