Transcript Cardiovascular Responses to Exercise (cont`d)

Chapter 8
Responses and Adaptations of
the Cardiorespiratory System
Copyright © 2012 American College of Sports Medicine
Ambient Vs. Resting (terminology)
•
Ambient heart rate (or BP) is frequently confused with resting heart rate. Ambient heart
rate is measured when the body is awake but sedentary – for example, when you are
resting in a sitting position but are awake and involved in a sedentary activity such as
working on a computer, watching television, or talking. Resting heart rate, on the other
hand, is taken in bed before you rise when the heart is at complete rest. Ambient heart
rates change because of the same stimuli that influence all heart rates, including body
position; external influences such as temperature, hydration, and food ingested; internal
influences such as level of fatigue, stress, hunger, and sleep; medication; and
others. Ambient heart rate or sitting heart rate, like most heart measurements, is relative,
not absolute. It’s a comparative number that needs to be assessed based on a sample of
other ambient heart rate measurements. Taking ambient heart rates repeatedly gives a
more accurate assessment than measuring the ambient heart rate once. The normal
range for ambient heart rate is usually between 50 and 90 bpm, but healthy ranges of
ambient heart rates are very broad. The training effect is also seen in ambient heart rates.
In other words, the fitter you become, the lower your ambient heart rate. Ambient heart
rates under 60 bpm are rare. An ambient heart rate over 80 bpm may indicate a
combination of different types of stress.
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• White Coat Syndrome: Even if setting foot into a doctor's office
doesn't feel like walking into a lion's den, your body may be priming
for a threat. As much as 20 percent of the population suffers from
"white coat syndrome," in whichblood pressure surges when
measured in the doctor's office. The syndrome produces a challenge
for physicians seeking an accurate blood pressure reading.
• Anticipatory Response: The Anticipatory Response is when the
heart rate increases at the beginning of exercise. The heart rate can
be changed by chemicals by neurotransmitters , called adrenaline and
noradrenaline which are released and found in the brain.
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The Cardiovascular (CV) System
• Consists of 3 major components: (1) the heart—the pump; (2) the
blood vessels—transport portals; (3) and the blood—fluid medium
• All other systems depend on the CV system—including the lungs.
• The lungs: essential for blood oxygenation and removal of CO2
• The CV system: delivers nutrients, oxygen, hormones to tissues,
removal of waste products and CO2, temperature control, pH control,
immunity and hydration.
• More than 100,000 miles of blood vessels within an average-sized
man.
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Anatomy of the Heart
• Heart
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Pump that circulates blood throughout body
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Four chambers (2 main pumps—pulmonary & systemic)
• Right & left atria: receivers
• Right & left ventricles: pump blood away
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2/3 of mass on left side
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Weighs 11 oz in men & 9 oz in women (proportional to body
size)
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Anatomy of the Heart (cont’d)
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Pathway of Blood Through the Heart
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1. Blood enters the right atrium from the superior and inferior venae cavae, and the coronary sinus.
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2. From right atrium, it goes through the tricuspid valve to the right ventricle.
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3. From the right ventricle, it goes through the pulmonary semilunar valves to the pulmonary trunk
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4. From the pulmonary trunk it moves into the right and left pulmonary arteries to the lungs.
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5. From the lungs, oxygenated blood is returned to the heart through the pulmonary veins.
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6. From the pulmonary veins, blood flows into the left atrium.
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7. From the left atrium, blood flows through the bicuspid (mitral) valve into the left ventricle.
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8. From the left ventricle, it goes through the aortic semilunar valves into the ascending aorta.
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9. Blood is distributed to the rest of the body (systemic circulation) from the aorta.
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Anatomy of the Heart (cont’d)
• Cardiac Musculature: Myocardium
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Contracts on its own
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Capable of hypertrophy & adapting to exercise
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Thickness affected by stress; thicker = stronger
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Larger, fewer T tubules compared with skeletal muscle
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Contracts forcefully at lower rate than skeletal muscle
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Cardiocytes: cardiac cells that have the ability to communicate
directly with adjacent cells via intercalated discs
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Intercalated discs enable rapid spread of action potentials
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Major Blood Vessels
• Arteries
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High-pressure vessels that deliver oxygen-rich blood to tissues
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Have walls containing smooth muscle & elastic fibers
• Arterioles
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Smaller arteries that constrict or relax to regulate blood flow
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Branch & form smaller vessels called metarterioles
• Capillaries
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Thin vessels that serve as site for nutrient/oxygen exchange
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2,000 to 3,000 per square mm of tissue
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Major Blood Vessels (cont’d)
• Venules
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Small veins joined to capillaries that drain blood toward heart
• Veins
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Vessels joined to venules that return blood to heart
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Low-pressure structures with extensible walls
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Storage site for blood when circulatory demands are low
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Approximately 68% of total blood supply circulates in veins at
rest.
