Chapter Objectives
 List five cardiovascular system functions
 Describe interactions among cardiac output,
total peripheral resistance, and arterial
blood pressure (BP)
Chapter 15
The Cardiovascular System
 Describe how the venous system acts as an
active blood reservoir
 Describe how to measure BP, and list typical
systolic and diastolic blood pressure values
during rest and physical activity
 Discuss how BP responds to resistance exercises
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Chapter Objectives, cont.
Cardiovascular System Components
 Explain the hypotensive response during
recovery from physical activity
• Consists of four components
 Diagram the major vessels of the
coronary circulation
 Describe
the pattern of myocardial blood
•
flow, VO2, and substrate use during rest
and various intensities of physical exertion
1. A pump that provides continuous linkage with
the other three components
2. A high-pressure distribution circuit
3. Exchange vessels
4. A low-pressure collection and return circuit
 Explain the rate–pressure product, its
meaning, and rationale for use in clinical
exercise physiology
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Schematic View of
the Cardiovascular
System Showing
Heart and Pulmonary
and Systemic
Vascular Circuits
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The Heart
• Four-chambered organ that provides the drive
for blood flow
• Weighs 11 oz. for average male, 9 oz. for female
• Pumps ~70mL for each beat (stroke volume)
at rest
 At rest in one day, ~1900 gallons pumped through
the heart, or 52 million gallons for a 75-y life span
• Heart muscle called myocardium; myocardial
fibers interconnect in latticework fashion to
allow the heart to function as a unit
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1
The Heart, cont.
The Heart’s Valves
• Right side
1. Atrioventricular valves:
 Receive blood returning from body
 Pumps blood to lungs for aeration through
pulmonary circulation
• Left side
 Receives oxygenated blood from lungs
 Pumps blood into thick-walled muscular aorta
for distribution via systemic circulation
 Tricuspid: provides one-way blood flow from
the right atrium to right ventricle
 Bicuspid/Mitral: provides one-way blood flow
from left atrium to left ventricle
2. Semilunar valves:
 Located in arterial wall just outside heart;
prevent blood from flowing back into the heart
between contractions
• Two sides separated by interventricular septum
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Myocardial Contraction
• Atrial chambers serve as “primer pumps” to
receive and store blood during ventricular
contraction
• About 70% of blood returning to atria flows
directly into ventricles before atrial contraction
• Simultaneous contraction of both atria forces
remaining blood into ventricles
• Almost immediately after atrial contraction,
ventricles contract and propel blood into
arterial system
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The Heart, its Vessels, and Flow of Blood
High-pressure tubing that propels O2-rich blood to tissues
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The Arterial System
• High-pressure tubing that propels oxygen-rich
blood to tissues
• Comprised of layers of connective tissue and
smooth muscle
• No gaseous exchange occurs between arterial
blood and surrounding tissues
• Blood pumped from left ventricle enters aorta
and is distributed throughout the body
through a network of arteries and arterioles
 Smooth muscle in arteriole walls either constrict
or relax to regulate blood flow to periphery
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Blood Pressure
• Force of blood against arterial walls during
cardiac cycle
• Peripheral vessels do not permit blood to
“run off” into arterial system as rapidly as it
ejects from heart
• Aorta “stores” some ejected blood, which creates
pressure within the entire arterial system
• Arterial blood pressure reflects the combined
effects of arterial blood flow per minute and
resistance to flow in peripheral vasculature
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2
Blood Pressure, cont.
Blood Pressure, cont.
• Systolic Blood Pressure (SBP)
Mean Arterial Pressure (MAP) = DBP + [0.333 (SBP – DBP)]
 Provides estimate of work of heart and force blood
exerts against arterial walls during systole
• Diastolic Blood Pressure (DBP): relaxation phase
of cardiac cycle (diastole)
 Indicates peripheral resistance or ease that blood
flows from arterioles into capillaries
• Mean Arterial Pressure (MAP): average force
exerted by blood against arterial wall during
cardiac cycle
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Adult Blood Pressure Classification Values
Classification
Normal
Systolic BP
(mm Hg)
Diastolic BP
(mm Hg)
<120
and <80
Prehypertension
120-139
or 80-89
Stage 1
Hypertension
140-159
or 90-99
Stage 2
Hypertension
≥160
or ≥100
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Structure of
Blood Vessels
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Cardiac Output (Q) and Total Peripheral
Resistance (TPR)
Q = MAP ÷ TPR
MAP and cardiac output estimate change in total
resistance to blood flow in the transition from
rest to exercise
TPR = MAP ÷ Q
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Blood Flow in Capillaries
• The precapillary sphincter consists of a ring
of smooth muscle that encircles the capillary
at its origin and controls its diameter
• Sphincter constriction and relaxation provide
a means for blood flow regulation within a
specific tissue to meet metabolic requirements
• Two factors trigger precapillary sphincter
relaxation to open more capillaries:
1. Driving force of increased local BP plus
intrinsic neural control
2. Local metabolites produced in exercise
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3
Capillary Blood
Flow During
Rest [A] and
Exercise [B]
The Venous System
• Capillaries feed deoxygenated blood into small
veins or venules
• Veins in lower body eventually empty into
