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

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

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 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 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: 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

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

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 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 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 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 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 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].

Shunting of blood via constricting arterioles and closing precapillary sphincters.

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 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 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

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 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 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.