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Cardio, #111
Monday, Feb 10, 10:00am
Dr. Smith
Deana Lanham for Melissa Pennington
Page 1 of 5
Exercise Physiology II
Factors That Control Cardiovascular Changes (NOT in PP)
1. Central Command
a. At the very beginning, and even a little before exercise, you have signals that originate
from the motor cortex of your brain. Central command sends signals to your body
(muscles) that exercise is about to begin.
b. Central Command is particularly important in regulating heart rate.
c. Parallel signals are sent to the brainstem as an anticipatory response.
d. Before exercising, you have already started some of the cardiovascular responses. This is
referred to as a feed-forward mechanism (you are not responsible for this concept).
e. As you increase  workload, the central command activity increases  as well.
2. Proprioceptive Stretch Receptors
a. Stretch receptors from your joints send afferent anticipatory signals to the brainstem.
3. Muscle Receptors
a. Metaboreceptors and muscle mechanical receptors send afferent feedback from the
muscle to the brainstem.
Cardiac Function During Exercise (Pressure-Volume Loop)
1. Preload increases some, but does not cause an
increase in afterload. This is because the low systemic
vascular resistance has a greater effect on afterload than
does preload.
LV
2. Contractility increases.
Pressure
3. Afterload decreases.
4. Aortic diastolic pressures decrease.
5. Rate of ejection increases.
6. Vascular Resistance decreases.
LV volume
7. Stroke volume is increasing.
8. External work of the heart has increased.
9. This is not shown here, but heart rate is also increasing. The more it beats, the more energy is
being consumed, and the harder the heart is working.
Cardiac Cycle During Exercise
1. Resting heart rate here is 60 bpm.
2. The exercise heart rate in this diagram is 150 bpm. The R-R interval is now 400 msec.
3. During Exercise:
a. AV nodal conduction velocity increases during exercise, and the AV nodal delay
decreases.
b. Shortened Q-T Interval & R-R interval.
c. The rate of depolarization and repolarization increases. You will have a faster reuptake
of calcium by the SR.
d. The increase in isovolumic contraction is a marker of increased contractility.
e. Diastolic pressure is decreased a little. Systolic pressures go up.
4. When the sympathetic system is turned on:
a. ESV decreases .
b. EDV increases .
Cardio, #111
Monday, Feb 10, 10:00am
Dr. Smith
Deana Lanham for Melissa Pennington
Page 2 of 5
c. Both lead to a greater
stroke volume and
rate of ejection.
d. Afterload decreases,
which leads to an
increase in the rate of
ejection.
e. All variables (preload,
afterload, etc.) are
depicted in this
diagram and you
should know this
diagram well. It
illustrates very
important concepts.
LV Volume During Exercise
1. As you increase workload, you increase contractility, increase EDV, and decrease ESV.
2. EDV plateaus because of progressively reduced filling times. The decrease in filling time leads
to a slight reduction in EDV at the end. The exact shape is NOT critical, but you should
understand that stroke volume tends to plateau. This is highly controversial and you are not
responsible for this.
SVR Responses to Exercise
1. Systemic vascular resistance and workload are indirectly related.
2. As you increase your metabolism, you get more vasodilation, which causes SVR to decrease.
3. Some arbitrary calculations for an example:
Rest
Skeletal
Muscle
Systemic
Variables
Exercise
Q
P
R
1
100
100
5
100
20
Skeletal
Muscle
Systemic
Variables
Q
P
R
19
125
7
25
125
5
4. With exercise you have more than a 90% decrease in resistance. The resistance for skeletal
muscle went from 100 to 7. Skeletal muscle went through profound vasodilation.
5. Systemic vascular resistance is still lower even with the incredible drop in resistance for skeletal
muscle. The skeletal muscle can also account for this SVR drop.
Cardio, #111
Monday, Feb 10, 10:00am
Dr. Smith
Deana Lanham for Melissa Pennington
Page 3 of 5
Pressures
Cardiac Function During Exercise
1. Systolic pressures will go up unless you have a failing heart.
2. Mean blood pressure goes up slightly and
progressively.
3. Diastolic pressures decrease some, especially at
S
higher work loads. At moderate work loads
diastolic pressure usually does not change much.
M
4. With stress tests you can detect early signs of
D
vascular disease, which is evident in the change in
diastolic pressure. If diastolic pressures do not go
down, then this is not healthy and the person is not
getting the proper vasodilation that he/she needs.
Workload (VO2)
Oxygen Extraction During Exercise (A-V O2 Difference)
1. Oxygen extraction is directly related to workload. There is no evidence of a plateau.
2. As you exercise you increase oxygen extraction up to a maximum.
3. We don’t know what happens if you increase this above the maximum, but this is not important
and will not be tested.