inferior vena cava, the body’s largest vein
 Vena cava returns blood to right atrium from
abdomen, pelvis, and lower extremities
• Venous blood from vessels in head, neck,
shoulder region, thorax, and abdominal wall
flows into superior vena cava to join inferior
vena cava at the heart (mixed-venous blood)
 Mixed-venous blood enters right atrium
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Venous Return
• Valves within veins allow blood to flow in only
one direction toward the heart
• Smallest muscular contractions or minor
pressure changes within the thoracic cavity with
breathing readily compressing veins
• Alternate compression and relaxation of veins
and one-way valve action provide a “milking”
action to propel blood back to the heart
 Without valves, blood would stagnate in
extremity veins; people would faint every
time they stood up because of reduced venous
return and diminished cerebral blood flow
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Blood Flow and
BP in Systemic
Circulation at
Rest
• Blood pressure
within each
portion of the
arterial system
relates to total
area (resistance)
in that section
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Valves in Veins
• Valves (A) prevent
backflow of blood, but
(B) do not hinder
normal 1-way flow;
(C) blood moves
through veins by
action of nearby active
muscle or, (D)
contraction of smooth
muscle
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Varicose Veins
• Valves within a vein fail to maintain one-way
blood flow; blood gathers in vein so they
become excessively distended and painful
• Usually occurs in surface veins of lower extremities
• In severe cases, phlebitis occurs where the
venous wall becomes inflamed and deteriorates
• People with varicose veins should avoid static,
straining-type exercises like resistance training
• Exercise does not prevent varicose veins, but
regular exercise can minimize discomfort and
complications
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4
Hypertension
• Systolic or diastolic pressure that exceeds
recommended values
Percentage of
U.S. Population
with Hypertension
 Chronically strains cardiovascular system; if
left untreated, leads to arteriosclerosis, heart
disease, stroke, and kidney failure
• Artery characteristics in hypertension
 Excessive resistance to peripheral blood
flow because of:
- Arterial hardening with fatty material in walls
- Neural hyperactivity or kidney malfunction
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Hypertension: Effective Treatment Options
Advice
Lose excess
weight
Follow a DASH
diet
Daily physical
activity
Limit sodium
Limit alcohol
Details
For every 20 lb reduced
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Pharmacologic Therapies for Hypertension
Drop in Systolic
Blood Pressure
5 to 20 mm Hg
Eat a lower-fat diet rich in vegetables, 8 to 14 mm Hg
fruits, and low-fat dairy foods
Do 30 min a day of aerobic activity like 4 to 9 mm Hg
brisk walking
Eat no more than 2400 mg a day
2 to 8 mm Hg
(1500 mg is better)
Consume no more than two drinks
2 to 8 mm Hg
daily (men) and one drink daily
(women) (one drink = 12 oz. beer, 5
oz. wine, or 1.5 oz. 80-proof whiskey)
2 to 4 mm Hg
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BP Response to Resistance Exercise
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Blood Pressure During Resistance Exercise
• Straining exercises mechanically compress
peripheral arteries that supply active muscle
 Arterial vascular compression dramatically
increases total peripheral resistance and
reduces muscle perfusion
 In an attempt to restore muscle blood flow,
substantial increases occur in sympathetic
nervous system activity, cardiac output, and MAP
• Acute cardiovascular strain with heavy
resistance exercise could prove harmful to
individuals with heart and vascular disease
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5
BP: Steady-Rate Physical Activity
• During rhythmic muscle activity, vasodilation
BP: Graded Exercise
in active muscles reduces TPR to enhance blood
flow through peripheral vasculature
• After an initial rapid rise from resting level,
• Alternate muscle contraction/relaxation propels
• DPB remains stable or decreases slightly at
• Increased blood flow during steady-rate exercise
• SBP may increase to 200 mm Hg or higher in
blood through the vascular circuit back to the heart
rapidly increases SBP during the first few minutes
• SBP often declines as steady-rate exercise continues
because arterioles in active muscles continue to
dilate, further reducing peripheral resistance to
blood flow; DBP generally remains unchanged
throughout exercise
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SBP and DBP During Graded Exercise
SBP increases linearly with exercise intensity
higher exercise levels
healthy, fit individuals during maximum
exercise (despite reduced TPR)
 This blood pressure most likely reflects
the heart’s large cardiac output during
maximal exercise by individuals with
high aerobic capacity
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BP: Upper-Body Physical Activity
• Exercise with arms produces higher SBP and
DBP than leg exercise
performed at a given
•
percentage of VO2max in each exercise mode
 Occurs because smaller arm muscle mass
and vasculature offer greater resistance to
blood flow than activation of larger leg mass
and blood supply
• Individuals with cardiovascular dysfunction
should rhythmically exercise relatively large
muscle groups in contrast to exercise that
engages a limited muscle mass
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Recovery From Physical Activity
The Heart’s Blood Supply
• On completion of a single bout of submaximal
• The heart has its own circulatory network, the
exercise, BP temporarily falls below
pre-exercise levels for normotensive and
hypertensive individuals due likely from
unexplained peripheral vasodilation
• The hypotensive response to exercise can
last up to 12 hr
 Occurs in response to either low- and
