Biomedical Engineering Reference
In-Depth Information
FIGURE 8-41
Photograph of the
VentrAssist LVAD.
market approval in Europe and Therapeutic Goods Administration (TGA) market approval
in Australia and was undergoing FDA trials in the United States. Unfortunately, early in
2009 the company folded.
8.5.7.2 Mohawk Innovative Technology/MiTi
Heart
Another third-generation blood pump has been under development for use as an LVAD
by Mohawk Innovative Technology, Inc. The innovation of this pump design is a novel,
patented, hybrid passive-active magnetic bearing system. The MiTi
Heart
LVAD is a high-
efficiency centrifugal pump that exhibits extremely low power loss, low vibration, low
hemolysis, and high reliability under transient conditions and varying pump orientations.
The original magnetic levitation bearing was developed for a liquid oxygen pump
for the space shuttle. Subsequent research was internally funded until 1996, when the
company received a Small Business Innovative Research (SBIR) grant from the NIH. The
development of the LVAD took until 2005 and cost about $15 million before the device
was evaluated in comprehensive in vitro and in vivo animal tests.
Magnetic suspension has advantages from the viewpoints of power loss, wear life, and
blood damage. Power lost due to bearing friction is extremely low, especially when com-
pared with hydrodynamic rotor support systems. Most active magnetic bearing supported
pumps use a magnetic bearing system with five active axes (one axial, two radial, and
two tilt) to provide complete control of the pump rotor during operation. The MiTi
Heart
design is different and uses a hybrid passive-active magnetic bearing system that requires
only one actively controlled axis. This reduces the power required to operate the bearings
and increases operating time before a battery change or recharge is required (MiTi
Heart
,
2006; Jahanmir, Hunsberger et al., 2008).
As shown in Figure 8-42, the cylindrical pump consists of four components: (1) the
pump housing; (2) the stator; (3) the rotor with integrated vanes; and (4) an end cap. It is
80 mm long with a diameter of 50 mm and a total mass of 640 g. The pump is designed
for a flow rate of 5 L/min at 100 mmHg pressure rise. In initial tests, flow rates from 2 to
7 L/min and pressure rises from 50 to 150 mmHg were measured. The nominal design flow
of 5 L/min at 100 mmHg pressure rise was successfully achieved at a speed of 3,000 rpm.
