Circulatory Responses to Exercise Dr. Kyle Coffey

1. Circulatory Responses to ExerciseDr. Kyle Coffey Week 8&9

2. The Circulatory System

3. Pulmonary and Systemic Circuits • Pulmonary circuit • Right side of the heart • Pumps deoxygenated blood to the lungs via pulmonary arteries • Returns oxygenated blood to the left side of the heart via pulmonary veins • Systemic circuit • Left side of the heart • Pumps oxygenated blood to the whole body via arteries • Returns deoxygenated blood to the right side of the heart via veins

4. Myocardium – “The Heart Wall” • Receives blood supply via coronary arteries • High demand for oxygen and nutrients even at rest • Myocardial Oxygen Consumption (MVO2) • Influenced by: • Force • Rate • Frequency • Rate Pressure Product (RPP): myocardial workload or stress • RPP = HR X SBP • Monitors exercise in patients with heart disease because value reflect cardiac function There is a linear correlation between RPP and MVO2

5. Cardiac v. Skeletal Muscle

6. The Cardiac Cycle • Systole • Contraction phase • Ejection of blood • ~2/3 blood is ejected from ventricles per beat • Diastole • Relaxation phase • Filling with blood

7. Cardiac Cycle at Rest and during Exercise

8. Pressure Changes during the Cardiac Cycle • Diastole • Pressure in ventricles is low • Filling with blood from atria • AV valves open when ventricular P < atrial P • Systole • Pressure in ventricles rises when atria contract and rises even sharper when ventricles contract • Forces closure of AV valves to prevent backflow into atria • Blood ejected in pulmonary and systemic circulation • Semilunar valves open when ventricular P > aortic P • Heart sounds • First: closing of AV valves • Second: closing of aortic and pulmonary valves

9. Pressure, Volume, and Heart Sounds During the Cardiac Cycle

10. Arterial Blood Pressure • Expressed as systolic/diastolic • Normal is 120/80 mmHg for males, 110/70 for females • Pulse pressure • Difference between systolic and diastolic • Represents force heart produces with each contraction • Indicator of mortality and risk for heart disease • Does not mean two individuals with equal pulse pressures have equal risk • Low = <25% of systolic mmHg value • Indicates poor left ventricular stroke volume or blood loss • High = stiffness of artery walls • Arterioscelrosisor atherosclerosis What happens to pulse pressure with exercise?

11. Mean Arterial Pressure (MAP) • Mean arterial pressure (MAP) • MAP = DBP + .33 (pulse pressure) • Determines rate of blood flow through systemic circuit • Average pressure in the arteries • Typically thought of as the “aortic pressure” • Can not be used during exercise, based on cardiac cycle at rest • Factors: • Cardiac output (Q) • Total vascular resistance • Clinical significance: perfusion pressure of organs in body • >60 mmHg is thought to be sufficient • 70-110 mmHg is normal

12. Factors that Influence Arterial Blood Pressure • Short-term regulation • Sympathetic nervous system • Baroreceptors in aorta and carotid arteries • Increase in BP = decreased SNS activity • Decrease in BP = increased SNS activity • Long-term regulation • Kidneys • Via control of blood volume • What hormone from kidney impacts blood pressure? • What was the name of the common medication?

13. Cardiac Output (Q) • The amount of blood pumped by the heart each minute • Product of heart rate and stroke volume • Heart rate • Number of beats per minute • = 208- 0.7(Age) • Stroke volume • Amount of blood ejected in each beat (mL) • Depends on: • Training state • Gender • Age • Disease Normal Levels: 5-6 L/min Exercise Levels: 20-35 L/min Q = HR x SV

14. Nervous System Regulation of Heart Rate

15. Autonomic Nervous System Sympathetic Parasympathetic Ach Ach Ach NE Effects: * Increase HR * Increase contractility * Innervate Atria and Ventricles Effects: * Decrease HR * Decrease contractility * Innervate Atria