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Circulatory System
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Regulation of the Heart
• Intrinsic Regulation of the Heart
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Heart can regulate its own rhythm
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Sinoatrial (SA) node: pacemaker of heart
• Spontaneously generates action potential
• Located in right atrium
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Wave of depolarization spreads across atria
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Atrioventricular (AV) node: delays wave of depolarization
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Bundle of His: arises from AV node & continues depolarization
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Wave spreads through ventricles via bundle branches & Purkinje
fibers
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Conductive System of the Heart
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Regulation of the Heart (cont’d)
• Extrinsic Regulation of the Heart
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Nervous & endocrine systems
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Cardiac center in medulla oblongata controls:
• Heart rate (HR)
• Vessel diameter
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Feedback from sensory motor centers in brain controls:
• HR
• Force of contraction
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Role of autonomic nervous system
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Blood Components
• Plasma
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55-60% of total blood volume
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Composition
• 90% is water
• 7% is plasma proteins
• 3% is nutrients & waste
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Blood Components (cont’d)
• Formed Elements
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40-45% of total blood volume
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Hematocrit: % of formed elements relative to total blood vol.
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Composition
• 99% red blood cells (RBCs)
• 1% white blood cells (WBCs) & platelets
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RBCs: transport oxygen bound to iron-containing protein
hemoglobin
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Platelets: small molecules required for blood clotting
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WBCs: critical to immune function
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Oxygen-Hemoglobin Dissociation Curve
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Partial Pressure of Oxygen and Carbon
Dioxide
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Blood Components (cont’d)
• Blood Flow
[at rest]
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Body contains about 5 L of blood
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Distribution
• 15-20% to skeletal muscle
• 25% to liver
• 20% to kidneys
• 10% to skin
• 14-15% to brain
• 10-12% to heart & other tissues
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Blood Components (cont’d)
• Blood Flow (cont’d)
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Blood flow to skeletal muscle increases to >80% of total flow to
meet metabolic demands
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Skeletal muscle contraction pumps venous blood back to heart
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Venous valves prevent backward flow of blood in veins
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Ischemia associated with RT is stimulus for muscle hypertrophy
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Tightly regulated
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Cardiovascular Function
• CV Variables
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Heart rate: frequency of heart beats per min
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Blood pressure: pressure in arteries after left ventricle
contracts
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Systolic blood pressure
• Pressure in left ventricle during systole
• Averages 120 mm Hg
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Diastolic blood pressure
• Peripheral resistance to flow during relaxation (diastole)
• Averages 80 mm Hg
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Cardiovascular Function (cont’d)
• CV Variables (cont’d)
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Stroke volume: - blood vol. ejected from left ventricle each
beat
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Cardiac output: HR x SV- total volume of blood pumped by
heart per min, usually about 5 L @ rest
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Cardiovascular Responses to Exercise
• Heart Rate (HR) Response
(p. 137)
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Increases during exercise from resting values to rates >195 bpm
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Upper limits for HR during exercise:
• 220 − person’s age in years = HR max
• Target range is based on % of HR max
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Magnitude of HR increase depends on muscle mass use, exercise
intensity, & degree of continuity of exercise
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HR increases linearly up to maximal
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Cardiovascular drift—
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Steady state HR—
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Cardiovascular Responses to Exercise
(cont’d)
• Stroke Volume (SV) Response
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Increases during exercise from resting values to rates >195 bpm
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Magnitude of SV increase determined by:
• Blood volume returning to heart
• Arterial pressure
• Ventricular contractility
• Distensibility
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Increases linearly up to about 40-60% of maximal exercise
capacity
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Cardiovascular Responses to Exercise
(cont’d)
• Cardiac Output (Qc)
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Is product of HR & SV
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Increases linearly during aerobic exercise
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May increase to 20-40 L min-1 depending on fitness level
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Increases over course of workout during RT
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The ability of the heart to change its force of contraction
and therefore stroke volume in response to changes in
venous return is called the Frank-Starling mechanism (or
Starling's Law of the heart).
