THE CARDIOVASCULAR SYSTEM

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CHAPTER 4 THE CARDIOVASCULAR SYSTEM
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Weight of the heart 300g Work 75/min, 10000
beats /day 35 million beats /year, 2.5 billion
beats/life 70ml/beat, 7200 l/day
The work of the heart in one life is equivalent
to lifting 30 tons to the Mount Everest
The busy and hard working heart!
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MAIN FUNCTIONS OF THE CIRCULATORY SYSTEM

• Transport and distribute essential substances to
  the tissues.
• Remove metabolic byproducts.
• Adjustment of oxygen and nutrient supply in
  different physiologic states.
• Regulation of body temperature.
• Humoral communication.

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Systemic and Pulmonary Circulation
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A. Heart location in the chest
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B. Heart Chambers
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B. Heart Chambers
1. Right Heart a. receives venous blood from
systemic circulation via superior and inferior
vena cava into right atrium

• b. pumps blood to pulmonary circulation and left
  ventricle from right ventricle
• 2. Left Heart
• a. receives oxygenated blood from pulmonary
  circulation
• b. pumps blood into systemic circulation

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C. Heart Valves

• 1. Atrioventricular
• a. tricuspid--between RA and RV three leaflets
• b. mitral--between LA and LV two leaflets

2. Semilunar a. pulmonic--three leaflets b.
aortic--three leaflets
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Heart Valves
Prevent backward regurgitation Provide low
resistance to forward flow
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Cardiac Cycle
Diastole
Systole
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• Section 1 The Heart as a Pump
• I. The Cardiac Cycle
• Concept
• The period from the end of one heart contraction
  to the end of the next

Properties 1) Diastole is longer than
systole 2) The sequence of systole and
diastole
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• 2 The Phases of the Cardiac Cycle
• Period of isometric (isovolumetric
• or isovolumic) contraction

Events ventricular contraction? ventricular
pressure rise ? atrioventricular valve close ?
the ventricular pressure increase
sharply Period 0.05 sec Importance enable the
ventricular pressure to rise from 0 to the level
of aortic pressure (after-load)
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• (2) Period of ejection
• Events ventricular contraction continuously
• the ventricular pressure rise above the arterial
  pressure
• semilumar valves open
• ? blood pours out of the ventricles

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1. Rapid ejection period (0.10s, 60 of the stroke
   volume)
2. Reduced ejection period (0.15s, 40 of the stroke
   volume)

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(3) Period of isometric (isovolumic) relaxation

• Events
• ventricular muscle relax
• the ventricular pressure fall
• lower than the aortic pressure
• aortic valve close
• the ventricular pressure fall sharply

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Period 0.06-0.08 s Importance Enable the
ventricular pressure fall to the level near the
atrial pressure
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(4) Period of filling of the ventricles Events
Ventricular muscle relax continuously ? the
ventricular pressure is equal or lower than the
atrial pressure ? atrioventricular valve open
? blood accumulated in the atria rushes into the
ventricular chambers quickly from the atrium to
the ventricle.
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1. Period of rapid filling. (0.11s, amount of
   filling, 2/3)
2. Period of reduced filling (0.22s, little blood
   fills into the ventricle)

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• (5) Atrial systole
• Significance, 30 of the filling
• During high output states or in the failing
  heart,
• the amount added by atrial contraction may be of
  major importance
• in determining the final cardiac output.

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LEFT VENTRICULAR PRESSURE/VOLUME P/V LOOP
120
F
E
D
80
LEFT VENTRICULAR PRESSURE (mmHg)
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B
A
C
0
100
150
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LEFT VENTRICULAR VOLUME (ml)
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2) Pressure changes in the atria, the a, c, and v
waves.
a wave, the atrial contraction
c wave, bulging of the A-V valves when the
ventricles begin to contract
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v wave, at the end of ventricle contraction,
caused by the accumulated blood in the atria
while the A-V valves are closed
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Heart Sounds
The sounds heard over the cardiac region produced
by the functioning of the heart.
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Heart Sounds

• S1- first sound
• Atrioventricular valves and surrounding fluid
  vibrations as valves close at beginning of
  ventricular systole

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• S2- second sound Results from closure of aortic
  and pulmonary semilunar valves at beginning of
  ventricular diastole
• S3- third sound is produced by vibrations of the
  ventricular walls when suddenly distended by the
  rush of blood from the atria

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CARDIAC CYCLE
Rapid Ventricular Filling
Reduced Ejection
Atrial Systole
Rapid Ejection
Isovolumic Relax.
Reduced Ventricular Filling
Atrial Systole
Isovolumic contract.
Aortic opens
gtO
Aortic closes
Mitral opens
Mitral Closes
S1
gtD
S2
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• II Cardiac Output
• Stroke Volume The volume pumped by the heart
  with each beat,
• end diastole volume end systole
  volume, about 70 ml
• 2. Ejection Fraction Stroke volume accounts for
  the percentage of the end diastolic volume,
• stroke volume / end diastole volume X
  100, normal range, 55-65