16. Stroke Volume (SV) • Regulation of SV (70 ml/beat) • 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”) • Mean arterial pressure • SV and afterload are inversely proportional • During exercise d/t arteriole dilation, afterload is minimized • Strength of the ventricular contraction (contractility) • Enhanced by: • Circulating epinephrine and norepinephrine • Direct sympathetic stimulation of heart • Stroke volume = EDV-ESV

17. End Diastolic Volume (EDV) – “Preload” • Frank-Starling mechanism • Greater EDV results in a more forceful contraction • Due to stretch of ventricles • Discuss! • Dependent on venous return • Venous return increased by: • Venoconstriction • Via SNS • Skeletal muscle pump • Rhythmic skeletal muscle contractions force blood in the extremities toward the heart • One-way valves in veins prevent backflow of blood • Respiratory pump • Changes in thoracic pressure pull blood toward heart

18. Factors that Regulate Cardiac Output

19. Video • Frank Starling Mechanism

20. Ejection Fraction (EF) • Percentage of blood pumped from left ventricle • Stroke Volume / EDV • 55-70% is considered normal • Helpful in diagnostics for: • Disease • Heart failure: systolic (HFrEF) or diastolic (HFpEF) • 40-55% indicates damage (heart attack or dilated cardiomyopathy) • >75% indicates hypertrophic cardiomyopathy • Efficiency • Function • Can be calculated via echocardiogram

21.  Pressure Blood flow = Resistance Relationships Among Pressure, Resistance, and Flow • Blood flow • Directly proportional to the pressure difference between the two ends of the system • Inversely proportional to resistance • Pressure • Proportional to the difference between MAP and right atrial pressure ( Pressure) What causes resistance in the circulatory system?

22. Redistribution of Blood Flow During Exercise • Increased blood flow to working skeletal muscle • At rest, 15–20% of cardiac output to muscle • Increases to 80–85% during maximal exercise • Vasoconstriction to visceral organs and inactive tissues • Liver, kidneys, GI tract • Decreases to only 20-30% of resting values • SNS vasoconstriction • Redistribution depends on metabolic rate • Exercise intensity

23. Changes in Muscle and Organ Blood Flow during Exercise

24. Regulation of Local Blood Flow during Exercise • Skeletal muscle vasodilation • Autoregulation – what does this mean? • At beginning of exercise • Blood flow increased to meet metabolic demands of tissue • Due to changes in O2 tension, CO2 tension, nitric oxide, potassium, adenosine, and pH • Level of vasodilation is regulated by metabolic need of muscle

25. Cardiac Function Curve

27. Cardiac Output Normal Values • Rest: 5-6 L/min • Exercise: 20-35 L/min

28. Heart Rate Normal Values • Rest: 50-70 beats/min • Exercise: 220-age (maximal)

29. Stroke Volume Normal Values • Rest: 70 ml/beat • Exercise: up to 200 ml/beat

30. Changes in Cardiac Output During Exercise • Cardiac output increases due to: • Increased HR • Linear increase to max • For adults: • For children: • Increased SV • Increase, then plateau at ~40% VO2 max in untrained • No plateau in highly trained subjects • WHY?! Max HR = 220 – age (years) Max HR = 208 – 0.7 x age (years)

31. Arteriovenous Oxygen Difference(a-vO2diff) • Difference in oxygen content of blood from arteries to veins • Amount of O2 that is taken up from 100 ml blood • Calculated in two ways: • Blood samples • Fick Equation • VO2= HR x SV x A-VO2diff

32. Changes in Arterial-Mixed Venous O2 Content During Single Bout of Exercise • Higher arteriovenous difference (a-vO2 difference) • Increase due to higher amount of O2 taken up • Used for oxidative ATP production • Factors • Extraction at muscles • Delivery of oxygen rich blood At the onset of exercise, do you think that A-vO2 is noticed right away? Why/why not?

