3 Hemodynamics 2ndyears


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3 Hemodynamics 2ndyears

  1. 1. Hemodynamics Physics of Blood flow in the circulation
  2. 2. Circulatory System <ul><li>Heart: </li></ul><ul><li>Has 2 collecting chambers - (Left, Right Atria) </li></ul><ul><li>Has 2 Pumping chambers - (Left, Right Ventricles) </li></ul>
  3. 4. Circulation Schematic Lungs Tissues Left Side of Heart Right Side of Heart A V V A Pulmonary Vein Pulmonary Artery Aorta Sup. & Inf. Vena Cava Mitral Valve Pulmonary Valve Aortic Valve Tricuspid Valve
  4. 5. Heart Valves <ul><li>Atrioventricular (A-V) valves - separate Atria from Ventricles </li></ul><ul><ul><ul><li>Bicuspid (Mitral) - Left Side </li></ul></ul></ul><ul><ul><ul><li>Tricuspid - Right Side </li></ul></ul></ul><ul><li>Semi-Lunar Valves - separate ventricles from Arteries </li></ul>
  5. 6. Opening, Closing of Valves - Depends on Pressure differences between blood in adjacent areas
  6. 7. Heart Sounds <ul><li>‘ Lubb’ (1 st sound) - Closure of A-V valves </li></ul><ul><li>‘ Dupp’ (2 nd sound) - Closure of S-L valves </li></ul><ul><li>Caused by Turbulence on closing. </li></ul><ul><li>Anything extra  ’ Murmur ’ (swishing of blood) </li></ul><ul><li>Could be due to: </li></ul><ul><li>Stenosis of Valves (calcification) </li></ul><ul><li>Valves not closing properly </li></ul><ul><li>(Incompetence, Insufficiency) </li></ul>Increases Pressure on heart
  7. 8. Blood Vessels <ul><li>Arteries </li></ul><ul><li>Capillaries </li></ul><ul><li>Veins </li></ul><ul><li>Systemic Pathway: </li></ul><ul><li>Left Ventricle Aorta Arteries Arterioles </li></ul><ul><li>of Heart </li></ul><ul><li> Capillaries </li></ul><ul><li>Venules Veins Right Atrium </li></ul><ul><li> of Heart </li></ul>
  8. 9. Blood <ul><li>Composition: </li></ul><ul><ul><li>Approx 45% by Vol. Solid Components </li></ul></ul><ul><ul><ul><ul><ul><li>Red Blood Cells (12  m x 2  m) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>White Cells </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Platelets </li></ul></ul></ul></ul></ul><ul><ul><li>Approx 55% Liquid (plasma) </li></ul></ul><ul><ul><ul><ul><ul><li>91.5% of which is water </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>7% plasma proteins </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>1.5% other solutes </li></ul></ul></ul></ul></ul>
  9. 10. Blood Functions <ul><li>Transportation </li></ul><ul><li>of blood gases, nutrients, wastes </li></ul><ul><li>Homeostasis (regulation) </li></ul><ul><li>of Ph, Body Temp, water content </li></ul><ul><li>Protection </li></ul>
  10. 11. As a Result ……. <ul><li>Blood behaves as a simple Newtonian Fluid when flowing in blood vessels </li></ul><ul><li>i.e. Viscous stresses  Viscosity, strain rate </li></ul>y u(y) No slip at wall
  11. 12. <ul><li>Viscosity of Blood = 3 3.5 times of water </li></ul><ul><li>Blood acts as a non-newtonian fluid in smaller vessels (including capillaries) </li></ul>
  12. 13. Cardiac Output <ul><li>Flow of blood is usually measured in l/min </li></ul><ul><li>Total amount of blood flowing through the circulation = Cardiac Output (CO) </li></ul><ul><li>Cardiac Ouput = Stroke Vol. x Heart Rate </li></ul><ul><li> = 5 l/min </li></ul><ul><li>Influenced by Blood Pressure & Resistance </li></ul>Force of blood against vessel wall <ul><li>Blood viscosity </li></ul><ul><li>Vessel Length </li></ul><ul><li>Vessel Elasticity </li></ul><ul><li>Vasconstriction / Vasodilation </li></ul> with water retention  with dehydration, hemorrage
  13. 14. Overall <ul><li>Greater Pressure  Greater Blood </li></ul><ul><li>Differences Flow </li></ul><ul><li>Greater Resistance  Lesser Blood Flow </li></ul>
  14. 15. Driving force for blood flow is pressure created by ventricular contraction Elastic arterial walls expand and recoil continuous blood flow <ul><li>Blood Pressure </li></ul>
  15. 16. <ul><li>Blood pressure is highest in the arteries (Aorta!) and falls continuously . . . </li></ul><ul><li>Systolic pressure in Aorta: 120 mm Hg </li></ul><ul><li>Diastolic pressure in Aorta: 80 mm Hg </li></ul><ul><li>Diastolic pressure in ventricle: ?? mm Hg </li></ul>
  16. 17. <ul><li>Ventricular pressure difficult to measure </li></ul><ul><li>arterial blood pressure assumed to indicate driving pressure for blood flow </li></ul><ul><li>Arterial pressure is pulsatile </li></ul><ul><li>useful to have single value for driving pressure: Mean Arterial Pressure </li></ul><ul><li>MAP = diastolic P + 1/3 pulse pressure </li></ul>
  17. 18. <ul><li>Pulse Pressure = systolic pressure - ?? </li></ul><ul><li>= measure of amplitude of blood pressure wave </li></ul>
  18. 19. MAP influenced by <ul><li>Cardiac output </li></ul><ul><li>Peripheral resistance </li></ul><ul><li>MAP CO x R arterioles </li></ul><ul><li>Blood volume </li></ul><ul><ul><li>fairly constant due to homeostatic mechanisms (kidneys!!) </li></ul></ul>
  19. 20. BP too low: <ul><li>Driving force for blood flow unable to overcome gravity </li></ul><ul><li>O 2 supply to brain  </li></ul><ul><li>Symptoms? </li></ul>
  20. 21. BP too high: <ul><li>Weakening of arterial walls - Aneurysm </li></ul><ul><li>Risk of rupture & hemorrhage </li></ul><ul><li>Cerebral hemorrhage: ? </li></ul><ul><li>Rupture of major artery: </li></ul>
  21. 22. <ul><li>Auscultation of brachial artery with stethoscope </li></ul><ul><li>Laminar flow vs. turbulent flow </li></ul>BP estimated by Sphygmomanometry
  22. 23. Principles of Sphygmomanometry Cuff inflated until brachial artery compressed and blood flow stopped what kind of sound?
