Cardiovascular system
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CARDIOVASCULAR SYSTEM . Juliet Ver-Bareng, M.D., FPSP. Outline. Physiologic properties of the heart Electrical properties < Excitability < Automaticity and Rhythmicity < Conductivity Mechanical properties < Contractility < Distensibility Regulation of cardiac activity

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Cardiovascular system

CARDIOVASCULAR SYSTEM

Juliet Ver-Bareng, M.D., FPSP


Outline

Outline

  • Physiologic properties of the heart

    Electrical properties

    < Excitability

    < Automaticity and Rhythmicity

    < Conductivity

    Mechanical properties

    < Contractility

    < Distensibility

  • Regulation of cardiac activity

    Neural control

    Humoral control


Circulation

Circulation

  • Role of the blood vessels

  • Hemodynamics

  • Blood Pressure determination

  • Microcirculation – fluid exchange

  • Factors affecting venous return

  • Regulation of blood flow

  • Regulation of blood pressure


Functions of the heart

Functions of the heart

  • Generating blood pressure

    - contraction of heart is responsible for movement of blood through the blood vessels

  • Routing blood to two circulation

    - pulmonary and systemic circulation

    3. Ensuring one way blood flow

    - presence of valves (AV and semilunar valves)

  • Regulating blood flow

    - change in heart rate and force of contraction to match blood delivery to the changing metabolic needs of the tissues


Physiologic properties of the heart

Physiologic Properties of the heart

  • Electrical Properties

    - Excitability = bathmotropy

    - Automaticity and Rhythmicity = chronotropy

    - Conductivity = dromotropy

  • Mechanical Properties

    - Contractility = inotropy

    - Distensibility = lucidotropy


Types of ion channels in the heart

Types of ion channels in the heart


Resting membrane potential

Resting membrane potential

  • the difference in ionic charge across the

    membrane of the cell

    = -70 to -9o mV

  • resting membrane potential is permeable

    to K+, and is relatively impermeable to

    other ions

  • maintenance of this electrical gradient is

    due to the:

    Na+- K+ pump and the

    Na+- Ca++ exchange mechanism


Electrical properties

Electrical Properties

A. Excitability – bathmotropy

SA node, AV node Myocardia, Purkinje

system

Slow response AP Fast response AP


Phases of fast response ap

Phases of fast response AP

4 = Resting Membrane Potential

0 = Rapid Depolarization

1 = Initial Repolarization

2 = Plateau

3 = Repolarization


Phases of fast response ap1

Phases of fast response AP

Phase 0 - Rapid depolarization

- due to opening of the fast Na+ channels and the

subsequent rapid increase in the membrane conductance to

Na+ (gNa) and a rapid influx of Na+ ions into the cell

The fast Na+ channel

made up of two gates at rest

m gate closed

h gate open

Upon electrical stimulation of the cell, the m gate opens

quickly while simultaneously the h gate closes slowly

For a brief period of time, both gates are open and Na+ can

enter the cell across the electrochemical gradient


Phases of fast response ap2

Phases of fast response AP

Phase 1 – Initial repolarization

- occurs with the inactivation of the fast Na+ channels

- the transient net outward current causing the small downward deflection of the action potential is due to the movement of K+ and Cl- ions

- Cl- ions movement across the cell membrane results from the change in membrane potential, from K+ efflux, and is not a contributory factor to the initial repolarization ("notch").


Phases of fast response ap3

Phases of fast response AP

Phase 2- Plateauphase

- sustained by a balance between inward movement of Ca2+ (ICa) through L-type calcium channels and outward movement of K+ through the slow delayed rectifier potassium channels, Iks.


