Chapter 9: Circulatory Adaptations to Exercise

1. Chapter 9:Circulatory Adaptations to Exercise EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

2. Introduction • One major challenge to homeostasis posed by exercise is the increased muscular demand for oxygen • During heavy exercise, oxygen demands may  by 15 to 25 times • Two major adjustments of blood flow are; •  cardiac output • Redistribution of blood flow • A thorough understanding of the cardiovascular system is essential to exercise physiology

3. Objectives • Give an overview of the design and function of the circulatory system • Describe cardiac cycle & associated electrical activity recorded via electrocardiogram • Discuss the pattern of redistribution of blood flow during exercise • Outline the circulatory responses to various types of exercise

4. Objectives • Identify the factors that regulate local blood flow during exercise • List & discuss those factors responsible for regulation of stroke volume during exercise • Discuss the regulation of cardiac output during exercise

5. The Cardiovascular System Purposes 1. 2. 3.

6. The Circulatory System • Heart • Pumps blood • Arteries and arterioles • Carry blood ________ from the heart • Capillaries • Exchange of __________ with tissues • Veins and venules • Carry blood __________ the heart

7. Structure of the Heart Fig 9.1

8. Systemic circuit ________ side of the heart Pumps _________ blood to the whole body via arteries Returns ____________ blood to the right heart via veins Pulmonary circuit ________ side of the heart Pumps __________ blood to the ______ via pulmonary arteries Returns ___________ blood to the ________ heart via pulmonary veins Pulmonary and Systemic Circuits

9. The Myocardium Fig 9.3

10. Systole ___________ phase Diastole _________ phase The Cardiac Cycle Fig 9.5

11. Arterial Blood Pressure • Expressed as systolic/diastolic • Normal is 120/80 mmHg • High is 140/90 mmHg • Systolic pressure (top number) • Pressure generated during ________________ (systole) • Diastolic pressure • Pressure in the arteries during _____________ (diastole)

12. Blood Pressure • ________________ • Difference between systolic and diastolic • ________________________ (MAP) • Average pressure in the arteries Pulse Pressure = Systolic - Diastolic MAP = _______________________

13. Mean Arterial Pressure Blood pressure of 120/80 mm Hg MAP =

14. Measurement of Blood Pressure Fig 9.7

15. Factors That Influence Arterial Blood Pressure Fig 9.8

16. How is Blood Pressure Regulated? • Acute regulation • Achieved by _____________________ • Long term regulation • Function of the ___________________ • They do so by control of ____________________

17. Electrical Activity of the Heart • Contraction of the heart depends on electrical stimulation of the myocardium • Impulse is initiated in the __________ and spreads throughout entire heart • May be recorded on an __________________ (ECG)

18. Conduction System of the Heart ___________________ Fig 9.9

19. ________________ The amount of blood pumped by the heart each minute • Product of _________________ • ______ = number of beats per minute • ______ = amount of blood ejected in each beat Q = _________

20. Regulation of Heart Rate • 2 prominent factors that influence HR • Decrease in HR 1. _____________________ • Via ______________ • Slows HR by inhibiting _________ • Increase in HR 2. _____________________ • Via cardiac ______________ • Increases HR by stimulating ________

21. Regulation of Stroke Volume • SV at rest or during exercise is regulated by 3 variables 1. __________________ (EDV) • Volume of blood in the ventricles at the end of diastole (“preload”) 2. __________________ • Pressure the heart must pump against to eject blood (“afterload”) 3. _________ of the ventricular contraction • “Contractility”

22. End-Diastolic Volume • __________________ • Greater preload results in stretch of ventricles and in a more forceful contraction • Affected by venous return: • What factors regulate venous return? 1. 2. 3.

