Page 72 - Control Theory in Biomedical Engineering

58 Control theory in biomedical engineering

effect can be observed for the increasing value of the parameter k 12 of more
1 1
than 3.6mgmin and decreasing value of k 21 of less than 1mgmin .
Based on the presented model, there was a significant effect of cholesterol
circulating with bile on its concentration in the blood. These relationships
show the importance of diet in increasing intestinal peristalsis (e.g., diet rich
in fiber). Increasing the intestinal peristalsis decreases the absorption time of
cholesterol, which in the model corresponds to a decrease in the value of the
parameter m in . This decrease can also explain the effect of an older genera-
tion drug that binds with the components of bile and gets excreted along
with the feces. When analyzing the significance of the m out , the parameter
describing the secretion of cholesterol in the bile, one can justify the ben-
eficial effect of choleretic agents. At present, inhibitors of cholesterol biosyn-
thesis (statins) are commonly used in medicine for lowering cholesterol. In
terms of our model, the effect of this drug can be taken into account by
reducing the value of parameter k, which is responsible for the rate of cho-
lesterol biosynthesis.
This two-compartment model demonstrated its didactic possibilities
about mechanisms of cholesterol homeostasis by using computers (Wrona
et al., 2015).
We hope that in the future our simple model will be expanded to support
prevention and to develop personalized therapeutic regime.

6 Summary and conclusion
The simplified two-compartment model enables studying the influence of
known factors, such as the rate of de novo synthesis, enterohepatic circulation
(Mishra et al., 2014), tissue demands, and the amount of cholesterol
absorbed from food, on cholesterol homeostasis (Afonso et al., 2018).
Although this model does not explicitly distinguish the lipoproteins contain-
ing cholesterol, it can be used to understand the importance of the rate of
formation of the main fractions, that is, LDL and HDL. Indirectly, the role
of CETP can also be examined.
In addition, the simplified two-compartment model helps in analyzing
the causes of disorders of cholesterol homeostasis and the different ways
to lower cholesterol concentration. In particular, it allows investigating:
• the effectiveness of therapy with drugs that inhibit the enterohepatic
circulation,
• the usage of inhibitors of cholesterol synthesis (statins),
• the significance of diet components that increase the intestine peristalsis,