Autonomic Nervous System Control Model

Lisbon, October 21st 2008

José Manuel Monteiro Grilo Lema Santos

Master Degree in Biomedical EngineeringInstituto Superior Técnico

ANS Control Model

• 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)

Baroreflex and

Physiological Background

ANS Control Model

• 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.

ANS Control Model

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.

ANS Control Model

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.

ANS Control Model

ANS Control Model

HN – Transfer function from the neural arc.

HP – Transfer function from the peripheral arc.

Model for the MAP from Kawada et al. (2002).

S – Sympathetic SystemV – Parasympathetic (Vagal)

System

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Proposed Model

• 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.

ANS Control Model

ANS Control Model

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.

Hope you have enjoyed!

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