Biomedical Engineering Reference
In-Depth Information
8.5.5 Pulsatile Pump Technology
Positive displacement mechanisms in electrically driven pulsatile pumps are commonly
actuated by cams, solenoids, and roller-screw devices. However, a number of other experi-
mental technologies are being investigated as the drive to smaller, lighter, and lower-power
devices continues. These technologies include linear motors and even shape memory alloy
(SMA).
8.5.5.1 Roller-Screw LVAD
A good example of the development of a planetary roller-screw LVAD similar to that used
in the Arrow LionHeart device is discussed in Takatani, Ouchi et al. (2001). This device
uses a brushless DC motor to drive the roller-screw to produce a stroke length of 12 mm
and volume of 55 cm
3
. The maximum pump output is 8 L/min at an electrical power of 8 W
and a 24% electrical-to-hydraulic efficiency. The pump is housed within a titanium alloy
shell 90 mm in diameter and 56 mm thick with a total volume of 285 cm
3
weighing 552 g.
Power is transferred to the device transcutaneously by inductive coupling at a frequency
of between 100 and 200 kHz.
As shown in Figure 8-30, the LVAD consists of a miniature 14-pole Y-wound brushless
DC motor from Kollmorgan Inc. and a planetary roller-screw from SKF. Motor rotation is
converted into rectilinear motion using the roller-screw attached to a pusher plate, which
compresses the diaphragm. It is then reversed after completion of each ejection cycle to
allow passive filling of the blood chamber. Hall effect sensors monitor the position of the
pusher plate so that the stroke volume and beat rate can be controlled.
The diaphragm is made from polyurethane manufactured by Polymer Technology Inc.
using a dip-coating method. The housing is manufactured from a titanium alloy containing
6% aluminium and 7% niobium. It was designed using a computer-aided manufacturing
FIGURE 8-30
Schematic diagram
of the roller-screw
LVAD components
(Takatani, Ouchi
et al., 2001),
reproduced with
permission.
