Analysis of arterial flowmotion in spinal cord injured and elderly subjects in an area at risk for the development of pressure sores.

Flowmotion (blood flow changes due to vasomotion) in the skin over a risk area for pressure sores, the sacrum, and a non-risk area, the gluteus muscle, was evaluated by laser Doppler fluxmetry during resting conditions and post-occlusive reactive hyperaemia (PRH) response. Measurements were made in healthy younger subjects and in two risk groups for pressure sores-spinal cord injured (SCI) and the elderly. The SCI were divided into two subgroups, one with and one without distinct flowmotion seen on the original recordings over the sacrum. The Prony spectral line estimation (PSLE) method was used to determine the power spectrum of the flowmotion activity. During the PRH, flowmotion frequencies were found in two separated bands, 5.4-6.6 cpm (cycles min-1) and 7.8-9.0 cpm. In the subgroup without distinct flowmotion, the PSLE method found flowmotion frequencies similar to the other groups. During the PRH, the flowmotion power pattern over the sacrum was similar within all groups, but the power was extremely low in one subgroup of SCI subjects. To conclude, flowmotion (vasomotion) was present in the two skin areas and increased during the PRH response, reaching a maximum within 50 s. This study shows that the flowmotion frequencies might be locally driven, whereas the power might be centrally mediated. Disturbances in microcirculatory flowmotion can be a part of the mechanisms leading to skin ischaemia and pressure sores. A new method has been developed for analysing differences in flowmotion behaviour such that statistical comparisons can be made.