Download The Cardiovascular System And Exercise

Chapter 10
The Cardiovascular
System and Exercise
Slide Show developed by:
Richard C. Krejci, Ph.D.
Professor of Public Health
Columbia College 10.18.11
Objectives
1. List important functions of the cardiovascular system.
2. Describe how to use the auscultatory method to measure
blood pressure, and give average values for systolic and
diastolic blood pressure during rest and moderate aerobic
exercise.
3. Describe the blood pressure response during (1) resistance
exercise, (2) upper-body exercise, and (3) exercise in the
inverted position.
4. State potential benefits of aerobic exercise for treating
moderate hypertension.
5. Identify the intrinsic and extrinsic factors that regulate heart
rate during rest and exercise.
Objectives (Cont.)
6. Identify the neural and local metabolic factors that regulate
blood flow during rest and exercise.
7. Compare average values of cardiac output during rest and
maximal exercise for an endurance-trained athlete and
sedentary person.
8. Explain three physiologic mechanisms that affect the heart’s
stroke volume.
9. Describe the relationship between maximal cardiac output and
maximal oxygen uptake among individuals with varied aerobic
fitness levels.
Cardiovascular System Anatomy
• Heart
• Arteries
• Capillaries
• Veins
Cardiovascular System Anatomy (Cont.)
Heart
• Provides the force to propel blood throughout the
vascular circuit
• Septum separates the left and right sides of the heart
• Atrioventricular valves
 Tricuspid valve: Between right atrium and ventricle
 Mitral or bicuspid valve: Between left atrium and
ventricle
• Semilunar valves
 Prevent regurgitation between ventricular contractions
Heart (Cont.)
Heart Pumps
• Functions of the chambers of the right heart pump:
 Receive deoxygenated blood returning from all parts of the
body
 Pump blood to the lungs for aeration via the pulmonary
circulation
• Functions of the chambers of left heart pump:
 Receive oxygenated blood from the lungs
 Pump blood into the thick-walled, muscular aorta for
distribution throughout the body via the systemic
circulation
Arteries
• The high-pressure tubing that conducts oxygen-rich
blood (except pulmonary arteries) to the tissues.
• Because of their thickness, no gaseous exchange
takes place between arterial blood and surrounding
tissues.
• Blood pumped from the left ventricle into the aorta
circulates throughout the body via a network of
arteries and arterioles.
• Arteriole walls contain circular layers of smooth
muscle that either constrict or relax to regulate
peripheral blood flow.
Capillaries
• A network of microscopic blood vessels so thin
they provide only enough room for blood cells to
squeeze through in single file.
• Gases, nutrients, and waste products rapidly
transfer across the thin, porous, capillary walls.
• Velocity progressively decreases as blood moves
toward and into the capillaries.
Veins
• Venules eventually empty into the superior and
inferior vena cavae.
• Thin, membranous, flap-like valves spaced at
short intervals within the vein permit one-way
blood flow back to the heart.
• Venous system acts as an active blood reservoir
to either retard or enhance blood flow to the
systemic circulation.
Valves in Veins
Blood Pressure
• Systolic blood pressure
 Highest arterial pressure measured after left
ventricular contraction
• Diastolic blood pressure
 Lowest arterial pressure measured during left
ventricular relaxation
• Read as 115/70
Blood Pressure
Changes During Exercise
• Rhythmic Exercise: Increases systolic pressure in the first
few minutes and then levels off; diastolic pressure remains
relatively unchanged
• Resistance Exercise: Can increase blood pressure
dramatically
• Upper-Body Exercise: Exercise at a given percentage of
V·O2max increases blood pressure substantially more in
upper-body compared with lower-body exercise
• In Recovery: After a bout of sustained light- to moderateintensity exercise, systolic blood pressure decreases below
pre-exercise levels for up to 12 hours in normal and
hypertensive subjects
Blood Pressure Changes During
Exercise
Heart’s Blood Supply
• Coronary circulation
 Right coronary artery: Supplies predominantly the right
atrium and ventricle
 Left coronary artery: Supplies the left atrium and
ventricle, and a small portion of the right ventricle
Heart’s Blood Supply
Myocardial Oxygen Utilization
• At rest, the myocardium extracts 70% to 80% of
the oxygen from the blood flowing in the
coronary vessels.
• Because near-maximal oxygen extraction occurs
in the myocardium at rest, increases in coronary
blood flow provide the primary means to meet
myocardial oxygen demands in exercise.
 In vigorous exercise, coronary blood flow increases
four to six times above the resting
level.
Rate-Pressure Product
• Provides a convenient estimate of myocardial
workload
• Three important mechanical factors determine
myocardial oxygen uptake:
1. Tension development within the myocardium
2. Myocardial contractility
3. Heart rate
• RPP = SBP x HR
Heart’s Energy Supply
• The myocardium relies almost exclusively on energy
released from aerobic reactions.
• Myocardial tissue contains the greatest mitochondrial
concentration of all tissues.
• Glucose, fatty acids, and lactate formed from glycolysis in
skeletal muscle all provide the energy for myocardial
functioning.
Heart Rate Regulation: Intrinsic
• Sinoatrial (S-A) node: Spontaneously depolarizes and
repolarizes to provide an “innate” stimulus to the heart.
• Atrioventricular (A-V) node: Delays the impulse about 0.10
seconds to provide sufficient time for the atria to contract and
force blood into the ventricles
• A-V bundle or Bundle of His
• Purkinje Fibers: Speed the impulse rapidly through the
ventricles
Heart Rate Regulation: Intrinsic (Cont.)
