Transcript Section 1

LIU Chuan Yong
刘传勇
Institute of Physiology
Medical School of SDU
Tel 88381175 (lab)
88382098 (office)
Email: [email protected]
Website: www.physiology.sdu.edu.cn
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
 receives venous blood from
systemic circulation
 via superior and inferior
vena cava into right atrium
pumps blood to pulmonary circulation from right
ventricle
2. Left Heart
receives oxygenated blood from pulmonary
circulation
pumps blood into systemic circulation
C. Heart Valves
 1. Atrioventricular
 tricuspid--between RA
and RV; three leaflets
 mitral--between LA and
LV; two leaflets
 2. Semilunar
 pulmonic--three leaflets
 aortic--three leaflets
Heart Valves
 Prevent backward regurgitation
 Provide low resistance to forward flow
Section 1 The Heart as a Pump
 I Cardiac Cycle
 The period from the end of one heart
contraction to the end of the next
Cardiac Cycle
Diastole is
longer than
systole
The sequence
of systole and
diastole
Cardiac Cycle: diastole and systole
Diastole
Systole
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
 Rapid ejection period (0.10s, 60% of the
stroke volume)
 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.
 Period of rapid filling. (0.11s, amount of filling, 2/3)
 Period of reduced filling (0.22s, little blood fills into the
ventricle)
(5) Atrial systole
 Significance, 30% of the filling
 Be of major importance in determining the final cardiac
output during high output states or in the failing heart
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


closure of aortic and pulmonary semilunar valves
at beginning of ventricular diastole
S3- third sound

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
 Stroke Volume – The volume pumped by the
heart with each beat,


= end diastole volume – end systole volume, about
70 ml
Ejection Fraction – Stroke volume accounts for
the percentage of the end diastolic volume,

= stroke volume / end diastole volume X 100%,
normal range, 55-65%
II Cardiac Output
3. Minute Volume, or Cardiac Output – the
volume of the blood pumped by one ventricle in
one minute
 = 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 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 3 mmHg (normal range 1 - 5)
2. PCWP 9 mmHg (normal range 2 - 13)
Frank-Starling Mechanism of the Heart
The intrinsic ability of the heart to adapt to
changing volumes of inflowing blood
the Frank - Starling mechanism of the heart:
 Left ventricle (LV) function curve, or
Frank - Starling curve (1914):
 Normal range of the LVEDP, 56 mmHg
 Optimal initial preload, 15-20
mmHg (Sarcomere, 2.0 – 2.2
µm
 When the LVEDP > 20 mmHg, LV
work is maintained at almost the same
level, does not change with the
increase of LVEDP
 Mechanism
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
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.
Definitions
Contractility
myocardium’s intrinsic ability to
efficiently contract and empty the
ventricle
(independent of preload &
afterload)
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