Erythrocytes (or red blood cells, for those of us that didn't ace hematology 101) are the most abundant cell in the blood, accounting for about 40-45 percent of its volume. Sadly, the mean life of erythrocytes is about 120 days, but with this aluminium cuff they can live on forever.
Technicam notitia (the technical bits)
Made of aircraft-grade aluminium - strong and light-weight