2. 1 Part 2 Mechanical Properties of the Lung and Chest Wall: Static and Dynamic

3. 2 Section I STATIC LUNG MECHNICS: The mechanical properties of a lung whose volume is not changing with time

4. 3 1. Pulmonary Volume and Capacity

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6. 5 Pulmonary Volumes Tidal volume ( 潮气量） –Volume of air inspired or expired during a normal inspiration or expiration (400 – 500 ml) Inspiratory reserve volume （补吸气量） –Amount of air inspired forcefully after inspiration of normal tidal volume (1500 – 2000 ml) Expiratory reserve volume （补呼气量） –Amount of air forcefully expired after expiration of normal tidal volume (900 – 1200 ml) Residual volume （残气量， RV ） –Volume of air remaining in respiratory passages and lungs after the most forceful expiration (1500 ml in male and 1000 ml in female)

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8. 7 Pulmonary Capacities A Capacity is composed of two or more volumes Inspiratory capacity （深吸气量） –Tidal volume plus inspiratory reserve volume Functional residual capacity （功能残气量, FRC ） –Expiratory reserve volume plus the residual volume Vital capacity （肺活量, VC ） –Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume Total lung capacity （肺总量, TLC ） –Sum of inspiratory and expiratory reserve volumes plus the tidal volume and residual volume

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10. 9 RV/TLC Normally less than 0.25 Increase by the obstructive pulmonary disease (RV) Increase during the restrictive lung disease (TLC)

11. 10 Minute and Alveolar Ventilation Minute ventilation: Total amount of air moved into and out of respiratory system per minute Respiratory rate or frequency: Number of breaths taken per minute Anatomic dead space: Part of respiratory system where gas exchange does not take place Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place

12. 11 Dead Space Area where gas exchange cannot occur Includes most of airway volume Anatomical dead space (=150 ml) –Airways Physiological dead space = anatomical + non functional alveoli

13. 12 Basic Structure of the Lung VDVDVDVD A tube = Airway (Trachea – Bronchi – Bronchioles) NO GAS EXCHANGE DEAD SPACE A thin walled Sac = Alveolus Blood Vessels GAS EXCHANGE OCCURS HERE VAVAVAVA Formula: Total Ventilation = Dead Space + Alveolar Space V T = V D + V A

14. 13 Physiological = Anatomical Dead Space Dead Space + Similar Concept: Physiological Dead Space Diseased lungs: Healthy Lungs: Blocked Vessel Additional Dead Space Anatomical Dead Space = Airways (constant) Anatomical Dead Space = Airways (constant) VAVAVAVA VDVDVDVD

15. 14 2. Lung Compliance Lung compliance (C L ) is a measure of the elastic properties of the lung, is a reflection of lung distensibility

16. 15 Elasticity Tendency to return to initial size after distension. High content of elastin proteins. –Very elastic and resist distension. Recoil ability. Elastic tension increases during inspiration and is reduced by recoil during expiration.

17. 16 Compliance Distensibility (stretchability): –Ease with which the lungs can expand. –The compliance is inversely proportional to elastic resistance Change in lung volume per change in transpulmonary pressure.  V/  P 100 x more distensible than a balloon. Specific compliance ( 比顺应性） : the compliance per unit volume

18. 17 0 100 50 030 Lung volume (%TLC) Transpulmonary pressure (cmH 2 O) Static lung compliance C =  V/  P inflation deflation normal breathing

19. 18 Section II DYNAMIC LUNG MECHANICS Aspects of mechanics that studies the lung in motion

20. 19 1. Dynamic Compliance

21. 20 Volume L RV Pleural Pressure 0 6 0 - 30 cm H 2 O - 15 3 Normal (with surfactant) Saline Filled Without surfactant Volume-pressure curves of lungs filled with saline and with air (with or without surfactant)

22. 21 Dynamic lung compliance Is always less than static compliance Increase during exercise Increase during sighing and yawning

23. 22 2. Airflow in Airways

24. 23 Types of Flow

25. 24 Laminar flow … is when concentric layers of gas flow parallel to the wall of the tube. The velocity profile obeys Poiseuille ’ s Law

26. 25 Poiseuille and Resistance Airway Radius or diameter is KEY.  radius by 1/2  resistance by 16 FOLD - think bronchodilator here!!

27. 26  The gas flow in the larger airways (nose, mouth, glottis, and bronchi) is turbulent  Gas flow in the smaller airway is laminar  Breath sounds heard with a stethoscope reflect the turbulent airflow  Laminar flow is silent

28. 27 3. Gas Flow Resistance Elastic Resistance Inelastic Resistance

29. 28 Elastic Resistance  Caused by  the elastic tissue of the lung and the thoracic wall  surface tension of the fluid that lines the inside wall of the alveoli  The elastic resistance caused by surface tension  are much more complex.  accounts for about two thirds of the total elastic resistance

30. 29 Inelastic Resistance  comprises 1.airway resistance (friction) 2.pulmonary tissue resistance (viscosity, and inertia).  the airway resistance account for 80%-90% of the inelastic resistance  the more important both in health and disease.

