Master Degree in Biomedical Engineering
Instituto Superior Técnico
Autonomic Nervous System
Control Model
José Manuel Monteiro Grilo Lema Santos
Lisbon, October 21st 2008
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• The blood pressure (BP) and heart rate are not static
variables in the human body. However, the dynamic of their
variation and control is not yet fully understood.
• What is the baroreflex?
• Description of the model used for the control of mean arterial
pressure (MAP) and the heart rate (HR)
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Baroreflex
and
Physiological Background
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• The baroreflex is a control system for the BP values with a
negative feedback loop. The autonomic nervous system
(ANS) is the controlling system.
• Baroreceptors and chemoreceptors discovery (Heymans &
Neil, 1958) in monkeys opened new doors to gain insight in
the control of blood pressure (BP) by the baroreflex.
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Neural arch of the baroreflex.
Baroreceptors triggers an ANS response.
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Peripheral arch of the baroreflex.
Innervation from ANS triggers
changes in the heart rate, systolic
volume and blood vessels’ radius.
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Cross-section of a blood vessel.
In general each vessels is
divided in three layers called
tunicas. BP is also affected in
this efferent pathways of the
ANS. The sympathetic system
innervates the smooth muscle
tissue,
providing
different
lumen diameters according to
the stimuli received by the
baroreceptors.
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Schematics of the
baroreflex functioning.
BP rise triggers
baroreceptors “spikes”
that cause the ANS to
respond and reduce
the blood pressure.
This is achieved by
activation of
parasympathetic fibers
and inhibition of
sympathetic fibers.
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Head-up Tilt Table Test
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Head-up Tilt table test is a common test of the
baroreflex. ECG and BP are monitored
continuosly while the bed is tilted from the
supine to the standing position. The baroreflex
response is typical.
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Control Model
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• The searching for mathematical models to resemble the
baroreflex is an active field of research
• In the last years, several models using control theory have
been created to further advance in our physiological
knowledge. The impossibility in carrying tests in human
subjects is a strong motivation.
• The inexistence of a mathematical model that provides a valid
explanation and a reasonable behaviour when compared to
the baroreflex is a major gap.
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Model for the MAP from Kawada et al. (2002).
HN – Transfer function from the neural arc.
HP – Transfer function from the peripheral arc.
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Proposed Model
S – Sympathetic System
V – Parasympathetic (Vagal) System
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• The multiplication of the
vascular resistance by the
cardiac output gives rise to
the MAP, the major output of
this model.
• Baroreceptors will sense MAP.
They regulate the values and
maintain the homeostasis.
• HUT disturbance is introduced
directly in the MAP signal.
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Results from the model
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Results from the model showing MAP,
HR and CO.
Experimental data results showing HR
and systolic blood pressure (SBP)
during HUT.
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• The incremental model proposed has a similar behaviour to
the baroreflex mechanism and to the raw data used as the
basis for the results.
• The model introduced new concepts like the division of the
peripheral arc into two distinct blocks: the heart block and the
cardiovascular block. The neural block division is also new.
• Systems of higher order can be applied to all blocks to better
approximate the results.
• Different parameters can be adjusted for different situations
and results.
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My thanks to…
• My tutors from Instituto Superior Técnico and Faculdade de Medicina
da Universidade de Lisboa;
• To the Instituto de Sistemas e Robótica;
• To the jury;
• To my family and my other half;
• To the audience.
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END
Hope you have enjoyed!