Biomedical Engineering Reference
In-Depth Information
Fig. 4.48.
The experimental arrangement for measurement of the catecholamine
concentrations using an electrochemical detector in conjunction with the microdia-
lysis technique
can feed back the concentrations of catecholamines and control the driving
parameters optimally during the exercise.
Thus, except for the resolution of the catecholamine concentration, the
system worked satisfactorily when buffered solution was used instead of actual
blood or plasma. However, when the sensing system was used in goat plasma,
the sensitivity of the sensor decreased greatly with time after immersion in
plasma, and the electrode came not to respond to the catecholamines in it
immediately.
It was observed that plasma proteins were adsorbed onto the electrode,
which was suspected to be the main cause of the decrease in sensor activity.
One of the possible solutions for preventing blood proteins from being
adsorbed onto the electrode is to adopt a microdialysis technique [175,176] in
conjunction with the above-mentioned electrochemical method. In our expe-
riments, a cellulose microtube (cutoff molecular weight = 50,000) was used for
dialysis; the microtube was immersed in the goat plasma, and a dialytic so-
lution (phosphate-buffered solution) was flushed through the microtube. The
catecholamines in the goat plasma were dialyzed into the dialytic solution
through the cellulose membrane, and catecholamine concentrations in this
dialytic solution were measured using the electrochemical detector described
above (Fig. 4.48). With this system, the ratio between catecholamine concen-
trations in the dialytic solution and that in the plasma was approximately
20% when the flow rate of the dialytic solution was 10
l/min, with a delay
of approximately 90 s between the time when the catecholamine concentra-
tion in the goat plasma was altered and that when the detector identified the
changes of the catecholamine concentrations as those of the dialytic solution
μ