Phases of fast response ap4

Phases of fast response AP

Phase 3 - Rapid Repolarization phase

- L-type Ca2+ channels close, while the slow delayed rectifier (IKs) K+ channels are still open

- this ensures a net outward current, corresponding to negative change in membrane potential, thus allowing more types of K+ channels to open

- this net outward, positive current (equal to loss of positive charge from the cell) causes the cell to repolarize

- the delayed rectifier K+ channels close when the membrane potential is restored to about -80 to -85 mV


Slow response ap

Slow response AP

Phases

4 - Spontaneous depolarization

0 - Triggered depolarization

3 - Repolarization


Phases of slow response ap

Phases of slow response AP

Phase 4 – Spontaneous Depolarization

- Prepotential

- Slow diastolic depolarization

  • depolarization by themselves

  • the resting potential of a pacemaker cell

    (-60mV to -70mV) is caused by;

    = a continuous outflow or "leak" of K+ through ion channel proteins in the membrane that surrounds the cells

    = a slow inward flow of Na+, called the funny current

    = an inward flow of calcium

  • This relatively slow depolarization continues until the threshold potential is reached

  • Threshold is between -40mV and -50mV


Phases of slow response ap1

Phases of slow response AP

Phase 0 – Upstroke

  • Triggered depolarization

  • The SA and AV node do not have fast sodium channels like neurons, and the depolarization is mainly caused by a slow influx of calcium ions

  • The calcium is let into the cell by voltage-sensitive calcium channels that open when the threshold is reached.


Phases of slow response ap2

Phases of slow response AP

Phase 3 - Repolarization

  • The Ca++channels are rapidly inactivated, soon after they open

  • Sodium permeability is also decreased

  • Potassium permeability is increased, and the efflux of potassium (loss of positive ions) slowly repolarizes the cell


Ion channel inhibitor blocker

Ion channel inhibitor/blocker

  • Na+ channel = phase 0 (fast response

    - Tetrodotoxin

  • Ca++ channel = phase 0 (slow response AP) and phase 2 (fast response AP)

    - Verapamil

    - Nifidipine

    - Manganese

  • K+ channel = phase 3

    - Amiodarone


Refractory period

Refractory period

  • Absolute refractory period

    - duration when Na

    channel is closed

  • Relative refractory period

    - m gate closing and

    h gate opening

  • Super normal period

    - membrane potential close to the RMP


Effective refractory period erp

effective refractory period (ERP)

  • absolute refractory period (ARP) of the cell

  • during the ERP, stimulation of the cell by an adjacent cell undergoing depolarization does not produce new, propagated AP → nontetanization of the heart

  • ERP acts as a protective mechanism in the heart by preventing multiple, compounded action potentials from occurring → limits the frequency of depolarization and therefore heart rate.


Electrical properties1

Electrical Properties

  • Automaticity and Rhythmicity = Chronotropy

    - rate and rhythm

    prepotential = phase 4


Heart rate

Heart Rate

Normal range

Bradycardia – vagal stimulation

Tachycardia – sympathetic effect

Vagal tone


Mechanism of change in heart rate

Mechanism of change in heart rate

Prepotential:

RMP

TP

Slope

RMP TP Slope

Parasympathetic ↓  ↓

Sympathetic  ↓ 


Automaticity

Automaticity

Pacemaker Discharge rate

  • SA node = 70 – 80 beats/min

    = primary pacemaker

    2. AV node = 40 – 60 beats/min

    3. Purkinje fibers = 30 – 40 beats/min

    Ectopic beat – successful impulses coming from other pacemaker cells and not from SA node


Arrhythmia

Arrhythmia

  • when the heart rate is too fast or too slow or when the electrical impulses travel in abnormal pathways is the heartbeat considered abnormal

    An arrhythmia may occur for one of several reasons:

  • Instead of beginning in the sinus node, the heartbeat begins in another part of the heart

  • The sinus node develops an abnormal rate or rhythm

  • A patient has a heart block


Abnormal heart rhythms

Abnormal Heart Rhythms


Symptoms of arrhythmia

Symptoms of Arrhythmia

  • Heartbeats are fast or slow, regular or irregular or short or long

  • Person feels dizzy, light-headed, faint or even loses consciousness

  • Person is experiencing chest pain, shortness of breath or other unusual sensations along with the palpitations

  • Palpitations happen when the patient is at rest or only during strenuous or unusual activity

