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Circulatory Adaptations to Exercise

Chapter 9. Circulatory Adaptations to Exercise. The Cardiovascular System. Components Circulatory system Pulmonary system Purposes Transport O 2 to tissues and removal of other products (“waste”) Transport of nutrients to tissues Regulation of body temperature. The Circulatory System.

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Circulatory Adaptations to Exercise

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  1. Chapter 9 Circulatory Adaptations to Exercise

  2. The Cardiovascular System • Components • Circulatory system • Pulmonary system • Purposes • Transport O2 to tissues and removal of other products (“waste”) • Transport of nutrients to tissues • Regulation of body temperature

  3. The Circulatory System • Heart • Pumps blood • Arteries and arterioles • Carry blood away from the heart • Capillaries • Exchange of materials with tissues • Veins and venules • Carry blood toward the heart

  4. Structure of the Heart

  5. Systemic circuit Left side of the heart Pumps oxygenated blood to the whole body via arteries Returns “deoxygenated” blood to the right heart via veins Pulmonary circuit Right side of the heart Pumps “deoxygen-ated” blood to the lungs via pulmonary arteries Returns oxygenated blood to the left heart via pulmonary veins Pulmonary and Systemic Circuits

  6. The Myocardium

  7. Systole Contraction phase Diastole Relaxation phase The Cardiac Cycle

  8. Pressure Changes During the Cardiac Cycle

  9. Arterial Blood Pressure • Expressed as systolic/diastolic • Normal is 120/80 mmHg • High is 140/90 mmHg • Systolic pressure (top number) • Arterial pressure during systole • Diastolic pressure • Arterial Pressure during diastole

  10. Arterial Blood Pressure • Pulse pressure • Difference between systolic and diastolic Pulse Pressure = Systolic - Diastolic • Mean arterial pressure (MAP) • Average pressure in the arteries MAP = Diastolic + 1/3(Systolic - Diastolic)

  11. Measurement of Blood Pressure

  12. Factors That Influence Arterial Blood Pressure

  13. Electrical Activity of the Heart • Contraction of the heart depends on electrical stimulation of the myocardium • Impulse is initiated by the SA node and spreads throughout entire heart • May be recorded on an electrocardiogram (ECG or EKG)

  14. Conduction System of the Heart

  15. Electrocardiogram

  16. Electrocardiogram • Records the electrical activity of the heart • P-wave • Atrial depolarization • QRS complex • Ventricular depolarization • T-wave • Ventricular repolarization

  17. Diagnostic Use of the ECG • ECG abnormalities may indicate coronary heart disease • ST-segment depression can indicate myocardial ischemia (reduced blood flow)

  18. Abnormal ECG Response to Exercise

  19. Cardiac Output • The amount of blood pumped by the heart each minute • Product of heart rate and stroke volume • Heart rate = number of beats per minute • Stroke volume = amount of blood ejected from the heart in each beat . Q = HR x SV

  20. Regulation of Heart Rate • Decrease in HR • Parasympathetic nervous system • Via vagus nerve • Slows HR by inhibiting SA node • Increase in HR • Sympathetic nervous system • Via cardiac accelerator nerves • Increases HR by stimulating SA node

  21. A Summary of Cardiovascular Control During Exercise: Fine Tuning

  22. Nervous System Regulation of HR

  23. Regulation of Stroke Volume • End-diastolic volume (EDV) • Volume of blood in the ventricles at the end of diastole (“preload”) • Average aortic blood pressure • Pressure the heart must pump against to eject blood (“afterload”) • Contractility • Strength of the ventricular contraction

  24. Incremental Exercise • Heart rate and cardiac output • Increases linearly with increasing work rate • Reaches plateau at 100% VO2max • Systolic blood pressure • Increases with increasing work rate • Double product • Increases linearly with exercise intensity • Indicates the work of the heart Double product = heart rate x systolic BP

  25. End-Diastolic Volume • Frank-Starling mechanism • Greater preload results in stretch of ventricles and in a more forceful contraction • Affected by: • Venoconstriction • Skeletal muscle pump • Respiratory pump

  26. The Skeletal Muscle Pump • Rhythmic skeletal muscle contractions force blood in the extremities toward the heart • One-way valves in veins prevent backflow of blood

  27. The Skeletal Muscle Pump

  28. Average Aortic Pressure • Aortic pressure is inversely related to stroke volume • High after load results in a decreased stroke volume • Requires greater force generation by the myocardium to eject blood into the aorta • Reducing after load results in higher stroke volume

  29. Ventricular Contractility • Increased contractility results in higher stroke volume • Causes: • Circulating epinephrine and norepinephrine • Direct sympathetic stimulation of heart

  30. Hemodynamics • Flow of blood through the circulatory system • Based on interrelationships between: • Pressure • Resistance • Flow

  31. Components of Blood

  32. Length x viscosity Resistance = Radius4 Hemodynamics: Resistance • Resistance depends upon: • Length of the vessel • Viscosity of the blood • Radius of the vessel • A small change in vessel diameter can have a dramatic impact on resistance!

  33.  Pressure Flow = Resistance Hemodynamics: Blood Flow • Directly proportional to the pressure difference between the two ends of the system • Inversely proportional to resistance

  34. Sources of Vascular Resistance • MAP decreases throughout the systemic circulation • Largest drop occurs across the arterioles • Arterioles are called “resistance vessels”

  35. Pressure Changes Across the Systemic Circulation

  36. Oxygen Delivery During Exercise • Oxygen demand by muscles during exercise is many times greater than at rest • Increased O2 delivery accomplished by: • Increased cardiac output • Redistribution of blood flow to skeletal muscle

  37. Changes in Cardiac Output • Cardiac output increases due to: • Increased HR • Linear increase to max after 120 bpm • Increased SV • Plateau at ~40% VO2max Max HR = 220 - Age (years) .

  38. Changes in Cardiovascular Variables During Exercise

  39. Redistribution of Blood Flow • Increased blood flow to working skeletal muscle • Reduced blood flow to less active organs • Liver, kidneys, GI tract

  40. Changes in Muscle and Splanchnic Blood Flow During Exercise

  41. Redistribution of Blood Flow During Exercise

  42. Circulatory Responses to Exercise • Heart rate and blood pressure • Depend on: • Type, intensity, and duration of exercise • Environmental conditions • Emotional influence

  43. Transition From Rest  Exercise and Exercise  Recovery • Increase in HR, SV, cardiac output • Plateau in sub maximal exercise • Recovery depends on: • Duration and intensity of exercise • Training state of subject

  44. Transition From Rest  Exercise  Recovery

  45. Incremental Exercise • Heart rate and cardiac output • Increases linearly with increasing work rate • Reaches plateau at 100% VO2max • Systolic BP • Increases with increasing work rate • Diastolic BP • Decreases slightly then remains even .

  46. Prolonged Exercise • Cardiac output is maintained • Gradual decrease in stroke volume • Gradual increase in heart rate • Cardiovascular drift • Due to dehydration and increased skin blood flow (rising body temperature)

  47. HR, SV, and CO During Prolonged Exercise

  48. Summary of Cardiovascular Adjustments to Exercise

  49. Chronic Endurance Training • Stronger/ thicker/ larger left ventricle • Lower resting and working HR • Greater resting and working SV • Lower resting and working blood pressure • Greater capillarization which decreases TPR – total peripheral resistance

  50. Questions?

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