Cardiovascular System
Cardiovascular Dynamics during Exercise
McArdle, Katch and Katch, 4th ed.
Cardiovascular Dynamics
During Exercise
Cardiac Output (Q): amount of blood pumped
per minute.
• Q = Heart Rate x Stroke Volume.
• Fick Equation. VO2 = HR x SV x a-v O2
diff
Resting Cardiac Output
• Cardiac Output = 5 L/min trained &
untrained
• Untrained = 70 bpm x 71 ml = 5000
ml/min
• Trained = 50 bpm x 100 ml = 5000
ml/min
• Larger stroke volumes after training due to
increased vagal tone & strengthen heart.
Exercise Cardiac Output
• Blood flow from heart
increases in direct
proportion to exercise
intensity.
• Increases @ higher
intensity mainly due to
increases in heart rate.
• Untrained max 22 L/min
• Trained max 35 L/min
Increased Cardiac Output
• Venous return must increase
• Venoconstriction - reduces capacity to hold
large volume of blood
• Muscle pump - active muscles squeeze
veins forcing blood back towards heart
• Respiratory pump - inspiration lowers
thoracic pressure
Stroke Volume
Stroke Volume: amount
of blood pumped each
cardiac cycle.
• Increased diastolic
filling before systole
occurs through any
factor that increases
venous return
(preload).
Left Ventricular End Diastolic Volume
Minus
Left Ventricular End Systolic Volume
Stroke Volume & VO2 max
• SV increases
progressively with
intensity up to about
50% max VO2
• After reach 50% max
VO2, Q increases
because of heart rate
• Well trained endurance
athletes’ SV rises to
maximal levels
Stroke Volume Increases
SV increases due to
• Enhanced filling
increases EDV (preload)
• Greater contractility from
neurohormonal influencegreater systolic emptying
• Expanded blood volume
and decreased afterload
Stroke Volume Increases
• Increased EDV
• fuller ventricle = greater
stroke volume
• Frank-Starling’s
mechanism
• Decreased ESV
• catecholamines increase
contractility via increased
Ca2+
• Afterload - pressure required
to open the aortic semilunar
valve
• decreases during exercise
due to vasodilation
Cardiovascular Drift
• Prolonged exercise in
warm environment
causes dehydration
• Dehydration reduces
blood volume
• Reduced blood volume
decreases stroke
volume
• Heart rate rises to
maintain required
cardiac output.
Exercise Heart Rate
• Heart rate and VO2 are
linearly related in
trained and untrained
throughout major
portion of exercise
range.
• Endurance training
reduces HR at any
given submaximal
workload due to ↑ SV.
Heart Rate and Oxygen
Consumption
• In healthy individuals, heart rate increases
linearly with exercise load or oxygen uptake
and plateaus just before maximal oxygen
consumption.
• If exercise load is held constant, below
lactate threshold, steady state is reached in
about 2 - 3 minutes.
Distribution of Cardiac Output
• Blood flow to tissues is proportional to
metabolic activity
• Muscle tissue receives about same amount
blood as kidneys at rest
• During intense exercise, significant blood is
shunted from kidneys & splanchnic regions
(areas that temporarily tolerate reduced flow)
Shunting of blood via constricting arterioles and closing precapillary sphincters.
Distribution during Exercise
• Blood flow to skin
increases during light
and moderate exercise
• During intense
exercise, nearly 85%
blood shunted to
muscles. Cutaneous
blood flow reduced
even when hot.
Cardiac Output and Oxygen
Transport
• Maximal cardiac output
relates to maximal
oxygen uptake in 6:1
ratio.
• Females have a larger
cardiac output compared
to males at any level of
submaximal VO2 – most
likely due to 10% lower
[hemoglobin].
• Children have small SV
Oxygen Extraction
VO2
SV
HR
a-v O2
(ml/min)
(L/min)
(bpm)
(ml/L)
Untrained
Rest
300 ml
.075
82
48.8
Max
3100 ml
.112
200
138
Trained
Rest
300 ml
.105
58
49.3
Max
3440 ml
.126
192
140.5
• Increased arterio-venous oxygen extraction with
increased work intensity
• Fick Equation:
• VO2 max = maximum cardiac output x maximum a-v O2 diff
• arterial O2 - venous O2 = extraction
Increasing Oxygen
Consumption During Exercise
• O2 extraction depends upon O2 content of blood
& removal rate by tissues
• O2 removal depends upon:
•
•
•
•
capillary density; improves with aerobic training.
myoglobin content; improves with aerobic training.
mitochondria number; improves with aerobic trg.
oxidative capacity of mitochondria; improves with
aerobic training.
• muscle fiber type
• PO2 gradient from capillaries to tissue
Upper-Body Exercise
• Highest VO2 attained during upper body exercise ranges
between 70%-80% of VO2 max in lower body exercise.
• Max HR and pulmonary ventilation probably less because
smaller muscle mass.
• Produces greater physiological strain (SBP) for any level
VO2 than lower-body exercise.
Illustration References
• McArdle, William D., Frank I. Katch, and
Victor L. Katch. 2003. Essentials of
Exercise Physiology 3rd ed. Image
Collection. Lippincott Williams & Wilkins.
• Plowman, Sharon A. and Denise L. Smith.
1998. Digital Image Archive for Exercise
Physiology. Allyn & Bacon.