Physiological regulation in pathogenesis cardiovascular

disease and in general

Stanislav Matoušek, M.D.

Regulated and unregulated variable

Unregulated variable

• Fallen bridge

• Broken leg

Regulated variable

• Cold café

• Hypertension

What are we going to cover?

• 1. Basic terminology of regulation theory• 2. Types of feedback loops in the body (positive,

negative)• 3. Origin of disturbance/disease in regulated system• 4. History of regulated systems and their description• 5. Different types of governors (automated regulators)• 6. Regulation of cardiac output and blood pressure

• heart• vessels• kidney regulator

Basic terminology

Regulation or (automatic) control

• if an environmental variable (such as temperature) ....changes and the system can nearly compensate for those changes ...then the system is said to be regulated.– Principia cybernetica web

• Regulation is every process that minimizes difference between the real and the desired (reference) value of the regulated variable.

Zdenek Wunsch, Basics of medical cybernetics (1977) in Czech

Regulation valve of central heating

Open-loop regulation

Feedback regulation

Regulator does not measure output variable (temperature) when it „computes“ the control action to take.

Output signal of the controlled system is measured and fed back for use in the control computation.

Open loop

tem

pera

ture

/ °C

time / hours

Open loop

tem

pera

ture

/ °C

time / hours

Open loop

Outside disturbance

Error of the output variable

tem

pera

ture

/ °C

time / hours

Feedback

tem

pera

ture

/ °C

time / hours

Feedback

tem

pera

ture

/ °C

time / hours

Feedback

tem

pera

ture

/ °C

time / hours

Outside disturbance

Error of the output variable

The Effect of Feedback

The output error is (5x) smaller then without the feedbackte

mpe

ratu

re/

°C

time / hours

Open loop vs. closed loop

Open loop regulated system:

Feedback (=closed loop) regulated system:

Feedback in physiology

RAAS system

General structure of control system

Room temperature regulation

Heater body

Thermo-meter

Heating

Thermostat setting vs. actual temperature

Room temperature

Outside temperature

Set tem-perature

Measured temperature

Hot water valve open/closed

Examples in physiology

Regulation of blood sugar

β cell

β cell

InsulinNormal glycemia

GLUT 4 tissue cell

Glycemia

Glc upta

ke

Types of feedback in the body (positive, negative)

Regulation in human body

• There are two systems specialized in control and regulation in the body:– endocrine system – nervous system

• Besides these two, every cell and tissue has many local feedback regulated processes

Local regulation

Systemic regulation

Negative feedback

PTH

Ca++

+-

Keeps the value of the regulated entity close to the equilibrium.

Positive feedback

+

+

faktor XII

faktor XII a

Kalikrein Prekalikrein

++

Rare – amplification of small original „disturbance“; Does not create any equillibrium

Disturbance/disease in regulated system (body)

Diabetes mellitus

β cells

β cells

InsulinNormal glycemia

GLUT 4 in tissue

Glycemia

Glc entering

cells +

-

Diabetes type I

Diabetes type II

Disease in general

1. Block in the feedback loop

2. Too high a disturbance

3. „Weak actuator“

4. Incorrectly set reference point

History of regulation and feedback control

History in engineering

• Float valve of ancient Greece and Rome.

Steam Engine by James Watt

James Watt – fly-ball governor 1788

System stability

20 century

• Maxwell stability criteria

• Problem of long-distance telephoning (use of electronic amplifiers)

• Bell Telephone Laboratories: H. Nyquist (1932) Nyquist criterium of stability

Today

History in biological sciences

• Living organism’s ability to keep life processes in balance and thus confront the disturbances is so apparent that was already noted in Antiquity.

Zdenek Wunschin Basics of Medical Cybernetics

Another important aspect seen as a source of diseases are the organism’s internal imbalances. This idea, while surely correct in its essence, is remarkably trans-cultural.

Stanislav Komarek in Salvation of the Body

Ancient Greece

• Empedocles from Agrigent

(504-443 BC)

Ancient Rome

Galenos

Ancient China

Late 18th century and 19th century

Lavoisier: Dynamic balance of known substances in metabolism (oxygen, food compounds, heat) is needed in body

Fredericq (1885): Living organism is a system able to respond to disturbing influence by a compensatory activity that neutralizes or repairs the developing perturbation. The higher the level of the living organism, the more common, more perfect and more complicated these regulatory activities become.

Homeostasis – Walter Cannon

– from the earlier idea of Claude Bernard of milieu interieur, – popularized it in his book The Wisdom of the Body,1932. – Four general features of homeostasis:

• Constancy in an open system, such as our bodies represent, requires mechanisms that act to maintain this constancy.