31. 30 Airway Resistance Airway resistance is the resistance to flow of air in the airways due to : 1) internal friction between gas molecules 2) friction between gas molecules and the walls of the airways

32. 31 Factors that influence airway resistance Airway diameter asthma ( 哮喘） and parasympathetic stimulation: Narrowing airways. Emphysema ( 肺气肿） : decreases small airway diameter during forced expiration Turbulence air flow Rapid breathing: Density and viscosity of the inspired gas

33. 32 Control of Airway Smooth Muscle Neural control –Adrenergic beta receptors causing dilatation –Parasympathetic-muscarinic receptors causing constriction –NANC nerves (non-adrenergic, non-cholinergic) Inhibitory release VIP and NO  bronchodilitation Stimulatory  bronchoconstriction, mucous secretion, vascular hyperpermeability, cough, vasodilation “neurogenic inflammation”

34. 33 Control of Airway Smooth Muscle Local factors –histamine binds to H 1 receptors-constriction –histamine binds to H 2 receptors-dilation –slow reactive substance of anaphylaxis ( 过敏反应） - constriction-allergic response to pollen –Prostaglandins （前列腺速） E series - dilation –Prostaglandins （前列腺素） F series - constriction

35. 34 Control of Airway Smooth Muscle (cont) Environmental pollution –smoke, dust, sulfur dioxide, some acidic elements in smog Elicit constriction of airways –mediated by : parasympathetic reflex local constrictor responses

36. 35 4. Measurement of Expiratory Flow - FVC

37. 36 FVC - forced vital capacity Defines maximum volume of exchangeable air in lung (vital capacity) –forced expiratory breathing maneuver –requires muscular effort and some patient training Initial (healthy) FVC values approx 4 liters –slowly diminishes with normal aging

38. 37 Significantly reduced FVC suggests damage to lung tissue –restrictive lung disease (fibrosis ，纤维化 ) –constructive lung disease –loss of functional alveolar tissue Intra-subject variability factors –age –sex –height –ethnicity FVC - forced vital capacity(cont)

39. 38 FEV1 - forced expiratory volume (1 second) maximum air flow rate out of lung in initial 1 second interval –forced expiratory breathing maneuver –requires muscular effort and some patient training FEV1/FVC ratio –normal FEV1 about 3 liters –FEV1 needs to be normalized to individual’s vital capacity (FVC) –typical normal FEV1/FVC ratio = 3 liters/ 4 liters = 0.75

40. 39 Standard screening measure for obstructive lung disease –FEV1/FVC reduction trend over time (years) is key indicator –calculate % predicted FEV1/FVC (age and height normalized) Reduced FEV1/FVC suggests obstructive damage to lung airways –episodic, reversible by bronchodilator drugs probably asthma ( 哮喘 ) –continual, irreversible by bronchodilator drugs probably COPD （ chronic obstructive pulmonary disease ，慢性阻塞性肺病） FEV1 - forced expiratory volume (1 second)

41. 40 Volume (litres) Time (sec) Forced Vital Capacity - FVC Total Lung Capacity Residual Volume Spirometry Forced Expiratory Volume in 1 sec - FEV 1 1 sec

42. 41 eg fibrosis / pulmonary oedema Assessment of RESTRICTIVE Lung Diseases These are diseases that reduce the effective surface area available for gas exchange Normal Lung Volume Lung Volume in Restrictive Disease

43. 42 REDUCED Volume (litres) Time (sec) Vital Capacity Total Lung Capacity Residual Volume Spirometry RESTRICTIVE lung disease

44. 43 eg asthma / bronchitis Assessment of OBSTRUCTIVE Lung Diseases These are diseases that reduce the diameter of the airways and increase airway resistance - remember Resistance increases with 1/radius 4 Normal Airway Calibre Airway Calibre in Obstructive Disease

45. 44 Forced Vital Capacity - FVC Forced Expiratory Volume in 1 sec - FEV 1 FEV 1 > 80% of FVC is Normal or in words - you should be able to forcibly expire more than 80% of your vital capacity in 1 sec.

46. 45 Forced Vital Capacity - FVC Volume (litres) Time (sec) Total Lung Capacity Residual Volume Spirometry Forced Expiratory Volume in 1 sec - FEV 1 1 sec FEV 1 < 80% of FVC OBSTRUCTIVE lung disease

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