Biomedical Engineering Reference
In-Depth Information
The mechanical power,
P
mech
(W), used to perform the pumping function is the work done
per unit time
E
t
ej
P
mech
=
1
.
1
=
0
.
33
33 W
Assuming that no energy is expended in reversing the pump stroke, then the average power
used over a full pump cycle is
=
3
.
t
ej
t
ej
+
P
ave
=
t
fill
P
mech
0
.
33
=
5
×
3
.
33
.
+
.
0
33
0
32 W
In previous sections of the chapter, pulsatile pump efficiencies of about 20% (
=
1
.
η
=
0
.
2) are
quoted; therefore, the average electric power required to drive the pump is
P
ave
η
P
elec
=
1
.
32
=
0
.
2
=
6
.
6W
This equates quite well with the8Wpowerrequirement quoted for most pulsatile devices.
8.7.4 Bearings
Impellers in rotary blood pumps must be supported by bearings. These can include con-
ventional sealed bearings made from stainless steel or ceramics, blood-immersed bearings,
magnetically supported bearings, hydrodynamically supported impellers, or combinations
of these.
It is believed that the high shear stresses formed around blood-immersed bearings may
lead to increased hemolysis, with the result that most new developments aim to eliminate
this and use magnetic or hydrodynamic bearings with quite large gaps.
Magnetic bearings are often supported by permanent magnets augmented by a number
of electromagnets used to maintain stability and drive the impeller. Such support is used
by the MiTi
Heart
.
8.8
REFERENCES
Abe, Y., T. Ono, T. Isoyama, S. Mochizuki, K. Iwasaki, T. Chinzei, I. Saito, A. Kouno and K.
Imachi. (2000). “Development of a Miniature Undulation Pump for the Distributed Artificial
Heart.”
Artificial Organs
24(8): 656-658.
Al-Ghazal, S. (2002). “Ibn Al-Nafis and the Discovery of Pulmonary Circulation.” Retrieved
September 2008 from http://www.islamonline.net/english/Science/2002/08/article06.shtml
