Breathing mechanics

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  • 1. Moderator : Dr Padmanabha Presenter : Dr Nikhil mp
  • 2.  
  • 3.
    • Diaphragm
    • Dome shaped muscle .
    • Inserted to lower rib.
    • Phrenic nerve- C 3, 4, 5..
    • Abdominal contents are pushed forward and downward & vertical dimension of chest cavity is increased.
    • Transverse diameter increased.
  • 4.
    • Paradoxical movement.
    • External intercostals
    • Ribs are pulled upward & forward causing increase in lateral & AP of thorax.
    • “ Bucket handle movement”
    • “ Pump handle movement”.
    • Accessory muscles
    • scalene & sternocliedomastoid.
  • 5.  
  • 6.  
  • 7.
    • Passive during quiet breathing.
    • Active - exercise and hyperventilation.
    • Muscles of abdominal wall.
    • When muscles contract intraabdominal pressure rise & diaphragm is pushed upwards.
  • 8.
    • Movements of lung is passive.
    • Impedence of the respiratory system.
    • Elastic resistance.
    • Non elastic resistance.
  • 9.
    • Lung & chest wall.
    • Surface forces at alveolar gas liquid interface.
  • 10.
    • Lungs and chest have elastic properties.
    • Chest has tendency to expand.
    • Lungs have tendency to collapse .
    • Recoil properties of chest due to components that resist deformation.
    • In case of lung - elastin fibres & surface tension forces acting at air fluid interface.
  • 11.
    • Elastic recoil of the lungs is measured in terms of compliance.
    • Compliance is defined as change in lung volume per unit change in transmural pressure gradient.
    • 150 to 200ml/cm H 2 O.
    • Static .
    • Dynamic.
    • Stiff lungs have low compliance.
  • 12.
    • Reduced compliance
    • fibrosis.
    • alveolar edema.
    • Increased compliance
    • emphysema.
    • aging .
  • 13.
    • Previously – elastin fibres.
    • Von-Neergaard – surface tension acting at the air water interface lining the alveoli.
  • 14.
    • Surface tension at an air-water interface produces forces that reduce the area of the interface.
    • Alveoli can be compared to a bubble.
    • Gas pressure within the bubble is higher than the sorrounding.
    • Laplace equation, P= 2T/R
    • P=Pressure within the bubble
    • T =surface tension
    • R = radius of bubble
  • 15.  
  • 16.
    • Low surface tension of alveolar lining fluid and its dependance on alveolar radius – surfactant.
    • Alveolar epithelial cells- type II.
    • 90% lipids & rest protiens and carbohydrate.
    • Dipalmitoyl phosphatidyl choline.
  • 17.
    • To maintain the stability of alveoli.
    • Immunology of the lung.
  • 18.  
  • 19.
    • Most
    • Frictional resistance to air flow.
    • Thoracic tissue deformation.
  • 20.
    • Gas flows from area of high pressure to area of low pressure
    • The rate at which it does is a function of the pressure difference and the resistance to gas flow
  • 21.
    • 2 types
    • Laminar flow
    • Turbulent flow
  • 22.
    • 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
  • 23.  
  • 24.  
  • 25.
    • FG will reach end of the tube while volume entering the tube is less than the volume of the tube
    • Significant alveolar ventilation
    • tidal volume < volume of the airways
  • 26.
    • Friction between tube wall and fluid is negligible.
    • Significant alveolar ventilation when the tidal volume < the volume of airways.
  • 27.
    • Inefficient for purging the contents of the tube.
    • Gas sampled from periphery may not be representative of the gas in the centre.
    • Requires a critical length of tubing
    • before typical flow pattern .
  • 28.
    • Gas flow is proportional to pressure gradient and constant being resistance to gas flow.
    • ∆ P =flow x resistance.
    • ∆ P = pressure gradient.
  • 29.
    • Hagen-poiseuille eqn,gas flow in straight unbranched tube
    • Pressure G X ∏ X r4
    • Flow rate=
    • 8 X length X viscosity
  • 30.
    • 8 X length X viscosity
    • Resistance =
    • ∏ X radius 4
    • Viscosity is the only property of gas relevant in laminar flow
  • 31.
    • High flow rates.
    • Branched or irregular tubes.
    • Sharp angles
    • Irregular movement of gas molecules .
    • Square front replaces cone front.
  • 32.  
  • 33.  
  • 34.
    • No FG can reach the end of the tube until amount of gas entering the tube is equal to the volume of the tube.
    • Frictional forces are important.
  • 35.
    • More effective in purging the contents of the tube.
    • Best conditions for drawing a representative sample of gas.
  • 36.
    • Driving pressure is proportional
    • To the square of the gas flow.
    • Density of gas.
    • Inversely proportional to the fifth power of radius.
    • Independent of viscosity.
  • 37.
    • The nature of gas flow .
    • Linear velocity of gas X tube diameter X gas density
    • gas viscosity
    • < 2000 - laminar.
    • > 4000 - turbulent.
    • Both between 2000 - 4000.
    • Low resistance .
    • Establishment of laminar flow faster.
  • 38.  
  • 39.
    • Frictional resistance
    • In healthy people,Larger airways responsible
    • Smaller airways : small contribution
  • 40.
    • Velocity of gas flow & airway diameter decreases in successive airway generations.
    • Entrance length greater.
    • Frequent divisions.
  • 41.
    • Gas mixtures having low Reynolds number beneficial in large airway disease.
    • Physical characteristics of airway lining will influence frictional resistance.
  • 42.
    • Primarily due to viscoelastic resistance.
    • Lung & chestwall tissues.
  • 43.
    • Airway diameter
    • Physical compression
    • Contraction of smooth muscles
  • 44.
    • Effect of lung volume on resistance to breathing
    • Airway resistance is an inverse function of lung volume
    • At low lung volume ,flow related airway collapse occurs
    • Expiratory airway collapse
    • Valve effect
    • Gas trapping
    • CPAP & PEEP
  • 45.
    • Closing capacity
    • Lung volume at which airways in the dependant part of the lung begins to close.
    • Closing volume = closing capacity – RV.
  • 46.
    • < FRC in young adults.
    • Equal to FRC at 44 yrs in supine position & 66yrs in upright position.
    • When FRC < closing capacity SHUNT.
  • 47.
    • Reversal of normal transmural pressure gradient
    • During maximal forced expiration –intrathoracic pressure is above atmospheric pressure
    • Pressure drops equal pressure point
    • Downstream transmural pressure is
    • reversed
    • Airway collapse
  • 48.  
  • 49.  
  • 50.
    • When expiration is passive
    • Work of breathing is done by inspiratory muscles.
    • Half dissipated as heat & half stored as PE.
    • PE is available for expiration.
  • 51.
    • Actual work by respiratory muscles is small.
    • 02 consumption – 3ml/min.
    • Efficiency is 10%.
    • When maximum ventilation is approached efficiency falls to lowest level.
  • 52.
    • Work done to overcome elastic resistance increases as tidal volume increases.
    • Work done to overcome airflow resistance increases as RR increases.
  • 53.
    • Nunn’s respiratory physiology,6 th edition.
    • Respiratory physiology ,JOHN B .WEST,8 th edition.
    • Millers anaesthesia,6 th edn.
    • Clinical anaesthesiology,G.Edward morgan,4 th edn.
  • 54.