C H A P T E R    7
CARDIOVASCULAR CONTROL DURING EXERCISE
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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)
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Cardiovascular System
w A pump (the heart)
w A system of channels (the blood vessels)
w A fluid medium (blood)

HEART
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Myocardium—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.

CORONARY CIRCULATION
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INTRINSIC CONDUCTION SYSTEM


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 s
w AV bundle (bundle of His)
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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.
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Resting heart rates in adults tend to be between
60 and 85 beats/min. However, extended
endurance training can lower resting heart rate to
35 beats/min or less. This lower heart rate is
thought to be due to decreased intrinsic heart rate
and increased parasympathetic stimulation.
Did You Know…?
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Main Cardiac Arrhythmias
Bradycardia—resting heart rate below 60 beats/min
Tachycardia—resting heart rate above 100 beats/min
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Electrocardiogram (ECG)
w Printout shows the heart's electrical activity
and can be used to monitor cardiac changes
w The P wave—atrial depolarization
w The QRS complex—ventricular depolarization and
atrial repolarization
w The T wave—ventricular repolarization

TAKING AN EXERCISE ECG
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PHASES OF A RESTING ECG
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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
wSystole—contraction phase during which the chambers expel blood (QRS to T wave)—38% of cycle
duration
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WIGGERS DIAGRAM
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Stroke Volume and Cardiac
Output
Stroke Volume (SV)
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
w Volume of blood pumped per contraction
w Total volume of blood pumped by the ventricle
per minute
Cardiac Output (Q)
.
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
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Vascular System
w Arteries
w Arterioles
w Capillaries
w Venules
w Veins
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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.
Did You Know…?
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MUSCLE PUMP
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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

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BLOOD DISTRIBUTION AT REST


Blood Pressure
w Systolic blood pressure (SBP) is the highest pressure and diastolic blood pressure (DBP) is the
lowest pressure
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w Blood vessel constriction increases blood pressure; dilation reduces blood pressure

Cardiovascular Response to Acute
Exercise
w Blood flow and blood pressure change.
wHeart rate (HR) increases as exercise intensity
increases up to maximal heart rate.
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wStroke volume (SV) increases up to 40% to 60% VO2max in untrained individuals and up to maximal
levels in trained individuals.
wIncreases in HR and SV during exercise cause cardiac output (Q) to increase.

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
wCan be estimated: HRmax = 220 – age in years or
HRmax = 208 – (0.7 ´ age)
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HEART RATE AND INTENSITY
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Heart rate detection
§Auscultation at the heart apex
§ECG record (R–R distance)
§Pulse palpation
§Photometric, piezoelectric or electric devices

Heart rate (HR) changes
§Average rest HR is 72 bpm
§The HR is higher in children
§The HR is higher during exercise, stress or fever
§During exercise the HR increases as much as twice
§After exercise the HR drops back to rest state within 3 minutes
§In trained individuals the rest HR reoccurs faster

§Initial increase of HR (mental preparation)
§Work state HR (followed by steady-state HR – corresponds to the load intensity)
§Subsequent HR (after the load, decrease to rest
HR)
§
§
HR during exercise

Pulse
§
§During systolic ejection a flexible wall of aorta expands.
§
§During diastole the wall of aorta contracts and empowers the bloodstream.
§
§The expansion and contraction of the arterial walls transmit throughout the body (from centre to
peripheries).
§
§This wave-like transmission is called a pulse. It could be palpated close to body surface.

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