1. Mechanism of Breathing Barasa Ambrose

2. 11-Jun-16Respiratory Movements2 Mechanical Factors in Breathing 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 atmos > P alv Inspiration P atmos < P alv Expiration P atmos P alv

3. 11-Jun-16Respiratory Movements3 Mechanical Factors in Breathing Two ways of producing the necessary pressure differences Alveolar pressure can be lowered below atmospheric pressure –Natural negative pressure breathing P atmos = P alv No air flow P atmos > P alv Inspiration P atmos < P alv Expiration P atmos P alv

4. 11-Jun-16Respiratory Movements4 Mechanical Factors in Breathing Atmospheric pressure can be increased above alveolar pressure –Positive pressure breathing P atmos = P alv No air flow P atmos > P alv Inspiration P atmos < P alv Expiration P atmos P alv

5. 11-Jun-16Respiratory Movements5 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

6. 11-Jun-16Respiratory Movements6 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

7. 11-Jun-16Respiratory Movements7 Respiratory Muscles Inspiratory muscles –Diaphragm,external intercostals –Others Scaleni, sternocleidomastoid, pectoralis minor Expiratory muscles –Internal intercostals –Abdominal recti

8. 11-Jun-16Respiratory Movements8 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

9. 11-Jun-16Respiratory Movements9 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 C 3,4,5 Diaphragm Abdominal content

10. 11-Jun-16Respiratory Movements10 Muscles of Inspiration When the diaphragm move down –Abdominal contents are forced downward –Increase the vertical dimension of the thorax Diaphragm Abdominal content

11. 11-Jun-16Respiratory Movements11 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

12. 11-Jun-16Respiratory Movements12 Muscles of Inspiration The area of the diaphragm –About 250 cm 2 During normal tidal breathing –It increases the thoracic volume by 250 x 1 = 250 cm 3 Diaphragm Abdominal content

13. 11-Jun-16Respiratory Movements13 Muscles of Inspiration During forceful inspiration –It increases the thoracic volume by 250 x 10 = 2500 cm 3 Diaphragm Abdominal content

14. 11-Jun-16Respiratory Movements14 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” Diaphragm Abdominal content External intercostals Lift sternum upwards and forwards AP diameter

15. 11-Jun-16Respiratory Movements15 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

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17. 11-Jun-16Respiratory Movements17 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

18. 11-Jun-16Respiratory Movements18 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

19. 11-Jun-16Respiratory Movements19 Expiration During exercise –Expiration is by active process Contraction of expiratory muscles Internal intercostal muscles –Assist active expiration by Pulling ribs downwards and inwards

20. 11-Jun-16Respiratory Movements20 Mechanics of Breathing From: Exercise Physiology by McArdle, Katch & Katch

21. 11-Jun-16Respiratory Movements21 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

22. 11-Jun-16Respiratory Movements22 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

23. 11-Jun-16Respiratory Movements23 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

24. 11-Jun-16Respiratory Movements24 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

25. 11-Jun-16Respiratory Movements25 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

26. 11-Jun-16Respiratory Movements26 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

27. 11-Jun-16Respiratory Movements27 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 0 -2 -4 -6 -8 +2 Trans- pulmonary pressure Alveolar pressure Pleural pressure Inspiration Expiration

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29. 11-Jun-16Respiratory Movements29 Elastic Resistance Lung tissue is elastic –Natural un-stretched volume Elastic element neither stretched nor compressed Is 1 liter Vol of lung 1 lt 5 lt Thorax Thoracic cavity & lung 2.5 lt

30. 11-Jun-16Respiratory Movements30 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 5 lt Thorax Thoracic cavity & lung 2.5 lt

31. 11-Jun-16Respiratory Movements31 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 5 lt Thorax Thoracic cavity & lung 2.5 lt

32. 11-Jun-16Respiratory Movements32 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 5 lt Thorax Thoracic cavity & lung 2.5 lt

33. 11-Jun-16Respiratory Movements33 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 5 lt Thorax Thoracic cavity & lung 2.5 lt

34. 11-Jun-16Respiratory Movements34 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 Pressure cm H 2 O Volume in ml Increased compliance decreased compliance ΔPΔP ΔVΔV

35. 11-Jun-16Respiratory Movements35 Compliance Compliance –Change in volume (liters)/change in pressure (cm H 2 O) Compliance of –Adult male = 0.09 to 0.26 L/ cm H 2 O –Newborn = 0.005 l/cm H 2 O –At 10 yrs = 0.06 L/ cm H 2 O –Old age = ↓ compliance Pressure cm H 2 O Volume in ml Increased compliance decreased compliance ΔPΔP ΔVΔV

36. 11-Jun-16Respiratory Movements36 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; 5 th Ed

37. 11-Jun-16Respiratory Movements37 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; 5 th Ed

38. 11-Jun-16Respiratory Movements38 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; 5 th Ed

39. 11-Jun-16Respiratory Movements39 Airway Resistance Within the chest –Trachea, lobar & segmental bronchi offer 80% of the remaining resistance –Small airways with diameter less than 2mm contribute 20% 0.08 0.06 0.04 0.02 5101520 Airway generations Airway resist (cm H 2 O/L/S) Segmental bronchi Terminal bronchi Airway resistance VS airway generations

40. 11-Jun-16Respiratory Movements40 Airway Resistance Cross section of individual peripheral airways are small –Their large numbers Generate large overall cross section area Lowers the resistance 0.08 0.06 0.04 0.02 5101520 Airway generations Airway resist (cm H 2 O/L/S) Segmental bronchi Terminal bronchi Airway resistance VS airway generations

41. 11-Jun-16Respiratory Movements41 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 4 3 2 1 2468 Lung volumes (L) Airway resist (cm H 2 O/L/S) Airway resistance VS lung volumes

42. 11-Jun-16Respiratory Movements42 Determinants of Airway Resistance Others –Resistance is proportional to Length of airway Physical properties of the gas –Density, viscosity –Resistance is inversely proportional to 4 th power of radius of the airway

43. 11-Jun-16Respiratory Movements43 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

44. 11-Jun-16Respiratory Movements44 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

45. 11-Jun-16Respiratory Movements45 Airway Resistance Certain disease condition –Increase airway resistance Asthma –Contraction of bronchial smooth muscles –Narrowing of airways –Increased airway resistance

46. 11-Jun-16Respiratory Movements46 Airway Resistance Chronic bronchitis –Oedema of bronchial mucosa Excessive secretion by bronchial mucosa Increase airway resistance Intramural masses –Bronchogenic carcinoma –Occlude airways

47. 11-Jun-16Respiratory Movements47 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

48. 11-Jun-16Respiratory Movements48 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