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Cardiac Output Response to Aerobic
Exercise
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Cardiovascular Responses to Exercise
(cont’d)
• Blood Pressure (BP)
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Increases during exercise
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Increases during RT with increase proportional to effort
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Muscle mass activation plays a role
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Valsalva maneuver (p. 138): temporary breath holding which
increases intrathoracic pressure [the pressure developed in the
chest cavity] and intra-abdominal pressure, which increases SBP
and DBP.
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BP Response to 3 Sets of Leg Press
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Cardiovascular Responses to Exercise
(cont’d)
• Plasma Volume
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Decreases during exercise
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Decreases up to 20% during endurance exercise
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Reductions can impair endurance performance & VO2max
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Decreased by 7-14% immediately after resistance exercise
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Cardiovascular Responses to Exercise
(cont’d)
• Oxygen Consumption
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Increases proportionally during exercise in relation to:
• Intensity
• Muscle mass activation
• Degree of continuity
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Represented by Fick equation:
• VO2 = Qc × A-VO2 difference
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The A-VO2 Difference
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A-VO2 Difference
• The arteriovenous oxygen difference, is the difference in
the oxygen content of the blood between the arterial blood
and the venous blood. It is an indication of how
much oxygen is removed from the blood in capillaries as
the blood circulates in the body.
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Relationship Between Exercise Intensity
and Oxygen Consumption
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CV Terms
• Hematocrit: The % of formed elements relative to total blood
volume
• Hemoglobin: RBC’s transport oxygen primarily bound to the ironcontaining protein hemoglobin
• Bohr effect: is a physiological phenomenon first described in 1904
by the Danish physiologist Christian Bohr, stating that hemoglobin's
oxygen binding affinity (see Oxygen–hemoglobin dissociation curve) is
inversely related both to acidity and to the concentration of carbon
dioxide
• The Haldane effect is a property of hemoglobin first described by
John Scott Haldane. Deoxygenation of the blood increases its ability
to carry carbon dioxide; this property is the Haldane effect.
Conversely, oxygenated blood has a reduced capacity for carbon
dioxide.
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CV Terms
•
Frank–Starling Mechanism states that the stroke volume of the heart increases in
response to an increase in the volume of blood filling the heart (the end diastolic volume)
when all other factors remain constant. The increased volume of blood stretches the
ventricular wall, causing cardiac muscle to contract more forcefully (the so-called Frank–
Starling mechanisms)
•
In cardiovascular physiology, end-diastolic volume (EDV) is the volume of blood in the
right and/or left ventricle at end load or filling in (diastole) or the amount of blood in the
ventricles just before systole.
•
Cardiovascular drift refers to the increase in heart rate that occurs during prolonged
endurance exercise with little or no change in workload. During steady-state aerobic
exercise, heart rate should reflect the intensity of the work being performed. (due mainly
to dehydration)
•
Baroreceptors are sensors located in the blood vessels of all vertebrate animals. They
sense the blood pressure and relay the information to the brain, so that a proper blood
pressure can be maintained.
•
The Fick equation is used to determine the rate at which oxygen is being used during
physical activity. VO2 = Q x A-VO2 difference: it is the basis for how the body responds to
the demand of physical activity.
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Chronic Adaptations at Rest and During
Exercise
• Pressure Overload
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Results from rise in BP & intrathoracic pressure that accompany
exercise
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Can alter several CV variables positively over time
• Volume Overload
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Results from greater venous return & blood flow to heart during
exercise
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Aerobic exercise is superior due to higher level of continuity
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Leads to positive changes in several CV variables
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Increases cardiac chamber size
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Cardiac Dimensions
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Adaptations governed by Law of Laplace:
• Wall tension is proportional to pressure & size of radius of curvature
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Greater heart size is characterized by greater left ventricular cavity
(eccentric hypertrophy) & thickening of cardiac walls (concentric
hypertrophy)
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Aerobic training leads to improvements in cardiac function
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RT leads to changes in left-side cardiac muscularity
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RT elicits very small to no changes in left ventricular cavity size
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Cardiac Output (Qc)
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Qc response to exercise is augmented
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Aerobic training reduces resting HR
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Resting SV may slightly increase or not change during RT
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Resting HR may not change or slightly decrease during RT
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Heart Rate Response During Exercise
Before and After Training
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• VO2max
• VO2 max (also maximal oxygen consumption, maximal oxygen
uptake, peak oxygen uptake or maximal aerobic capacity) is the
maximum rate of oxygen consumption as measured during incremental
exercise, most typically on a motorized treadmill. Maximal oxygen
consumption reflects the aerobic physical fitness of the individual, and is an
important determinant of their endurance capacity during prolonged, submaximal exercise. The name is derived from V - volume, O2 - oxygen, max maximum.
