1 / 47

Mechanism of Breathing

Mechanism of Breathing. Barasa Ambrose. Mechanical Factors in Breathing. P atmos. Air flows from region of high pressure to region of low pressure Flow = (P 1 – P 2 )/R 1/R = k Flow = k(P 1 – P 2 ). P atmos = P alv No air flow. P alv. P atmos. P atmos > P alv Inspiration. P alv.

annettet
Download Presentation

Mechanism of Breathing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Mechanism of Breathing Barasa Ambrose

  2. Mechanical Factors in Breathing Patmos • Air flows from region of high pressure to region of low pressure • Flow = (P1 – P2)/R • 1/R = k • Flow = k(P1 – P2) Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv Respiratory Movements

  3. Mechanical Factors in Breathing Patmos • Two ways of producing the necessary pressure differences • Alveolar pressure can be lowered below atmospheric pressure • Natural negative pressure breathing Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv Respiratory Movements

  4. Mechanical Factors in Breathing Patmos • Atmospheric pressure can be increased above alveolar pressure • Positive pressure breathing Patmos = Palv No air flow Palv Patmos Patmos > Palv Inspiration Palv Patmos Patmos < Palv Expiration Palv Respiratory Movements

  5. Natural Breathing • Accomplished by • Active contraction of inspiratory muscles • Thoracic volume increases • Intrathoracic pressure decreases • Pulls on the lungs • Enlarges the alveoli Increase in thoracic volume decrease intrathoracic pressure Respiratory Movements

  6. Natural Breathing • Expands alveolar gas • Decreases its pressure below atmospheric pressure • Air at atmospheric pressure • Flows into lungs Increase in thoracic volume decrease intrathoracic pressure Respiratory Movements

  7. Respiratory Muscles • Inspiratory muscles • Diaphragm,external intercostals • Others • Scaleni, sternocleidomastoid, pectoralis minor • Expiratory muscles • Internal intercostals • Abdominal recti Respiratory Movements

  8. Respiratory Muscles • Have no inherent rhythm • Do not contract if they do not receive motor impulses • Motor impulses originate from • Higher centers, respiratory centers, spinal cord Respiratory Movements

  9. Muscles of Inspiration • Diaphragm • Most important muscle of inspiration • In quite breathing • May be the only active inspiratory muscle • Its motor nerve leaves the spinal cord C3,4,5 Diaphragm Abdominal content Respiratory Movements

  10. Muscles of Inspiration • When the diaphragm move down • Abdominal contents are forced downward • Increase the vertical dimension of the thorax Diaphragm Abdominal content Respiratory Movements

  11. Muscles of Inspiration • In quite breathing • Diaphragm moves down by about 10mm (1 cm) • In forceful inspiration • It can move down by 10 cm Diaphragm Abdominal content Respiratory Movements

  12. Muscles of Inspiration • The area of the diaphragm • About 250 cm2 • During normal tidal breathing • It increases the thoracic volume by • 250 x 1 = 250 cm3 Diaphragm Abdominal content Respiratory Movements

  13. Muscles of Inspiration • During forceful inspiration • It increases the thoracic volume by • 250 x 10 = 2500 cm3 Diaphragm Abdominal content Respiratory Movements

  14. Muscles of Inspiration • External intercostals • Connect adjacent ribs • Slope downwards & forwards • When they contract • Ribs are lifted upwards • Causing an increase in AP diameter • “Pump handle” External intercostals Lift sternum upwards and forwards AP diameter Diaphragm Abdominal content Respiratory Movements

  15. Muscles of Inspiration • When the external intercostals contract • Ribs are lifted upwards • In addition they are also moved outwards • “Bucket handle” effect • This increases the transverse diameter (From Hassen Taha Sherrif ) Textbook of Physiology CD Respiratory Movements

  16. Respiratory Movements

  17. Overall Effects • Inspiratory muscles • Increase the thoracic volume • Increase lung volumes • Decrease in intrapulmonary pressure • Cause influx of air • From region of high pressure • To region of low pressure From Textbook of Work Physiology by Astrand, Rodahl, Dahl & Stromme Respiratory Movements