23. 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 Fig 9.16

24. Average Aortic Pressure • Aortic pressure is ___________ related to stroke volume • High afterload results in a ___________ stroke volume • Requires greater force generation by the myocardium to eject blood into the aorta • Reducing aortic pressure results in _______ stroke volume

25. Ventricular Contractility • Increased contractility results in ________ stroke volume • Circulating epinephrine and norepinephrine • Direct sympathetic stimulation of heart

26. Factors that Regulate Cardiac Output Parasympathetic nerves Mean arterial pressure Cardiac = Cardiac Rate x Stroke Volume Output Contraction strength EDV Sympathetic nerves Stretch Frank- Starling Fig 9.18

27. Hemodynamics The study of the physical principles of blood flow

28. Physical Characteristics of Blood • ___________ • Liquid portion of blood • Contains ions, proteins, hormones • Cells • ___________ • Contain hemoglobin to carry oxygen • ___________ • ___________ • Important in blood clotting

29. ____________ Percent of blood composed of cells Fig 9.19

30. Hemodynamics Based on interrelationships between: • ___________ • ___________ • ___________ • Since large increases in P are hazardous to health – decreasing resistance is the primary factor used to achieve increases in BF during exercise with a small rise in P

31. Hemodynamics: Pressure • Blood flows from ___  ___ pressure • Proportional to the difference between MAP and right atrial pressure (P) • BF depends on P at 2 ends of vascular system • P at 2 ends of a vessel are equal = __________

32. Blood Flow Through the Systemic Circuit Fig 9.20

33. Resistance = Hemodynamics: Resistance • What factors contribute to the resistance of blood flow? 1. 2. 3. • A _________ change in vessel diameter can have a dramatic impact on resistance! Resistance is directly proportional to these 2 factors Most important factor determining vascular resistance

34. Flow = Hemodynamics: Blood Flow • ___________ proportional to the pressure difference between the two ends of the system • ___________ proportional to resistance

35. Sources of Vascular Resistance • MAP __________ throughout the systemic circulation • Largest drop occurs across the _____________ • Arterioles are called “resistance vessels”

36. Pressure Changes Across the Systemic Circulation Fig 9.21

37. Oxygen Delivery During Exercise • Oxygen demand by muscles during exercise is many times greater than at rest • Increased O2 delivery accomplished via 2 mechanisms: 1. 2.

38. Changes in Cardiac Output • Cardiac output increases due to: • Increased ____ • Linear increase to max • Increased ____ • Plateau at ~40% VO2max • Oxygen uptake by the muscle also ______ • Higher arteriovenous difference Max HR = 220 - Age (years)

39. Changes in Cardiovascular Variables During Exercise Fig 9.22

40. Redistribution of Blood Flow • Muscle blood flowto working skeletal muscle • Splanchnic blood flow to less active organs • Liver, kidneys, GI tract

41. Changes in Muscle and Splanchnic Blood Flow During Exercise Fig 9.23

42. Increased Blood Flow to Skeletal Muscle During Exercise • What regulates blood flow to various organs during exercise? 1. 2. • Blood flow increased to meet metabolic demands of tissue • This happens because of muscle vasodilation • O2 tension, CO2 tension, pH, nitric oxide

43. Redistribution of Blood Flow During Exercise Fig 9.24

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

45. Transition From Rest  Exercise and Exercise  Recovery • Rapid increase in HR, SV, cardiac output • Plateau in submaximal (below lactate threshold) exercise • Recovery depends on: • Duration and intensity of exercise • Training state of subject

46. Incremental Exercise • Heart rate and cardiac output • Increases linearly with increasing work rate • Reaches plateau at 100% VO2max • Stroke volume • Systolic blood pressure • Increases with increasing work rate • Double product – also called___________ • Increases linearly with exercise intensity • Indicates the work of the heart Double product =

47. Arm vs. Leg Exercise • At the same oxygen uptake arm work results in higher: • _______ • Due to higher ______________ stimulation • _______ • Due to _____________ of large inactive muscle mass .

48. Heart Rate and Blood Pressure During Arm and Leg Exercise If these 2 factors increase so will _________________________ Fig 9.26

49. Prolonged Exercise • Cardiac output is maintained • Gradual decrease in _________ • Gradual increase in _________ • Cardiovascular drift • What is the drift due to? 1. 2. .

50. HR, SV, and Q During Prolonged Exercise Fig 9.27