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Cardiovascular Control During Exercise

Cardiovascular Control During Exercise. Learning Objective: To understand the functional anatomy of the CV system. “How is the system designed anatomically to function physiologically ?”. 1. Introduction to Cardiovascular System. Key Points: Pulmonary Circulation Circuit Low Pressure

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Cardiovascular Control During Exercise

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  1. Cardiovascular Control During Exercise Learning Objective: To understand the functional anatomy of the CV system. “How is the system designed anatomically to function physiologically?”

  2. 1. Introduction to Cardiovascular System • Key Points: • Pulmonary Circulation Circuit • Low Pressure • O2 and CO2 Exchange (Hb Affinity) • Systemic Circulation Circuit • High Pressure • Overcome gravity/hydrostatic pressure • Bulk flow of blood to and from tissue • Key CV Components • Heart (the pump) • Blood Vessels (system of tubes) • Blood (a fluid medium) Figure from Marieb and Hoehn, 2010

  3. Major CV Functions • O2 and Nutrient Delivery • CO2 and Metabolic Waste Removal • Transport (e.g. hormones) • Thermoregulation • Acid-base and Body Fluid Balance

  4. Heart To body From body To lungs From lungs http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html

  5. Myocardium- Cardiac Muscle • Adaptable: • Myocardial thickness will increase when “stressed” • Myocardial volume will increase with endurance training • Myocardial fibers are homogenous and contain only one fiber type (similar to type I)

  6. Left Ventricle • Most powerful of the four chambers • Must contract to pump blood through entire body (to the systemic circulation) • Higher the intensity of exercise, working muscles require more blood, increase demand of LV to deliver blood to exercising muscles, therefore, LV will hypertrophy

  7. Skeletal Muscle Heart Muscle Heart Muscle: Rich in Mitochondria to support perpetually active muscle • Key Points: Cardiac muscle fibers interconnected by intercalated disks • Allows for rapid transmission of action potentials for uniform contractions

  8. Cardiac muscle contraction occurs by “calcium-induced calcium release” • Calcium enters cell • Calcium released from SR • Primary blood supply to heart provided by right and left coronary arteries • Ability of myocardium to contract as a single unit depends on cardiac conduction system

  9. Intrinsic Conduction System • Cardiac muscle is able to generate own electrical signal-spontaneous rhythmicity • Without neural or hormonal stimulation, intrinsic HR is ~100 bpm • Four main components: • Sinoatrial (SA) node • Atrioventricular (AV) node • AV bundle (bundle of His) • Purkinje fibers (terminal branches of AV bundle)

  10. SA Node • Group of specialized cardiac muscle fibers located in upper posterior wall of right atrium • Where impulse for normal heart contractions is initiated • Known as heart’s pacemaker because generates electrical impulse at ~100 bpm

  11. AV Node • Located at the base of atria • Electrical Connection: Conducts electrical impulse from atria to ventricles • Slows conduction velocity to ~0.13 s as it passes through AV node and into AV bundle • Delay allows blood from atria to empty into ventricles to facilitate ventricular filling before ventricles contract

  12. AV bundle • Runs along ventricular septum and sends right and left bundle branches into both ventricles • Branches send impulse toward apex then outward • Purkinje Fibers • Transmit impulse 6x faster than through rest of cardiac conduction system

  13. Extrinsic Control of The Heart Autonomic Nervous System: • Parasympathetic nervous system (PNS) • Sympathetic nervous system (SNS) • Endocrine system (hormones)

  14. Parasympathetic Nervous System • Originates in medulla oblongata and reaches heart through vagus nerve • Vagus nerve carries impulses to SA and AV nodes • when stimulated, releases acetylcholine hyperpolarization of conduction cells decrease in HR • Predominates at rest: “vagal tone” • Able to decrease HR to 20-30 bpm • Vagal Withdrawal, increase HR to 100 bpm Powers and Howley, Exercise Physiology, 2004

  15. Parasympathetic Regulation of Heart At the molecular and cellular level

  16. Sympathetic Nervous System • Increases HR and contraction force of the ventricles • Allows HR to increase to ~250 bpm • Predominate during physical or emotional stress (when HR >100 bpm) • When exercise begins, HR first increases due to withdrawal of vagal tone, then later due to SNS Powers and Howley, Exercise Physiology, 2004

  17. Graphical Depiction of HR • Increasing slope increases HR • Decreasing slope decreases HR

  18. Cardiac Cycle • Includes all mechanical and electrical events that occur during one heartbeat • Consists of chambers that undergo diastole (relaxation phase) and systole (contraction phase) • Diastole-chambers fill with blood, ventricles contract and send blood into aorta and pulmonary veins http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html http://people.eku.edu/ritchisong/301notes5.htm

