Biomedical Engineering Reference
In-Depth Information
8.6
ENGINEERING IN HEART ASSIST DEVICES
8.6.1 Fluid Dynamics in Pulsatile LVADs
Thrombosis formation is determined by the physiological condition of the patient, the bio-
compatibility of the materials in contact with the blood, and fluid dynamic characteristics
of the blood pump. Adverse flow factors that can induce thrombosis include turbulence,
recirculation stasis (stagnation), and high shear stresses. Pump performance can be deter-
mined after manufacture, but that is expensive if major redesign is required. Therefore, it
is more cost-effective to produce accurate models of the device and to use computational
fluid dynamic (CFD) analysis to predict flow prior to manufacture.
Detailed analysis has been performed for a typical pusher-plate LVAD (Okamoto,
Fukuoka et al., 2001) under the following conditions:
•
Inflow pressure 10 mmHg
•
Outflow pressure 100 mmHg
•
Pusher-plate velocity 27 mm/s
Pump stroke volume 65 cm
3
•
•
Pump stroke 12 mm
Blood density 1.06
×
10
−
3
g/mm
3
•
10
−
3
g/mm
•
Blood viscosity 6
×
·
s
The analysis can be used to estimate the NIH normalized index of hemolysis for each
of the different pump configurations as follows.
It is first necessary to use CFD to determine the distribution of the flow velocity during
the filling and ejection cycles. This is shown in Figure 8-51.
The turbulent kinetic energy,
k
, can then be determined from the time-averaged fluc-
tuating component of the fluid velocity,
u
i
,
1
2
u
i
k
=
(8.2)
FIGURE 8-51
Distribution of flow
velocity for a
pulsatile pump.
(a) During filling.
(b) During ejection.
(Okamoto, Fukuoka
et al., 2001),
copyright Informa
Healthcare,
reproduced with
permission
