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Breathing mechanics


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Breathing mechanics

  1. 1. Moderator : Dr Padmanabha Presenter : Dr Nikhil mp
  2. 3. <ul><li>Diaphragm </li></ul><ul><li>Dome shaped muscle . </li></ul><ul><li>Inserted to lower rib. </li></ul><ul><li>Phrenic nerve- C 3, 4, 5.. </li></ul><ul><li>Abdominal contents are pushed forward and downward & vertical dimension of chest cavity is increased. </li></ul><ul><li>Transverse diameter increased. </li></ul>
  3. 4. <ul><li>Paradoxical movement. </li></ul><ul><li>External intercostals </li></ul><ul><li>Ribs are pulled upward & forward causing increase in lateral & AP of thorax. </li></ul><ul><li>“ Bucket handle movement” </li></ul><ul><li>“ Pump handle movement”. </li></ul><ul><li>Accessory muscles </li></ul><ul><li>scalene & sternocliedomastoid. </li></ul>
  4. 7. <ul><li>Passive during quiet breathing. </li></ul><ul><li>Active - exercise and hyperventilation. </li></ul><ul><li>Muscles of abdominal wall. </li></ul><ul><li>When muscles contract intraabdominal pressure rise & diaphragm is pushed upwards. </li></ul>
  5. 8. <ul><li>Movements of lung is passive. </li></ul><ul><li>Impedence of the respiratory system. </li></ul><ul><li>Elastic resistance. </li></ul><ul><li>Non elastic resistance. </li></ul>
  6. 9. <ul><li>Lung & chest wall. </li></ul><ul><li>Surface forces at alveolar gas liquid interface. </li></ul>
  7. 10. <ul><li>Lungs and chest have elastic properties. </li></ul><ul><li>Chest has tendency to expand. </li></ul><ul><li>Lungs have tendency to collapse . </li></ul><ul><li>Recoil properties of chest due to components that resist deformation. </li></ul><ul><li>In case of lung - elastin fibres & surface tension forces acting at air fluid interface. </li></ul>
  8. 11. <ul><li>Elastic recoil of the lungs is measured in terms of compliance. </li></ul><ul><li>Compliance is defined as change in lung volume per unit change in transmural pressure gradient. </li></ul><ul><li>150 to 200ml/cm H 2 O. </li></ul><ul><li>Static . </li></ul><ul><li>Dynamic. </li></ul><ul><li>Stiff lungs have low compliance. </li></ul>
  9. 12. <ul><li>Reduced compliance </li></ul><ul><li>fibrosis. </li></ul><ul><li>alveolar edema. </li></ul><ul><li>Increased compliance </li></ul><ul><li>emphysema. </li></ul><ul><li>aging . </li></ul>
  10. 13. <ul><li>Previously – elastin fibres. </li></ul><ul><li>Von-Neergaard – surface tension acting at the air water interface lining the alveoli. </li></ul>
  11. 14. <ul><li>Surface tension at an air-water interface produces forces that reduce the area of the interface. </li></ul><ul><li>Alveoli can be compared to a bubble. </li></ul><ul><li>Gas pressure within the bubble is higher than the sorrounding. </li></ul><ul><li>Laplace equation, P= 2T/R </li></ul><ul><li>P=Pressure within the bubble </li></ul><ul><li>T =surface tension </li></ul><ul><li>R = radius of bubble </li></ul>
  12. 16. <ul><li>Low surface tension of alveolar lining fluid and its dependance on alveolar radius – surfactant. </li></ul><ul><li>Alveolar epithelial cells- type II. </li></ul><ul><li>90% lipids & rest protiens and carbohydrate. </li></ul><ul><li>Dipalmitoyl phosphatidyl choline. </li></ul>
  13. 17. <ul><li>To maintain the stability of alveoli. </li></ul><ul><li>Immunology of the lung. </li></ul>
  14. 19. <ul><li>Most </li></ul><ul><li>Frictional resistance to air flow. </li></ul><ul><li>Thoracic tissue deformation. </li></ul>
  15. 20. <ul><li>Gas flows from area of high pressure to area of low pressure </li></ul><ul><li>The rate at which it does is a function of the pressure difference and the resistance to gas flow </li></ul>
  16. 21. <ul><li>2 types </li></ul><ul><li>Laminar flow </li></ul><ul><li>Turbulent flow </li></ul>
  17. 22. <ul><li>Gas flows along a straight unbranched tube as a series of concentric cylinders that slide over one another,with peripheral cylinder stationary and central fastest,advancing cone forming a parabola </li></ul>
  18. 25. <ul><li>FG will reach end of the tube while volume entering the tube is less than the volume of the tube </li></ul><ul><li>Significant alveolar ventilation </li></ul><ul><li>tidal volume < volume of the airways </li></ul>
  19. 26. <ul><li>Friction between tube wall and fluid is negligible. </li></ul><ul><li>Significant alveolar ventilation when the tidal volume < the volume of airways. </li></ul>
  20. 27. <ul><li>Inefficient for purging the contents of the tube. </li></ul><ul><li>Gas sampled from periphery may not be representative of the gas in the centre. </li></ul><ul><li>Requires a critical length of tubing </li></ul><ul><li>before typical flow pattern . </li></ul>
