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CHAPTER 7
CARDIOVASCULAR CONTROL
DURING EXERCISE
Learning Objectives
w Review the structure and function of the heart, vascular
system, and blood.
w Find out how the cardiovascular system responds to
increased demands during exercise.
w Explore the role of the cardiovascular system
in delivering oxygen and nutrients to active
body tissues.
(continued)
Major Cardiovascular Functions
w Delivery (e.g., oxygen and nutrients)
w Removal (e.g., carbon dioxide and waste products)
w Transportation (e.g., hormones)
w Maintenance (e.g., body temperature, pH)
w Prevention (e.g., infection—immune function)
The Cardiovascular System
w A pump (the heart)
w A system of channels (the blood vessels)
w A fluid medium (blood)
THE HEART
Myocardium—The Cardiac Muscle
w Thickness varies directly with stress placed on chamber
walls.
w Left ventricle is the most powerful of chambers and thus,
the largest.
w With vigorous exercise, the left ventricle size increases.
w Due to intercalated disks—impulses travel quickly in
cardiac muscle and allow it to act as one large muscle
fiber; all fibers contract together.
THE INTRINSIC
CONDUCTION
SYSTEM
The Cardiac Conduction System
w Sinoatrial (SA) node—pacemaker (60-80 beats/min
intrinsic heart rate)
w Atrioventricular (AV) node—built-in delay of 0.13 sec.
w AV bundle (bundle of His)
wPurkinje fibers—6 times faster transmission
Extrinsic Control of the Heart
w Parasympathetic nervous system acts through the vagus
nerve to decrease heart rate and force of contraction
(predominates at rest—vagal tone).
w Sympathetic nervous system is stimulated by stress to
increase heart rate and force of contraction.
w Epinephrine and norepinephrine—released due to
sympathetic stimulation—increase heart rate.
Did You Know…?
Resting heart rates in adults tend to be between 60 and 85
beats per min. However, extended endurance training can
lower resting heart rate to 35 beats per minute or less. This
lower heart rate is thought to be due to decreased intrinsic
heart rate and increased parasympathetic stimulation.
Cardiac Arrhythmias
Bradycardia—resting heart rate below 60 bpm
Tachycardia—resting heart rate above 100 bpm
Premature ventricular contractions (PVCs)—feel like
skipped or extra beats
Ventricular tachycardia—three or more consecutive PVCs
that can lead to ventricular fibrillation in which contraction of
the ventricular tissue is uncoordinated
Did You Know…?
The decrease in resting heart rate that occurs as an
adaptation to endurance training is different from
pathological bradycardia, an abnormal disturbance in the
resting heart rate.
Electrocardiogram (ECG)
w Records the heart's electrical activity and monitors
cardiac changes
w The P wave—atrial depolarization
w The QRS complex—ventricular depolarization and
atrial repolarization
w The T wave—ventricular repolarization
PHASES OF THE RESTING ECG
Key Points
Structure and Function of the
Cardiovascular System
w The two atria receive blood into the heart;
the two ventricles send blood from the
heart to the rest of the body.
w The left ventricle has a thicker myocardium
due to hypertrophy resulting from the force
with which it must contract.
w Cardiac tissue has its own conduction
system through which it initiates its own
pulse without neural control.
(continued)
Key Points
Structure and Function of the
Cardiovascular System
w The pacemaker of the heart is the SA
node; it establishes the pulse and
coordinates conduction.
w The autonomic nervous system or the
endocrine system can alter heart rate and
contraction strength.
w ECG records the heart's electrical function
and can be used to diagnose cardiac
disorders.
Cardiac Cycle
w Events that occur between two consecutive heartbeats
(systole to systole)
w Diastole—relaxation phase during which the chambers fill
with blood (T wave to QRS)—62% of cycle duration
w Systole—contraction phase during which the chambers
expel blood (QRS to T wave)—38% of cycle duration
Stroke Volume and Cardiac Output
Stroke Volume (SV)
w Volume of blood pumped per contraction
w End-diastolic volume (EDV)—volume of blood in ventricle
before contraction
w End-systolic volume (ESV)—volume of blood in ventricle
after contraction
w SV = EDV – ESV
.
