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 MAIN FUNCTIONS OF THE CIRCULATORY SYSTEMCIRCULATORY SYSTEM

Transport and distribute essential substances to the tissues.

Remove metabolic byproducts.Adjustment of oxygen and nutrient supply in d

ifferent physiologic states.Regulation of body temperature.Humoral communication.

Systemic and Pulmonary Circulation

A. Heart location in the chest

B. Heart Chambers

B. Heart Chambers

b. pumps blood to pulmonary circulation and left ventricle from right ventricle

2. Left Hearta. receives oxygenated blood from pulmonary

circulation

b. pumps blood into systemic circulation

1. Right Heart

a. receives venous blood from systemic circulation via superior and inferior vena cava into right atrium

C. Heart Valves1. 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

Prevent backward regurgitation

Provide low resistance to forward flow

Heart ValvesHeart Valves

Cardiac Cycle

DiastoleSystole

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/VOLUME P/V LOOP

LE

FT

VE

NT

RIC

UL

AR

PR

ES

SU

RE

(m

mH

g)

LEFT VENTRICULAR VOLUME (ml)

A BC

D

EF

100 150500

120

40

80

c wave, bulging of the A-V valves when the ventricles begin to contract

2 ） Pressure changes in the atria, the a, c, and v waves.

a wave, the atrial contraction

v wave, at the end of ventricle contraction, caused by the accumulated blood in the atria while the A-V valves are closed

The sounds heard over the cardiac region produced by the functioning of the heart.

Heart SoundsHeart Sounds

Heart Sounds• S1- first sound • Atrioventricular valves and surrounding fluid vibrations as valve

s 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

CARDIAC CYCLE

Atr

ial S

ysto

le

Mitral Closes

Isov

olum

ic c

ontr

act.

Aortic opens

S1

Rap

id E

ject

ion

Red

uced

Eje

ctio

n

Isov

olum

ic R

elax

.

Aorticcloses

Rap

id V

entr

icul

arF

illi

ng

Mitralopens

S2

Red

uced

Ven

tric

ular

F

illi

ng Atr

ial S

ysto

le

:>O

:>D

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)

Preload

Heart Rate

Afterload

Contractility

Cardiac Output

Stroke Volume

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 OutputDeterminants of Cardiac Output

1. Preload1. Preload

Preload = ventricular filling or volume

Determinants of Cardiac Determinants of Cardiac Output- PreloadOutput- 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)

Determinants of Cardiac Output - PreloadDeterminants of Cardiac Output - Preload

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 - AfterloadDeterminants 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

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.

Determinants of Cardiac Output Determinants of Cardiac Output - Contractility- Contractility

Action of Sympathetic StimulationSympathetic 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

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.

Determinants of Cardiac Output Determinants of Cardiac Output

- - The heart rate

1, at rest (without any regulation)

2, during exercise (with humoral and neural regulation)

IV Cardiac Output ReserveThe maximal cardiac output subtracts the normal value.

It reflects the ability of the heart to adapt the change of environment (internal or external)

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

Normal rangeEnd 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