From Johns Hopkins Medicine: While using an IPC (Intermittent Pneumatic Compression) device, your calf or whole leg is enclosed in a cuff. The cuff fills with air and squeezes the leg, much like a blood pressure cuff. Then the cuff deflates and relaxes. The process then repeats over and over. The compression helps move blood through your veins towards your heart.  IPC also promotes the natural release of substances in your body that help prevent clots. Between compressions, the cuffs of the device relax, and oxygen-rich blood continues to flow in the arteries of your leg.