  21. 28. <ul><li>Gas flow is proportional to pressure gradient and constant being resistance to gas flow. </li></ul><ul><li>∆ P =flow x resistance. </li></ul><ul><li>∆ P = pressure gradient. </li></ul>
  22. 29. <ul><li>Hagen-poiseuille eqn,gas flow in straight unbranched tube </li></ul><ul><li>Pressure G X ∏ X r4 </li></ul><ul><li>Flow rate= </li></ul><ul><li>8 X length X viscosity </li></ul>
  23. 30. <ul><li>8 X length X viscosity </li></ul><ul><li>Resistance = </li></ul><ul><li>∏ X radius 4 </li></ul><ul><li>Viscosity is the only property of gas relevant in laminar flow </li></ul>
  24. 31. <ul><li>High flow rates. </li></ul><ul><li>Branched or irregular tubes. </li></ul><ul><li>Sharp angles </li></ul><ul><li>Irregular movement of gas molecules . </li></ul><ul><li>Square front replaces cone front. </li></ul>
  25. 34. <ul><li>No FG can reach the end of the tube until amount of gas entering the tube is equal to the volume of the tube. </li></ul><ul><li>Frictional forces are important. </li></ul>
  26. 35. <ul><li>More effective in purging the contents of the tube. </li></ul><ul><li>Best conditions for drawing a representative sample of gas. </li></ul>
  27. 36. <ul><li>Driving pressure is proportional </li></ul><ul><li>To the square of the gas flow. </li></ul><ul><li>Density of gas. </li></ul><ul><li>Inversely proportional to the fifth power of radius. </li></ul><ul><li>Independent of viscosity. </li></ul>
  28. 37. <ul><li>The nature of gas flow . </li></ul><ul><li>Linear velocity of gas X tube diameter X gas density </li></ul><ul><li>gas viscosity </li></ul><ul><li>< 2000 - laminar. </li></ul><ul><li>> 4000 - turbulent. </li></ul><ul><li>Both between 2000 - 4000. </li></ul><ul><li>Low resistance . </li></ul><ul><li>Establishment of laminar flow faster. </li></ul>
  29. 39. <ul><li>Frictional resistance </li></ul><ul><li>In healthy people,Larger airways responsible </li></ul><ul><li>Smaller airways : small contribution </li></ul>
  30. 40. <ul><li>Velocity of gas flow & airway diameter decreases in successive airway generations. </li></ul><ul><li>Entrance length greater. </li></ul><ul><li>Frequent divisions. </li></ul>
  31. 41. <ul><li>Gas mixtures having low Reynolds number beneficial in large airway disease. </li></ul><ul><li>Physical characteristics of airway lining will influence frictional resistance. </li></ul>
  32. 42. <ul><li>Primarily due to viscoelastic resistance. </li></ul><ul><li>Lung & chestwall tissues. </li></ul>
  33. 43. <ul><li>Airway diameter </li></ul><ul><li>Physical compression </li></ul><ul><li>Contraction of smooth muscles </li></ul>
  34. 44. <ul><li>Effect of lung volume on resistance to breathing </li></ul><ul><li>Airway resistance is an inverse function of lung volume </li></ul><ul><li>At low lung volume ,flow related airway collapse occurs </li></ul><ul><li>Expiratory airway collapse </li></ul><ul><li>Valve effect </li></ul><ul><li>Gas trapping </li></ul><ul><li>CPAP & PEEP </li></ul>
  35. 45. <ul><li>Closing capacity </li></ul><ul><li>Lung volume at which airways in the dependant part of the lung begins to close. </li></ul><ul><li>Closing volume = closing capacity – RV. </li></ul>
  36. 46. <ul><li>< FRC in young adults. </li></ul><ul><li>Equal to FRC at 44 yrs in supine position & 66yrs in upright position. </li></ul><ul><li>When FRC < closing capacity SHUNT. </li></ul>
  37. 47. <ul><li>Reversal of normal transmural pressure gradient </li></ul><ul><li>During maximal forced expiration –intrathoracic pressure is above atmospheric pressure </li></ul><ul><li>Pressure drops equal pressure point </li></ul><ul><li>Downstream transmural pressure is </li></ul><ul><li>reversed </li></ul><ul><li>Airway collapse </li></ul>
  38. 50. <ul><li>When expiration is passive </li></ul><ul><li>Work of breathing is done by inspiratory muscles. </li></ul><ul><li>Half dissipated as heat & half stored as PE. </li></ul><ul><li>PE is available for expiration. </li></ul>
  39. 51. <ul><li>Actual work by respiratory muscles is small. </li></ul><ul><li>02 consumption – 3ml/min. </li></ul><ul><li>Efficiency is 10%. </li></ul><ul><li>When maximum ventilation is approached efficiency falls to lowest level. </li></ul>
  40. 52. <ul><li>Work done to overcome elastic resistance increases as tidal volume increases. </li></ul><ul><li>Work done to overcome airflow resistance increases as RR increases. </li></ul>
  41. 53. <ul><li>Nunn’s respiratory physiology,6 th edition. </li></ul><ul><li>Respiratory physiology ,JOHN B .WEST,8 th edition. </li></ul><ul><li>Millers anaesthesia,6 th edn. </li></ul><ul><li>Clinical anaesthesiology,G.Edward morgan,4 th edn. </li></ul>