33. Circulatory Responses to Single Bout of Exercise • Transition from Rest to Exercise • Rapid increase in HR, SV, and Q • If work rate constant and below lactate threshold • Steady state plateau in HR, SV, and Q within 2-3 minutes • Recovery from Exercise • Rapid from short-term, low intensity exercise • Recovery speeds varies: Trained vs. untrained • Slower with long-term exercise • Particularly in hot/humid environments

34. Transition from Rest to Exercise to Recovery

35. Incremental Exercise • Heart rate and cardiac output • Increases linearly with increasing work rate • Reaches plateau at 100% VO2 max • Blood pressure • Mean arterial pressure (MAP) increases linearly • Systolic BP increases • Diastolic BP remains fairly constant • Rate pressure product • Increases linearly with exercise intensity • Exercise v. rest: 5x • Used to prescribe exercise to cardiac patients

37. Intermittent Exercise • Recovery of heart rate and blood pressure between bouts depend on: • Fitness level • Temperature and humidity • Duration and intensity of exercise

38. Prolonged Exercise • Cardiac output is maintained • Gradual decrease in stroke volume • Due to dehydration and reduced plasma volume • Gradual increase in heart rate • Cardiovascular drift • Helps keep constant Q

39. VO2Max • Maximal oxygen uptake • Most valid measurement of cardiovascular fitness • “Critical point during exhaustive exercise in which oxygen uptake reaches a plateau, beyond which greater increments in exercise intensity elicit no further rise in oxygen uptake.” • Physiological ceiling – what do I mean by this again?

40. VO2max • Affected by genetics and training, age, gender… • Dependent on: • Maximum ability of cardiorespiratory system to deliver oxygen to the muscle • Ability of muscles to use oxygen and produce ATP aerobically

41. VO2 max

42. Muscle Fiber and VO2max

43. VO2max Test Termination Criteria Exhaustion 4 • Plateau in O2 uptake with • increasing intensity • ( of < 2.1 ml/kg/min) RER VO2 (L/min) 2. Reach RER of > 1.1 1.1 3 8 mmol • Reach blood lactate of • > 8 mmol 0.8 Lactate • Reach age-predicted Hrmax • (220 – age) 2 mmol 2 0 5 10 15 % Grade

44. VO2 Max Can VO2max be Calculated? *Fick Equation * VO2max = HRmax x SVmax x A-VO2diffmax = QmaxX A-VO2diffmax Example: Q: What is the VO2max of a person with a HRmaxof 185 b/min, SVmaxof 150 ml/b, and A-VO2diff of 15 ml/100 ml blood (assume all are max values)? A: 4.16 L/min

45. VO2max Classification

46. VO2max and Genetics Genetic (untrained) VO2max (ml/kg/min)Population 551 in 6 people 651 in 40 people 701 in 2,000 people 80“Very, very Few” From: Shephard and Astrand, 1992

47. Gender and Aging 5 Men typically have a ~15% higher VO2max (ml/kg/min) than women VO2max declines ~ 1% each year after age 20 VO2 (L/min) 3 M F 1 10 20 30 40 50 60 Age

48. VO2max and Gender Q: Why do men typically have higher VO2max values than women? A: (1) More lean body mass (active tissue that can use O2) Example: Man weighs 70 kg and has VO2max of 4.5L/min = 64.3 ml/kg/min Woman weighs 60 kg and has VO2max of 3.3L/min = 55.0 ml/kg/min = 14.5% higher in man If man is 15% body fat (59.5 kg is FFM), then VO2max = ~ 75.6 ml/kgFFM/min If woman is 22% body fat (47 kg is FFM), then VO2max = ~ 70.5 ml/kgFFM/min = 6.7% higher in man Why is VO2max still higher in man after controlling for LBM?

49. VO2max and Gender Q: Why do men typically have higher VO2max values than women? A: (2) Higher Hb concentration (Larger O2 carrying capacity) • Carry more oxygen • Transport more oxygen

50. Oxygen Transport: Limitations to VO2max Hemoglobin Ventilation Cardiac Output Muscle Mass/ Circulation/ Metabolism