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The Cardiovascular System

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The Cardiovascular System

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    1. The Cardiovascular System

    2. The Heart

    3. Myocardium Similar to skeletal muscle Different from skeletal muscle Shorter cells Greater capillary density Greater mitochondria (40% of volume compared to 2-6%)

    4. Coronary Blood Flow

    5. Coronary Blood Flow Metabolic adenosine ? vasodilation Mechanical collapse of coronary vessels

    6. Myocardium Intercalated disks Gap junctions Syncytium

    7. Myocardium

    9. Action Potential Fast and slow response Fast response is more negative Greater up-slope, amplitude, and overshoot Slow conduction increases rhythm disturbances

    11. Electrical Activity Autorhythmicity SA node AV node Bundle of His Bundle branches Purkinje fibers

    12. Cardiac Cycle Diastole Systole

    13. Cardiac Cycle

    14. Cardiac Cycle Stroke volume 82 ± 20 ml per beat End diastolic volume 125 ± 31 ml End systolic volume 42 ± 17 ml Ejection fraction ~ 67%

    15. Cardiac Output CO = HR x SV Ave. resting value = 5 L/min Exercise value = 20-30 L/min

    16. Control of Heart Rate Autonomic nervous system Sympathetic Parasymathetic Hormonal control Epinephrine

    17. Sympathetic Stimulation Release acetylcholine and norepinephrine Heart Increase HR and strength of contraction Blood Vessels Vasoconstriction Organs, muscle (adrenergic), and skin (adrenergic) Vasodilation Coronary arteries, muscle (cholinergic) and skin (cholinergic)

    18. Parasympathetic Stimulation Release acetylcholine Heart Decrease HR and strength of atrial contraction Blood Vessels Vasoconstriction of coronary arteries Vasodilation of skin

    19. Catecholamines Heart Both increase HR and SV ß1 adrenergic receptors Blood vessels Epinephrine vasoconstriction via a adrenergic receptors (muscles) vasodilation via ß2 adrenergic receptors (lungs) Norepinephrine vasoconstriction via a adrenergic (muscles)

    20. Factors Affecting Heart Rate Age Gender (females have lower resting HR) Posture (lower: lying down or standing? Ingestion of food Smoking Emotion Body temperature Heat and humidity

    21. Control of Stroke Volume Autonomic nervous system Sympathetic Hormonal control Frank-Starling Law

    22. Frank-Starling Law Increase EDV Stretch increase actin-myosin cross bridges Increase force of contraction Increase SV

    23. Factors Affecting Stroke Volume Heart size Neural stimulation Gravity venous return Muscular activity Preload Diameter of arteries Afterload

    24. Preload Venous Return Muscle pump Isometric contraction Venoconstriction

    25. Afterload

    26. Cardiac Hypertrophy Non-pathologic hypertrophy Pathologic hypertorphy

    27. Introduction At rest: oxygen supply = oxygen demand Exercise: demand increases To the muscles To the heart To the skin Maintain flow to the brain How can the heart supply enough O2 to meet the demand? Increase in cardiac output

    28. How does the heart increase cardiac output? Increase heart rate* Increase stroke volume

    29. Heart Rate During Exercise

    30. Heart Rate and Exercise Increases with intensity and levels off at VO2max 220 – age (± 12) Lance Armstrong Age 21 = 207 Age 28 = 200 207 - 0.7 x age [MSSE, May 07]

    31. Stroke Volume & Exercise Increase preload (?EDV) Increase venous return Venoconstriction Muscle pump, etc. Decrease afterload (? ESV) Vasodilation Local control Sympathetic stimulation Increase contractility (? ESV) Increase sympathetic stimulation

    32. Cardiovascular Drift

    33. Stroke Volume & Exercise Increases until about 25-50% of maximum in less trained individuals Decrease in SV near maximal effort After that it may plateau or continue to increase

    34. Static Exercise (e.g. resistance training) Acute effect Less increase in HR Lower stroke volume Less venous return (preload) Greater afterload Chronic effect Increase myocardial mass

    35. Blood Vessels

    36. Arteries

    37. Arterioles & Metarterioles Smooth muscle sphincters

    38. Capillaries

    39. Veins One-way valves

    40. Hemodynamics Pressure Flow / Distribution Resistance

    41. Blood Pressure Blood Pressure = Cardiac Output x Total Peripheral Resistance

    42. Blood Pressure Systolic blood pressure Diastolic blood pressure Mean arterial blood pressure

    43. Mean Arterial Pressure Pulse Pressure = SBP - DBP MAP = DBP + 1/3 (Pulse Pressure) Blood pressure of 120/80 mm Hg MAP = 80 mm Hg + .33(120-80) = 80 mm Hg + 13 = 93 mm Hg

    44. Blood Pressure

    45. Blood Pressure

    46. Blood Pressure How does an increase in blood pressure during exercise help increase blood flow to the muscles?

    47. Blood Pressure Changes During Exercise Systolic? Diastolic?

    48. Blood Flow Flow = (P1 - P2) p R4 / 8LN flow is influenced by pressure (P), radius (R), and viscosity (N) Which factor (P, R or N) has the greatest ability for increasing blood flow to the muscles?

    49. Blood Distribution Arteries and arterioles Constriction and dilation Sympathetic Vasoconstriction Organs, muscle (adrenergic), and skin (adrenergic) Sympathetic Vasodilation Coronary arteries, muscle (cholinergic) and skin (cholinergic)

    50. Blood Distribution Dilation of Metarterioles Local or Metabolic Control nitric oxide adenosine acid carbon dioxide nitric oxide

    52. Blood Flow

    53. Blood Flow Vasodilation to increase blood flow to muscles and skin Sympathetic stimulation - muscles Parasympathetic stimulation - skin Metabolic control - muscles Vasoconstriction to maintain blood pressure Maximum muscle blood flow is limited by the ability to maintain blood pressure

    54. “Cardiovascular Triage” Vasoconstriction to inactive tissues during exercise Heart and CNS spared vasoconstriction What happens near maximal effort? Do we take blood away from the heart and CNS or the muscles?

    55. Measure of oxygen extraction a = O2 in arteries (20 ml/100 ml of blood) v = O2 in veins (15 ml/100 ml of blood) Therefore, (a-v)O2 = 5 ml/100 ml of blood a-v O2 Difference

    56. a-v O2 difference Depends on mitochondria, O2 diffusion, hemoglobin, myoglobin, etc. Arterial blood: 20 ml O2 / 100 ml blood a-v O2 difference a-vO2 at rest =5 ml O2 / 100 ml blood a-vO2 during exercise ~16 ml O2 / 100 ml blood However, nearly 20 ml O2 / 100 ml blood in some muscles during maximal exercise

    57. a-v O2 difference

    58. a-v O2 difference During exercise... No change in PaO2 in the arterial blood Decrease in PaO2 in the muscle Greater pressure difference between the blood and the muscles Therefore, more O2 diffuses into the muscles a-v O2 difference can approach 20 near maximal exercise

    59. Oxygen Consumption Fick Equation VO2 = Cardiac Output x a-v O2 difference

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