Cardiac Output (Q)
w Total volume of blood pumped by the ventricle per minute
.
w Q = HR  SV
Ejection Fraction (EF)
w Proportion of blood pumped out of the left ventricle each
beat
w EF = SV/EDV
w Averages 60% at rest
CALCULATIONS .
OF SV, EF, AND Q
The Vascular System
w Arteries
w Arterioles
w Capillaries
w Venules
w Veins
Did You Know…?
Arteries always carry blood away from the heart; veins
always carry blood back to the heart with the help of
breathing, the muscle pump, and valves. Pulmonary “veins”
carry oxygenated blood from the lungs to the heart and
pulmonary “arteries” carry blood with lower oxygen levels to
the lungs for oxygenation.
THE MUSCLE
PUMP
Blood Distribution
w Matched to overall metabolic demands
w Autoregulation—arterioles within organs or tissues dilate
or constrict in response to the local chemical environment
w Extrinsic neural control—sympathetic nerves within walls
of vessels are stimulated causing vessels to constrict
w Determined by the balance between mean arterial
pressure and total peripheral resistance
BLOOD
DISTRIBUTION
AT REST
Blood Pressure
w Systolic blood pressure (SBP) is the highest pressure and
diastolic blood pressure (DBP) is the lowest pressure
w Mean arterial pressure (MAP)—average pressure exerted
by the blood as it travels through arteries
w MAP = DBP + [0.333  (SBP) – (DBP)]
w Blood vessel constriction increases blood pressure;
dilation reduces blood pressure
Key Points
The Vascular System
w Blood returns to the heart with the help of
breathing, the muscle pump, and valves in
the veins.
w Blood is distributed throughout the body
based on the needs of tissues; the most
active tissues receive the most blood.
w Autoregulation controls blood flow by
vasodilation in response to local chemical
changes in an area.
(continued)
Key Points
The Vascular System
w Extrinsic neural factors control blood flow
primarily by vasoconstriction.
w Systolic blood pressure (SBP) is the
highest pressure within the vascular
system while diastolic blood pressure
(DBP) is the lowest.
w Mean arterial pressure (MAP) is the
average pressure on the arterial walls.
Functions of the Blood
w Transports gas, nutrients, and wastes
w Regulates temperature
w Buffers and balances acid base
THE COMPOSITION OF TOTAL
BLOOD VOLUME
Hematocrit and Blood Formed Elements
Ratio of formed elements to the total blood volume
w White blood cells—protect body from disease organisms
w Blood platelets—cell fragments that help blood
coagulation
w Red blood cells—carry oxygen to tissues with
the help of hemoglobin
Blood Viscosity
w Thickness of the blood
w The more viscous, the more resistant to flow
w Higher hematocrits result in higher blood viscosity
Key Points
The Blood
w Blood and lymph transport materials to and
from body tissues.
w Blood is about 55% to 60% plasma and
40% to 45% formed elements (white and
red blood cells and blood platelets).
w Oxygen travels through the body by
binding to hemoglobin in red blood cells.
w An increase in blood viscosity results in
resistance to flow.
Cardiovascular Response to Acute Exercise
w Heart
rate (HR), stroke volume (SV), and cardiac output
.
(Q) increase.
w Blood flow and blood pressure change.
w All result in allowing the body to meet the increased
demands placed on it efficiently.
Resting Heart Rate
w Averages 60 to 80 beats per minute (bpm); can range
from 28 bpm to above 100 bpm
w Tends to decrease with age and with increased
cardiovascular fitness
w Is affected by environmental conditions such as altitude
and temperature
Maximum Heart Rate
w The highest heart rate value one can achieve in an all-out
effort to the point of exhaustion
w Remains constant day to day and changes slightly from
year to year
w Can be estimated: HRmax = 220 – age in years
HEART RATE AND INTENSITY
Steady-State Heart Rate
w Heart rate plateau reached during constant rate of
submaximal work
w Optimal heart rate for meeting circulatory demands at that
rate of work
w The lower the steady-state heart rate, the more efficient
the heart
Stroke Volume
w Determinant of cardiorespiratory endurance capacity at
maximal rates of work
w May increase with increasing rates of work up to
intensities of 40% to 60% of max
w May continue to increase up through maximal exercise
intensity, generally in highly trained athletes
w Depends on position of body during exercise
STROKE VOLUME
STROKE VOLUME INCREASES IN
CYCLISTS
Stroke Volume Increases During Exercise
w Frank Starling mechanism—more blood in the ventricle
causes it to stretch more and contract with more force.
w Increased ventricular contractility (without end-diastolic
volume increases).
w Decreased total peripheral resistance due to increased
vasodilation of blood vessels to active muscles.