moderate-intensity aerobic exercise or
resistance exercise
coronary circulation, that arises from the
heart’s top portion
• Right and left coronary arteries
 Greatest blood volume flows in left coronary artery,
to left atrium and left ventricle, and right ventricle
• Blood leaves tissues of left ventricle through
coronary sinus and right ventricle from the
anterior cardiac veins
• Normal blood flow to myocardium at rest =
200 to 250 mL/min
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6
Anterior and Posterior View of Coronary
Circulation
Myocardial Oxygen Supply and Use
• At rest, myocardium extracts 70 to 80% of
O2 from blood in the coronary vessels
• Proportionate increase in coronary blood flow
in exercise provides sole mechanism to
increase myocardial O2 supply
• Two factors increase myocardial blood flow:
 Elevated myocardial metabolism dilates
coronary vessels
 Increased aortic pressure during exercise
forces a proportionately greater volume of blood
into coronary circulation
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Impaired Myocardial Blood Supply
• Myocardium depends on adequate O2 supply
because it has limited anaerobic capacity
• Extensive vascular perfusion supplies at least
one capillary to each of the heart’s muscle fibers
• Tissue hypoxia provides a potent stimulus to
myocardial blood flow
 Can produce chest pains, or angina pectoris
Plaque or Blood Clot
• Plaque (A) or blood clot
(thrombus) (B) lodged
in a coronary vessel
impairs normal heart
function and can result
in a myocardial
infarction
• Exercise provides an effective way to
evaluate adequacy of myocardial blood flow
 A blood clot in a coronary vessel can impair normal
heart function, leading to a myocardial infarction
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Myocardial Metabolism
Rate-Pressure Product (RPP)
•
• Estimate of myocardial workload and VO2
• Computed from product of peak SBP measured
at the brachial artery and heart rate (HR)
 Index of relative cardiac work
- relates closely to directly measured myocardial
VO2 and coronary blood flow in healthy subjects
over a wide range of exercise intensities
RPP = SBP x HR
 Ranges from 6000 at rest to ≥40,000 during
exercise, depending on intensity and mode
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• Relies almost exclusively on aerobic energy release
• Contains greatest mitochondrial concentration of all
tissues
• Glucose, fatty acids, and lactate from glycolysis in
skeletal muscle provide myocardial energy
 At rest, myocardial energy comes mainly from FFA
 Following a meal, the myocardium “prefers”
glucose as an energy substrate
 During intense exercise, myocardium derives
its major energy by oxidizing circulating lactate
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7
Generalized
Pattern of
Myocardial
Substrate
Use
Summary
1. Myocardium is composed of striated muscle fibers
2. Heart functions as two separate pumps: one pump
receives blood from the body and pumps it to the
lungs for aeration (pulmonary circulation); the
other receives oxygenated blood from the lungs
and pumps it throughout systemic circulation
3. Pressure changes created during the cardiac cycle
act on the heart’s valves to provide one-way blood
flow in the vascular circuit
4. Surge of blood with ventricular contraction and
subsequent runoff of blood in relaxation creates
pressure changes within the arterial vessels
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Summary, cont.
Summary, cont.
5. Ventricular contraction generates systolic SBP
9. At rest, the myocardium extracts
approximately
•
SBP increases in proportion to VO2 and blood flow
during graded exercise; DBP remains relatively
unchanged or decreases slightly
6. DBP represents lowest BP in relaxation before
the next systole
7. Compression and relaxation of veins by muscle
action impart energy to facilitate venous return.
This “muscle pump” mechanism provides
justification for active recovery immediately
following vigorous effort
8. Abnormal elevated BP (hypertension) imposes a
chronic cardiovascular stress that damages arterial
vessels and leads to arteriosclerosis, heart disease,
stroke, and kidney failure
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10.At same relative and absolute exercise levels,
upper-body exercise produces greater rise in
SBP than leg exercise
11.Following physical activity, BP decreases
below pre-exercise level and can remain
lower for up to 12 h
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Summary, cont.
12.Performing intense resistance exercises poses a risk to
individuals with hypertension or other forms of heart
disease
13.At rest, the myocardium extracts approximately
80% of O2 flowing through the coronary arteries
14.The rate-pressure product (HR x SBP) estimates
myocardial workload
15.Percentage myocardial use of macronutrients
for energy varies with physical activity severity
and duration and the individual’s training status
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Chapter 16
Cardiovascular Regulation
and Integration
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8
Chapter Objectives
Chapter Objectives, cont.
 Explain intrinsic and extrinsic factors that
regulate heart rate (HR) during rest and
physical activity
 Describe the effects of aerobic training on
neural regulation of heart rate
 Draw and identify the major components
of a normal electrocardiogram (ECG)
 Describe local metabolic factors that regulate
blood flow during rest and physical activity
 Explain “central command” in cardiovascular
regulation during exercise
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 Distinguish between chemoreceptors,
mechanoreceptors, and the metaboreflex in
cardiovascular regulation during activity
 List three factors that affect blood flow
 Describe two differences in blood flow
dynamics to different tissues at exercise
onset and during exercise
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Chapter Objectives, cont.
