INTRODUCTION: Intermittent pneumatic compression (IPC) has been well documented as a means for prophylaxis against deep vein thrombosis (DVT), which frequently occurs during and after surgery and in some nonsurgical situations, especially in the conditions of prolonged immobilization. Although studies demonstrated that hemodynamic alterations produced by IPC is not limited to the venous blood flow in the area of compression, but involved in alteration of systemic circulation, the exact mechanism is still unclear. By using a rat cremaster muscle model, the purpose of the present study was to observe the changes of microcirculation of the distant skeletal muscle during and after application of IPC on the legs, and to observe whether nitric oxide (NO) is involved in mediating this microcirculation change caused by IPC application. MATERIALS AND METHODS: A specially designed IPC device with a cycle of 5 sec of 60 mm Hg pressure and 25-sec interval was applied to both legs of the rats weighing 120 to 150 g. The left cremaster muscle was exposed under microscope. Microcirculation was assessed by measuring the diameter of multiple vessel segments. Vessels were recorded prior to beginning IPC (baseline) and then at 10-min interval, and were divided into three subgroups according to their baseline diameters (10 < d < 20 m; 20 < d < 40 m; and 40 < d < 70 m). The study was performed in two protocols. First, vessel diameters were recorded for 120 min both in experimental group (n โซืกโฌ 24) with 60 min of IPC application and in sham group (n โซืกโฌ 10). Second, with a 120-min infusion of L-NMMA (N g -monomethyl-Larginine, a NOS inhibitor, 10-mol/min/100 g body weight) through a jugular vein cathaterization with a micropump, the vessel diameters were recorded for 120 min with (n โซืกโฌ 10) and without (n โซืกโฌ 10) 60 min of IPC application. The data were analyzed by one-way analysis of variance (ANOVA). A P < 0.05 was taken as significant. RESULTS: When compared to baseline, the mean diameter of both arterial and venous vessels in the sham group remained at the baseline level during the 120-min experiment. In the IPC group, the diameter was increased at 10 min of IPC application and reached the maximal level at 30 min with an increase of 130% ยฑ 12%, 119% ยฑ 8%, and 113% ยฑ 5% in each venous category and 119% ยฑ 17%, 108% ยฑ 13%, and 124% ยฑ 18% in each arterial category, respectively. The diameters were remained at the 10-min level at the end of IPC application and were gradually decreased to the baseline level after then. When compared to the sham group, a significant difference of venous vessels was present from 10 to 50 min in 10-21 m segments and at each time point during the first 10 min after IPC application in 21-40