  23. 24. turbulent flow Slowly release pressure in cuff:
  24. 25. Pressure at which . . . <ul><li>. . . sound (= blood flow) first heard: </li></ul><ul><li>. . . sound disappeared: </li></ul>
  25. 26. <ul><li>Pressure can be stated in terms of column of fluid. </li></ul><ul><li>Pressure Units </li></ul><ul><li>mm Hg cm H 2 O PSI ATM </li></ul><ul><li>50 68 0.9 0.065 </li></ul><ul><li>100 136 1.9 0.13 </li></ul><ul><li>200 272 3.8 0.26 </li></ul><ul><li>300 408 5.7 0.39 </li></ul><ul><li>400 544 7.6 0.52 </li></ul>
  26. 27. <ul><li>Pressure = Height x Density </li></ul><ul><li>or P =  gh </li></ul><ul><li>If Right Atrial pressure = 1 cm H 2 O in an open column of blood </li></ul><ul><li> Pressure in feet = 140 cm H 2 O </li></ul><ul><li>  Rupture </li></ul><ul><li>  Venous Valves </li></ul>Density of blood = 1.035 that of water Incompetent venous valves  Varicosities Actual Pressure in foot = 4-5 cm H 2 O
  27. 28. Pressures in the circulation <ul><li>Pressures in the arteries, veins and heart chambers are the result of the pumping action of the heart </li></ul><ul><li>The right and left ventricles have similar waveforms but different pressures </li></ul><ul><li>The right and left atria also have similar waveforms with pressures that are similar but not identical </li></ul>
  28. 29. 1. The LV pressure begins to rise after the QRS wave of the ECG 2. Pressure rises until the LV pressure exceeds the aortic pressure  The blood begins to move from the ventricle to the aorta 3. As blood enters the aorta, the aortic pressure begins to rise to form the systolic pulse 4. As the LV pressure falls in late systole the aortic pressure falls until the LV pressure is below the aortic diastolic press. 5. Then the aortic valve closes and LV pressure falls to LA pressure
  29. 30. <ul><li>The first wave of atrial pressure (the A wave) is due to atrial contraction </li></ul><ul><li>The second wave of atrial pressure (the V wave) is due to ventricular contraction </li></ul>
  30. 31. Normal Pressures <ul><li>RV and pulmonary systolic pressure are 12-15 mm Hg </li></ul><ul><li>Pulmonary diastolic pressure is 6-10 mm Hg </li></ul><ul><li>LA pressure is difficult to measure because access to the LA is not direct </li></ul>
  31. 32. <ul><li>The severity of AS is determined by the pressure drop across the aortic valve or by the aortic valve area </li></ul><ul><li>The high velocity of blood flow through the narrowed valve causes turbulence and a characteristic murmur AS can be diagnosed with a stethoscope </li></ul>AS produces a pressure gradient between the aorta and LV i.e. For blood to move rapidly through a narrowed aortic valve orifice, the pressure must be higher in the ventricle
  32. 33. Pressure Measurement <ul><li>Accurate pressure measurements are essential to understanding the status of the circulation </li></ul><ul><li>In 1733 Steven Hales connected a long glass tube directly to the left femoral artery of a horse and measured the height of a column of blood (8 feet, 3 inches) to determine mean BP </li></ul><ul><li>Direct pressure measurements are made frequently in the cardiac catheterization laboratory, the ICU and the OR </li></ul>
  33. 34. <ul><li>A tube is inserted into an artery and connected to an electrical strain gauge that converts pressure into force that is sensed electrically </li></ul><ul><li>The output of the transducer is an electrical signal that is amplified and recorded on a strip chart </li></ul><ul><li>For correct pressure measurements the cannula and transducer must be free of air, the cannula should be stiff and short </li></ul>
  34. 35. Cardiac Output ( CO) Measurement <ul><li>The measurement of blood flow through the circulation is usually done clinically using either the Fick method </li></ul><ul><li>The Fick method states that the cardiac output is equal to the oxygen consumption divided by the arterial-venous oxygen difference </li></ul><ul><li>CO = Oxygen consumption / A-V O 2 </li></ul>
  35. 36. <ul><li>The measurement is done by determining the oxygen consumption using respiratory gas measurements and the O 2 content of arterial and mixed venous blood </li></ul><ul><li>The mixed venous blood sample is obtained from a PA with a catheter </li></ul><ul><li>The arterial sample can be drawn from any artery </li></ul>