  18. Expiration • During quite breathing • Expiration is Passive • After inspiratory muscles relax • Elastic recoil of lungs and chest wall • Cause movement of air from lungs to atmosphere Respiratory Movements

  19. Expiration • During exercise • Expiration is by active process • Contraction of expiratory muscles • Internal intercostal muscles • Assist active expiration by • Pulling ribs downwards and inwards Respiratory Movements

  20. Mechanics of Breathing From: Exercise Physiology by McArdle, Katch & Katch Respiratory Movements

  21. Pressure Changes in the Lungs and Thorax • Lungs are separated from the rib cage by • Parietal & visceral pleura • Between these there is • Pleural fluid • Lubricant film 20 m thick Respiratory Movements

  22. Pressure Changes in the Lungs and Thorax • The thoracic cage • Has a tendency to expand • The lungs • Have a tendency to collapse • Held together by the action of pleural fluid Respiratory Movements

  23. Pressure Changes in the Lungs and Thorax • Intrathoracic (intra pleural) pressure • Normally = -5 mm Hg • At the end of expiration during quiet breathing • During inspiration it is = -8 to –10 mm Hg • It is a measure of elastic recoil of the stretched lungs and the compressed thoracic cage Respiratory Movements

  24. Pressure Changes in the Lungs and Thorax • Alveolar pressure • Pressure of the air inside the lung alveoli • When glottis is open & no air flowing into or out of the lung • This pressure is equal to atmospheric pressure P atmos P alv Alveolus P alv = P atmos Respiratory Movements

  25. Pressure Changes in the Lungs and Thorax • To cause inward flow of air into alveoli during inspiration • Pressure falls to values below atmospheric (-1 cm of water) • This is enough to cause 0.5 liters of air move into lungs P atmos P alv Alveolus P alv < P atmos Respiratory Movements

  26. Pressure Changes in the Lungs and Thorax • During expiration • Alveolar pressure increases (+1 cm of water) • Enough to cause movement of 0.5 liters of air out of the lung P atmos P alv Alveolus P alv > P atmos Respiratory Movements

  27. Pressure Changes in the Lungs and Thorax • Trans-pulmonary pressure • Pressure difference between alveolar pressure and pleural pressure • It is a measure of elastic forces in the lungs that tend to collapse the lungs • Recoil pressure Inspiration Expiration Alveolar pressure +2 0 Trans-pulmonary pressure -2 -4 -6 Pleural pressure -8 Respiratory Movements

  28. Elastic Resistance • Lung tissue is elastic • Natural un-stretched volume • Elastic element neither stretched nor compressed • Is 1 liter Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax Respiratory Movements

  29. Elastic Resistance • Human lung at the end of expiration • Volume = 2.5 liters • Thus the elastic tissue is always under tension • Tends to oppose expansion of the lungs Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax Respiratory Movements

  30. Elastic Resistance • The natural un-stretched thorax volume is 5 liters • At end of expiration • Volume of thorax is 2.5 liters • The elastic tissues of thorax are compressed Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax Respiratory Movements

  31. Elastic Resistance • Thus • Lungs tend to contract • Thorax tends to expand • The lungs and thorax • Held together by the integrity of the pleural cavity Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax Respiratory Movements

  32. Elastic Resistance • If a gas is introduced in the pleural space • Chest volume tends to expand • Lung volume tend to decrease (collapse of the lungs) Vol of lung 1 lt 2.5 lt Thoracic cavity & lung 5 lt Thorax Respiratory Movements

  33. Compliance • Compliance • Measure of the ability of the lung or chest cavity to be expanded • The degree to which • The lung volume can be changed • By imposed intrapulmonary pressure Increased compliance ΔP ΔV Volume in ml decreased compliance Pressure cm H2O Respiratory Movements