• Steady-state conditions require that any tendency toward change automatically meets with factors that resist change. An increase in blood sugar results in thirst to dilute the sugar.

• The regulating system - number of cooperating mechanisms acting simultaneously or successively. e.g. Blood sugar is regulated by insulin, glucagons, and other hormones, thirst.

• Homeostasis is the result of organized self-government.

Cybernetics – Norbert Wiener

• 1948 book Cybernetics: Or Control and Communication in the Animal and the Machine.

• The book formalizes the notion of feedback and has gained large influence in many fields: control engineering, computer science, biology, philosophy, sociology and philosophy.

Advent of computational biology – Arthur Guyton and Thomas Coleman

Thomas Coleman and laboratory of biocybernetics of our institute

Little intermezzo

Reminder of high-school calculus

Derivative

Important functions

Integral

Different types of governors / controllers

Types of feedback regulators

• The simplest controller is so called proportional (P) controller.

There is always a difference between the reference and actual value.

The difference depends on the size of the disturbance and sensitivity of the feedback mechanism (so called gain)

With high sensitivity (gain) of feedback, system might become

unstable

Integral controllerThis controller can bring the difference between the reference and real value to zero over time.

It is not very fast and has tendency to destabilize the system

Derivative controller

• Cannot be used alone.

• Stabilizes the system

PID controllerProportional – integrative – derivative controller

Regulation of blood pressure

Cardiac output and blood pressure depend on:

• Characteristics of the heart:• Contractility• Frequency

• Characteristics (diameter) of the vessels

• Tone of arteriols influences mainly resistence• Tone of veins (or less mid-size arteries)

influences the volume of vascular bed. Volume of the bed is connected to pressure and vascular tone (compliance)

• Volume of circulating blood

Heart

• Autonomous nervous system

• Endocrine system

• Local tissue factors

Heart characteristicsContractilityFrequency

Blood vessels

• Vascular tone– compliance– resistance

Autonomous nervous systemEndocrine systemLocal tissue factors

Volume of circulating blood

• Is given by difference between the intake of salt and water and their output.

• The output is governed by kidney regulator

• Resistance of kidney arteriols

• Kidney filtration and resorption rate

• Renin-angiotensin-aldosteron system

Kidney-fluid mechanism of pressure control

Heart and vessels are regulated by mechanisms that are of a proportional controller type.

Kidney fluid regulator is a integral (I) controller type. (its long term sensitivity/gain is infinity)

= kidneys excrete more fluid until the pressure is set exactly on the equilibrium (reference) value

Kidney-fluid mechanism of pressure control

TimeNet

flo

w t

o th

e sy

stem

Kidney fluid mechanism of pressure control

Increased peripheral

resistance is common

in hypertensive individuals, but it is not the main

cause

Why is antihypertensive treatment effective?

• Diuretics

• Beta-blockers

• ACE inhibitors

• Ca++ channel blockers

What did we cover?

• 1. Basic terminology of regulation theory• 2. Types of feedback loops in the body (positive,

negative)• 3. Origin of disturbance/disease in regulated system• 4. History of regulated systems and their description• 5. Different types of governors (automated regulators)• 6. Regulation of cardiac output and blood pressure

• heart• vessels• kidney regulator

Guyton’s model of circulation

• peripheral resistance, heart rate and contractility and vessel tone are primarily regulated variables. They are controlled directly by:

• Autonomous nervous system • Endocrine system• Local tissue factors

• blood pressure, and cardiac output are secondarily (regulated) variables.

They are controlled by • peripheral resistance, • heart rate and • vessel tone

Kidney-fluid mechanism of pressure control

Kidneys excrete more fluids until the pressure is exactly the equilibrium (reference) point.

This is an I (integral) controller

Review

• Regulation• Closed loop = feedback regulation• Same structure of regulatory loops in

engineering and medicine • Stability in regulation is only accomplished by

negative feedback• History of control theory• PID controllers• Blood pressure is determined only by kidney-

fluid mechanism in the long-run (the Integral controller)

Mathematical models and formalization

• Anything that can be quantified in words can also be expressed in formulas (language of mathematics)

• Mathematics gives us powerful methods of deducing correct implications from the underlying statements.

• “Uncritical enthusiasm of mathematical formulation often has the tendency to hide the key meaning nuances of the argumentation taking place behind facade of algebraic symbolism and “certainty””

Wassily Leontief winner of Nobel Prize for economics

System without feedback – mathematical formalization

• If we want to mathematically express the behaviour of a feedback regulated system, we first need to depict behavior of the system without feedback