  • Palpitations start and stop suddenly or gradually


Electrical properties2

Electrical Properties

  • Conductivity = Dromotropy

    Conducting tissues:

  • SA node

  • AV node

  • Internodal tract

  • Interatrial tract or

    Bachmann’s bundle

    5. Atrial muscles

    6. Bundle of His

    7. Bundle branches

  • Purkinje fibers

  • Ventricular muscles


Conduction time

Conduction time


Conduction of impulses

Conduction of impulses

  • Physiologic delay – occurs at the AV node

    Mechanisms:

  • Size of the fibers - small

    a. interatrial tracts - enter the AV node

    b. His-nodal tract – leaves AV node

  • Contains fewer gap junctions

    Significance: allows time for ventricular filling


Conduction of impulses1

Conduction of impulses

Fastest conduction velocity - purkinje fibers

Mechanism: fibers have the largest diameter

Significance: ensures an almost simultaneous contraction of ventricles


Characteristics of conduction

Characteristics of conduction

Mechanism

  • One way directionARP

    2. Decrementalsizes of fibers

    3. IndefatigableARP


Cardiovascular system

ECG

P wave QRS T wave

complex


Basic information derived from ecg tracings

Basic Information derived from ECG tracings

  • Heart rate

  • Origin of excitation

  • Rhythm = regular or irregular

    4. Conduction velocity = PR interval

    = normal, delayed or blocked

  • Mean Electrical Axis

  • Primary cardiac impairment = ST segment

  • Blood supply = large Q wave, ST segment and T wave


Cardiovascular system

EKG


Cardiovascular system

ECG

Large boxes are used to estimate heart rate

Measure from QRS to QRS1 large box = 300 bpm2 large boxes = 150 bpm3 large boxes = 100 bpm4 large boxes = 75 bpm5 large boxes = 60 bpm


Cardiovascular system

EKG

Normal Sinus Rhythm (NSR)

  • originates in the SA node and follows the appropriate conduction pathways.

  • rate is normal, and the rhythm is regular

  • every beat has a P wave followed by QRS complex

  • EKG CriteriaRate: 60-100 bpm

    Rhythm: Regular P waves: look the same and originate from the same locus (SA node)PR interval: 0.12 - 0.20 secQRS: 0.08 -0.12 sec, narrow


Ekg heart block

EKG: Heart Block

First degree:

regular rhythm

PR interval > 0.12 sec

Second degree:

Mobitz I: Wenkebach:

Rhythm:IrregularPR interval:Progressive lengthening followed by dropped beat

QRS's appear to occur in groups.

Mobitz II:

PR interval:Constant on conducted complexes until a sudden block of

AV conduction = P wave is abruptly not followed by a QRS

Third degree:

P wave: Independent P waves and QRS's (AV dissociation)QRS: wide (>0.12 sec) and slower (30-40 bpm) with ventricular escape rhythm.


Cardiovascular system

EKG

Limb leads Precordial leads

Mean Electrical Axis

-30° to +110° limb leads


Mean electrical axis

Mean Electrical Axis

Lead with the tallest QRS complex

Perpendicular to the lead with equipotential QRS complex

Complimentary Leads:

I and aVF

II and aVL

III and aVR


Mechanical properties

Mechanical Properties

  • Contractility – Inotropy Cardiac wall

    Sarcomere length = 2.2 – 2.6 μm


Excitation contraction coupling

Excitation-Contraction Coupling


Contractility inotropy

Contractility = Inotropy


Systole ejection of blood into the circulation

Systole = ejection of blood into the circulation


Cardiovascular system

Systole = contraction

  • Stroke volume = amount of blood ejected per contraction (beat)

  • Cardiac output = amount of blood ejected per minute


Inotropism

Inotropism

(+) = greater force of contraction → more blood ejected

= results from an increased Ca++ concentration

- sympathetic stimulation = via β2 receptors

- epinephrine and norepinephrine

- cardiac glycosides (digitalis)