  34. Compliance • Compliance • Change in volume (liters)/change in pressure (cm H2O) • Compliance of • Adult male = 0.09 to 0.26 L/ cm H2O • Newborn = 0.005 l/cm H2O • At 10 yrs = 0.06 L/ cm H2O • Old age = ↓ compliance Increased compliance ΔP ΔV Volume in ml decreased compliance Pressure cm H2O Respiratory Movements

  35. The Airways Resistance • Resistance offered to air as it flows through the respiratory airways • Flow = (P1-P2)/R • Vol of air that flow in/out of alveolar • Directly proportional to pressure gradient • Indirectly proportional to resistance From: Nunn’s Applied Respiratory physiology; 5th Ed Respiratory Movements

  36. The Airways Resistance • Airway resistance • Frictional resistant offered by the walls of tracheobronchial tree • This is note evenly distributed From: Nunn’s Applied Respiratory physiology; 5th Ed Respiratory Movements

  37. The Airways Resistance • During quiet breathing with mouth closed • Nose offers 50% of total resistance • During mouth breathing • Pharynx offers 25% of overall resistance • This figure can increase up to 50% during exercise From: Nunn’s Applied Respiratory physiology; 5th Ed Respiratory Movements

  38. Airway Resistance • Within the chest • Trachea, lobar & segmental bronchi offer 80% of the remaining resistance • Small airways with diameter less than 2mm contribute 20% Airway resistance VS airway generations 0.08 0.06 Airway resist (cm H2O/L/S) 0.04 Segmental bronchi Terminal bronchi 0.02 5 10 15 20 Airway generations Respiratory Movements

  39. Airway Resistance • Cross section of individual peripheral airways are small • Their large numbers • Generate large overall cross section area • Lowers the resistance Airway resistance VS airway generations 0.08 0.06 Airway resist (cm H2O/L/S) 0.04 Segmental bronchi Terminal bronchi 0.02 5 10 15 20 Airway generations Respiratory Movements

  40. Determinants of Airway Resistance • Lung volumes • Greater tethering effect of lung parenchyma on airways • Produce an increase in cross section area of each airway • Results in reduced resistance Airway resistance VS lung volumes 4 3 Airway resist (cm H2O/L/S) 2 1 2 4 6 8 Lung volumes (L) Respiratory Movements

  41. Determinants of Airway Resistance • Others • Resistance is proportional to • Length of airway • Physical properties of the gas • Density, viscosity • Resistance is inversely proportional to • 4th power of radius of the airway Respiratory Movements

  42. Determinants of Airway Resistance • Under normal condition • Airways diameter “large” • Interaction between gas molecules negligible • Length of conducting tube relatively constant • Resistance is largely controlled by radius • Bronchial tree contain smooth muscle • Under the influence of autonomic nerves • Parasympathetic • Sympathetic Respiratory Movements

  43. Determinants of Airway Resistance • Parasympathetic activity causes • Constriction of smooth muscles • Reduction in cross section of airways • Increased resistance • Increased secretion of mucous glands • Sympathetic activity • Bronchodilatation • Inhibition of mucous glad secretion • Reduction in resistance Respiratory Movements

  44. Airway Resistance • Certain disease condition • Increase airway resistance • Asthma • Contraction of bronchial smooth muscles • Narrowing of airways • Increased airway resistance Respiratory Movements

  45. Airway Resistance • Chronic bronchitis • Oedema of bronchial mucosa • Excessive secretion by bronchial mucosa • Increase airway resistance • Intramural masses • Bronchogenic carcinoma • Occlude airways Respiratory Movements

  46. The Work of Breathing • Breathing involves • Application of force over distance • Work is performed by respiratory muscles • Stretching elastic tissues of chest wall & lungs • Elastic work, compliance work • Moving inelastic tissue (viscous resistance) • Tissue resistance work Respiratory Movements

  47. Work of Breathing • Work involved in moving air through the respiratory passages • To overcome airway resistance • Normally negligible • But can be marked • With increase in ventilation (turbulence) • In asthma Respiratory Movements

More Related