Abstract: Objective To evaluate the therapeutic effects of VSD combined with irrigation of oxygen loaded fluid on the growth of granulation tissue and macrophage polarization in chronic venous leg ulcers. Methods Thiry-four patients with chronic venous leg ulcers hospitalized in our department from December 2010 to July 2014 were divided into VSD group (A, n=11), VSD+ irrigation group (B, n=11), and VSD+ oxygen loaded fluid irrigation group (C, n=12) according to the random number table. After admission, debridement was performed, and granulation tissue in the center of the wound was harvested during the operation. After debridement, the patients in group A were treated with VSD only (negative pressure from -30 to -25 kPa, the same below); the patients in group B were treated with VSD combining irrigation of normal saline; the patients in group C were treated with VSD combining normal saline loaded with oxygen irrigation (flow of 1 L/min). On post treatment day (PTD) 7, the VSD devices were removed. Gross observation was conducted before debridement and on PTD 7. On PTD 7, the granulation tissue in the center of the wound was harvested for histopathological observation with HE staining and Masson staining, following calculation of granulation tissue coverage rate. After debridement but before the negative pressure therapy (hereinafter referred to as before treatment) and on PTD 7, partial pressure of oxygen of the skin around the wound was measured by transcutaneous tissue oxygen tension survey meter. On PTD 7, expression of vascular endothelial growth factor (VEGF) was determined with immunohistochemistry. Before treatment and on PTD 7, cells with double positive expressions of induced nitric oxide synthase plus CD68 (type Ⅰ macrophage) and arginase 1 plus CD68 (type Ⅱ macrophage) were observed with immunofluorescence staining and quantified. Data were processed with Fisher's exact test, one-way analysis of variance, covariance analysis, paired t test, and LSD test. Results (1) The gross observation showed that before debridement there was a certain amount of necrotic tissue and little granulation tissue in the wounds of patients in all the 3 groups. On PTD 7, new granulation tissue was found in the wounds of patients in all the 3 groups, and in group C its amount was the largest. (2) On PTD 7, the granulation tissue coverage rate of wounds in patients of group C was higher than that of group A or B (P<0.05 or P<0.01). (3) On PTD 7, HE staining showed that there appeared more abundant new born microvessels and fibroblasts in the wounds of patients in group C than those in groups A and B; Masson staining showed that there was more abundant fresh collagen distributed orderly in the wounds of patients in group C compared with group A or B. (4) On PTD 7, it was found that partial pressure of oxygen of the skin around the wounds in patients of group C [(40.7±4.1) mmHg, 1 mmHg=0.133 kPa] was higher than that of group A [(35.0±3.1)mmHg] or B [(35.4±2.7) mmHg, with P values below 0.01]; the partial pressure of oxygen of the skin around the wounds of patients in all the 3 groups was increased significantly compared with that before treatment (with t values from 10.38 to 22.52, P values below 0.01). (5) On PTD 7, the expression of VEGF in the wounds of patients in group C was higher than that in group A or B (P<0.05 or P<0.01). (6) On PTD 7, the number of type Ⅰ macrophages in granulation tissue of patients was respectively 14.3±2.3, 11.5±3.0, and 10.7±2.3 per 400 times vision field in groups A, B, and C (F=25.14, P<0.01), while the number in group C was less than that in group A or B (P<0.05 or P<0.01). Compared with that before treatment, the number of type Ⅰ macrophages was significantly decreased on PTD 7 in all the 3 groups (with t values from 14.76 to 23.73, P values below 0.01). On PTD 7, the number of type Ⅱ macrophages in granulation tissue of patients was respectively 32.7±3.2, 35.1±3.3, and 41.3±3.2 per 400 times vision field in groups A, B, and C (F=81.10, P<0.01), and the number in group C was lager than that in group A or B (with P values below 0.01). Compared with that before treatment, the number of type Ⅱ macrophages in all the 3 groups was significantly increased (with t values from -69.34 to -47.95, P values below 0.01). Conclusions VSD combined with irrigation of oxygen loaded fluid can raise the partial pressure of oxygen of the skin around the wounds effectively, promoting the transition of macrophages from type Ⅰ to type Ⅱ, thus it may promote the growth of granulation tissue, resulting in a better recipient for skin grafting or epithelization.