(-) = weaker force of contraction → less blood ejected

- parasympathetic stimulation

- hypoxia

- acidosis


Diastole ventricular filling

Diastole = ventricular filling


Cardiovascular system

Diastole = relaxation

= Lucidotropy

  • End Diastolic Volume (EDV) – amount of blood contained in the ventricle at the end of diastole

  • End Systolic Volume (ESV) – amount of blood left in the ventricle at the end of systole

  • SV = EDV - ESV


Frank starling law of the heart

Frank-Starling Law of the heart

  • relationship between the initial length of the ventricular myocardia at the end of diastole and the force of contraction

    = initial length - dependent on the EDV

    = force of contraction → SV

    - ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return


Cardiac cycle

Cardiac cycle


Cardiac cycle1

Cardiac cycle


Cardiac cycle2

Cardiac cycle

  • Phase 1 = Atrial systole

  • Phase 2 = Isovolumetric contraction

  • Phase 3 = Rapid ejection

  • Phase 4 = Reduced ejection

  • Phase 5 = Isovolumetric relaxation

  • Phase 6 = Rapid filling

  • Phase 7 = Reduced filling


Heart sounds

Heart sounds

  • S1

    = closure of semilunar valves

    aortic and pulmonic component

    = isovolumetric relaxation

    = sounds like “dub”

  • S2

    = closure of semilunar valves

    aortic and pulmonic component

    = isovolumetric relaxation

    = sounds like “dub”


Heart sounds1

Heart sounds

  • S3

    - during rapid filling

  • S4

    - during atrial systole

    Not normal in adults


Murmur turbulent blood flow

Murmur – turbulent blood flow

  • Valvular defect

  • Congenital abnormalities

    Patent Ductus Arteriosus

    Septal defect: ASD VSD


Effects of valvular lesions on circulation

Effects of valvular lesions on circulation

  • Reduction of cardiac output

  • Additional cardiac work = due to extra volume load

  • Backflow of blood is produced


Pressure volume loop

Pressure Volume Loop

Pressure (mm Hg) Points

A = opening AV valves

D C B = closure AV valves

SV C = opening of SL valves

D = closure of SL valves

A B

Volume (ml)

Lines

AB = Ventricular filling

BC = Isovolumetric contraction

CD = Ejection

DA = Isovolumetric relaxation


Cardiac output

Cardiac Output

CO = SV X HR

Factors affecting cardiac function

  • Preload

  • Afterload

  • Contratility

  • Heart rate

    Ejection Fraction = SV/EDV x 100

    ≥ 55%


Preload end diastolic volume

Preload = End Diastolic Volume


Regulation of cardiac activity

Regulation of cardiac activity

  • Intrinsic control – autoregulation

    = regulation of SV

  • Extrinsic regulation

    = regulation of heart rate


Autoregulation sv edv esv

Autoregulation (SV = EDV – ESV)

