cardiovascular system 2
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Cardiovascular system 2. Cardiovascular responses to exercise. Blood supply during rest and exercise. - PowerPoint PPT PresentationTRANSCRIPT
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Cardiovascular system 2
Cardiovascular responses to
exercise
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Blood supply during rest and exercise
• Blood pressure must be maintained at the correct level so that there is sufficient blood flow
around the body. Coordinated relaxation and constriction of some blood vessels maintains
pressure, but also redistributes blood flow to the active muscles during exercise.
• Cardiac output provides the most important indicator of the circulatory system’s
functional capacity to meet the demands for physical activity. As with any
pump, the rate of pumping (heart rate) and quantity of blood ejected with
every stroke (stroke volume)
• Cardiac output (L./min-1) = (heart rate x stroke volume) ÷ 1000• Cardiac output increases in proportion to the intensity of the exercise up to a maximum
attainable value. Increased cardiac output is a product of increased stroke volume (more
venous back flow to heart and increased contraction strength) and increased heart rate.
Stroke volume and heart rate increase during exercise
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Cardiac output in different populations
• With the ventilatory system
providing sufficient gas
exchange in healthy individuals,
the cardiovascular system is
crucial to maintain function and
to maintain homeostasis during
exercise, or to meet the
demands for physical activity.
• Factors such as gender, age
and fitness status influence the
total cardiac output during rest
and exercise.
Resting CO (L/min)
HR(b.)
Stroke V. (ml.)
Male 5.6 70 72
Female 4.1 76 55
Adult 5.3 73 73
Child 4.8 85 56
Trained 5.0 42 120
Untrained
4.9 64 76
Cardiac Output (CO) during rest
Why would stroke volume increase when HR is low?
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Cardiac output in different populations
Exercise CO (L./min)
HR (b.)
Stroke V. (ml)
Male 39.0 195 200
Female 31.2 195 160
Adult 35.1 195 180
Child 30.0 208 144
Trained 34.9 195 179
Untrained
22.0 195 113
Differences in stroke volume between men and women (with similar training) are mostly due to smaller body size. Stroke volume for women usually averages 25% below men’s values.
The difference in size and age influences the cardiac output of a child compared to an adult. A child has a 20% smaller stroke volume but a higher Maximum HR.
The difference in cardiac output between trained and untrained individuals relies solely on the stroke volume. Two factors probably interact as aerobic fitness improves- Increased vagal tone slows the
heart, allowing more time for ventricular filling ( Vagal tone)
- Enlarged ventricular volume and a more powerful myocardium eject a larger volume of blood with each systole
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• Average adult cardiac
output: ± 5 L.
(5000ml)
• Average adult
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Systolic and diastolic pressure during exercise
Systolic pressure the force exerted by blood on
arterial walls during ventricular contraction.
In resting healthy adult the pressure is 120mmHg,
this is the ideal balance for emptying and filling the
heart chambers
• During exercise the blood pressure changes and
is dependent upon intensity and type of exercise
• During high intensity isometric and anaerobic
exercise, both systolic and diastolic pressure rise
significantly due to increased resistance of the
blood vessels. This is a result of muscles
squeezing veins, increasing peripheral resistance
and an increase in intra-thoracic pressure due to
the contracting of the abdomen.
Diastolic pressure the force exerted by blood on
the arterial walls during ventricular relaxation.
• In resting adult the pressure is 80 mmHg. The
pressure lessens as the blood goes from arteries
to arterioles to capillaries. The pressure in the
venules and veins is low and consistent.
• During steady aerobic exercise involving large
muscle groups, the systolic pressure increases
as a result of an increased cardiac output, while
the diastolic pressure remains constant (or in
well trained athletes may even drop)
• High blood pressure can cause serious
complications to the heart, brain and kidneys,
whereas low pressure can result in insufficient
oxygen and other nutrients reaching the muscle
cells.
