Class materials taught on April 25 and May 2, 2016

Physiology of the Cardiovascular SystemFanny Casado, [email protected]

ING338: Human Physiol. for Engineers. 2016-1

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Learning objectives Describe the assumptions necessary to illustrate

the heart working as a pump in the context of the vasculature

Understand the basis for the use of electrocardiograms to study heart condition assuming that heart muscle fibers act as electric dipoles

Explain using the sphygmomanometer to estimate arterial blood pressure.


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The cardiovascular system

Feher - Quantitative Human Physiology - Unit 5 The Cardiovascular System

• Heart• Blood vessels• Blood

Blood contentsNutrients Waste products Chemical

signalsThermal energy

WaterOxygenGlucoseAmino acidsFatty acidsVitaminsLipids and lipoproteinsMinerals and salts: Na+, K+, Ca2+, Mg2+, Fe2+/3+, Zn2+, Cu2+/3+, Mn2+, Cl-1, I-1, (PO4)2-, (SO4)2-

CO2UreaAmmoniaUric acidMetabolites: Creatinine, lactic acid, acetone, acetic acid, beta hydroxybutyric acidEnzymes

Endocrine hormones: growth hormone, oxytocin, insulin, glucagon, epinephrine, erythropoietinGI hormones: gastrin, secretin, somatostatin

Metabolic heatRadiation

Circulation becomes necessary because diffusion from and to the environment is too slow to transport materials

Flux occurs by diffusion and convection


The cardiovascular system

Human circulation


• The circulatory system consists of the pulmonary circulation and the systemic circulation

• The pulmonary circulation is in series with the systemic circulation

• The heart is a dual pump, with simultaneous pumping

• Most circulatory beds are arranged in parallel

Main functions of the vascular system1. Transform pulsatile flow from the heart

beat into more continuous flow2. Distribute the blood to various organs3. Exchange materials in the tissues4. Veins serve as a volume reservoir


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Pressure drives flow through the vascular system.


Vessels are characterized by a compliance. Elastic, closed system

Q: Flow (volume per unit of time)P: (pressure difference separated by a distance where flow occurs)R: Resistance (vasoconstriction or vasodilation)

P: (pressure difference separated by a distance where flow occurs)V: resistance (vasoconstriction or vasodilation)C: compliance (elastic)

Blood consists of cells suspended in plasma


Or “White” blood cells

Whole blood after

centrifugation in a cylindrical

tube

Blood makes up 6-8% by weight of body massDensity 1.05-1.06 g cm-3

Viscosity 2.5-3.9 mPa s

Hemostasis maintains the integrity of the blood volume by a delicate balance of activation and inhibition of coagulation

Vasoconstriction and back pressure reduces bleeding (thrombin thromboxane, serotonin)

The platelet plug can seal small vascular holes

Blood coagulation seals the leak (fibrinogen fibrin)

Clot retraction draws the edges of the wound together

Plasmin dissolves clots (plasmin fibrin)


Plasma proteins

Plasma proteins and ions buffer changes in plasma pH

Pr: plasma protein

The oncotic pressure of plasma proteins retains circulatory volume

: osmotic pressureR: gas constantT: temperatureC: molar concentration : osmotic coefficient


Feher - Quantitative Human Physiology - Unit 5 - The Cardiovascular System

Contraction of cardiac muscle produces a pressure within the chamber

HealthyThin-walled sphere

P: pressureconstant pi

r: radiusT: tension per unit length

The law of LaPlace for thick-walled spheres

Cardiomyopathy or hypertrophyThick-walled sphere

P: pressurewall stress

F: forceA: area

T: tension per unit lengthL: length W: widthr: radius


Four heart valves are coplanar

The cardiac cycle.

Phonocardiogram



The cardiac action potential is heterogeneous


T-type and L-type Ca channels

SA nodal currents that produce the

SA node action

potential


Effects of sympathetic and parasympathetic stimulation on SA node action potential

Molecular mechanisms of autonomic effects of SA node action potential


Equilibrium potentials:

Ion [Ion]outside (mM)

[Ion]inside (mM)

E (Volts)

K+ 4 140 -0.094Na+ 145 10 +0.071Ca2+ 1.2 1x10-4 +0.125Cl- 114 30 -0.036

States of the fast Na channel during myocyte action potential

Effect of epinephrine on the cardiomyocyte action potential


The heart muscle fibers act as electric dipoles

Assuming that the body is an ideal spherical dipole (which is not), equivalent electric dipole is produced by heart

muscle during depolarization, and produces an electrical potential through the thorax that is projected onto the skin

P: dipole moment q: charge separated in the dipoled: distance vectorV: voltage (charge/capacitance)

Einthoven’s triangle



The voltage differences between electrodes can be measured three ways

Kirchoff´s voltage law: Voltage drop in closed

circuit is zero.