  • Homeometric autoregulation = ↑ contractility→↓ ESV → ↑ SV

    Systole

    Diastole

    2. Heterometric autoregulation = ↑ EDV →

    ↑ SV

    = Frank-Starling’s Law of the heart


Extrinsic regulation of the heart effect on heart rate

Extrinsic regulation of the heart = effect on Heart Rate

  • Neural

  • Extrinsic nerves to the heart

    vagal tone

  • Cardiac centers: CIC and CAC

  • Higher centers: cerebral cortex, limbic system

  • Cardiac reflexes

    Baroreceptor - bradycardia

    Chemoreceptor

    Bainbridge

    Somatic afferent

    hot temperature – tachycardia

    cold temperature - bradycardia


Nerve supply to the heart

Nerve supply to the heart

  • Parasympathetic nervous system – vagus

    Right vagus = SA node, AV node, Atrial

    muscles

    Left vagus = AV node, Atrial muscle, SA

    node

  • Sympathetic nervous system

    Right nerve = SA node, AV node, Atrial

    muscles and Ventricular muscles

    Left nerve = AV node, SA node, Atrial

    muscles and Ventricular muscles


Nerve supply to the heart1

Nerve supply to the heart

  • Parasympathetic nervous system – vagus

    Right vagus = SA node, AV node, Atrial

    muscles

    Left vagus = AV node, Atrial muscle, SA

    node

  • Sympathetic nervous system

    Right nerve = SA node, AV node, Atrial

    muscles and Ventricular muscles

    Left nerve = AV node, SA node, Atrial

    muscles and Ventricular muscles


Baroreceptors

Baroreceptors

  • Marey’s Law Sinoaortic reflex

  • Stimulus = high BP

  • Receptors = carotid and aortic sinuses

  • Afferent nerve = IX and X nerves

  • Center = medulla

  • Efferent nerve = X nerve

  • Effector = SA node

  • Effect = slowing HR


Chemoreceptors

Chemoreceptors

  • Peripheral

    Stimulus = hypoxia

    Receptors = carotid and aortic bodies

    Effect = increase in HR

  • Central

    Stimulus = high H+ in CSF

    Receptor = medulla

    Effect = increase in HR


Extrinsic regulation of the heart

Extrinsic regulation of the heart

  • Humoral

    Tachycardia Bradycardia

    1. Hormones

    Epinephrine, NE Acetylcholine

  • Ions

    Ca++ (Ca ++ rigor) K+ (K+ inhibition)

  • Gases

    ↑ CO2↓ O2


Circulation1

CIRCULATION

  • Pulmonary = from

    RV to the lungs for

    Oxygenation

  • Systemic = from

    LV to different organs

    of the body


Blood vessels

Blood Vessels


Functions of blood vessels

Functions of blood vessels

  • Aorta – windkessel vessel

  • Large arteries – conducting vessels

  • Medium arteries – distributing vessels

  • Small arteries and arterioles – resistance vessels

  • Capillaries – exchange vessels

  • Veins = capacitance vessels

  • Vena cava = conduits


Distribution of blood at rest

Distribution of blood at rest

60 – 70 %veins and venules

10 – 12%pulmonary circulation

8 – 11%heart

10 – 12%arteries

4 - 5% capillaries


Hemodynamics

HEMODYNAMICS

  • Blood Flow (Q) = amount of blood from point 1 to point 2 in one minute

    = Poiseuille’s Equation

    = ml/min

    Q = ΔP/R

    R = 8 η lη = viscocity

    π r4 l = vessel length

    r = vessel radius

    Q = π ΔP r4

    8 η l


Hemodynamics1

HEMODYNAMICS

  • Character of flow = Reynold’s Number

    (Re # = ρ V D

    η

    ρ = blood density

    V = velocity of blood flow

    D = vessel diameter

    > Laminar or Streamlined

    = flow of components

    of blood runs parallel to

    the wall of blood vessel

    > Turbulent

    = flow of components of blood runs tangential to the wall producing eddy currents


Hemodynamics2

Hemodynamics

  • Wall Tension (T) Laplace’s Law

    T = Pr

    P = transmural pressure

    r = vessel radius


Relationship of velocity of blood flow and total cross sectional area

Relationship of velocity of blood flow and total cross sectional area


Blood pressure

Blood Pressure

Q = ΔP/R

ΔP = Q x R

BP = CO x TPR

Methods:

1 Palpatory

2 Auscultatory

3 Oscillometric

SP

DP

Korotkoff sounds


Components of bp

Components of BP


Arterial pressure

Arterial Pressure

  • Pulse Pressure = SP – DP

  • Mean Arterial Pressure

    MAP = DP + 1/3PP


Cardiovascular system

.

