Biomedical Engineering Reference
In-Depth Information
(a)
(b)
10
8
10
μ
m
0020
80 kV
×600
0016
80 kV
×600
10
μ
m
6.3
Scanning electron microscopy evaluation of oxygenator fi bers
postoperatively: (a) coated surface; (b) uncoated surface.
tion on oxygenator fi bers were analyzed with optical microscopy, and
desorbed protein was evaluated quantitatively by a spectrophotometer
using samples obtained when the oxygenators were dismantled after CPB.
Laboratory results were much better than clinical outcome. Coated circuits
reduced platelet adhesion, platelet aggregation and protein adsorption on
fi bers.
Four different coatings were later compared with the identical uncoated
circuitry.
16
Microscopic evaluation of blood cells demonstrated signifi cantly
increased adhesion and aggregation of platelets in uncoated groups. Light
microscopy of Giemsa stained samples and optical micrographs demon-
strated increased aggregation of platelets in the fi bers of uncoated circuits.
Similarly, blood protein (microalbumin) adsorption analysis demonstrated
a signifi cantly increased amount of microalbumin on uncoated fi bers. On
scanning electron microscopic evaluation, coated circuits were almost com-
pletely free from debris, protein and cells in contrast to uncoated circuits
(Fig. 6.3). The data did not strongly demonstrate the clinical superiority of
coating, especially considering the imbalance of the cost effectiveness in
low risk patients. Following studies on lowering heparin dosage on heparin-
coated circuits confi rmed the feasibility of this procedure.
17
The high standard of current CPB systems has made it increasingly dif-
fi cult to test technical improvements in clinical studies involving relatively
small patient groups. In most cases, the statistical power of such studies will
not suffi ce to show a signifi cant clinical benefi t associated with changes in
the CPB circuit. The signifi cance of showing biocompatibility through
reduced biologic markers has not correlated with measurable clinical
benefi t of surface modifi cation during CPB. The idea of powerful precept
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