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Understanding EKGs
A Practical Approach
For the Dental Hygienist
CHAPTER
2
Cardiovascular
Physiology: Function
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiovascular Physiology
• Objectives
– Describe the sequence of blood flow through
the heart
– Describe the cardiac cycle, including
 Definition
 Systole
 Diastole
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiovascular Physiology
• Objectives (continued)
– Discuss the term stroke volume
– Discuss cardiac output, preload, Starling’s
law, and afterload
– Describe the autonomic nervous system
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Blood Flow Through The Heart
• First component: blood
flow through right
heart:
– Unoxygenated blood
flows from inferior and
superior vena cava,
into the right atrium,
through the tricuspid
valve, into the right
ventricle, and through
the pulmonic valve
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Blood Flow Through The Heart
• Second component:
blood flow through the
pulmonary circulation
continues when
– The blood travels from
pulmonary arteries,
into the lungs, through
the pulmonary
alveolar-capillary
network, and into the
pulmonary veins
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Blood Flow Through The Heart
• The third and final
component: blood flow
through the pulmonary
circulation continues
when:
– Blood travels from the
pulmonary veins into
the left atrium, through
the mitral valve, into the
left ventricle, through
the aortic valve, and out
to the rest of the body
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Cycle
• Cardiac cycle
– Represents the actual time sequence
between ventricular contraction and
ventricular relaxation
• Systole
– Simultaneous contraction of the ventricles
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Cycle
• Diastole
– Synonymous with ventricular relaxation
– Ventricles fill with 70% of blood passively from
atria
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Cycle
• During periods of ventricular relaxation,
cardiac filling and coronary perfusion
occur passively
– One cardiac cycle = every 0.8 seconds
– Systole lasts
= about 0.2 seconds
– Diastole lasts
= about 0.52 seconds
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Cycle
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Relation of Blood Flow to Cardiac
Contraction
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Stroke Volume
• Stroke volume
– Volume of blood pumped out of one ventricle
of the heart in single beat or contraction
– Estimated at approximately 70 ml per beat
• Heart rate
– Number of contractions/beats per minute
– Normal heart rate
 60-100 bpm
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Output
• Cardiac output
– Amount of blood pumped by left ventricle in 1
min
• FORMULA to determine cardiac output
Cardiac output (CO) =
Stroke volume (SV) X heart rate (HR)
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Output
• Cardiac output
– Varies from person to person
– Inadequate cardiac output may be caused by
CHF, MI, or shock
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Cardiac Output
• Cardiac output
– May see combinations of symptoms:
 Shortness of breath
 Dizziness
 Chest pain
 Decreased blood pressure
 Cool and clammy skin
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
End-Diastolic Pressure
• Preload
– Pressure in the ventricles at the end of diastole
 Directly affected by volume of blood that returns to
right atrium
 May be decreased or increased based on returning
volume
• Afterload
– Resistance against which the heart must pump
• Affects stroke volume and cardiac output
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Starling’s Law of the Heart
• This concept is a law of physiology which
states that the more the myocardial fibers
are stretched, up to a certain point, the
more forceful the subsequent contraction
will be
• “Rubber band theory”
– The farther you stretch a rubber band, the
harder it snaps back to original size
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Peripheral Vascular Resistance (PVR)
• Peripheral vascular resistance
– Amount of opposition to blood flow offered by
arterioles
– Determined by vasoconstriction and
vasodilation
Blood pressure (BP) =
Cardiac output (CO) x peripheral
vascular resistance (PVR)
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Autonomic Nervous System
• Regulates functions of the body that are
involuntary or are not under conscious
control
• HEART RATE and BLOOD PRESSURE
are regulated by this component of
nervous system
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Two Major Divisions of Autonomic
Nervous System
• Sympathetic nervous system
– Preparation of body for physical activity
(“fight or flight”)
• Parasympathetic nervous system
– Regulates the calmer (“rest and digest”)
functions of our existence
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Nervous Control of the Heart
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Receptors and Neurotransmitters
• Sympathetic nervous system
– Receptors are alpha- and beta-receptors
– Chemical neurotransmitter is norepinephrine
– These nerve endings are called adrenergic
 Increases the heart rate and contractile forces of
cardiac muscle and vasoconstriction
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Receptors and Neurotransmitters
• Parasympathetic nervous system
– Chemical neurotransmitter is acetylcholine
– Nerve endings are known as cholinergic
 The heart rate slows, as do atrioventricular
conduction rates
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Adrenergic Receptors and Their
Effect on Heart Rate
• Adrenergic
– Sympathetic nerve fibers that use epinephrine
or epinephrine-like substances as
neurotransmitters
• Receptor
– A reactive site or cell surface or within that
combines with molecule to produce
physiological effect
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Adrenergic Receptors and Their
Effect on Heart Rate
• Cholinergic
– Parasympathetic nerve fibers that use
acetylcholine as neurotransmitter
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Effects of Alpha/Beta Receptors
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Effects
Effectsof
ofAlpha/Beta
Alpha/Beta Receptors
Receptors
Understanding EKGs: A Practical Approach, Third Edition
Brenda M. Beasley
Copyright ©2010 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.