PURPOSE: The V.A.C. technique has been shown to accelerate the rate of new tissue formation and thus decrease the time to wound closure. Similar to tissue expansion, mechanical stretching of cells in the periwound tissue by vacuum application causes an increase in the mitotic rate. In fact, deformation of vascular endothelial cells can cause activation of the vascular endothelial cell growth factor (VEGF) pathway even in the absence of VEGF. This study was designed to determine the extant of deformation of periwound tissues of abdominal wounds in cadavers with various vacuum dressings. METHODS: Fresh female cadavers (n=2) were obtained and 10 cm (lateral) by 15 cm (axial) full thickness wounds extending down to the rectus muscles were created. Radio-opaque markers of differing shapes were placed at 4 cm intervals on the skin, mid-fat, and under the fat but above the rectus muscles. The markers were arrayed laterally, superiorly, and inferiorly. Radiographs and digital photographs were taken for baseline measurements. Five different dressing materials were placed in the wound and covered with a thin film dressing to create an airtight seal: only drape (control); black V.A.C. foam (Granufoam); one layer of white V.A.C. foam (Versafoam); two layers of white foam; and three layers of white foam. 125 mm Hg vacuum was applied to each dressing and radiographs and photographs were taken. Surface area of the wound with and without vacuum application for each dressing (and control) was calculated. Displacement of the markers was determined and the magnitude of displacement determined for the different tissue levels. RESULTS: The wounds increased to 104% of the original size when excised. This area was used as reference for surface area comparisons. Application of vacuum alone (only drape with no dressing) resulted in an increase of wound surface area to 104% of the reference size). Ranked by greatest change is size, the dressings under vacuum were: black foam (84% of original surface area); 3 layers of white foam (84.4%); 2 layers of white foam (87.4%); 1 layer of white foam (100%). Deformation was greatest at the wound edge (18%), and decreased as the distance from the wound edge increased. Deformation was greater laterally than axially. CONCLUSIONS: Deformation of the tissues extends radially outward form the wound and decreases as distance increases. Deformation increased as the thickness of the dressings increased: 1, 2, 3 layers of white foam, black foam). Similar to increases seen with tissue expanders, deformation of tissues distant from the wound edge may increase the rate of cell division in these distant tissues. These additional tissues may migrate and be incorporated during wound closure.
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