1. Cardiovascular System
Cardiovascular Dynamics during Exercise
McArdle, Katch and Katch, 4th ed.

2. 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

3. 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.

4. Exercise Cardiac Output
Blood flow from heart increases in direct proportion to exercise intensity.
higher intensity mainly due to increases in heart rate.
Untrained max 22 L/min
Trained max 35 L/min

6. 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

7. 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

8. 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

9. Stroke Volume Increases
SV increases due to
Enhanced filling increases EDV (preload)
Greater contractility from neurohormonal influence- greater systolic emptying
Expanded blood volume and decreased afterload

10. 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

11. 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.

12. 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.

13. 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 minutes.

14. 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)
Splanchnic syn. visceral. Visceral pleural viscus. Viscus an organ of the digestive, respiratory, urogenital, and endocrine systems, as well as the spleen, heart, and great vessels; [L. the soft parts, internal organs].

15. Shunting of blood via constricting arterioles and closing precapillary sphincters.

16. 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.

17. 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

18. Oxygen Extraction
VO2
(ml/min) SV
(L/min) HR
(bpm)
a-v O2
(ml/L)
Untrained
Rest
300 ml
.075 82
48.8
Max
3100 ml
.112
200
138
Trained
.105 58
49.3
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
Increased arterial capacity to carry oxygen because of hemoconcentration

19. 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

20. 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.

21. Illustration References
McArdle, William D., Frank I. Katch, and Victor L. Katch Essentials of Exercise Physiology 3rd ed. Image Collection. Lippincott Williams & Wilkins.
Plowman, Sharon A. and Denise L. Smith Digital Image Archive for Exercise Physiology. Allyn & Bacon.