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Cardiovascular Response to Acute Exercise

Cardiovascular Response to Acute Exercise. Chapter 7. Goal. To meet the increased demands needed to perform exercise Heart rate (HR)- Good indicator of intensity of exercise Stroke volume (SV) Cardiac output (Q) Blood pressure (BP) Blood flow Blood. RHR. Typically 60-80 bpm

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Cardiovascular Response to Acute Exercise

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  1. Cardiovascular Response to Acute Exercise Chapter 7

  2. Goal • To meet the increased demands needed to perform exercise • Heart rate (HR)- Good indicator of intensity of exercise • Stroke volume (SV) • Cardiac output (Q) • Blood pressure (BP) • Blood flow • Blood

  3. RHR • Typically 60-80 bpm • Preexercise HR usually increases above normal resting values-anticipatory response • Not reliable estimate of RHR • Can be affected by environmental factors such as temperature and altitude

  4. Steady-State HR • HR increases until it reaches a plateau, when rate of work is held constant at sub-maximal intensity • Optimal HR for meeting the circulatory demands at that rate of work • The lower the steady-state HR at each exercise intensity, the greater the cardiorespiratory fitness

  5. Maximum HR • Highest HR value achieved in an all-out effort to the point of exhaustion • Remains constant from day to day but decreases with age • Approximated by: HRmax= 220-age or HRmax = 208- (0.7 x age)

  6. Stroke Volume • Major determinant of cardiorespiratory endurance capacity at near-maximal and maximal exercise intensities • Determined by: • Volume of venous blood returned to the heart • Ventricular distensibility • Ventricular contractility • Aortic or pulmonary artery pressure

  7. Stroke Volume • May increase with increasing rates of work up to intensity between 40% and 60% of maximal capacity • May continue to increase up through maximal exercise intensities • Magnitude of changes in SV depends on position of body before and during exercise

  8. Stroke Volume

  9. Stroke Volume in Cyclists

  10. Stroke Volume Increases Explained • Increased venous return (preload)-extent to which ventricle fills with blood and stretches and subsequently contracts more forcefully: Frank-Starling mechanism • Increased ventricular contractility from neural stimulation (without end-diastolic volume increases) • Decreased total peripheral resistance due to vasodilation of blood vessels in exercising skeletal muscle

  11. The Muscle Pump • During exercise the muscle pump functions to return blood to the heart, or increase venous return; the thoracic pump serves the same function, i.e., to compress veins in the chest and abdomen to increase venous return to the heart

  12. Changes in Q and SV

  13. Cardiac Output • Resting Q is about 5.0 L/min, but does vary with size of person • Linear relationship between Q and exercise intensity up to 20-40 L/min • When level of exercise exceeds 40% to 60% of maximal exercise capacity, SV either plateaus or increases at a much slower rate • Further increases in Q due to increases in HR

  14. Cardiac Output and Intensity

  15. Changes in HR, SV, and Q with Changes in Posture and Exercise

  16. Blood Pressure • Cardiovascular Endurance Exercise: • SBP increase in direct proportion to increase in exercise intensity • DBP does not change significantly (may even decrease) • Therefore little change in MAP • Resistance Exercise: • Can exaggerate BP as high as 480/350 bpm • Some BP increases can be attributed to the Valsalva maneuver

  17. Blood Pressure Response to Exercise Note the peripheral wave amplification Rowell, Human Circulation, 1986

  18. Blood Pressure Response to Exercise McArdle et al., Exercise Physiology, Lippincott, 2001

  19. Blood Pressure Responses

  20. Blood Flow • Acute changes in Q and BP during exercise allow for increased total blood flow to the body. • Blood flow patterns change in transition from rest to exercise • Through SNS, blood is redirected to active areas during exercise

  21. Distribution of Q at Rest and During Exercise Relative to total blood volume Absolute

  22. Cardiovascular Drift • With prolonged aerobic exercise or aerobic exercise in the heat, at constant exercise intensity: • Decrease in and arterial blood pressure • HR increases, allows maintenance of Q

  23. Cardiovascular Drift • Progressive increase in the amount of Q directed to the vasodilated skin to facilitate heat loss and attenuate the increase of body core temperature • More blood in skin for purpose of cooling the body • Less blood available to return to heart-decreases preload

  24. Cardiovascular Drift

  25. Arterial-Venous Oxygen Difference • The extent to which oxygen is extracted from the blood as it passes through the body • Calculated as the difference between the oxygen content of arterial blood and right atrial blood • Difference increases with increasing exercise intensity, with more oxygen being extracted from the blood

  26. Changes in (a-v)O2

  27. Blood Plasma Volume • With onset of exercise, <10% loss of plasma from the blood to interstitial fluid space • With increases in sweating, additional plasma volume losses may occur • Excessive loss can lead to dehydration, as well as increase blood viscosity, which can impede blood flow and limit O2 transport and impair performance

  28. Hemoconcentration • Results from a reduction in plasma volume • The fluid portion of the blood is reduced, and the cellular and protein portions represent a larger fraction of the total blood volume • Increases RBC concentration up to 20%-25%increases the number of RBCs per unit of blood

  29. Hemoconcentration

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