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3. Minute Volume, or Cardiac Output the volume
of the blood pumped by one ventricle,
stroke volume X heart rate. It varies
with sex, age, and exercise 4. Cardiac Index, the
cardiac output per square meter of body surface
area. the normalized data for different
size individuals, the normal range is
about 3.0 3.5 L/min/m2
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Determinants of Cardiac Output (CO)
Contractility
Stroke Volume

• Preload

Afterload
Heart Rate
Cardiac Output
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Definitions

• Preload
• amount of stretch on the ventricular myocardium
  prior to contraction
• Afterload
• the arterial pressure (or some other measure of
  the force) that a ventricle must overcome while
  it contracts during ejection
• impedance to ventricular ejection

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Definitions

• Contractility
• myocardiums intrinsic ability to efficiently
  contract and empty the ventricle
• (independent of preload afterload)

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Determinants of Cardiac Output 1. Preload
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Determinants of Cardiac Output- Preload

• Preload ventricular filling or volume

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Determinants of Cardiac Output - Preload

• Preload approximated by measuring
• 1. Central venous pressure (CVP) right atrial
  pressure.
• 2. Pulmonary capillary diastolic wedge pressure
  (PCWP) LVEDP
• Parameters
• 1. CVP 3mm Hg (normal range 1 - 5)
• 2. PCWP 9mm Hg (normal range 2 - 13)

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the Frank - Starling mechanism

• Left ventricle (LV) function curve, or Frank -
  Starling curve (1914)
• Normal range of the LVEDP, 5-6 mmHg
• Optimal initial preload, 15-20 mmHg (Sarcomere,
  2.0 2.2 µm
• When the LVEDP gt 20 mmHg, LV work is maintained
  at almost the same level, does not change with
  the increase of LVEDP
• Mechanism
• Concept of heterometric regulation

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• Factors determining the preload (LVEDP)
• Period of the ventricle diastole (filling)
  heart rate
• Speed of the venous return (difference between
  the venous pressure and atrial pressure)
• Importance of the heterometeric regulation
• In general, heterometric regulation plays only a
  short-time role, such as during the body posture
  change, artery pressure increase, and unbalance
  of ventricular outputs.
• In other conditions, such as exercise, cardiac
  output is mainly regulated by homometric
  regulation.

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Determinants of Cardiac Output - Afterload
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• Short time change of the arterial pressure
• Transit arterial pressure rise
• isovolumetric contraction phase become longer
• period of ejection shorter
• stroke volume less
• more blood left in the ventricle left
• LVEDP increase
• through heterometeric regulation
• stroke volume return to normal in next beat.

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• Long time high arterial pressure
• through neural and humoral regulation
• the stroke volume is maintained at normal level
• pathogenesis of the cardiovascular system

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Determinants of Cardiac Output - Contractility
Contractility (neural and humoral
regulation) Sympathetic nerve (norepinephrine) or
the epinephrine and norepinephrine (adrenal
gland) enhance the strength and the velocity of
the cardiac contraction. The change of
myocardial property is independent of the
preload. We call it the contractility. Importance
exert a long time influence on the cardiac
output.
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Action of Sympathetic Stimulation

• Sympathetic nerve stimulation increases cardiac
  contractility.
• At rest the heart is under sympathetic tone.
• Noradrenaline enhances calcium entry into cardiac
  cells.
• Parasympathetic stimulation has little affect on
  contractility due to the innervation pattern of
  the heart.

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PRESSURE/VOLUME RELATIONSHIPS UNDER DIFFERENT
CONDITIONS
PRELOAD
AFTERLOAD
CONTRACTILITY
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Determinants of Cardiac Output - The heart rate

• Normal range of the heart rate 60 100 beats/min
• Within physiological limit?, the higher the heart
  rate, the more blood that the heart pump.

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1, at rest (without any regulation) 2, during
exercise (with humoral and neural regulation)
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• IV Cardiac Output Reserve
• The maximal cardiac output subtracts the normal
  value.
• It reflects the ability of the heart to adapt the
  change of environment (internal or external)

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Normal range End diastole volume 145ml end
systole volume 75ml stroke volume 70 ml Heart
rate 75 beats/min Normal cardiac output 70 X 75
5.25 L /min
Maximal level Maximal diastole volume 160 ml
(reserve 15ml) Maximal systole residual volume
20 ml (reserve 55ml) Maximal heart rate (without
the stroke volume decrease )180 beats/min
(reserve 105 beats/min) Maximal cardiac output
(160 20) X 180 25.2 L/min