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diac wall, covers surtrauma

face of heart and great

vessels

Myocardium

Central layer of thick

Provides major pumping force

muscular tissue

of the venrricles

Endocardium

Thin layer of endothe

Lines [he inner surface of hearr,

liurn and connective

valves, chordae rendineae,

tissue

and papillary muscles

Right atrium

Heart chamber

Receives blood from venous

system and is a primer

pump for the right ventricle

Tricuspid

Atrioventricular valve

Prevents back flow of blood

valve

between right atrium

from right ventricle to

and ventricle

atrium during ventricular

systole

Right

Hearr chamber

Pumps blood to pulmonary

ventricle

circulation

Pulmonic

Semilunar valve between

Prevents back flow of blood

valve

right ventricle and

from pulmonary artery to

pulmonary arrery

right ventricle during diastole

Left atrium

Heart chamber

Acts as a reservoir for blood

and primer pump for left

ventricle

Mitral valve

Atrioventricular valve

Prevents backflow of blood

between left atrium

from left ventricle to

and ventricle

atrium during ventricular

systole

Left ventricle

Heart chamber

Pumps blood to systemic circulation

Aortic valve

Semilunar valve between

Prevents backflow of blood

left ventricle and aorta

from aorta to left ventricle

during ventricular diastole

CARDIAC SYSTEM

5

Table 1-1. Continued

Structure

Description

Function

Chordae

Tendinous attachment of

Prevents valves from everting

tendineae

atrioventricular valve

into atria during ventricular

cusps to papillary

systole

muscles

Papillary

Muscle that connects

Constricts and pulls on

muscle

chordae tendineae to

chordae tendineae to prevent

floor of ventricle wall

eversion of valve cusps during ventricular systole

• Conductivity-the ability to transmit electrical impulse from

cell to cell within the heart

• Contractility-the ability to stretch as a single unit and then

passively recoil while actively contracting

• Rhythmicity-the abiliry to repeat the cycle in synchrony with

regularity

Table 1-2. Great Vessels of the Heart and Their Function

Structure

Description

Function

Aorta

Primary artery from the left ven-

Ascending aorta delivers

tricle that ascends and then

blood to neck, head,

descends after exiting the heart

and arms.

Descending aorta deliv-

ers blood to visceral

and lower body

tissues.

Superior

Primary vein that drains into the

Drains venous blood

vena cava

right atrium

from head, neck, and

upper body.

Inferior

Primary vein that drains into the

Drains venous blood

vena cava

right atrium

from viscera and lower

body.

Pulmonary

Primary artery from right

Carries blood to lungs.

artery

ventricle

6

AarrE CARE HANDBOOK FOR PHYSICAL THERAPISTS

Cardiac Cycle

Blood flow throughout the cardiac cycle depends on circulatOry and

cardiac pressure gradients. The right side of the heart is a lowpressure system with little vascular resistance in the pulmonary arteries, whereas the left side of the heart is a high-pressure system with high vascular resistance from the systemic circulation. The cardiac

cycle is the period from the beginning of one contraction, starting

with sinoatrial (SA) node depolarization, to the beginning of the next

contraction. Systole is the period of contraction, whereas diastole is

the period of relaxation. SystOle and diastOle can also be categorized

into atrial and ventricular components:

1 . Atrial diastole is the period of atrial filling. The flow of blood is

directed by the higher pressure in the venous circulatory system.

2.

Atrial systole is the period of atrial emptying and cOntrac-

tion. Initial emptying of approximately 70% of blood occurs as a

result of the initial pressure gradient between the atria and the ventricles. Atrial contraction then follows, squeezing our the remaining 30%.3 This is commonly referred to as the atrial kick.

3.

Ventricular diastole is the period of ventricular filling. It initially

occurs with ease; then, as the ventricle is filled, atrial contraction is necessary to squeeze the remaining blood volume into the ventricle. The amount of stretch placed on the ventricular walls during diastOle,

referred to as left ventricular end diastolic pressure (LVEDP), influences

the force of contraction during systOle. (Refer to description of preload in

the section Factors Affecting Cardiac Output.)

4.

Ventricular systole is the period of ventricular contraction.

The initial contraction is isovolumic (meaning it does nOt eject blood),

which generates pressure necessary to serve as the catalyst for rapid

ejection of ventricular blood. The left ventricular eiectiOlt fraction

(EF) represents the percent of end diastOlic volume ejected during systOle and is normally approximately 60%.3

Cardiac Output

CO is the quantiry of blood pumped by the heart in 1 minute. It can

also be described relative to body mass as the cardiac index, the

CARDIAC SYSTEM

7

amount of blood pumped per minute per square meter of body mass.

Regional demands for tissue perfusion (based on local metabolic needs)

compere for systemic circularion, and roral CO adjusts ro meet these

demands. Adjustment ro CO occurs with changes in hearr rate (HR)

(chronotropic) or stroke volume (SV) (inotropic).· Normal resting CO

is approximarely 4-8 liters per minute, and normal cardiac index is

approximately 2.5-4.0 liters per minute per meter'·' (with a resting HR

of 70 beats per minute [bpml, resring SV is approximately 71 ml/beat).

The maximum value of CO represents the functional capacity of the

circulatory system to meet the demands of physical activity.

CO (liters per minute) = HR (bpm) x SV (liters)

Facrors Affecting Cardiac Output