LEFT VENTRICULAR VOLUMES
Cardiac Output
w Resting value is approximately 5.0 L/min.
w Increases directly with increasing exercise intensity to
between 20 to 40 L/min.
wThe magnitude of increase varies with body size and
endurance conditioning.
w When exercise
. intensity exceeds 40% to 60%, further
increases in Q are more a result of increases in HR than
SV since SV tends to plateau at higher work rates.
CARDIAC OUTPUT
.
CHANGES IN HR, SV, AND Q
Changes in Heart Rate, Stroke
Volume, and Cardiac Output
Activity
Heart rate Stroke volume
(beats/min)
(ml/beat)
Cardiac output
(L/min)
Resting (supine)
55
95
5.2
Resting (standing
and sitting)
60
70
4.2
Running
190
130
24.7
Cycling
185
120
22.2
Swimming
170
135
22.9
CARDIAC OUTPUT DURING EXERCISE
CARDIAC OUTPUT DURING EXERCISE
Cardiovascular Drift
w Gradual decrease in stroke volume and systemic and
pulmonary arterial pressures and an increase in heart
rate.
w Occurs with steady-state prolonged exercise or exercise
in a hot environment.
CIRCULATORY RESPONSES
Blood Pressure
Cardiovascular Endurance Exercise
w Systolic BP increases in direct proportion to increased
exercise intensity
w Diastolic BP changes little if any during endurance
exercise, regardless of intensity
Resistance Exercise
w Exaggerates BP responses to as high as 480/350 mmHg
w Some BP increases are attributed to the Valsalva
maneuver
BLOOD PRESSURE RESPONSES
Key Points
Cardiovascular Response
to Exercise
w As exercise intensity increases, heart rate,
stroke volume, and cardiac output increase
to get more blood to the tissues.
w More blood pumped from the heart per
minute during exercise allows for more
oxygen and nutrients to get to the muscles
and for waste to be removed more quickly.
w Blood flow distribution changes from rest to
exercise as blood is redirected to the
muscles and systems that need it.
(continued)
Key Points
Cardiovascular Response
to Exercise
w Cardiovascular drift is the result of
decreased stroke volume, increased heart
rate, and decreased systemic and
pulmonary arterial pressure due to
prolonged steady-state exercise or
exercise in the heat.
w Systolic blood pressure increases directly
with increased exercise intensity while
diastolic blood pressure remains constant.
w Blood pressure tends to increase during
high-intensity resistance training, due in
part to the Valsalva maneuver.
Arterial-Venous Oxygen Difference
w Amount of oxygen extracted from the blood as it travels
through the body
w Calculated as the difference between the oxygen content
of arterial blood and venous blood
w Increases with increasing rates of exercise as more
oxygen is taken from blood
w The Fick equation represents .the relationship of the
body’s oxygen consumption (VO2), to the arterial-venous
.
oxygen
(a-vO2 diff) and cardiac output (Q);
.
. difference
VO2 = Q  a-vO
2 diff.
CHANGES IN ARTERIOVENOUS OXYGEN
Blood Plasma Volume
w Reduced with onset of exercise (goes to interstitial fluid
space)
w More is lost if exercise results in sweating
w Excessive loss can result in impaired performance
w Reduction in blood plasma volume
results in hemoconcentration
THE CARDIOVASCULAR
RESPONSE TO
EXERCISE
Key Points
Blood Changes During Exercise
w The a-vO
2 diff increases as venous oxygen
concentration decreases during exercise
due to the body extracting oxygen from the
blood.
w Plasma volume decreases during exercise
due to water being drawn from the blood
plasma and out of the body as sweat.
w Hemoconcentration occurs. Plasma fluid is
lost resulting in a higher concentration of
red blood cells per unit of blood and, thus,
increased oxygen-carrying capacity.
w Blood pH decreases due to increased
blood lactate accumulation with increasing
exercise intensity.