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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


Juliet Ver-Bareng, M.D., FPSP

  • Physiologic properties of the heart

Electrical properties

< Excitability

< Automaticity and Rhythmicity

< Conductivity

Mechanical properties

< Contractility

< Distensibility

  • Regulation of cardiac activity

Neural control

Humoral control

  • 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

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


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


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





RMP TP Slope

Parasympathetic ↓  ↓

Sympathetic  ↓ 


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

  • 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
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 of impulses
Conduction of impulses
  • Physiologic delay – occurs at the AV node


  • 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


  • One way direction ARP

2. Decremental sizes of fibers

3. Indefatigable ARP


P wave QRS T wave


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

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


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.


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


Systole = contraction

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

(+) = 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 = 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 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


Volume (ml)


AB = Ventricular filling

BC = Isovolumetric contraction

CD = Ejection

DA = Isovolumetric relaxation

cardiac output
Cardiac Output


Factors affecting cardiac function

  • Preload
  • Afterload
  • Contratility
  • Heart rate

Ejection Fraction = SV/EDV x 100

≥ 55%

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



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



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


Left vagus = AV node, Atrial muscle, SA


  • 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


Left vagus = AV node, Atrial muscle, SA


  • 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

  • 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
  • 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

  • Pulmonary = from

RV to the lungs for


  • Systemic = from

LV to different organs

of the body

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

  • 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

  • Character of flow = Reynold’s Number

(Re # = ρ V D


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

  • Wall Tension (T) Laplace’s Law

T = Pr

P = transmural pressure

r = vessel radius

blood pressure
Blood Pressure

Q = ΔP/R

ΔP = Q x R



1 Palpatory

2 Auscultatory

3 Oscillometric



Korotkoff sounds

arterial pressure
Arterial Pressure
  • Pulse Pressure = SP – DP
  • Mean Arterial Pressure

MAP = DP + 1/3PP



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


  • Capillaries
  • Venules
  • Terminal



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)]

  • 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

bp regulation onset of action
BP regulation - Onset of action
  • Immediate

Cardiovascular reflexes

CNS ischemic effect

  • Intermediate

Capillary fluid shift

Renin-Angiotensin system

  • Delayed


Renal vascular system


Effect of :

  • Acute pain → increased sympathetic stimulation
  • Deep pain → increased parasympathetic stimulation

Vasoconstriction Vasodilation

  • pH decreased increased
  • Temperature low high