Categories for Blood Pressure Levels in Adults (in mmHg)The ranges in the table apply to most adults (aged 18 and older) who don't have short-term serious illnesses


Risk factors of developing hypertension

Risk factors of developing hypertension

  • Family history of high blood pressure, heart

  • disease, or diabetes

  • Age greater than 55

  • Overweight

  • Not physically active (sedentary)

  • Alcohol excessive drinking

  • Smoking

  • Food high in saturated fats or sodium use

  • Race

  • Gender

  • Certain medications such as NSAIDs, cocaine

  • decongestants


Composition of microcirculation

Composition of microcirculation

  • Arterioles

    Metarterioles

  • Capillaries

  • Venules

  • Terminal

    lymphatic

    vessels


Fluid exchange governed by starling s forces

Fluid Exchange = governed by Starling’s forces


Filtration occurs mainly through the intercellular junctions of the small pore system

Filtration occurs mainly through the intercellular junctions of the small pore system

As formulated is Starling’s hypothesis:

  • the fluid filtered across a capillary membrane is proportional to the net filtration pressure

  • the sum of hydrostatic pressures and the colloidal osmotic pressure

  • expressed as:

    Vf  =  kf [(Pc - Pif) - (πc - πif)]

    or = kf [(Pc+ πif) - (πc+ Pif)]


Fluid exchange

Fluid exchange


Veins

Veins

  • Capacitance vessels

  • Reservoir of blood

  • Low pressure

  • Low resistance


Factors affecting venous return

Factors affecting Venous Return

  • Muscle contraction - rhythmical contraction of limb muscles as occurs during normal locomotory activity (walking, running, swimming) = promotes venous return by the muscle pump mechanism

  • Decreased venous compliance - following Sympathetic activation of veins, increases central venous pressure and promotes venous return indirectly by augmenting cardiac output through the Frank-Starling mechanism = increases the total blood flow through the circulatory system

  • Respiratory activity - during respiratory inspiration, the decrease in right atrial pressure = increases the venous return  

  • Vena cava compression - increases vena cava resistance which occurs when the thoracic vena cava becomes compressed during a Valsalva maneuver or during late pregnancy = decreases return

  • Gravity - the effects on venous return when a person stands up, the hydrostatic forces cause the venous pressure in the dependent limbs to increase = venous return decreases


Regulation of blood flow

Regulation of blood flow

  • Local regulation

    1. Intrinsic

    a. Myogenic theory

    b. Endothelial derived =Nitric Oxide,

    Endothelin, Thromboxane

    2. Metabolic

    a. Oxygen demand

    > active hyperemia - ↑ O2 consumption

    > reactive hyperemia – hypoxia due

    previous occlusion of blood supply

    b. Vasodilator agents = H+, histamine, kinins


Extrinsic regulation of blood flow

Extrinsic regulation of blood flow

  • Neural

    Sympathetic tone

    Vascular centers: VCC and VDC

    Cardiovascular reflexes:

    Baroreceptor = ↓ TPR

  • Humoral

    1. Hormones

    Vasodilators : ACh, Epinephrine

    Vasoconstrictors: Epinephrine, NE,

    Angiotensin, ADH, Serotonin

    2. Ions

    Ca++ – vasoconstriction

    H+ and K+ - vasodilation

    3. Gases

    ↑CO2 and↓O2 - vasodilation


Delayed regulation of blood flow

Delayed regulation of blood flow

  • Opening of collaterals

    - blood flowing to more blood vessels

  • Angiogenesis

    - formation of more arteries


Neural mechanisms

Neural mechanisms

  • ANS on vessel caliber

    - sympathetic tone

    - parasympathetic = vasodilatation

  • Vasomotor centers - medulla

    - Vasoconstrictor center

    - Vasodilator center

  • Higher centers

    - cerebral cortex

    - limbic system

  • Vasomotor reflexes

    - baroreceptor

    - chemorecpetor

    - somatosympathetic


Humoral mechanisms

Humoral mechanisms


Bp regulation onset of action

BP regulation - Onset of action

  • Immediate

    Cardiovascular reflexes

    CNS ischemic effect

  • Intermediate

    Capillary fluid shift

    Renin-Angiotensin system

  • Delayed

    Aldosterone

    Renal vascular system


Cardiovascular system

Effect of :

  • Acute pain → increased sympathetic stimulation

  • Deep pain → increased parasympathetic stimulation

    Vasoconstriction Vasodilation

  • pH decreased increased

  • Temperature low high


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