Typical ECG on Lead II


The electrocardiogram records the electrical activity of the heart that is projected onto the surface of the body where it is

measured by surface electrodes

Time (s)

Reconstruction of the heart electric dipole from leads I and III

At the top of the R wave, lead I reads 0.35 mV and lead III reads 0.75 mV. Calculate the heart vector at this time


Origin of the P wave of the ECG

Origin of the QRS complex of the ECG

The cardiac cycle,

revisited

Cardiac output is the flow produced by the heart:


CO: cardiac output (L min-1)SV: stroke volumeHR: heart rate

Typical CO at rest: 4-6 L/minIt can increase as 5-fold during strenous exercise

Stroke volume is determined by: preload (central venous pressure), afterload (arteries) and contractility (ability to produce force at any given stretch).

SV: Stroke volumeEDV: End-systolic volumeESV: End-diastolic volume


The integral of the pressure-volume loop is the PV work

The total work of the heart includes pressure, kinetic and gravitational terms.

The equivalent pressure is given as

: densityg: acceleration due to gravityH: height to which the blood is raised

Energy difference per unit volume, between any two points in the cardiovascular system can be expressed in terms of equivalent pressure as

The Starling experimental set-up


Right atrial P, SV of both ventricles


Energetic constrains:The ventricular function curve predicts an intrinsic regulation of the heart to its input independently of nervous regulation, and explains that the autonomic nervous system exerts an extrinsic regulation

Effect of preload and afterload on PV loops

Sympathetic stimulation marginally increases cardiac output


Sympathetic stimulants:Cardiac glycosidesNorepinephrineEpinephrine

Effect of sympathetic stimulation

on ventricular function curve


Effect of sympathetic stimulation on PV loop



Fick´s principle determines cardiac output from oxygen consumption

Qa[O2]a+QO2=Qv[O2]v

At rest QO2 is typically 250 mL O2/min (STPD conditions). The arterial blood obtained from the radial, brachial, or femoral artery is 19.5 mL% (volume per 100 mL of blood). The venous blood obtained from the right ventricle outflow tract through a cardiac catheter inserted through the antecubital vein had 14.5 mL%. What is the cardiac output? (5 L/min)


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Cardiac output can be determined by the

indicator dilution method

Heart failure or congestive heart failure is the inability of the heart to pump enough blood to meet demands Treatment focuses either on removal of the load on

the heart or increasing cardiac contractility Coronary artery disease and heart attack (fat deposits,

reduced arterial lumen, weaker contractions) Hypertension (increased afterload, larger heart,

stronger contractions to maintain P) Faulty valves (blockage, leakage) Cardiomyopathy (damaged heart muscle) Arrhythmias (tachycardia) http://www.webmd.com/heart-disease/ss/slideshow-

visual-guide-to-heart-disease


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Main functions of the vascular system1. Transform pulsatile flow from the heart

beat into more continuous flow2. Distribute the blood to various organs3. Exchange materials in the tissues4. Veins serve as a volume reservoir


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The circulatory system uses four major physical principles:

Laminar flow

Flow is driven by a pressure difference.

The total mechanical energy is:

The total equivalent pressure is:


Bernoulli´s principle

Compliance describes the relation between pressure and volume

The compliance of the veins is much greater than the compliance of the arteries.

Ejection of blood into the arterial tree cause the arterial pressure pulse.

The pulse pressure depends on the stroke volume and arterial compliance.

Arterial pressure pulse measured in the subclavian artery


Pressure and flow waves propagate down the arterial tree

Diastolic pressure plus one-third pulse pressure estimates mean arterial

pressure

SYSTOLYC P DIASTOLYC P

Major pressure drop occurs in the arterioles


Poiseuille’s Law approximately describes flow in the vasculature.

Assumptions for Poiseuille Flow:

The fluid is Newtonian (viscosity is independent of shear rate)Flow is laminar No “slippage” at the wallsTube is cylindrical with circular cross section, parallel wallsThe walls of the tube are rigidThe tube is long compared to the entrance length

Microcirculation and solute exchange


KidneyIntestineExocrine glands

MuscleSkin Lung

LiverBone marrowSpleen

Capillaries exchange uses passive mechanisms


Regulation of solute delivery to the tissues


Lymphatic circulation


• Preservation of the circulatory volume

• Absorption of nutrients

• Immune surveillance


Effect of changing arteriolar resistance on steady-state operating point


Effect of changes in blood volume on the steady-state operating point


Effect of changing cardiac contractility on the steady state operating point


Changes in the steady-state operating point during exercise


Education

Class materials taught on April 25 and May 2, 2016