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CHAPTER 4
THE CARDIOVASCULAR SYSTEM
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!
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.
Systemic and Pulmonary Circulation
A. Heart location in the chest
B. Heart Chambers
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
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
C. Heart Valves
Heart Valves
Prevent backward regurgitation
Provide low resistance to forward flow
Cardiac Cycle
Diastole
Systole
Section 1 The Heart as a Pump
I. The Cardiac Cycle
1. 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
2 The Phases of the Cardiac Cycle
(1) 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)
(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
1) Rapid ejection period (0.10s, 60% of the
stroke volume)
2) Reduced ejection period (0.15s, 40% of the
stroke volume)
(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
Period: 0.06-0.08 s
Importance: Enable the ventricular pressure fall to
the level near the atrial pressure
(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.
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)
(5) Atrial systole
1) 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.
LEFT VENTRICULAR PRESSURE (mmHg)
LEFT VENTRICULAR
PRESSURE/VOLUME P/V LOOP
120
F
E
D
80
40
A
0
50
B
C
100
150
LEFT VENTRICULAR VOLUME (ml)
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
v wave, at the end of ventricle contraction, caused by
the accumulated blood in the atria while the A-V
valves are closed
Heart Sounds
The sounds heard over the cardiac
region produced by the functioning of
the heart.
Heart Sounds
• S1- first sound
• Atrioventricular valves and surrounding fluid vibrations as
valves close at beginning of ventricular systole
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
Mitral
Closes
:>D
S2
Atrial Systole
Reduced Ventricular
Filling
Rapid Ventricular
Filling
Isovolumic Relax.
Reduced Ejection
Rapid Ejection
Isovolumic contract.
Atrial Systole
:>O
CARDIAC
CYCLE
Aortic
opens
Aortic
closes
Mitral
opens
S1
II Cardiac Output
1. 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%
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
Determinants of Cardiac Output (CO)
Contractility
Preload
Heart
Rate
Stroke
Volume
Cardiac
Output
Afterload
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
Definitions
• Contractility
• myocardium’s intrinsic ability to
efficiently contract and empty the
ventricle
• (independent of preload &
afterload)
Determinants of Cardiac Output
1. Preload
Determinants of Cardiac
Output- Preload
Preload = ventricular filling or volume
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
2. PCWP
3mm Hg (normal range 1 - 5)
9mm Hg (normal range 2 - 13)
the Frank - Starling mechanism
Left ventricle (LV) function curve, or
Frank - Starling curve (1914):
1) Normal range of the LVEDP, 5-6
mmHg
2) Optimal initial preload, 15-20 mmHg
(Sarcomere, 2.0 – 2.2 µm
3) When the LVEDP > 20 mmHg, LV
work is maintained at almost the same
level, does not change with the
increase of LVEDP
Mechanism
Concept of heterometric regulation
Factors determining the preload (LVEDP)
1) Period of the ventricle diastole (filling) – heart rate
2) 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.
Determinants of Cardiac Output - Afterload
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.
Long time high arterial pressure
through neural and humoral regulation
 the stroke volume is maintained at normal level
pathogenesis of the cardiovascular system
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.
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.
PRESSURE/VOLUME
RELATIONSHIPS UNDER
DIFFERENT CONDITIONS
PRELOAD
AFTERLOAD
CONTRACTILITY
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.
1, at rest (without
any regulation)
2, during exercise
(with humoral and
neural regulation)
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)
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