Cardiovascular System

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Transcript Cardiovascular System

Cardiovascular System
Lecture 5 (part I-II)
September 28, 2005
October 5, 2005
EXS 558
Dr. Moran
Major Cardiovascular Functions
w Delivery (e.g., oxygen and nutrients)
w
w Transportation (e.g., hormones)
w
w Prevention (e.g., infection—immune function)
Just Some Facts
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For an average person the heart pumps
~5L/min

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With exercise programs the heart
(cardiac muscle) can adapt as well
Heart
Myocardium – Cardiac Muscle
w Thickness varies directly with stress placed on chamber
walls.
w
w With vigorous exercise, the left ventricle size increases.
w
Heart Function

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At rest, the heart spends most of its time filling (60%
- diastole) than expelling (40% - systole)
Following systole, the AV valves rapidly open and fill
the ventricles up to 70-80%
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The middle 1/3 of diastole has little filling and is known as
diastasis
Stroke Volume & Cardiac Output
Stroke Volume (SV)
w Volume of blood pumped per contraction
w
w End-systolic volume (ESV)—volume of blood in ventricle after contraction
w SV = EDV – ESV
.
Cardiac Output (Q)
w
.
w Q = HR  SV
w Varies considerably between people
wTrained athletes have lower resting HR and higher SV (Table 4.1)
Ejection Fraction
w Proportion of blood pumped out of the left ventricle each
beat
w
w Averages 60% at rest
w
Calculation of SV, EF, and Q
Vascular System
w Arteries
w Arterioles
w Capillaries
w
wCreates a large surface area ideal for gas exchange
w Venules
w Veins
Blood Flow controlled by the autonomic nervous system
During REST 
During EXERCISE 
Muscle Pump
w Blood distribution matched to overall
metabolic demands
w Autoregulation—
w Extrinsic neural control—sympathetic
nerves within walls of vessels are stimulated
causing vessels to constrict
w
Blood Pressure
w Systolic blood pressure (SBP: s=squeeze) is the highest
pressure and diastolic blood pressure (DBP) is the lowest
pressure
w
w MAP = DBP + [0.333  (SBP – DBP)]
w
Review
Vascular System
w Blood returns to the heart with the help of
breathing, the muscle pump, and valves in
the veins.
w
w Autoregulation controls blood flow by
vasodilation in response to local chemical
changes in an area.
(continued)
Review
(continued)
w Extrinsic neural factors control blood flow
primarily by vasoconstriction.
w
w Mean arterial pressure (MAP) is the
average pressure on the arterial walls.
Blood Functions
w Transports gas, nutrients, and wastes
w
w Buffers and balances acid base
Blood Volume
Composition
Blood Formed Elements & Hematocrit
Blood formed elements
w White blood cells—protect body from disease organisms
w
w Red blood cells—carry oxygen to tissues with the help of hemoglobin
Hematocrit
w Ratio of formed elements to the total blood volume
Oxygen Transport

Oxygen transported in blood combined
to hemoglobin (98%) or dissolved in
plasma (2%)

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Oxygen saturation affected by:
1.)
2.)
3.)
Bohr Effect
Erythropoietin (EPO)

Protein hormone produced by kidney


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Medically used to treat anemia (chronic
kidney failure)
Increase oxygen carrying capacity of
blood

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“Sludging” of blood VERY dangerous
Cardiovascular Response to Acute Exercise
w Heart rate (HR) increases as exercise intensity increases
up to maximal heart rate.
.
w
w Increases
. in HR and SV during exercise cause cardiac
output (Q) to increase.
w
w All result in allowing the body to efficiently meet the
increased demands placed on it.
Heart Rate During Exercise

Initial increase b/c of withdrawal of
parasympathetic input
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Feedback from peripheral mechanical and
chemical receptors
Stroke Volume During Exercise

Stroke volume changes are because of
an increase in EDV
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Suctioning Mechanism:

Frank-Starling Mechanism: with a greater volume of
blood returning to the heart the ventricles become stretched
and respond with a more powerful contraction
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Cardiac Drift
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Increase in HR and decrease in SV
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Reason: greater % of blood flowing to skin to
dissipate heat  lower EDV causes an increased HR
Arteriovenous Oxygen Difference

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Rest  25% of O2 extracted from blood
Exercise  up to 75% of O2 extracted from
blood (used by exercising muscles)
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Fick Equation:
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Cardiovascular Response to Training
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Cardiac Output
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Heart Rate
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Cardiac Morphology
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Table 4.2 (p. 52)
Cardiac Output

VO2 max increases due to
1.) Improved oxygen extraction

2.) Increased cardiac output
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3.) Max HR NOT affected from training
Stroke Volume

Endurance-trained athletes have 60%
greater SV
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Enlarged left ventricular chamber
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(eccentric hypertrophy)
Stroke Volume & Training
Changes in EDV, ESV, EF
Heart Rate

Decrease in resting HR

 Highly trained endurance
athletes may have resting
heart rates of 30 to 40
beats/min
Heart Rate Recovery
w
w With training, heart rate returns to resting level more
quickly after exercise
w
w Conditions such as altitude or heat can affect it
w
Heart Rate Recovery
(continued)
Blood Pressure

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In hypertensive individuals, endurance exercise
reduces both systolic and diastolic blood pressure
(3-5x week; 30 min)
Conflicting results from the result of resistance
training
w
Blood Flow Increases With Training
w Increased capillarization of trained muscles (higher
capillary-to-fiber ratio)
w
w More effective blood redistribution—blood goes where
it is needed
w
Blood Volume and Training
w Endurance training, especially intense
training, increases blood volume.
w
w Red blood cell volume increases, but
increase in plasma volume is higher; thus,
hematocrit decreases.
w
w Changes in plasma volume are highly
.
correlated with changes in SV and VO2max.
Blood Volume and Training
Cardiac Morphology

Law of LaPlace: ventricular wall pressure is proportional to pressure
and the radius of curvature (Ford 1976)
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Adaptations from Exercise Programs
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Endurance Athletes
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Greater than normal left ventricular internal diameter
Resistance Athletes
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Left ventricular mass 45% greater than age-matched sedentary
controls
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(Fleck 1988)
Differences in Heart Size
Intraventricular septal thickness
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The effect of acute aerobic exercise on stress
related blood pressure responses: A
systematic review and meta-analysis
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Hamer et al. (2005)
Left Ventricular Mass Index and Sports: the
influence of different sports activities and
arterial blood pressure
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Cubero et al. (2000)
Echocardiograph (ultrasound)
Research Design
Cross Sectional
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collected all at the same time (“snapshot”)
Randomized Controlled Trial
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Two groups
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Treatment group  receives the treatment under
investigation,
Control group 
VO2 Max Testing
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Depends on testing protocol
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Triathletes

cycling ergometer protocol will be 3-6% less
than that seen in treadmill running, while
swimming is 13-18% less (O'Toole and
Douglas, 1995)