lecture 3 (circulatory adaptation to exercise( dr sani)
TRANSCRIPT
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Circulatory Adaptationsto Exercise
PHYSIOLOGY OF PHYSICAL ACTIVITYAdapted from
Theory and Application to Fitness and Performance, 5
th
editionScott K. Powers & Edward T. Howley
Presentation revised and updated by
MOHD SANI MADON
UNIVERSITI PENDIDIKAN SULTAN IDRIS
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Introduction• One major challenge to homeostasis
posed by exercise is the increasedmuscular demand for oxygen
• During heavy exercise, oxygen
demands may by 15 to 25 times• Two major adjustments of blood flow
are;
–
cardiac output – Redistribution of blood flow
• A thorough understanding of thecardiovascular system is essential to
exercise physiology
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Objectives
• Give an overview of the design andfunction of the circulatory system
• Describe cardiac cycle & associatedelectrical activity recorded viaelectrocardiogram
• Discuss the pattern of redistribution ofblood flow during exercise
• Outline the circulatory responses tovarious t es of exercise
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Objectives
• Identify the factors that regulate localblood flow during exercise
• List & discuss those factors responsiblefor regulation of stroke volume duringexercise
• Discuss the regulation of cardiac outputduring exercise
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The Cardiovascular System
Purposes
1. Transport O2 to tissues and
removal of waste2. Transport of nutrients to tissues
3. Regulation of body temperature
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The Circulatory System
• Heart
– Pumps blood
• Arteries and arterioles – Carry blood away from the heart
• Capillaries
– Exchange of nutrients with tissues• Veins and venules
– Carry blood toward the heart
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Structure of the Heart
Fig 9.1
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Pulmonary and SystemicCircuits
Systemic circuit
• Left side of the
heart
• Pumps oxygenatedblood to the whole
body via arteries
• Returnsdeoxygenated
blood to the right
Pulmonary circuit
• Right side of the
heart
• Pumpsdeoxygenated
blood to the lungsvia pulmonaryarteries
• Returns oxygenated
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The Myocardium
Fig 9.2
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The Cardiac Cycle
Systole
• Contraction phase
Diastole
• Relaxation phase
Fig 9.3
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PressureChanges
During the
CardiacCycle
Fig 9.4
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Arterial Blood Pressure
• Expressed as systolic/diastolic
– Normal is 120/80 mmHg
– High is 140/90 mmHg
• Systolic pressure (top number)
– Pressure generated during ventricularcontraction (systole)
• Diastolic pressure
– Pressure in the arteries during cardiacrelaxation (diastole)
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Blood Pressure
• Pulse pressure
– Difference between systolic and diastolic
• Mean arterial pressure (MAP)
– Average pressure in the arteries
Pulse Pressure = Systolic - Diastolic
MAP = Diastolic + 1/3(pulse pressure)
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Mean Arterial Pressure
Blood pressure of 120/80 mm Hg
MAP = 80 mm Hg + .33(120-80)
= 80 mm Hg + 13
= 93 mm Hg
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Measurementof BloodPressure
Fig 9.5
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Factors That Influence ArterialBlood Pressure
Fig 9.6
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Electrical Activity of the Heart
• Contraction of the heart depends on
electrical stimulation of the
myocardium• Impulse is initiated in the right atrium
and spreads throughout entire heart
• May be recorded on anelectrocardiogram (ECG)
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Conduction System of the Heart
Fig 9.7
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Electrocardiogram
• Records the electrical activity of the heart
• P-wave
– Atrial depolarization
• QRS complex
– Ventricular depolarization
• T-wave – Ventricular repolarization
Fig 9.9
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Electrocardiogram
Fig 9.9
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CardiacCycle&
ECG
Fig 9.10
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Diagnostic Use of the ECG
• ECG abnormalities may indicate
coronary heart disease
– ST-segment depression can indicatemyocardial ischemia
Fig 9.8
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Abnormal ECG
Fig 9.8
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Cardiac Output
The amount of blood pumped by the
heart each minute
• Product of heart rate and stroke volume
–Heart rate = number of beats per minute
– Stroke volume = amount of blood ejected ineach beat
Q = HR x SV
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Regulation of Heart Rate
• Decrease in HR
– Parasympathetic nervous system
• Via vagus nerve
– Slows HR by inhibiting SA node
• Increase in HR
– Sympathetic nervous system
• Via cardiac accelerator nerves
– Increases HR by stimulating SA node
Fig 9.11
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Nervous System Regulation ofHeart Rate
Fig 9.11
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Regulation of Stroke Volume
• End-diastolic volume (EDV)
– Volume of blood in the ventricles at the end ofdiastole (“preload”)
• Average aortic blood pressure
– Pressure the heart must pump against to ejectblood (“afterload”)
• Strength of the ventricular contraction – “Contractility”
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End-Diastolic Volume
• Frank-Starling mechanism
– Greater preload results in stretch of ventriclesand in a more forceful contraction
• Affected by:
– Venoconstriction
– Skeletal muscle pump
– Respiratory pump
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The Skeletal Muscle Pump
• Rhythmic skeletalmuscle contractions
force blood in theextremities toward theheart
• One-way valves in veinsprevent backflow ofblood Fig 9.12
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Average Aortic Pressure
• Aortic pressure is inversely related tostroke volume
• High afterload results in a decreased
stroke volume – Requires greater force generation by the
myocardium to eject blood into the aorta
• Reducing aortic pressure results in higherstroke volume
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Ventricular Contractility
• Increased contractility results in higherstroke volume
– Circulating epinephrine and norepinephrine
– Direct sympathetic stimulation of heart
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Factors that Regulate CardiacOutput
Cardiac = Cardiac Rate x Stroke VolumeOutput
Mean arterialpressure
EDV
Contraction
strength
Frank-Starling
Stretch
Sympatheticnerves
Parasympatheticnerves
Fig 9.13
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Hemodynamics
The study of thephysical principles of
blood flow
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Physical Characteristics of Blood
• Plasma – Liquid portion of blood
– Contains ions, proteins, hormones
• Cells – Red blood cells
• Contain hemoglobin to carry oxygen
– White blood cells – Platelets• Important in blood clotting
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Hematocrit
Fig 9.14
Percent of blood composed of cells
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Hemodynamics
Based on interrelationships
between:
–Pressure –Resistance
–Flow
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Hemodynamics: Pressure
• Blood flows from high low pressure
– Proportional to the difference betweenMAP and right atrial pressure (P)
Fig 9.15
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Blood Flow Through theSystemic Circuit
Fig 9.15
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Hemodynamics: Resistance
• Resistance depends upon:
– Length of the vessel
– Viscosity of the blood
– Radius of the vessel
• A small change in vessel diameter can have adramatic impact on resistance!