Intrinsic Regulation of Heart Rate
 Describe how nitric oxide regulates local
blood flow
• Unlike other tissues, cardiac muscle maintains
 Outline the cardiovascular response to
physical activity by a heart transplant patient
• Left to its inherent rhythmicity, the heart would
its own rhythm
beat ~100 b/min
• The sinoatrial (SA) node provides the innate
stimulus for heat action
 SA node is referred to as the heart’s pacemaker
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Normal Route for Impulse Transmission
Within the Myocardium
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The Heart’s Electrical Activity
• In right atrium the SA node spontaneously
depolarizes and repolarizes
• The impulse spreads across the atria to
atrioventricular (AV) node
• A 0.10-s delay occurs to allow atria to
contract and propel blood into ventricles
Normal route for excitation and
conduction of cardiac impulse
Time sequence for impulse
transmission from SA node though
the myocardium
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9
The Heart’s Electrical Activity, cont.
• The AV node gives rise to the AV bundle,
also called the bundle of His
• The AV bundle transmits the impulse to the
Purkinje system that penetrates the right and
left ventricles
• The transmission of the cardiac impulse flows In
the following direction:
SA node
Atria
Purkinje fibers
AV node
Ventricles
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Normal Transmission of Electrical Impulse
Through the Myocardium
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ECG Waves
• P wave: depolarization of atria before atria contract
• QRS complex: Signals electrical changes from
ventricular depolarization before ventricles contract
 Atrial repolarization follows P wave, but produces a
wave so small that QRS complex usually obscures it
• T wave: Represents ventricular repolarization that
occurs during ventricular diastole
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Electrocardiogram (ECG)
• The myocardium’s electrical activity creates
an electrical field throughout the body
• The ECG represents a composite record of the
heart’s electrical events during a cardiac cycle
 These electrical events can monitor HR during
physical activities and exercise stress testing
• A valid ECG tracing requires proper
electrode placement
 ECG leads transmit electrical signal to a recorder,
which creates the composite electrical “picture”
of myocardial activity
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Different
Phases of the
Normal ECG
from Atrial
Depolarization
to Ventricular
Repolarization
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Extrinsic Regulation of Heart Rate
and Circulation
• Nerves that directly supply the myocardium, and
chemical “messengers” that circulate in blood
accelerate the heart in anticipation before
exercise begins, and then rapidly adjust to
intensity of physical effort intensity
• Input from the brain and peripheral nervous system
continually bombards the cardiovascular control center
in the ventrolateral medulla to regulate the heart’s
output of blood and blood’s preferential distribution to
all body’s tissues
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10
Neural Mechanisms for Cardiovascular
Regulation Before and During Activity
Sympathetic and Parasympathetic
Neural Input
• Neural influences override the myocardium’s
inherent rhythm
• Originate in cardiovascular center and flow
through sympathetic and parasympathetic
components of autonomic nervous system
 Large numbers of sympathetic and
parasympathetic neurons innervate the atria,
whereas the ventricles receive sympathetic
fibers almost exclusively
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Distribution of Sympathetic
and Parasympathetic Nerve
Fibers Within the Myocardium
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Sympathetic Influence
• Stimulation of sympathetic cardioaccelerator
nerves releases epinephrine and norepinephrine
 Cause chronotropic and inotropic effects on heart
• Sympathetic stimulation also produces
generalized vasoconstriction except in coronary
arteries
 Norepinephrine, released by adrenergic
fibers, acts as a vasoconstrictor
 Dilation of blood vessels under adrenergic
influence occurs from decreased adrenergic
activity
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Chemical,
Anatomic,
and Functional
Organization of
Sympathetic and
Parasympathetic
Divisions of the
Autonomic Nervous
System
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Parasympathetic Influence
• Parasympathetic neurons release acetylcholine,
which delays rate of sinus discharge to slow HR
• Bradycardia results from stimulation of vagus
nerve from medulla’s cardioinhibitory center
• Parasympathetic stimulation excites some tissues
and inhibits others
• At start and during low/moderate intensity
exercise, HR increases largely by inhibition of
parasympathetic stimulation
• HR in strenuous exercise increases by additional
parasympathetic inhibition and direct activation of
sympathetic cardioaccelerator nerves
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11
Central Command: Input from
Higher Centers
• Impulses originating in brain’s higher somatomotor
central command center continually modulate medullary
activity
• Central command provides greatest control over
HR during exercise
• Heart rapidly “turns on” during exercise by decreasing
Influence
of Central
Command
on Heart
Rate When
Movement
Begins
parasympathetic inhibitory input and increasing
stimulating input from central command
• Central command in cardiovascular regulation explains
how emotional state can affect cardiovascular response
(thus, creating difficulty obtaining “true” resting values
for HR and BP)
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Peripheral Input
Peripheral Input, cont.
