Cardiovascular system 2
Cardiovascular responses to exercise
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
Cardiac output in different populations
• With the ventilatory system
Resting CO
(L/min)
HR
(b.)
Stroke
V. (ml.)
providing sufficient gas exchange
in healthy individuals, the
Male
5.6
70
72
cardiovascular system is crucial
Female
4.1
76
55
to maintain function and to
Adult
5.3
73
73
maintain homeostasis during
Child
4.8
85
56
Trained
5.0
42
120
Untrained 4.9
64
76
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.
Cardiac Output (CO) during rest
Cardiac output in different populations
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
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
• Average adult cardiac
output: ± 5 L. (5000ml)
• Average adult
Systolic and diastolic pressure during exercise
Systolic pressure the force exerted by blood on
Diastolic pressure the force exerted by blood on the
arterial walls during ventricular contraction.
arterial walls during ventricular relaxation.
In resting healthy adult the pressure is 120mmHg, this is
•
In resting adult the pressure is 80 mmHg. The
the ideal balance for emptying and filling the heart
pressure lessens as the blood goes from arteries to
chambers
arterioles to capillaries. The pressure in the venules
•
and veins is low and consistent.
During exercise the blood pressure changes and is
dependent upon intensity and type of exercise
•
•
muscle groups, the systolic pressure increases as a
During high intensity isometric and anaerobic
result of an increased cardiac output, while the
exercise, both systolic and diastolic pressure rise
diastolic pressure remains constant (or in well
significantly due to increased resistance of the
trained athletes may even drop)
blood vessels. This is a result of muscles squeezing
veins, increasing peripheral resistance and an
During steady aerobic exercise involving large
•
High blood pressure can cause serious
increase in intra-thoracic pressure due to the
complications to the heart, brain and kidneys,
contracting of the abdomen.
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
VO2Max, Fick equation
Cardiac output (mL./min-1) =
The most commonly used
marker of an individual’s
[VO2(mL/min-1) / a-vO2(ml/dl blood-1)] x 100
Stroke volume = 71 ml/b
aerobic fitness is the
HR = 70 b
relationship between
Cardiac Output = 5000 ml
cardiac output, oxygen
aVO2 rest = 20ml/dl
uptake, and difference
mixed venous vO2 rest = 12-15 ml/dl
between the oxygen
content of arterial and
mixed-venous blood (a-vO2
difference). This principle
was discovered by German
physiologist Adolf Fick in
1870
mixed vO2 max = 2 – 4 ml/dl
a-vO2 diff. at rest = 5 ml/dl
=> 75% O2 is “unused” bound to Hb
In 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
VO2
Maximal aerobic and anaerobic capacities
•
•
increases proportionally to the intensity of the
Oxygen consumption (uptake) is the amount of
exercise, until a maximal work rate is reached.
oxygen a person consumes per unit of time (usually
a minute).
•
•
Highest VO2 achieved is VO2max, this maximum
oxygen uptake is known also as aerobic power
•
VO2max can therefore be quantitatively
This amount can be measured indirectly by
represented as the maximum amount of oxygen
collecting expired air and comparing it with the
that a person can consume per minute during a
composition of inspired air (how much oxygen has
progressive exercise test to exhaustion. The highest
been used and CO2 produced).
value represents the individual’s maximal
physiological capacity to transport and use oxygen
At rest the oxygen uptake varies between 0.2 and
0.3 L./min-1
•
•
The oxidation (burning) of fuel foods requires a
definite amount of oxygen per unit mass of fuel.
During exercise the total body oxygen uptake
•
±3.5L/min and females ±2.7L./min
(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.)
A mean value of VO2max for male students is
•
Endurance athletes may reach between 4 and
6L./min
VO2max 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
Factors affecting maximum aerobic power
•
Chemical ability of the muscular tissues to
use oxygen in breaking down fuels
•

Combined ability of the cardiovascular and
Oxygen consumption as an indirect way of
the pulmonary systems to transport oxygen
measuring energy costs: a hypothetical example
to the muscular system
Net oxygen cost (oxygen consumed during exercise above which
VO2max decreases by about 10% per
is needed during rest)
decade with ageing, starting in the late
0.3 L/min at rest
teens for women and mid-20’s for men.
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
Exercising in a hot environment
Cardiovascular 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.
Cardiovascular drift
Prevention / minimization
•
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
• Consistently replace fluids and
electrolyte imbalance
• Acclimatize to environment
• Weight training to supplement
cardiovascular efforts