Biomedical Engineering Reference
In-Depth Information
magnetic field that causes it to spin at high speed. The impeller is supported by blood-
immersed ceramic bearings, and the whole construction is housed within a titanium shell.
The normal operating speed is 8000 to 12,000 rpm, which will generate an average pump
flow rate of 5 L/min. Smaller versions of the pump, suitable for children (15-25 kg) and
infants (3-15 kg), are under development at the University of Maryland Medical School.
A small transcutaneous cable delivers power to the impeller. In the BTT implants the
cable exits through the abdomen as shown, but in the latest permanent implants the cable
exit point is via a skull-mounted pedestal similar to those used for cochlear implants.
The pump speed is controlled by an analog controller, which can adjust the speed
from 8000 to 12,000 rpm in increments of 1000 rpm. The control unit also monitors the
pump function and the remaining power in the batteries. Audible and visual alerts notify
the user of any problems.
Preliminary human trials have been positive, with few complications and only slightly
increased hemolysis levels compared with preoperative levels (Siegenthaler, Martin et al.,
2002). So far, the Jarvik-2000 has been used to treat more than 200 patients in the United
States, Europe, and Asia. Of those, roughly 79% received the Jarvik-2000 as a BTT and
21% as a permanent implant, with a number of patients in each group being very ill,
near-death cases. Nearly 70% of those patients treated as BTT have either undergone
transplantation already or are currently being supported by the Jarvik-2000 (Jarvik Heart,
2008).
8.5.8.2 Micromed/DeBakey LVAD
The DeBakey VAD HeartAssist-5 pump system consists of a lightweight titanium pump
(92 g), as shown in Figure 8-46. It is based on technology developed by NASA and
licensed for use by the company for cardiovascular applications. As with all the other
LVADs discussed so far, the pump is attached to an inlet cannula that is placed into the left
ventricle. A graft is connected to the pump outlet and attached to the ascending aorta. In
the latest versions of the system, a noninvasive probe fits around the outflow to generate
an accurate measure of flow rate.
The inducer/impeller (rotor) is the only moving part of the pump. It has six blades with
eight magnets hermetically sealed in each blade. The rotating magnetic field generated by
FIGURE 8-46
DeBakey LVAD.
(a) Graphic showing
installation of pump
in a human patient.
(b) Detailed cross
section of the pump
mechanism.
[Adapted from
(MedGadget 2006).]