• Cardiovascular center receives reflex sensory
• Three mechanisms continually assess the
input from peripheral receptors in blood
vessels, joints, and muscles
• Chemoreceptors and mechanoreceptors
within muscle and its vasculature monitor
its chemical and physical state
 Modifies either parasympathetic or sympathetic
outflow to bring about the appropriate
cardiovascular and respiratory responses to
various intensities of physical activity
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nature and intensity of exercise and muscle
mass activated:
1. Reflex neural input from mechanical
deformation of type III afferents within
active muscles
2. Chemical stimulation of type IV afferents
within active muscles
3. Feed-forward outflow from motor areas of
central command
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Peripheral Input, cont.
Peripheral Input, cont.
• Specific mechanoreceptor feedback governs
• Function as negative feedback controllers to:
central nervous system’s regulation of blood
flow and BP during dynamic exercise
 Aortic arch and carotid sinus contain
pressure-sensitive baroreceptors
 Inhibit sympathetic outflow from the
cardiovascular center
 Blunt inordinate rise in arterial BP
 Cardiopulmonary receptors assess mechanical
activity in the left ventricle, right atrium, and
large veins
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12
Carotid Artery Palpation
• External pressure against the carotid artery can
slow HR from direct baroreceptor stimulation
• Consistently low HR estimation with carotid
artery palpation in susceptible individuals
would push the person to a higher exercise
level. It has no effect in healthy individuals
• Vascular disease affects carotid sinus
sensitivity and produce low heart rate values
Distribution of Blood: Physical
Factors Affecting Blood Flow
• Blood flow through the vascular circuit follows
physical laws of hydrodynamics applied to rigid,
cylindrical vessels
• Volume of flow in an vessel relates to two factors:
1. Directly to pressure gradient between two ends
of the vessels
2. Inversely to resistance encountered to fluid flow
• A substitute location measures pulse rate at
the radial artery or temporal artery
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Distribution of Blood: Physical
Factors Affecting Blood Flow, cont.
Distribution of Blood: Physical Factors
Affecting Blood Flow, cont.
• Friction between blood and internal vascular wall
• Poiseuille’s Law: expresses relationship among
creates resistance (force) that impedes blood
flow
• Three factors determine resistance:
pressure differential, resistance, and flow
Flow = pressure gradient × vessel radius4
÷vessel length × fluid viscosity
1. Blood thickness (viscosity)
The transport vessel length remains constant
2. Length of conducting tube
Blood viscosity varies only slightly
3. Blood vessel radius
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- radius affects blood flow the most
- physiologically, constriction and dilation
of smaller arterial blood vessels provide
mechanism to regulate regional blood flow
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Exercise Effect on Blood Flow
Exercise Effect on Blood Flow, cont.
• Any increase in energy expenditure requires
• Two factors contribute to reduced blood flow
rapid adjustments in blood flow that impact the
cardiovascular system
• During exercise, local arterioles of active
muscles dilate while vessels to tissues that can
temporarily compromise their blood supply
constrict
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to non-active tissues:
1. Increased sympathetic nervous system outflow
2. Local chemicals that directly stimulate
vasoconstriction or enhance effects of
other vasoconstrictors
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13
Factors Within Active Muscle
Factors Within Active Muscle, cont.
• Skeletal muscle blood flow closely couples to
• The opening of dormant capillaries in exercise:
metabolic demands
 Regulation occurs from interaction of neural
vasoconstriction activity and locally derived
vasoactive substances within endothelium and
red blood cells
• At rest, 1 in 30 to 40 muscle capillaries
 Increases total muscle blood flow
 Delivers a large blood volume with only a minimal
increase in blood flow velocity
 Increases effective surface for gas and nutrient
exchange
remains open
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Factors Within Active Muscle, cont.
• Vasodilation occurs from local factors related to
tissue metabolism that act directly on smooth
muscle bands of small arterioles and precapillary
sphincters
 Examples include decreased tissue oxygen and local
increases in blood flow, temperature, carbon dioxide,
acidity, adenosine, magnesium and potassium ions,
and nitric oxide production by endothelial cells lining
the blood vessels
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Nitric Oxide (NO) and Autoregulation of
Tissue Blood Flow
• Nitric oxide serves as a signal molecule that dilates
blood vessels and decreases vascular resistance
• Stimuli from diverse signal chemicals and sheering
stress and vessel stretch from increased blood flow
through the vessel lumen provoke NO synthesis
and release by vascular endothelium
 In CHD, vascular endothelium produces less NO
 Venous system may also increase local blood flow
by “assessing” increases in the metabolic needs of
active muscle and releasing vasodilatory factors
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Nitrous Oxide Regulation of Local Blood Flow
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Integrative Response During
Physical Activity
• Neural command center above medullary region
initiates cardiovascular changes before and during
movement
• HR and myocardial contractility increase from
feed-forward input from cardiovascular center,
which depresses parasympathetic activation
• Predictable changes in regional blood flow occur in
proportion to exercise intensity
• Modulation of dilation/constriction optimizes
blood flow to needed areas while maintaining BP
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14
Integrative Response During
Physical Activity, cont.
• Local metabolic factors act directly to dilate
resistance vessels in active muscle
• Vasodilation reduces peripheral resistance
for greater blood flow in active areas
• Vascular constriction in inactive tissues
maintains adequate perfusion within active
muscle, while maintaining the blood supply to
satisfy local metabolic demands of the
inactive areas
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Summary, cont.