  19. Cardiac Cycle • One cardiac spans the time between one systole to another • Systole (ventricular contraction) starts during the QRS complex and ends in the T wave • Diastole (ventricular relaxation) occurs during T wave and to next contraction • Heart spends more time in diastole (~2/3 of time) than in systole (~1/3 of time)

  20. The Wiggers Diagram: Events of Cardiac Cycle for LV Function http://library.med.utah.edu/kw/pharm/hyper_heart1.html

  21. Vascular System: Closed System • Arteries: transport blood away from heart to arterioles • Arterioles: site of greatest control of circulation by SNS (resistance vessels) • Capillaries: where exchange between blood and tissues occur • Venules: collect blood from capillaries • Veins: transport blood back to heart

  22. Functional Anatomy

  23. http://www.uta.edu/coehp/kinesiology/ms/MS/BoneLab/images_videos.htmlhttp://www.uta.edu/coehp/kinesiology/ms/MS/BoneLab/images_videos.html

  24. Blood Pressure • Pressure exerted by blood on vessel walls • Systolic blood pressure (SBP)-highest pressure in the artery • Diastolic blood pressure (DBP)-lowest pressure in the artery

  25. Blood Pressure • Mean arterial pressure (MAP): average pressure • MAP=2/3 DBP + 1/3 SBP • MAP=DBP + [0.333 x (SBP-DBP)] • i.e.) MAP=80 + [0.333 x (120-80)] = 93mmHg

  26. Arterioles responsible for ~70%-80% of drop in MAP

  27. General Hemodynamics • Blood flows in closed-system because of pressure gradient between arterial and venous sides • Pressure, Flow and Resistance • Blood flows from high pressure to low pressure • MAP in aorta = ~100 mmHg • MAP in right atrium = ~0 mmHg

  28. Stroke Volume (SV=EDV-ESV) • Volume of blood pumped per beat (contraction) • End-diastolic volume (EDV)-volume of blood in ventricle before contraction • End-systolic volume (ESV)-volume of blood in ventricle after contraction • i.e.) SV= 100ml-40ml= 60ml

  29. Ejection Fraction • Fraction of blood present in the left ventricle before the contraction in relation to the amount of blood pumped out of the left ventricle. • EF=SV/EDV x 100 • For Example: Ejection Fraction = (60ml/100ml) x 100 = 60%

  30. Cardiac Output (Q) • Total volume of blood pumped by the ventricle per minute • Q=HR x SV For Example: Q= (60 beats/min) x (70 ml/min) = 4,200ml/min or 4.2L/min

  31. General Hemodynamics • Blood flow is proportional to pressure difference across system and inversely proportional to resistance • Blood flow = ∆pressure/resistance • Regulation of blood flow to organs accomplished by vasoconstriction and vasodilation

  32. Blood • Function of Blood in exercise and sport: • Transportation • Temperature regulation: transports heat from exercising muscle to skin to be dissipated • Acid-base (pH) balance

  33. Blood Volume and Composition • Hermatocrit is the ratio of the formed elements in blood (red cells, white cells, and platelets) to total blood volume.

  34. Red Blood Cells • Erythrocytes have no nucleus-cannot reproduce • Hematopoiesis-process of replacing red blood cells with new ones • Life span about 4 months • Transport O2 mainly bound to hemoglobin • Hemoglobin contains iron which binds to O2

  35. Hemeglobin

  36. Blood Viscosity • Refers to thickness of the blood • The more viscous, the more resistant to flow • For optimal performance, a low hematocrit with normal or slightly elevated RBC count is desirable • Facilitates O2 transport

  37. General CV Adjustments to Exercise “Think of Cardiac Output (CO) as Blood Flow” • Increase CO • Rest=5L/min • Max=20L/min • Redistribute CO • Rest=25% to muscle • Max=85% to muscle • Increase Venous Return • Rest=5L/min • Max=20L/min

  38. Increase CO • ↓PNA to SA node • ↑SNA to SA node • ↑SNA to LV • Redistribute CO • ↑SNA to non-contracting tissues • Increase Venous Return • ↑ SNA to veins

  39. Distribution of Blood • Varies depending on immediate needs of a specific tissue • Skeletal muscle receives ~15% of blood flow at rest and up to 80% during heavy endurance exercise • Changes in distribution in cardiac output (Q) controlled by SNS mainly by arteriolar diameter

  40. Intrinsic Control of Blood Flow • Ability of local tissues to vasodilate or vasoconstrict arterioles and alter regional blood flow depending on tissue need • Metabolic-increased O2 demand, decreases in other nutrients, increases in by-products (CO2, K+, H+, lactic acid) • Endothelium mediated vasodilation: NO

  41. How does muscle get Blood if SNA is increasing?

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