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Gold standard of aerobic fitness
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Increases during training due to increases in SV, Qc, & small increase in A-VO2
difference
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Increases 10-30% with aerobic training during first 6 months
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Increases only minimally with anaerobic training
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• Women have V02 max values 15%-30% lower than men due to less
muscle mass, higher body fat, less testosterone, and lower
hemoglobin, age (V02 declines with age), body size, and genetics.
Genetics contributes 20%-50% of V02 max.
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Comparison of VO2max Data From Different
Male Athletes
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Pressure
(p. 144)
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Decreased systolic & diastolic BP with aerobic training
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Largest reductions seen in hypertensive people
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Not affected or reduced with RT
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Rate pressure product: (HR x SBP), is used to estimate
myocardial work and decreases after RT. This indicates that the
left ventricle performs less work over time and is a positive
adaptation.
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Volume
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Increased with aerobic training, mostly due to increase in plasma
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Plasma volume increases 12-20% within first few weeks of AT
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Endurance athletes have blood volumes about 35% greater than
untrained people
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RT may have limited effect
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Hypervolemia: Increased blood volume
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Lipids and Lipoproteins
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Major factors in CV health—lipids perform several critical functions
including energy storage and liberation, protection, insulation, providing
structure to cell membranes, vitamin transport and cellular signaling.
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Cholesterol serves as a precursor in steroid synthesis, cell membrane
structure, and bile and vitamin D synthesis.
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Include triglycerides, cholesterol, LDL-C, VLDL-C, HDL-C, & lipoprotein A
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Factors affecting: genetics, diet, stress, smoking, body weight, &
exercise
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Increased HDL-C, decrease in other lipids with AT
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RT has no or very small effects in improving lipid profiles
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Respiratory System
• Overview
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Essential for introducing oxygen into the body & removing CO2
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Respiration includes:
• Breathing (normally about 15 per min @ rest)
• Inspiration: breathing in
(less pressure in than outside of lungs)
• Expiration: breathing out
(more pressure in than outside of lungs)
• Pulmonary diffusion
• Oxygen transport
• Gas exchange
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The Human Respiratory System
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Respiratory System (cont’d)
• Lung Volumes and Capacities
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Tidal volume: volume of air inspired or expired every breath
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Inspiratory reserve volume: volume of air inspired after
normal tidal volume
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Expiratory reserve volume: volume of air expired after normal
tidal volume
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Residual volume: volume of air left in lungs after maximal
expiration
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Total lung capacity: volume of air in lungs after maximal
inspiration
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Respiratory System (cont’d)
• Lung Volumes and Capacities (cont’d)
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Forced vital capacity: maximal volume of air expired after maximal
inspiration
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Inspiratory capacity: maximal volume of air after tidal volume
expiration
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Functional residual capacity: volume of air in lungs after tidal volume
expiration
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Forced expiratory volume (FEV): volume of air maximally expired
forcefully in 1 second after maximal inhalation
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Maximum voluntary ventilation (MVV): maximum volume of air
breathed rapidly in 1 minute
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Minute ventilation (V): volume of air breathed per minute. At rest
typically 6 L min—12 breaths per min. During exercise 35-45 up to 60-70
in athletes.
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Respiratory System (cont’d)
• Control of Breathing
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Involuntary, but can be controlled voluntarily to some extent
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Neural & hormonal factors
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Circulatory (humoral factors)
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Rapid increase in ventilation during exercise, followed by slower
rise as exercise progresses
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Ventilatory threshold: the point at which V and CO2 rise
exponentially
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Overview of Respiratory Control
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Pulmonary Ventilation During Exercise
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Respiratory System (cont’d)
• Pulmonary Adaptations to Training
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Little change in lung volumes & capacities with AT
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Gender differences exist. Women have pulmonary structural differences
than age and height matched men that include smaller vital capacity and
maximal expiratory flow rates, reduced airway diameter, and a smaller
diffusion surface. Women have smaller airways and lung volumes, lower
resting maximal expiratory flow rates, and have higher metabolic costs
of breathing relative to men… p-148
• Ventilatory Muscle-Specific Training
(p 148)
–
Involves RT during respiration
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Used to increase respiratory function by improving strength & endurance
of inhalation muscles
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