Optimisation of indices of external pneumatic compression for prophylaxis against deep vein thrombosis: Radionuclide gated imaging studies

Summary: The amoun and rate of blood expelled with different modes of intermitten external pneumatic compression applied to the lower leg were studied on a regional basis in a series of experiments on healthy human volunteers. Radionuclide imaging of the labelled blood pool, with acquisition of counts synchronised to the pressurisation cycle, provided data on regional blood volumes in the leg in relation to time. To determine the changes in blood volume of the lower leg resulting from external pneumatic compression labelled red blood cell counts were determined during 10 different types of compression cycle. Since venous stasis is considered to be a major cause of venous thrombosis the red blood cell counts were used to calculate regional values of the fraction of blood ejected as well as comparative indices proportional to regional flow rate, regional velocity, and regional wall shear stress. All these indices should be maximised for optimal prophylaxis agains deep vein thrombosis. The four compartmen cuff in each compression mode applied a mean pressure of 45 mm Hg, bu different combinations of values were used for intercompartmental pressure gradation (†p) and for intercompartmental time sequencing to the onse of compression (†t). Uniform compression (†p=0; †t=0) was substantially inferior to cycles with gradation and sequencing. The optimal values of △p were in the range 5-10 mm Hg and of †t in the range 0-0.5 seconds.