Blood O2 Content During Graded Exercise
1. Arterial oxygen content remains constant during
Arterial
increasing workloads.
Oxygen
2. There is less oxygen content in the veins as you
Content
exercise. The veins are where the extraction of
oxygen takes place.
3. The venous oxygen content will never go down
Venous
to zero.
4. Training and exercise can improve the rate of
Workload
oxygen extraction.
5. Role of Lungs:
a. The role of the lungs is to load hemoglobin with oxygen rapidly and effectively. It has
nothing to do with the body’s extraction of that oxygen. In a healthy person, the lungs
are not a limiting factor.
b. However, in disease processes, such as pulmonary edema, the lungs cannot exchange as
much oxygen. In this state, the lungs are the limiting factor.
Ventilation
threshold (breakpoint)
Ventilation
Ventilatory Threshold
1. This is also known as the “anaerobic threshold” or
Dr. Smith prefers “lactate threshold.”
2. Definition: Exercise workload at which ventilation
and lactate accumulation begin to increase at
progressively greater rates.
3. Ventilation increases in a linear fashion up to this
threshold point. Then the decrease in pH leads to an
increased drive to breathe, so here ventilation goes
up at a much faster rate.
Plasma
Lactate
Workload (VO2)
Cardio, #111
Monday, Feb 10, 10:00am
Dr. Smith
Deana Lanham for Melissa Pennington
Page 4 of 5
4. Until this point, your plasma lactate (added onto graph) has not increased much. However, your
central command can sense a progressive decrease in pH, which adds to your drive to breathe.
This point is what defines your ventilation threshold.
5. Remember that the decrease in pH is not due to a high PO2, but rather from the acidic
lactate.
6. What happens to the following at workloads higher than the ventilatory threshold?
a. PCO2 
i. When you are working hard, you are breathing harder and in a state of
hyperventilation. You are breathing off your PCO2 at faster rates at it decreases.
b. VCO2 
c. Plasma lactate 
d. Muscle pH 
e. Plasma pH 
Endurance Training Effects
1. Heart Rate
a. Reduced at rest.
i. HR alone does not show you if a person is athletic or not.
b. Reduced at any given submaximal absolute work. This is the most important concept
and you will use it in clinical situations. This is a good reason for cardio rehab.
c. Similar at any given relative workload (% of max).
d. Similar maximal heart rate (~ 220 -- age).
2. Stroke Volume
a. Increased at rest.
b. Increased at all workloads.
c. This tends to plateau as well.
3. Cardiac Output
a. Similar at rest and at any given submaximal workload.
b. Higher workloads (above the untrained maximum) can be reached. Q increases
progressively up to maximum.
4. Systemic Vascular Resistance
a. Similar at rest.
b. Greater decrease at progressive workloads.
c. Much less at maximal workloads.
5. Distribution of Cardiac Output
a. The greater the increases in Q at max go to the skeletal muscle and the heart. Most goes
to the skeletal muscle.
6. Blood Volume
a. Up to 20% expansion of plasma volume.
7. Cardiac Chamber Size
a. Increased ventricular chamber size
8. Cardiac Hypertrophy
a. Eccentric hypertrophy: proportional increase in chamber to increase in mass (wall
thickness)
b. Concentric Hypertrophy: mostly an increase in mass (e.g. HTN). This is NOT
proportional.
Cardio, #111
Monday, Feb 10, 10:00am
Dr. Smith
Deana Lanham for Melissa Pennington
Page 5 of 5
9. Cardiac work will decrease.
10. Capillary Density
a. Increased density
b. More capillaries are produced in skeletal muscle.
c. The diffusion distance decreases, O2 delivery and extraction are much better.
11. Graphs
a. Trained individuals will be able to achieve a higher VO2 max.
b. At a trained state your heart rate is lower. However, relative to the maximum your heart
rate will remain the same.
70% max
HR
Training effect
trained
70% max
Q
Untrained
Maximum
VO2
VO2
Exercise-Induced Cardioprotection (NOT in PP)
1. Ischemia of course causes damage, but injury can also occur upon reperfusion of the vessel (when
the vessel opens back up after ischemia). This is referred to as ischemia reperfusion injury.
2. When you are ischemic, the cardiac function becomes impaired and the heart is unable to
generate as much contractile force.
3. During reperfusion, it remains depressed and in some cases may go even lower.
4. With a trained individual, you don’t experience as much damage and he/she has a profoundly
reduced impairment. This is referred to as exercise-induced cardioprotection.
5. This is gained with exercise, but it is also lost when you stop exercising.
Trained
LVSP
Untrained
Control
Ischemia
Reperfusion