Heart Rate Regulation: Intrinsic
Heart Rate Regulation: Extrinsic
• Sympathetic Influence
 Releases catecholamines epinephrine and nor-epinephrine
 Leads to tachycardia (>100 beats/min)
• Parasympathetic Influence
 Releases acetylcholine
 Leads to bradycardia (<60 beats/min)
Heart Rate Regulation: Extrinsic
Heart Rate Regulation: Extrinsic
• Cortical Influence
 Central command provides the greatest control over
heart rate
 Exerts its effect during exercise, at rest and in the
immediate pre-exercise period
 Produces an anticipatory heart rate, which becomes
particularly apparent prior to all-out physical effort
Heart Rate Regulation: Extrinsic
Heart Rate Regulation: Extrinsic
• Peripheral Input
 Mechanoreceptors and chemoreceptors
 Stimuli from these peripheral receptors monitor the state
of active muscle
Heart Rate Regulation: Extrinsic
Arrhythmias
• Extrasystoles: Extra beats
• Premature atrial contraction or PAC: Parts of the
atria become prematurely electrically active and
depolarize spontaneously prior to S-A node
excitation
 Linked PACs can create atrial fibrillation.
• Premature ventricular contraction or PVC:
Premature excitation of ventricles
 Ventricular fibrillation
Blood Distribution During
Exercise
• Increased energy expenditure requires rapid
readjustments in blood flow that affect the entire
cardiovascular system.
• The vascular portion of active muscles increases
through dilation of local arterioles.
• At the same time, other vessels constrict to “shut
down” blood flow to tissues that can temporarily
compromise blood supply.
Blood Flow Regulation
• Flow = Pressure ÷ Resistance
• Three factors determine resistance to blood flow:
1. Viscosity or blood thickness
2. Length of conducting tube
3. Radius of blood vessel
• Poiseuille’s Law
 Flow = (Pressure gradient x Vessel radius4) ÷
(Vessel length x Fluid viscosity)
Three Blood Flow Regulation
Factors
1. Local: Local increases in temperature, carbon dioxide,
acidity, adenosine, nitric oxide, and magnesium and
potassium ions enhance regional blood flow.
2. Neural: Central vascular control via sympathetic and
parasympathetic portions of the autonomic nervous
system overrides vasoregulation afforded by local factors.
3. Hormonal: With sympathetic activation, adrenal glands
release epinephrine and norepinephrine to cause a general
constrictor response except in blood vessels of the heart
and skeletal muscles.
Cardiac Output
• The most important indicator of the circulatory
system’s functional capacity to meet the
demands for physical activity
• Cardiac output = Heart rate x Stroke volume
• Cardiac output, mL·min-1 = [VO2, mL·min-1 ÷ avO2 diff, mL·dL blood-1] x 100
Cardiac Output
Exercise Stroke Volume
• Three physiologic mechanisms that increase the
heart’s stroke volume during exercise:
1. Enhanced cardiac filling in diastole followed by a
more forceful systolic contraction.
2. Neurohormonal influence causes normal ventricular
filling with a subsequent forceful ejection and
emptying during systole.
3. Training adaptations can expand blood volume and
reduce resistance to blood flow in peripheral tissues.
Exercise Stroke Volume
Diastolic Filling and Systolic
Emptying
• Preload: Greater ventricular filling in diastole
during the cardiac cycle from an increase in venous
return
• Afterload: Resistance to flow from increased
systolic pressure
Cardiovascular Drift
• A gradual time-dependent downward “drift” in
several cardiovascular responses, most notably
stroke volume with a compensatory heart rate
increase, during prolonged steady-rate exercise
Exercise Heart Rate
Trained vs. Untrained People
• Heart rate increases rapidly and levels off within
several minutes during sub-maximum steady-rate
exercise.
• Heart rate for the untrained person accelerates
relatively rapidly with increasing exercise
demands.
• A much smaller heart rate increase occurs for the
trained person so that they achieve a higher level
of exercise oxygen uptake at a particular
submaximal heart rate than a sedentary person.
Cardiac Output and Oxygen
Transport
• A low aerobic capacity links closely to a low
maximum cardiac output.
• An increase in maximum cardiac output directly
improves a person’s capacity to circulate oxygen
and profoundly impacts the maximal oxygen
consumption.
Cardiac Output and Oxygen
Transport
Cardiac Output Differences
• Cardiac output and oxygen consumption remain
linearly related during graded exercise for boys and
girls and men and women.
 Teenage and adult females exercise at any level of
submaximal oxygen consumption with a 5-10% larger
cardiac output than males.
• Compared to adults, children have
smaller cardiac outputs at any given
submaximal exercise oxygen
consumption from smaller stroke
volumes.
A-VO2 Difference During Exercise
• VO2max = Max cardiac output x Max a-vO2 difference
• The capacity of each dl of arterial blood to carry oxygen
actually increases during exercise from an increased
hemo-concentration from the progressive movement of
fluid from the plasma to the interstitial space.
• Diverting a large portion of the cardiac output to active
muscles influences the magnitude of the a-vO2 difference
in maximal exercise.
• An increase in the capillary to fiber ratio reflects a
positive training adaptation that enlarges the interface for
nutrient and gas exchange during exercise.
A-VO2 Difference During Exercise
Cardiovascular Adjustments to
Upper-Body Exercise
• The highest oxygen uptake during upper-body exercise
generally averages between 70% to 80% of the VO2max in
bicycle and treadmill exercise.
• Maximal heart rate and pulmonary ventilation remain lower in
exercise with the arms from a relatively smaller muscle mass.
• Any level of submaximal power output produces a higher
oxygen uptake with arm compared with leg exercise.
Cardiovascular Adjustments to
Upper-Body Exercise
The End