Cardiovascular SystemCardiovascular System

Cardiovascular Dynamics during Exercise

McArdle, Katch and Katch, 4th ed.

Cardiovascular DynamicsCardiovascular DynamicsDuring ExerciseDuring 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 OutputResting 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 OutputExercise 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 OutputIncreased 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 VolumeStroke 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

MinusLeft Ventricular End Systolic Volume

Stroke Volume & VOStroke Volume & VO22 maxmax

• 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 IncreasesStroke 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 IncreasesStroke 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 DriftCardiovascular 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 RateExercise 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 Heart Rate and Oxygen ConsumptionConsumption

• 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 OutputDistribution 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 ExerciseDistribution 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 Cardiac Output and Oxygen TransportTransport

• 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 ExtractionOxygen ExtractionVO2

(ml/min)

SV(L/min)

HR(bpm)

a-v O2

(ml/L)

UntrainedRest

300 ml .075 82 48.8

Max 3100 ml .112 200 138

TrainedRest

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 Increasing Oxygen Consumption During ExerciseConsumption 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 ExerciseUpper-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 ReferencesIllustration 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.