Biomedical Engineering Reference
In-Depth Information
genderdata{i,m}
¼
processavg(averagedata(datamag, intersect(trials, z)), SR) ;
end
end
trialdiff
¼
processavg(avgdata, SR) ;
disp('Done');
end
There are several functions, such as bandpass filtering,
that are in separate MATLAB scripts. These scripts are
not included here, but are available on the companion
Web site for this text.
Notice that most of the references here are with re-
spect to the cell array called data. The reader is encour-
aged to study Chapter 2.1b and the MATLAB help files
for more information on how to use cell arrays.
The signal processing steps involved in the filtering
are not shown here. The EOG is removed using
a technique called a matched filter: the frequency
spectra of the EOG signal is computed by the FFT of
the A1-A2 difference signal. This frequency content
is then subtracted from the frequency content of the
other six signals in the recordings for a given trial.
The amount of data is too large to present or an-
alyze here, but an example of the type of analysis is
shown in
Table 2.2-3
, where positive differences are to
the left hemisphere and negative differences to the
right. The task numbers are references to the list
above.
This data suggests that there is a large activation in the
left occipital lobe during the geometry task (task 3) and
a significant but less left occipital activation during the
other mathematics tasks. Although these differences
were expected in the parietal region, there were only six
electrodes used in the study and it is possible that the
signals measured at O1 and O2 had components from the
parietal region.
of normality. Since glucose regulation is a dynamic
process, this model will take the form of a set of differ-
ential equations that express how the concentrations of
plasma glucose change over time. If the observed con-
centrations are comparable to those predicted by the
model, then the results can be interpreted by the clini-
cian as normal.
These models can vary in level of detail from the very
simple (called
minimal
) to the complex. The level of
detail changes with the number of compartments or
systems: Either glucose alone or glucose and insulin
concentrations in the blood can be modeled; and the
abdomen, kidneys and pancreas can be modeled alone or
as a combined system.
Van Riel (2004) describes a
minimal
model with three
compartments:
Plasma Glucose,
G
(
t
), in units of mg/dL,
Plasma Insulin,
I
(
t
), in units of
m
U/mL, and
Interstitial Insulin,
X
(
t
) in units min
1
The latter is a parameter of a single compartment
that accounts for insulin in the abdomen, kidneys and
pancreas. The variable
X
(
t
) is not a physiological quantity,
but is used to model insulin activity. The pair of differ-
ential equations that govern this system are
dGðtÞ
dt
¼ k
1
ðG
b
GðtÞÞ XðtÞGðtÞ
(2.2.1)
dxðtÞ
dt
¼ k
2
ðIðtÞI
b
Þk
3
XðtÞ
2.2.4 Diabetes and insulin
regulation
where
G
(
t
0
)
¼ G
0
, the initial concentration of plasma
glucose, and
X
(
t
0
)
¼
0, that is, there is no interstitial in-
sulin. The term
G
b
represents the basal level of glucose in
the blood; if the glucose concentration is less than the
basal level, glucose enters the blood and if the concen-
tration rises above this level then glucose leaves the plasma
compartment. The basal levels are typically measured
before the administration of the glucose in a GTT.
The second equation expresses that insulin enters,
or leaves, the interstitial tissues at rates
k
2
or
k
3
, re-
spectively. Insulin enters the interstitial tissues if the
plasma insulin concentration rises above the basal level
I
b
,
and insulin leaves the interstitial tissues if the plasma
level falls below the basal level.
This system of equations can be easily solved in either
MATLAB or Simulink.
Most, but not all, diabetics are required to use insulin to
manage their glucose (blood sugar) levels. The insulin,
administered either as a tablet or injection, acts as
a feedback control system to stabilize the blood sugar or
keep it within an acceptable range.
Glucose is typically monitored with a glucose toler-
ance test (GTT). In a GTT, blood samples are taken
from a fasting subject at regular intervals of time,
following a single intravenous injection of glucose. The
blood samples are then analyzed for glucose and insulin
content.
To determine what is ''normal,'' or to be expected,
requires comparison of the measured data to a model
