The two sets of bladders (foot/ankle and calf) within the cuff are inflated with a rise time of approximately 300 milliseconds (0.3 seconds). The foot/ankle bladder is inflated first, followed by the calf bladder, one second later. Both bladders have their pressures maintained for 8 seconds. The foot/ankle bladder is deflated first, which is again followed by calf bladder deflation, one second later. Inflation pressures are preset at the factory and can range from 20 to 100 mmHg. However, 80 mmHg is thought to be optimal. The bladders are deflated to approximately 6 mmHg for 60 seconds to allow for venous refilling in the supine patient. The 6mmHg deflation pressue allows for venous filling. It also helps the bladders to fill rapidly with less air. A smaller, quieter pump is therefore possible.

The calf bladder is inflated through a fitting that is on the distal portion of the bladder. The bladder fills with air from the distal to proximal calf. That, coupled with the initial inflation of the foot/ankle bladder, creates what is called "progressive compression," which returns the venous blood quickly and efficiently toward the heart.

The foot/ankle bladder compresses veins in that region rapidly in order to empty them into the calf veins. The so-called "foot-pump" is therefore being activated by VenAssist® to prime the calf pump. The compression by the calf bladder rapidly empties the calf veins which constitute a relatively large volume of blood and are the most common site of DVT. The rapid nature of compression, combined with the large blood volumes of the foot, ankle and calf, creates a dramatically large increase in common femoral vein velocity.

Rapid compression is also associated with higher blood shear rates, which have been shown to stimulate endothelial release of fibrinolytic biochemical factors. VenAssist® also rapidly releases its cuff pressures with the intention of further shear rate stimulation of the endothelial cells. Pressure fall times are approximately 300 milliseconds (0.3 seconds).

Rise time and fall time are defined under the strict engineering definition of "time taken for a waveform to rise from 10% to 90% (or fall from 90% to 10%) of its full change in amplitude.

Accomplishing these fast rise- and fall-times was a significant engineering design task. The internal pump was designed specifically for this application to be housed within a pressue reservoir. The reservoir and pump operate as a tuned system for maximum performance and minimal noise. The pressure regulator, switching valves and other pneumatic components are custom devices that have large flow capacities. The tubing and connectors are of large bore (compared with all other EPC devices) to accommodate larger airflows.