Resistance = Length x viscosity
Radius4
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Hemodynamics: Blood Flow
• Directly proportional to the pressuredifference between the two ends of thesystem
• Inversely proportional to resistance
Flow =
Pressure
Resistance
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Sources of Vascular Resistance
• MAP decreases throughout the
systemic circulation
• Largest drop occurs across thearterioles
– Arterioles are called “resistance vessels”
Pressure Changes Across the
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Pressure Changes Across theSystemic Circulation
Fig 9.16
O D li D i
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Oxygen Delivery DuringExercise
• Oxygen demand by muscles duringexercise is many times greater than at rest
• Increased O2 delivery accomplished by:
– Increased cardiac output
– Redistribution of blood flow to skeletal muscle
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Changes in Cardiac Output
• Cardiac output increases due to:
– Increased HR
• Linear increase to max
– Increased SV
• Plateau at ~40% VO2max
• Oxygen uptake by the muscle alsoincreases
– Higher arteriovenous differenceMax HR = 220 - Age (years)
Fig 9.17
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Changes inCardiovascular
Variables DuringExercise
Fig 9.17
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Redistribution of Blood Flow
• Muscle blood flow to working
skeletal muscle
• Splanchnic blood flow to less activeorgans
– Liver, kidneys, GI tract
Fig 9.18
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Changes in
Muscle andSplanchnic
Blood FlowDuring
Exercise
Fig 9.18
I d Bl d Fl t Sk l t l
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Increased Blood Flow to SkeletalMuscle During Exercise
• Withdrawal of sympatheticvasoconstriction
• Autoregulation
– Blood flow increased to meet metabolicdemands of tissue
– O2 tension, CO2 tension, pH, potassium,adenosine, nitric oxide
R di t ib ti f Bl d Fl
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Redistribution of Blood FlowDuring Exercise
Fig 9.19 (c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Ci l t R t
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Circulatory Responses toExercise
• Heart rate and blood pressure
• Depend on:
– Type, intensity, and duration of exercise – Environmental condition
– Emotional influence
Transition From Rest Exercise
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Transition From Rest Exerciseand Exercise Recovery
• Rapid increase in HR, SV, cardiac
output• Plateau in submaximal (below
lactate threshold) exercise
• Recovery depends on:
– Duration and intensity of exercise
– Training state of subject
Fig 9.20
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TransitionFrom Rest
Exercise Recovery
Fig 9.20
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Incremental Exercise
• Heart rate and cardiac output – Increases linearly with increasing work rate
– Reaches plateau at 100% VO2max
• Systolic blood pressure – Increases with increasing work rate
• Double product
– Increases linearly with exercise intensity – Indicates the work of the heart
Double product = heart rate x systolic BP
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Arm vs. Leg Exercise
• At the same oxygen uptake arm workresults in higher:
– Heart rate
• Due to higher sympathetic stimulation
– Blood pressure
• Due to vasoconstriction of large inactive musclemass
.
Fig 9.21
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Heart Rate
and BloodPressure
During Armand LegExercise
Fig 9.21
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Prolonged Exercise
• Cardiac output is maintained
– Gradual decrease in stroke volume
– Gradual increase in heart rate• Cardiovascular drift
– Due to dehydration and increased skin
blood flow (rising body temperature)
.
Fig 9.22
HR SV and CO During
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HR, SV, and CO DuringProlonged Exercise
Fig 9.22
Cardiovascular Adjustments
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Cardiovascular Adjustmentsto Exercise
Fig 9.23
Summary of Cardiovascular
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Summary of CardiovascularControl During Exercise
• Initial signal to “drive” cardiovascular system comes from higher braincenters
• Fine-tuned by feedback from: – Chemoreceptors
– Mechanoreceptors
– Baroreceptors
Fig 9.24
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A Summaryof
Cardiovascu
lar ControlDuring
Exercise
Fig 9.24