6. Input from peripheral receptors in blood vessels, joints,
and muscles provides feedback to the cardiovascular
center with feedback
7. Neural and hormonal extrinsic factors modify the
heart’s inherent rhythm
8. HR can reach 200b/min during maximal exercise
9. Carotid artery palpation accurately accesses HR except
in certain pathologic conditions
10.Nerves, hormones, and local metabolic factors
act on blood vessels’ internal diameter to
regulate blood flow
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Summary
1. The cardiovascular system provides for rapid HR
regulation and effective blood distribution throughout
the body
2. Cardiac rhythm originates at the SA node
3. The ECG records the sequence of the heart’s
electrical events during the cardiac cycle
4. Epinephrine and norepinephrine accelerate HR and
increase myocardial contractility; acetylcholine
acts through the vagus nerve to slow HR
5. The heart turns on in the transition from rest to
physical activity from increased sympathetic and
decreased parasympathetic activity
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Summary, cont.
11.Blood flow changes with the vessels’ radius
raised to the fourth power
12.Nitric oxide facilitates blood vessel dilation and
decreases vascular resistance
13.Blood flow decreases to kidneys and splanchnic
area while muscle blood flow increases during
exercise
14.Patients who successfully undergo orthotopic
transplantation have a depressed cardiovascular
response to exercise
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Chapter Objectives
 Discuss advantages and disadvantages of methods
to measure cardiac output (CO)
 Compare CO during rest and maximal exercise for
the endurance athlete and sedentary person
Chapter 17
Functional Capacity of the
Cardiovascular System
 Explain the influence •of each component of
the Fick equation on VO2max
 Discuss physiologic factors that influence SV
 Contrast components of CO during rest and
maximal effort for trained vs. untrained
 Explain the effects of the Frank-Starling
mechanism during physical activity
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15
Chapter Objectives, cont.
Cardiac Output
 Explain cardiovascular drift
• Cardiac output expresses the amount of blood
 Describe cardiac output distribution to major body
organs during rest and exercise
 Describe the relationship
between maximum
•
cardiac output and VO2max along a broad range of
fitness levels
pumped by the heart during a 1-min period
 Maximal values reflect the functional capacity of
the cardiovascular system
Cardiac output = Heart rate × Stroke volume
• Methods to assess cardiac output:
 List three factors that contribute to expanding
the a-vO
2 differences during graded exercise
 Direct Fick
 Contrast cardiovascular and metabolic dynamics
during upper-body versus lower-body exercise
 CO2 rebreathing
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 Indicator dilution
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The Fick Principle
Direct Fick Method
•
• Expresses relationships between VO2 (mL/min) ,
- diff (mL/100mL blood) to determine
and a-vO
2
cardiac output (mL/min)
•
- diff
Cardiac output = VO ÷ a-vO
2
2
 Requires complex invasive methodology
•
- VO2 (L/min) using open circuit spirometry
- average difference between O2 content of
arterial and mixed-venous blood (a-vO2diff)
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Indicator Dilution Method
CO2 Rebreathing Method
• Injects a known quantity of inert dye into
• Same open-circuit
spirometry method for
•
a large vein
• The indicator material remains in vascular stream
and mixes as blood travels to lungs and returns
to heart before ejection through systemic circuit
• Assessment of arterial blood samples and area
under dilution–concentration curve reflects
average concentration of blood leaving heart
Cardiac Output = Amount dye injected ÷ Average
dye concentration in blood for duration of curve
× duration of curve
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determining •VO2 in typical Fick technique but
determines VCO2 in the rebreathing method
• Using a rapid CO2 gas analyzer and making
reasonable assumptions about gas exchange
the method provides valid estimates of
mixed-venous and arterial CO2 levels
 Requires breath-by-breath CO2 analysis
 Does not require blood sampling or medical supervision
 Can only be used during steady-rate conditions
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16
Cardiac Output at Rest
Cardia Output: Untrained Individuals
• Can vary considerably during rest
• Resting HR for typical untrained = 70 b/min,
• Influencing factors include emotional conditions
that alter cortical outflow to cardio-accelerator
nerves and nerves that modulate arterial
resistance vessels
 5 L/min = average cardiac output for males
and resting SV = 60 to 70 mL/b
• SV and cardiac output for women = 25% below
male values
 Generally relates to a smaller body size
- average HR = 70 b/min, average SV = 71 mL/b
 4 L/min = average cardiac output for females
- average HR = of 70 b/min, average
SV = 50 to 60 mL/b
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Cardiac Output: Endurance Athletes
• Resting HR of healthy endurance athletes = 50
b/min at rest and resting SV = 100 mL/b
• Factors that explain large SV and low HR of
endurance-trained athletes:
 Increased vagal tone and decreased
sympathetic drive, both of which slow the heart
 Increased blood volume, myocardial contractility,
and compliance of the left ventricle, all of which
augment the heart’s stroke volume
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Cardiac Output During Physical Activity
• Systemic blood flow increases directly with
intensity of physical activity
 Cardiac output increases rapidly during the
transition from rest to steady-rate exercise and
then rises gradually until it plateaus when blood
flow meets the exercise metabolic requirements
• The endurance athlete achieves a large
maximal cardiac output solely through a
large SV
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Average Cardiac Output, HR, and SV
for Endurance-trained and Untrained
Men During Maximal Activity
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Maximal Values for Cardiac Output,
