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Mechanics of respiration

Mechanics of respiration. Dr.Kalpana. Specific Learning objectives. At the end of class students should be able to List the muscles of inspiration and expiration Explain the mechanism of action of muscles of respiration Explain the volume and pressure changes during respiration.

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Mechanics of respiration

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  1. Mechanics of respiration Dr.Kalpana

  2. Specific Learning objectives • At the end of class students should be able to • List the muscles of inspiration and expiration • Explain the mechanism of action of muscles of respiration • Explain the volume and pressure changes during respiration

  3. VENTILATION • Breathing in – inspiration / inhalation • Breathing out – expiration / exhalation

  4. Ventilation • Occurs because the thoracic cavity changes volume • Insipiration uses external intercostals and diaphragm • Expiration is passive at rest, but uses internal intercostals and abdominals during severe respiratory load • Breathing rate is 10-20 breaths / minute at rest, 40 - 45 at maximum exercise in adults

  5. PRIMARY MUSCLES OF INSPIRATION • Diaphragm - increases the vertical diameter of chest wall (75% of inspiration) • External intercostals - increase the transverse and A-P diameters of chest wall (25% of inspiration)

  6. Diaphragm is the main muscle of Inspiration • When the diaphragm contracts, it pulls from the ribcage, flattening out. • Innervated by phrenic nerves.

  7. Inspiration Diaphragmatic movement Diaphragm relaxes Diaphragm contracts

  8. Movement of the Diaphragm Figure 17-9b

  9. External intercostal muscle

  10. External intercostals muscles • Connect higher rib to lower • When the muscle contracts-raises the lower ribs • Transverse and anteroposterior diameters of thorax.

  11. Bucket handle movement-increase the transverse diameter of the thoracic cavity. 2nd to 10th ribs rotate upward and outward • Pump-handle movement increase the anteroposterior diameter. Upper 4 ribs rotate the sternum upward and outward direction.

  12. Movement of the Rib Cage during Inspiration Figure 17-10a

  13. Movement of the Rib Cage during Inspiration Figure 17-10b

  14. Rib Cage Contract IntercostalsContractto Lift Spine Rib Volume Ribs Diaphragm Volume Mechanisms of Breathing: How do we change the volume of the rib cage ? • To Inhale is an ACTIVE process • Diaphragm • External Intercostal Muscles

  15. ACCESSORY MUSCLES OF INSPIRATION • Sternomastoid • Scaleni • Neck and back muscles • Muscles of upper respiratory tract ( Work during forced inspiration, exercise, airway obstruction)

  16. EXPIRATION • Passive process • Results from elastic recoil of chest wall and lungs • No primary muscles of expiration.

  17. MUSCLES OF FORCED EXPIRATION Accessory muscles • Abdominal muscles-internal oblique, external oblique • Internal intercostals • Neck and back muscles

  18. Internal intercostal muscle Abdominals

  19. Expiration

  20. Modes of Breathing • Quiet Breathing • Inhalation requires muscles • Contraction of diaphragm (75%), external intercostals (25%) • Exhalation passive • Lungs recoil due to elasticity • Forced Breathing • Inhalation • Accessory muscles include sternocleidomastoid and scalenes (muscles of the neck) • Exhalation • Internal intercostals, abdominal muscles

  21. Pressures That Cause the Movement of Air In and Out of the Lungs(Pressure changes during ventilation)

  22. Pressure Relationships in the Thoracic Cavity • Respiratory pressure is always described relative to atmospheric pressure • Atmospheric pressure (Patm) - pressure exerted by the air surrounding the body • Intrapulmonary pressure (PA) – pressure within the alveoli • Intrapleural pressure (Pip) – pressure within the pleural cavity

  23. Inspiration Expiration

  24. Intra pulmonary pressure/ alveolar pressure: pressure in the alveolus/lungs Expiration -+1mm Hg Inspiration -1 mm Hg Factors affecting Intra pulmonary pressure: 1. Valsalva manoeuvre-forced expiration against closed glottis 2. Muller`s manoeuvre-forced inspiration against closed glottis

  25. Intra pleural pressure : • pressure in the pleural space Quiet breathing • Expiration -2.5 to -4 mm Hg(app -5 cm H20) • Inspiration -6 mm Hg(app -8 cm H20) • Forced expiration, intra pleural pressure becomes positive and during forced inspiration upto -30 mm Hg • Measurement-introducing balloon catheter through mouth into esophagus-intraesophageal pressure

  26. Elastic recoil effects of lung and chest wall are exerted equally but in opposite directions

  27. Factors affecting intrapleural pressure: Physiological factors • Effect of gravity: ppl-in standing position is more negative at the apex compared to base. • Deep inspiration • Valsalva manoeuvre

  28. Pathological factors: Emphysema Injury to thoracic wall

  29. Physiological significance • Decrease in intrapleural pressure helps the lung to expand • Maintains the normal shape of chest wall and lungs. Clinical significance pneumothorax

  30. Pressure in the Pleural Cavity Pneumothorax results in collapsed lung that can not function normally Figure 17-12b

  31. Injury to the Chest Wall • Pneumothorax: • allows air into pleural cavity

  32. TRANSMURAL PRESSURE TRANSPULMONARY PRESSURE –pressure difference across lung wall • The difference between the alveolar pressure and the pleural pressure. Keeps the lungs inflated and prevent lung collapse. TRANSAIRWAY PRESSURE-pressure difference across airway • Difference between airway and pleural pressure.-keeps the airway open during forced expiration.

  33. Inspiration • Inspiration-Active process • More volume -> lowered pressure -> air in. (Negative pressure breathing.) • Intrapulmonary pressure decreases (759 mm Hg

  34. Contraction of diaphragm • Expansion of thoracic cage • Intrapleural pressure becomes more negative • Increased transpulmonary pressure • Inflation of lung • Decreased alveolar pressure which becomes sub atmospheric • Air flows into airway and lungs • Cessation of contraction of inspiratory muscles ends inspiration

  35. Inspiration 1) Our diaphragm pulls down 4) Air is sucked through the tubes into the lungs 2) Our intercostal muscles contract 3) Our chest expands Mechanics of Breathing

  36. Expiration • Relaxation of inspiratory muscles • Dropping of rib cage • Intrapleural pressure becomes less negative • Decrease transpulmonary pressure • Deflation of lung • Increased alveolar pressure which becomes more than atmospheric pressure • Air flows out of the lungs • Expiration continues till alveolar pressure equals atmospheric pressure.

  37. Expiration 1) Our diaphragm relaxes into its dome position 4) Air is forced out 2) Our intercostal muscles relax 3) Our chest becomes smaller GCSE PE Mechanics of Breathing

  38. Summary

  39. References • Comprehensive Textbook of Medical physiology (Vol 2 first edition) G K Pal • Text book of medical physiology (Vol 2 6 th edition) A K Jain AEJ

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