Transcript (1). heart rate ↑→cardiac output

Wu Minfan
Department of Physiology, Shenyang Medical College
Introduction
The cardiovascular system consists
of the heart and the blood vessels.
The right ventricle pumps blood through
the pulmonary circulation to the left atrium.
The left ventricle ejects blood through the
systemic circulation to the right atrium.
(F)
The function of blood circulation is to
transport substances in human body.
Systemic and Pulmonary Circulation
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 then to
left heart.
2. Left Heart
– a. receives oxygenated blood from pulmonary
circulation via pulmonary vein into left atrium.
– b. pumps blood into systemic circulation, and then to
right heart.
1. Atrioventricular V
a. mitral--between LA
and LV; two leaflets
b. tricuspid--between
RA and RV; three
leaflets
2. Semilunar V
a. aortic--three
leaflets
b. pulmonary-three leaflets
Heart Valves
Function of Heart Valves
Prevent backward flow
Provide low resistance to forward flow
Section one Pump function of the heart
The busy and hard working heart!
I. Cardiac Cycle
1.Concept: The period of one contraction and one
relaxation of the heart.
2.Relationship of the cardiac cycle and Heart rate
60s
Cardiac cycle= ————
Heart rate
Heart rate:75 beats/min
60s
Cardiac cycle = —— =0.8sec
75
A cardiac cycle consists
of a systole and a diastole.
Atrial cycle equals to
ventricular cycle.
Diastole is longer than
systole.
When heartbeat becomes more rapid, the cardiac
cycle is shorter, and the diastole is much shorter than
normal. Tachycardia is unfavourable for the heart.
Whole heart relaxation phase means this period of
the first 0.4s of the ventricular relaxation in which
atrium is also in relaxation state.
0.7s
0.1s
Atrium
Ventricle
0.3s
Contraction
0.5s
Relaxation
II. Mechanical events of the cardiac cycle
1. For example: Processess of blood ejection and
filling in the left ventricle
Ventricular Systole
（1）Period of isovolumic
contraction 0.05s
（2）Period of rapid
ejection 0.1s
（3）Period of slow
ejection 0.15s
Ventricular Diastole
（4）period of isovolumic relaxation 0.07s
（5）Period of rapid filling 0.11s
（6）Period of slow filling 0.22s
（7）Atrial systole 0.1s
Atria
S D DD D D D D
Ventricles
D S S S D D D D
.1 .2 .3 .4 .5 .6 .7 .8
2. The Phases of the Cardiac Cycle
(1) Period of isovolumic contraction
Events: ventricular contraction
ventricular pressure rise 
atrioventricular valve close 
the ventricular pressure increase
sharply
Period: 0.05 sec
atrioventricular valve close 
S1- first heart sound
Importance: enable the ventricular
pressure to rise from 0 to the level
of aortic pressure
(2) Period of ejection
Events: ventricular contraction continuously
 the ventricular pressure rise above the arterial pressure
 semilunar valves open
 blood pours out of the ventricles
1) Rapid ejection period (0.10s, 66% of the total
ejected blood volume, stroke volume)
2) Reduced ejection period (0.15s, 34% of the
total ejected blood volume , stroke volume)
The aortic pressure actually exceeds the
ventricular pressure, but momentum keeps
the blood moving forward.
(3) Period of isovolumic relaxation
Events:
ventricular muscle relax
 the ventricular
pressure fall
 lower than the aortic
pressure
 aortic valve close
 the ventricular
pressure fall sharply
second heart sound ←closure of
aortic and pulmonary semilunar valves at
beginning of ventricular diastole
S2-
Period: 0.06-0.08 s
Importance: Enable the ventricular
pressure to 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
ventricle
 blood flow quickly
from the atrium to the
ventricle.
1) Period of rapid filling.
(0.11s, amount of filling, 2/3 of total filling
blood volume)
2) Period of reduced filling
(0.22s, little blood fills into the ventricle)
(5) Atrial systole
Significance, 25% of total filling blood volume
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.
Correlation of
events in the
left side of the
heart in each
cardiac cycle
Mitral
Closes
:>D
S2
Atrial Systole
Reduced Ventricular
Filling
Rapid Ventricular
Filling
Isovolumic Relax.
Reduced Ejection
Rapid Ejection
Isovolumic contract.
Atrial Systole
:>O
Aortic
opens
Aortic
closes
Mitral
opens
S1
Heart sounds
Action of the heart produces mechanical
vibrations which are audible at the chest wall
as the heart sounds.
The first heart sound is caused by closure of the
atrioventricular valves and so marks the
beginning of ventricular systole.
The second heart sound is caused by closure of
the aortic and pulmonary valves and so
marks the beginning of ventricular diastole.
The third heart sound is caused by sudden
stretch of the ventricular wall and papillary
muscle, and sudden deceleration of filling
flow at the end of rapid filling period.
The fourth heart sound is caused by unusually
strong atrial contraction at the end of
ventricular diastole.
III. Cardiac Output
1.Stroke volume
The amount of blood
pumped out of each
ventricle per beat is
called the stroke volume,
about 70mL in a resting
adult.