HR, and SV for Men• with Very Low,
Normal, and High VO2max Values
Cardiac output = HR x SV
• Untrained: 22,000 mL/min = 195 b/min x 113 mL/b
• Trained: 35,000 mL/min = 195 b/min x 179 mL/b
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VO2max
(L ∙ min-1)
Max Heart
Rate
(B ∙ min-1)
Mitral stenosis
1.6
190
50
9.5
Sedentary
3.2
200
100
20.0
Athlete
5.2
190
160
30.4
Group
Max Stroke
Volume
(mL)
Max Cardiac
Output
(L ∙ min-1)
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17
Enhancing Stroke Volume: Diastolic
Filling Versus Systolic Emptying
• Mechanisms that could increase the heart’s
SV during exercise:
1. Enhanced cardiac filling in diastole followed
by a more forceful systolic contraction
2. Normal ventricular filling with subsequent more
forceful ejection and emptying during systole
3. Training adaptations that expand blood
volume and reduce resistance to blood flow
in peripheral tissues
Enhanced Diastolic Filling
• Any factor that increases venous return or
slows the heart produces greater preload
during the cardiac cycle’s diastolic phase
 An increase in end-diastolic volume stretches
myocardial fibers and initiates a more
powerful ejection stroke during systole
- Ejects the normal SV plus additional blood
that entered ventricles during diastole
• Frank-Starling law: force of contraction of
cardiac muscle remains proportional to its
initial resting length
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Greater Systolic Emptying
Cardiovascular Drift
• Enhanced systolic ejection occurs despite
• Describes the gradual time-dependent
increased resistance to blood flow in arterial
circuit from exercise-induced elevation
of systolic BP
• Enhanced systolic ejection occurs because
ventricles always contain a functional residual
blood volume
 Catecholamine release in exercise enhances
myocardial contractile force to augment stroke
power and facilitate systolic emptying
downward “drift” in cardiovascular responses,
most notably SV with concomitant HR increase,
during prolonged steady-rate exercise
 Person must exercise at lower intensity than if
cardiovascular drift did not occur
• Submaximal exercise for >15 minutes decreases
plasma volume, thus decreasing SV
 Reduced SV initiates a compensatory HR
increase to maintain a nearly constant cardiac output
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SV, HR, and Cerebral
Blood Flow (CBF) Under
ß-adrenoceptor Blockade
and Control Treatments
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Cardiac Output Distribution During Rest
• At rest, typical 5-L cardiac output distributes as
follows:
 One fifth flows to muscle tissue
(4 to 7 mL/min/100 g muscle)
 Major portion of remaining blood flows to digestive
tract, liver, spleen, brain, and kidneys receive
major portions of the remaining blood
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18
Cardiac Output Distribution During Exercise
• Cardiac output diverts to active muscles at maximal
exertion
Distribution of Cardiac Output During
Rest and Strenuous Exercise
 50 to 75 mL/100 g muscle/min Most diverts
to oxidative portions of muscle at the expense
of portions with high glycolytic capacity
• For trained individuals, blood redistribution
begins just prior to exercise (anticipatory)
• Hormonal vascular regulation and local metabolic
conditions divert blood flow to active muscles
from areas that tolerate compromised blood flow
• Blood redistribution among specific tissues
occurs primarily during intense exercise
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Blood Flow to the Heart and Brain
• The heart and brain cannot tolerate
compromised blood supply
• At rest, the myocardium uses ~75% of O2 in
blood flowing through the coronary circulation
• During exercise, the coronary circulation
has a four- to fivefold increase in blood flow
• Cerebral blood flow increases during exercise
by ~25-30% compared with the resting flow
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Cardiac Output and Oxygen Transport: Rest
• Arterial blood carries 200 mL O2/L
• At rest cardiac output equals 5 L, therefore 1000
mL O2 are available to body
•
• Resting VO2 averages 250-300 mL/min,
allowing 750 mL O2 to return unused to heart
• Extra oxygen circulating above resting
requirement represents oxygen “in reserve”
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Close Association Between Maximal
Cardiac Output and VO2max
•
Cardiac Output and Oxygen Transport:
Physical Activity
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•
• In the untrained, 3200 mL O2 circulates each
• Low VO2max corresponds with low maximal cardiac
• An increase in maximal cardiac output produces
• 5- to 6-L increase
in blood flow accompanies each 1-L
•
minute via a 16-L cardiac output during exercise
proportionate increase
in capacity to circulate
•
O2 and increases VO2max
output
increase in VO2 above rest; this ratio remains
unchanged regardless of exercise mode
•
• High levels of VO2max and maximal cardiac output are
distinguishing characteristics for preadolescent
and adult endurance athletes
• Proportionate increase in maximal
cardiac output
•
accompanies increases in VO2max with endurance
training
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19
Cardiac Output Differences Among
Men and Women and Children
Close
Relationship
Between
Maximal
Cardiac
Output
and VO2max
•
• Cardiac output and VO2 linearly relate during graded
exercise for boys and girls and men and women
• Teenage and •adult women exercise at
submaximal VO2 with 5 to 10% larger cardia output
than males due to their 10% lower Hb concentration
•
• Higher submaximal exercise HR in children do not
compensate for a smaller SV
 Produces smaller cardiac output for children
- a-vO
diff expands to meet the O requirements
2
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Oxygen Extraction: The a-vO
2 Difference
- diff relationship
• VO2, cardiac output, and a-vO
2
•
expressed in the equation:
VO2 = cardiac output × a-vO2diff
•
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2
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a-vO
2 Difference During Rest
- diff = 5 mL O /dL blood
• During rest, a-vO
2
2
perfusing the whole-body tissue–capillary bed
 15 mL of O2 (75% of blood’s original O2 content)
