Biomedical Engineering Reference
In-Depth Information
FIGURE 8-38
Thoratec Heartmate
II. (a) Graphic
showing installation
into a human
patient. (b) Detailed
cross section of the
pump. [Adapted
from (Cleveland
Clinic 2008).]
by the blood flow. A cylindrical magnet within the rotor is excited by a rotating magnetic
field generated by the stator coils.
Blood flows from the inlet conduit past three neutral aerofoil-shaped guide vanes that
straighten the blood flow before it encounters the rotor. Three curved blades on the rotor
impart a radial velocity to the blood before it passes into the outlet stator vanes. These are
twisted and convert the radial velocity to an axial one. The exit orifice narrows to convert
flow velocity to pressure.
The inlet and outlet conduits are made from woven Dacron and require preclotting, the
pump rotor and cowling are made from smooth titanium, and the intraventricular conduits
are textured with titanium microspheres.
The performance of continuous flow pumps such as this one is determined primarily
by the speed of the rotor and the pressure difference across the pump. As shown in
Figure 8-39, flow rate is inversely proportional to the pressure differential across the
pump. Pump characteristics are obtained by measuring the pressure differential and the
flow rate as outflow resistance is gradually increased until pump shutoff.
Unlike rates of flow in pulsatile devices that are easily evaluated, the pressure-flow
characteristics of dynamic pumps require a different interpretation. During the cardiac
FIGURE 8-39
Characteristics of
Heartmate II
[Adapted from
(Griffith, Kormos
et al., 2000).]