• The blood pressure is regulated by the
vasomotor control center. The redistribution is
controlled primarily by vasoconstriction and
vasodilatation
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VO2Max, Fick equation
The most commonly
used marker of an
individual’s aerobic
fitness is the
relationship between
cardiac output, oxygen
uptake, and difference
between the oxygen
content of arterial and
mixed-venous blood (a-
vO2 difference). This
principle was discovered
by German physiologist
Adolf Fick in 1870
Cardiac output (mL./min-1) =
[VO2(mL/min-1) / a-vO2(ml/dl blood-1)] x
100
Stroke volume = 71 ml/b
HR = 70 b
Cardiac Output = 5000 ml
aVO2 rest = 20ml/dl
mixed venous vO2 rest = 12-15 ml/dl
mixed vO2 max = 2 – 4 ml/dl
a-vO2 diff. at rest = 5 ml/dl
=> 75% O2 is “unused” bound to HbIn reality, this method is rarely used due to the difficulty of collecting and analyzing the gas concentrations. However, by using an assumed value for oxygen consumption, cardiac output can be closely approximated without the cumbersome and time-consuming oxygen consumption measurement
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VO2
Maximal aerobic and anaerobic capacities
• Oxygen consumption (uptake) is the amount
of oxygen a person consumes per unit of time
(usually a minute).
• The oxidation (burning) of fuel foods requires
a definite amount of oxygen per unit mass of
fuel. This amount can be measured indirectly
by collecting expired air and comparing it
with the composition of inspired air (how
much oxygen has been used and CO2
produced).
• At rest the oxygen uptake varies between 0.2
and 0.3 L./min-1
• (Based on that 1 L. of oxygen liberates 22kJ of
energy from glycogen, the BMR (basal
metabolic rate) converts to between 4.4 and
6.6 kJ. For a 60kg person the BMR would be
between 0.073 and 0.110 kJ per minute per
kg of body mass.)
• During exercise the total body oxygen uptake
increases proportionally to the intensity of the
exercise, until a maximal work rate is reached.
• Highest VO2 achieved is VO2max, this maximum
oxygen uptake is known also as aerobic power
• VO2max can therefore be quantitatively
represented as the maximum amount of oxygen
that a person can consume per minute during a
progressive exercise test to exhaustion. The
highest value represents the individual’s
maximal physiological capacity to transport and
use oxygen
• A mean value of VO2max for male students is
±3.5L/min and females ±2.7L./min
• Endurance athletes may reach between 4 and
6L./minVO2max depends on body mass as well as physical fitness, so often expressed in milliliters per kilogram of body mass per
minute (mL kg-1 min-1) so that comparisons can be made
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Factors affecting maximum aerobic power• Chemical ability of the muscular tissues
to use oxygen in breaking down fuels
• Combined ability of the cardiovascular
and the pulmonary systems to
transport oxygen to the muscular
system
VO2max decreases by about 10% per
decade with ageing, starting in the late
teens for women and mid-20’s for men.
Oxygen consumption as an indirect way of
measuring energy costs: a hypothetical
example
Net oxygen cost (oxygen consumed during exercise above
which is needed during rest)
0.3 L/min at rest
2.275 L/min (65% of VO2max in males @
3.5L/min)
20 min Jog x net oxygen cost = total net
oxygen cost
20 x 1.975 = 39.5 L.
1 liter of oxygen produces 22kJ of heat
energy in combination with food fuel:
22 x 39.5 = 869 kJ
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Exercising in a hot environmentCardiovascular drift
When exercising in a warm or neutral
environment for 15 min or more your
HR increases.
This increase in HR is to compensate
for the decrease in pulmonary
arterial pressure and reduced stroke
volume. To maintain cardiac output
at reduced pressure the heart rate
must be increased.
Under these circumstances, a person
usually must exercise at a lower
intensity than if cardiovascular drift
did not occur.
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Cardiovascular drift• The drop in venous return is a
result of the muscles demand for
more blood, however, in warm
environments the blood is also
shunted to the skin for
themoregulation (cooling) causing a
shift in fluids to skin tissue.
• The redistribution of blood plasma
and water loss through sweating
causes a reduced pulmonary
arterial pressure and decreased
stroke volume
Prevention / minimization
• Consistently replace fluids and electrolyte imbalance
• Acclimatize to environment• Weight training to
supplement cardiovascular efforts