lecture 3 (circulatory adaptation to exercise( dr sani)

8/3/2019 Lecture 3 (Circulatory Adaptation to Exercise( dr sani)

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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




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




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




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




The Cardiovascular System

Purposes

1. Transport O2 to tissues and

removal of waste2. Transport of nutrients to tissues

3. Regulation of body temperature




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



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



The Myocardium

Fig 9.2



The Cardiac Cycle

Systole

• Contraction phase

Diastole

• Relaxation phase

Fig 9.3



PressureChanges

During the

CardiacCycle

Fig 9.4



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)



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)



Mean Arterial Pressure

Blood pressure of 120/80 mm Hg

MAP = 80 mm Hg + .33(120-80)

= 80 mm Hg + 13

= 93 mm Hg



Measurementof BloodPressure

Fig 9.5



Factors That Influence ArterialBlood Pressure

Fig 9.6




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)




Conduction System of the Heart

Fig 9.7




Electrocardiogram

• Records the electrical activity of the heart

• P-wave

– Atrial depolarization

• QRS complex

– Ventricular depolarization

• T-wave – Ventricular repolarization

Fig 9.9




Electrocardiogram

Fig 9.9




CardiacCycle&

ECG

Fig 9.10




Diagnostic Use of the ECG

• ECG abnormalities may indicate

coronary heart disease

– ST-segment depression can indicatemyocardial ischemia

Fig 9.8




Abnormal ECG

Fig 9.8




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




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




Nervous System Regulation ofHeart Rate

Fig 9.11




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”




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




The Skeletal Muscle Pump

• Rhythmic skeletalmuscle contractions

force blood in theextremities toward theheart

• One-way valves in veinsprevent backflow ofblood Fig 9.12




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




Ventricular Contractility

• Increased contractility results in higherstroke volume

– Circulating epinephrine and norepinephrine

– Direct sympathetic stimulation of heart




Factors that Regulate CardiacOutput

Cardiac = Cardiac Rate x Stroke VolumeOutput

Mean arterialpressure

EDV

Contraction

strength

Frank-Starling

Stretch

Sympatheticnerves

Parasympatheticnerves

Fig 9.13




Hemodynamics

The study of thephysical principles of

blood flow




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




Hematocrit

Fig 9.14

Percent of blood composed of cells




Hemodynamics

Based on interrelationships

between:

–Pressure –Resistance

–Flow




Hemodynamics: Pressure

• Blood flows from high low pressure

– Proportional to the difference betweenMAP and right atrial pressure (P)

Fig 9.15




Blood Flow Through theSystemic Circuit

Fig 9.15




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




Hemodynamics: Blood Flow

• Directly proportional to the pressuredifference between the two ends of thesystem

• Inversely proportional to resistance

Flow =

Pressure

Resistance




Sources of Vascular Resistance

• MAP decreases throughout the

systemic circulation

• Largest drop occurs across thearterioles

– Arterioles are called “resistance vessels”

Pressure Changes Across the




Pressure Changes Across theSystemic Circulation

Fig 9.16

O D li D i




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




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




Changes inCardiovascular

Variables DuringExercise

Fig 9.17




Redistribution of Blood Flow

• Muscle blood flow to working

skeletal muscle

• Splanchnic blood flow to less activeorgans

– Liver, kidneys, GI tract

Fig 9.18




Changes in

Muscle andSplanchnic

Blood FlowDuring

Exercise

Fig 9.18

I d Bl d Fl t Sk l t l




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




Circulatory Responses toExercise

• Heart rate and blood pressure

• Depend on:

– Type, intensity, and duration of exercise – Environmental condition

– Emotional influence

Transition From Rest Exercise




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




TransitionFrom Rest

Exercise Recovery

Fig 9.20




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




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




Heart Rate

and BloodPressure

During Armand LegExercise

Fig 9.21




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




HR, SV, and CO DuringProlonged Exercise

Fig 9.22

Cardiovascular Adjustments




Cardiovascular Adjustmentsto Exercise

Fig 9.23

Summary of Cardiovascular




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



A Summaryof

Cardiovascu

lar ControlDuring

Exercise

Fig 9.24

lecture 3 (circulatory adaptation to exercise( dr sani)

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