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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 precapillary sphincters.

  • 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 precapillary sphincters.

  • 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 precapillary sphincters.

  • 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 precapillary sphincters.

  • 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 precapillary sphincters.

  • 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 precapillary sphincters.

  • 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.