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Cardiovascular System

Cardiovascular System. Cardiovascular Dynamics during Exercise McArdle, Katch and Katch, 4 th ed. Cardiovascular Dynamics During Exercise. Cardiac Output (Q): amount of blood pumped per minute. Q = Heart Rate x Stroke Volume. Fick Equation. VO 2 = HR x SV x a-v O 2 diff.

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Cardiovascular System

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

  2. Cardiovascular DynamicsDuring 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. • Increases @ higher intensity mainly due to increases in heart rate. • Untrained max 22 L/min • Trained max 35 L/min

  5. 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

  6. 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

  7. Stroke Volume & VO2max • 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

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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)

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

  15. 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.

  16. 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

  17. Oxygen Extraction • Increased arterio-venous oxygen extraction with increased work intensity • Fick Equation: • VO2 max = maximum cardiac output xmaximum a-v O2 diff • arterial O2- venous O2= extraction

  18. 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

  19. 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.

  20. 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.

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