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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

Cardiovascular System

Cardiovascular Dynamics during Exercise

McArdle, Katch and Katch, 4th ed.

cardiovascular dynamics during exercise
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
resting cardiac output
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
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
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

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


Left Ventricular End Systolic Volume

stroke volume vo 2 max
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
stroke volume increases
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
stroke volume increases1
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
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
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
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
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)
distribution during exercise
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
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
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
increasing oxygen consumption during exercise
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
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
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.