Stroke volume =
end diastolic volume – end
systolic volume
the normal range is:
2.Ejection fraction
stroke volume
End diastolic volume
55-65%
× 100% = ejection fraction
70×100%
—— =56%
125
125
70
55
3.Cardiac output
The output of each ventricle per minute is
called the cardiac output.
Cardiac Output = Stroke Volume× Heart Rate
CO=SV×HR
=70 × 75
=5250（ml）
It varies with sex, age, and exercise
4.Cardiac index
There is a correlation between resting
cardiac output and body surface area. The
cardiac output per square meter of body
surface area is known as the cardiac index.
It averages 3.2L/ min·m2
5-6L/min
1.6-1.7m2
the normal range is:
3.0 – 3.5 L/min·m2
5.Cardiac work
Like any machine, the heart does work in
moving the blood through the circulatory
system.
5.Cardiac work
Stroke work (J)= stroke volume(L) ×gravity of blood
(mean arterial pressure-mean left atrial pressure)
(mmHg) ×13.6 ×9.807 ×(1/1000)
Minute work (J)= stroke work(J) ×Heart rate
Minute work of the right heart = 1/6 of minute work
of the left heart
IV. Factors Affecting Cardiac Output
Contractility
Preload
Heart
Rate
Stroke
Volume
Cardiac
Output
Afterload
Definitions
• Preload
– amount of stretch on the ventricular myocardium
prior to contraction
– Ventricular end-diastolic volume or pressure
• 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)
1. Preload (Initial length in Cardiac muscle )
Define：Regulation of contractility and cardiac
Stroke volume
output as a result of changes in cardiac muscle fiber
initial length is called heterometric autoregulation, or
Starling’s law of the heart.
Frank-Starling
curve
Ventricular end-diastolic volume
the Frank - Starling mechanism
Frank - Starling curve (1914):
1)Normal range of the LVEDP,
5-6 mmHg; Optimal initial
preload, 12-15 mmHg ( 2.0 –
2.2 µm )
2)When the LVEDP is 15-20
mmHg, LV work is maintained
at almost the same level.
Left ventricle (LV)
function curve
3)When the LVEDP > 20 mmHg,
LV work does not change or
slightly decreases.
• Starling Mechanism :
The heart can automatically regulate and
balance the relation between stroke volume
and volume of venous return :
Volume of venous return ↑=>
the end-diastolic volume ↑ (preload↑)=>
ventricular contraction ↑→ stroke volume ↑
Factors determining the preload (LVEDP)
1. Blood volume of venous return.
1) Period of the ventricle diastole (filling) – heart rate
2) Speed of the venous return (difference between the
venous pressure and atrial pressure)
3) pericardial fluid
4) ventricular compliance =ΔV/ΔP
--denotes the ease or difficulty with which something can
be stretched. myocardial fibrosis
2. Ventricular residual blood volume after contraction
Importance of the heterometric regulation
• In general, heterometric regulation plays only a shorttime role, such as during the body posture change,
artery pressure increase, and unbalance between the
left and the right ventricular outputs.
• In other conditions, such as exercise, cardiac output is
mainly regulated by homometric regulation.
2.Afterload（Aortic pressure）
Cardiac output
5
3
1
100
200 mmHg
Aortic pressure (mmHg)
Short time change of the arterial pressure
Arterial pressure rises :
isovolumetric contraction phase becomes longer
 period of ejection becomes shorter
 stroke volume less
 more blood left in the left ventricle
LVEDP increase
 through heterometric 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
hypertension
myocardial hypertrophy
heart failure
3.Myocardial Contractility
（homometric regulation）
the regulation due to changes in
contractility independent of initial length.
numbers of activated cross bridge
Ca2+ concentration
ATPase activity
4.Heart rate
Heart rate
(beat/min)
40
75
120
200
Cardiac cycle
(sec)
1.5
0.8
0.5
0.3
Systole
(sec)
0.3
0.25
0.16
Cardiac output
40
180
Heart rate (beat/min)
Diastole
(sec)
0.5
0.25
0.14
(1). heart rate ↑→cardiac output ↑
(40—180beats/min)
(2). heart rate > 160—180beats/min
heart rate <40beats/min
=>cardiac output ↓
V. Cardiac reserve
The capacity of the heart to increase cardiac
output to satisfy human metabolic needs is
called cardiac 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)
During muscular exercise, there is
increased cardiac output.
Myocardial contractility
Heart rate
Diastolic inflow
Stroke volume
CO
SV
HR
EDV
ESV
LVW
(L/min) (mL/beat) (beat/min) (mL)
(mL)
(J/min)
Rest
5
Exercise
35
120~140 180~210
Reserve
volume
30
60~80 130~140
60~80
70~80
120~160 60~80
60
130~170 10~20
195
10~20
135
40~50
1 Heart rate rises：2-2.5 times
2 Reserve of stroke volume ：
200 beats/min
140 ( ml )
15
End-diastolic volume
15 ml
125
70
55
End-systolic volume
35-40
35-40 ml
15-20