Download Stroke Volume - emseducation.info

CARDIAC EMERGENCIES
Anatomy
• Cardiovascular System's two major components
• Size
•
•
•
•
Location
The heart and peripheral blood vessels
Size of a closed fist
Center of chest in the Mediastinum
Position
• Approximately 2/3 is to the left of the midline
• Apex
Bottom; above the diaphragm
• Base:
Top; lies approximately at the level of the second
rib
Great Vessels connect here
Layers
Endocardium
• Inner most layer
• Lines the heart’s chambers
• Bathed in blood
Layers
Myocardium
• Thick middle layer of the heart
• Cells are unique
Cells physically resemble skeletal muscle,
But have electrical properties similar to smooth
muscle.
Contain specialized structures to help to rapidly
conduct electrical impulses from one muscle to
another enabling the heart to contract
Layers
Pericardium
• Protective sac
• Consists of two layers
– Visceral aka epicardium: Epicardium: Inner layer
in contact with the heart muscle itself
– Parietal outer fibrous layer
Contains:
Layers
Pericardial Fluid
• Between the two layers
• 25 ml
• Straw colored
• Reduces friction as the heart beats and changes
position
• Epicardium:
Inner layer in contact with the heart muscle itself
Chambers
4 Chambers
• Atria
– separated by the interatrial septum
• Ventricles
– separated by the interventricular septum
Valves
• The heart contains two pairs of valves
• Atrioventricular Valves
• Semilunar valves
Made of endocardial and connective tissue
Valves
• Atrioventricular
Control blood flow between atria and
ventricles
Trisucspid Valve
• Between the right atrium and right ventricle
• Has three leaflets or cusps;
Mitral Valve
• Between the left atrium and left ventricle
• Two leaflets
Atrioventricular Valves
• The valves are connected to specialized papillary
muscles in the ventricles
• When relaxed they open the valves to allow for
blood flow
Chordae Tendoneae
• Specialized fibers; connect the valve leaflets to the
papillary muscle; prevents the valves from prolapsing
into the atria, allowing back flow
Valves
• Semilunar Valves
• Regulate blood flow between the ventricles and the
arteries into which they empty
• Left: Aortic valve; connects left ventricle to the aorta
• Right: Pulmonic valve; connects right ventricle to the
pulmonary artery
Next: Cardiac Cycle
CARDIAC CYCLE
• Defined: The period of time from the end of one cardiac contraction to
the end of the next
• Diastole: First phase; The relaxation phase; Ventricular filling begins, blood
enters through the mitral and tricuspid valves; Pulmonic and aortic valves
are closed
Encompasses:
• Ejection Fraction
• Stroke Volume
• Preload
• Starling’s Law
• After Load
Cardiac Cycle
• Ejection Fraction
The normal ventricle ejects about 2/3 of the
blood it contains at the end of the diastole
• Each time the ventricle pumps blood into the aorta, it generates pressure
wave along the major arteries which we feel as a pulse
The amount of blood ejected is the Stroke
Volume
Stroke Volume
The amount of blood ejected by the heart in one
cardiac cycle
• Each time the ventricle pumps blood into the
aorta, it generates pressure wave along the
major arteries which we feel as a pulse
• Stroke Volume varies between 60 and 100ml
with the average being 70ml
Stroke Volume
Is dependent on three factors
• Preload
• Cardiac Contractility
• Afterload
Cardiac Cycle
The heart can pump only the blood it receives from
the venous system
• Preload
The pressure within the ventricles at the
end of diastole
Influences the force and amount of the next
Contraction and is based on Starling’s Law
of the Heart
Cardiac Cycle
• Starling’s law of the heart:
The more the myocardial muscle is
Stretched, the greater it’s force of
contraction will be
So………
Cardiac Cycle
• The greater the volume of blood filling the
chamber----the more forceful the cardiac
contraction----the greater the venous return---the greater the preload----the greater the
stroke volume
Cardiac Cycle
Afterload
• Myocardial muscle has its limits. If stretched
too far, it will not contract properly and will
weaken
Cardiac Cycle
Afterload
• The resistance against which the heart must
pump
• Increase in peripheral vascular resistance will
decrease stroke volume
• Decrease in Peripheral Vascular Resistance will
increase stroke volume
Cardiac Cycle
• Cardiac Output
• Volume of blood that the heart pumps in one
minute
• Stroke volume (mL) x heart rate (bpm) = cardiac output (mL/min)
?cardiac output using a value of 70 for heart rate?
Cardiac Cycle
• 70 mL x 70 bpm = 4,900 mL/min
ELECTROPHYSIOLOGY
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Overview
Sinoatrial node
Atrioventricular junction
AV node
Bundle of His
His-Purkinje System
Automaticity
Excitablity
Conductivity
Contratility
Action potential
Depolarization
Repolarization
Excitability
Thresholds
Electrophysiology
The heart is comprised of three types of
cardiac muscle
• Atrial
• Ventricular
• specialized excitatory and conductive fibers