Biomedical Engineering Reference
In-Depth Information
FIGURE 8-23
Schematic diagram
showing the
installation of the
Novacor LVAD.
[Adapted from
(Cleveland Clinic
2008).]
pusher plates together compressing the blood-sac to eject the blood from the pump in a
controlled manner.
The pusher plates are epoxy bonded to a seamless flexible blood sac, consisting of
a butyl rubber layer sandwiched between two layers of polyurethane. The polyurethane,
which is manufactured by Ethicon Inc. (Somerville, NJ), is used in most existing blood
pumps because of its durability and biocompatibility, whereas the butyl rubber layer
increases the pump's impermeability.
The blood sac is supported within a cylindrical aluminium annulus that forms the
pump housing. The inflow and outflow ports are positioned tangentially on opposite sides
of the housing to ensure straight-through blood flow. The ports are formed by an epoxy-
impregnated Kevlar fabric shell that is integrated into the housing and support trileaflet
inlet and outlet valves made from bovine pericardium tissue.
Tangential inflow into the pump sac initiates a circular flow pattern that is coupled
directly to the tangentially mounted outflow to maximize pumping efficiency. It also creates
a flow pattern that “washes” all of the internal surfaces of the pump, reducing the potential
for blood clot formation.
The external controller is connected to the implanted pump by a percutaneous lead—a
small tube that passes control and power wires through the recipient's skin. The
microprocessor-based controller regulates pumping action and monitors system function.
During normal, untethered operation, the controller receives power from two recharge-
able power packs. The controller and power packs may be worn on a belt or carried in a
shoulder bag, vest, or back pack. The portable nature of the Novacor system facilitates
out-of-hospital use and allows recipients to return home and lead near normal lives.
The power pack contains rechargeable nickel metal hydride (NiMH) batteries that
last approximately 6 hours per pair (at a flow rate of 6 L/min). A monitor circuit displays
charge capacity and alarms for low charge, accidental disconnect, or fault conditions.
Users typically have a battery charger that maintains a number of packs on full charge
ready to be swapped into place.
