1. Autonomic Nervous System Control Model Lisbon, October 21 st 2008 José Manuel Monteiro Grilo Lema Santos Master Degree in Biomedical Engineering Instituto Superior Técnico

2. 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)

3. Baroreflex and Physiological Background Baroreflex and Physiological Background ANS Control Model

4. 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. ANS Control Model

5. Neural arch of the baroreflex. Baroreceptors triggers an ANS response. ANS Control Model

6. Peripheral arch of the baroreflex. Innervation from ANS triggers changes in the heart rate, systolic volume and blood vessels’ radius. ANS Control Model

7. 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. ANS Control Model

8. 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. ANS Control Model

9. Head-up Tilt Table Test ANS Control Model

10. 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

11. Control Model ANS Control Model

12. 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

13. H N – Transfer function from the neural arc. H P – Transfer function from the peripheral arc. Model for the MAP from Kawada et al. (2002).

14. S – Sympathetic System V – Parasympathetic (Vagal) System ANS Control Model Proposed Model

15. ANS Control Model First order system

16. PID – Proportional, Integrative and Derivative PID – Proportional, Integrative and Derivative ANS Control Model

17. CO = SV X HR CO – Cardiac Output SV – Systolic Volume HR – Heart Rate ANS Control Model

18. R – Vascular resistance r – Vessel radius µ – Blood viscosity l – Vessel length ANS Control Model Second order system

19. 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. ANS Control Model

20. Results from the model ANS Control Model

21. Results from the model showing MAP, HR and CO. Experimental data results showing HR and systolic blood pressure (SBP) during HUT. ANS Control Model

22. 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

23. 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.

24. Hope you have enjoyed! END ANS Control Model