Heart: A History

by Sandeep Jauhar

The most recent devices produce continuous blood flow, so patients emerge from the operating room without a pulse. Continuous-flow devices are simpler than devices that send out pulses of blood, mimicking the native heart. They don’t require valves and have fewer moving parts, resulting in less wear and tear. They still pump blood, of course, but the flow is constant, not periodic. Incredibly, humans, we now know, can live for long periods without pulsatile blood flow. However, continuous-flow hearts produce their own complications. They chew up blood cells because of the shear forces generated by the device and may strip the blood of clotting proteins. For unclear reasons, they cause tiny blood vessels that are prone to rupture to sprout up in the gastrointestinal tract, so patients often bleed internally. They can also cause degeneration in arterial walls and scarring. Continuous blood flow is antithetical to the way that humans, pulsatile beings, evolved. Though continuous flow can keep us alive, it alters our physiology in idiosyncratic and unpredictable ways.