This paper presents the results of a numerical study of the technique of periodic external compression for the prevention of deep vein thrombosis. In the model the veins of the lower leg are portrayed as a continuous system rather than as discrete elements as in previous models. Consequently, we are able to explore the detailed effects of different modes of compression including (i) uniform compression, the simultaneous application of uniform pressure over the entire lower leg, (ii) graded compression, the application of nonuniform pressure, maximum at the ankle and minimum at the knee, and (iii) wavelike compression, a wave of compression proceeding from the ankle toward the knee. These numerical results indicate that the effectiveness of uniform compression is severely compromised by the formation of a flow-limiting throat at the proximal end of the compression cuff that reduces both the rate at which blood is discharged from the lower leg and the total blood volume removed. Both of these detrimental effects can be avoided by the use of either wavelike or graded compression. Both alternate methods are shown to produce more uniform augmentation of volume flow rate, flow velocity, and shear stress, throughout the entire lower leg. In the companion paper, Part II [18] (see following article), these same compression modes are tested using a simple hydraulic model consisting of a single latex tube inside a foam cylinder as a highly simplified representation of a human leg.

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