still remains bound to hemoglobin
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a-vO
2 Difference During Physical Activity
a-vO
2 Difference During Exercise, cont.
• Arterial blood O2 content varies little from
• Capacity of each deciliter of arterial blood to
• Mixed-venous O2 content varies between
• Two factors contribute to hemoconcentration
20 mL/dL at rest throughout the exercise
intensity range
12 to 15 mL/dL during rest to 2 to 4 mL/dL
during maximal exercise
- diff results
 Progressive expansion of a-vO
2
from an increased cellular O2 extraction
leading to a reduced venous O2 content
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carry O2 increases slightly during exercise from
increased hemoconcentration
from progressive movement of fluid from plasma
to interstitial space:
 Increases in capillary hydrostatic pressure as
blood pressure rises
 Metabolic byproducts of exercise metabolism
that osmotically draw fluid from plasma into tissue
spaces from plasma
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20
Changes in
a-vO
2 Difference
From Rest to
Maximal Effort
Factors That Affect the a-vO
2 Difference
During Physical Activity
• Central and peripheral factors interact to
increase O2 extraction in active tissue during
exercise
 Large portion of the cardiac output diverts to
active tissue
 Some tissues temporarily decrease blood
supply to make more O2 available to tissues
in need
 Exercise training redirects a greater portion
of central circulation to active muscle
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Cardiovascular Adjustments to
Upper-Body Exercise
•
• Highest VO2 during arm exercise averages
20 to 30% lower than leg exercise
 Arm exercise produces lower maximal values
for HR and pulmonary ventilation compared
to leg exercise
 Differences relate to smaller muscle mass
activated in arm exercise
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Submaximal Oxygen Consumption:
Upper-Body Exercise
• Higher VO2 during arm exercise at all
submaximal power outputs
• Two factors that produce additional O2 cost
at higher intensities of arm exercise include:
1. Lower mechanical efficiency in upper-body
exercise from the additional cost of static
muscle actions that do not contribute
to external work
2. Recruitment of additional musculature to
stabilize torso during arm exercise
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•
VO2 in Arm
Exercise
Versus Leg
Exercise VO2
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Physiologic Response:
Upper-Body Exercise
•
• Any level of submaximal VO2 or power output
with upper-body exercise provides greater
physiologic strain than lower-body exercise
•
 Submaximal arm exercise produces higher HR,
pulmonary ventilation, perception of effort, BP
• Elevated HR response results from two factors:
 Greater feed-forward stimulation from the brain’s
central command to medullary control center
 Increased feedback stimulation to the medulla
from peripheral receptors in active muscle
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21
Implications of Upper-Body Exercise
Summary
• Standard submaximal exercise load with the
1. Cardiac output reflects functional capacity of the
cardiovascular system: cardiac output = HR x SV
upper body produces greater metabolic and
physiologic strain than leg exercise
• Exercise prescriptions based on running and
bicycling do not apply to arm exercise
•
• Low
correlations between VO2max− arm versus
•
VO
2max− leg exercise do not allow accurate
•
VO2max predictions for arm exercise based on
leg exercise and vice versa
• Lack of strong association between two exercise
modes verifies the exercise specificity concept
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2. Cardiac output increases proportionally with effort;
from 5 L/min during rest to 20-25 L/min in untrained
to 30 to 40 L/min in trained during maximal exercise
3. Differences in maximal cardiac output between
athletes and untrained are due to larger SV of
athletes
4. SV increases during upright exercise occurs from
interaction between greater ventricular filling during
diastole and more complete emptying during systole
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Summary, cont.
Summary, cont.
5. Sympathetic hormones augment systolic ejection
to increase SV during systole
10.Arm exercise generates a 25% lower VO2max than
leg exercise
6. Blood flows to specific tissues in proportion to
metabolic activity
11.Power output with upper-body exercise provides
greater physiologic strain than
lower body
•
exercise at any submaximal VO2
7. Most cardiac output diverts to active muscle during
exercise from reduced blood flow to kidneys and
splanchnic region
•
- diff
8. Maximal cardiac
output and maximal a-vO
2
•
determine VO2max
9. A large cardiac output differentiates endurance
athletes from untrained persons
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22