Respiration

1. Respiration Xia Qiang, PhD Department of Physiology Zhejiang University School of Medicine Email: xiaqiang@zju.edu.cn

3. The major parts of the “airways,” along which air movements (ventilation) occur during breathing.

4. The relaxation/contraction of circular smooth muscle lining these “airways’” determines how easily airflow can occur (bronchodilation vs. bronchoconstriction). Most gas exchange occurs in the ~8,000,000 alveolar sacs.

6. Respiratory process External respiration Internal respiration

7. Pulmonary ventilation • Definition: The process of moving air into and out of the lungs

9. Thorax & respiratory muscle Primary muscles of respiration: external intercostals & diaphragm

10. Breathing is an active process • To inhale • Contraction of external intercostal muscles  elevation of ribs & sternum  increased front- to-back dimension of thoracic cavity  lowers air pressure in lungs  air moves into lungs • Contraction of diaphragm  diaphragm moves downward  increases vertical dimension of thoracic cavity  lowers air pressure in lungs  air moves into lungs

11. Breathing is an active process • To exhale • Relaxation of external intercostal muscles & diaphragm  return of diaphragm, ribs, & sternum to resting position  restores thoracic cavity to preinspiratory volume  increases pressure in lungs  air is exhaled

12. Pattern of respiration • Eupnea • Forced breathing

13. Intrapulmonary pressure

14. The Heimlich maneuver increases the alveolar pressure (Palv) by supplementing the upward movement of the diaphragm, thus compressing the thoracic cavity to dislodge foreign objects in the airways.

15. Pleural pressure • Pleural cavity • Pleural cavity is the closed space between parietal pleura & lungs covered with visceral pleura

16. Pleural pressure • Pleural pressure is the pressure within pleural cavity

17. Measurement of intrapleural pressures • Direct method

18. Measurement of intrapleural pressures • Indirect method

20. Inspiration is the result of the expansion of the thoracic cage in response to skeletal muscle contraction. The expansion reduces alveolar pressure (Palv) below atmospheric pressure (Patm), so air moves into the lungs.

21. Expiration is the result of reducing the volume of the thoracic cage; in a resting person, this occurs in response to skeletal muscle relaxation. The volume reduction increases alveolar pressure (Palv) above atmospheric pressure (Patm), so air moves out of the lungs.

22. Formation of intrapleural pressure • Fetus lung

23. Formation of intrapleural pressure • Air in lungs after delivery

24. Intrapleural pressure • Pressures involved • Atmospheric (760 mmHg) pressure =Intrapulmonary pressure • Elastic recoil • Intrapleural pressure

26. Intrapleural pressure • Physiological significance of intrapleural negative pressure • Allow expansion of the lungs • Facilitate the venous & lymphatic return

27. Pneumothorax • Air escapes from the lungs or leaks through the chest wall and enters the pleural cavity

28. Lateral Bilateral

30. Compliance of the lungs • Compliance: the extent to which the lungs expand for each unit increase in pressure C=ΔV/ΔP (L/cmH2O)

31. Compliance varies within the lung according to the degree of inflation. Poor compliance is seen at low volumes (because of difficulty with initial lung inflation) and at high volumes (because of the limit of chest wall expansion), with best compliance in the mid-expansion range

32. Lung compliance is a measure of the lung’s “stretchability.” When compliance is abnormally high, the lungs might fail to hold themselves open, and are prone to collapse. When compliance is abnormally low, the work of breathing is increased.

33. Elasticity of lungs • Definition • Tendency to return to initial structure after being distended • Elastic force (R) C=1/R

34. Elastic forces of the lungs • 1/3 Elastic forces of the lung tissue itself • 2/3 Elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli

35. Surface tension • Definition • Tension of a liquid's surface. Due to the forces of attraction between molecules

36. Effect of detergent

37. Pierre Simon Laplace(1749 - 1827) Laplace’s law: P=2T/r

38. Effect of size of sphere

39. Alveolar surfactant • Surfactant is a complex mixture • Several phospholipids (dipalmitoylphosphatidylcholine) • Proteins (apoproteins) • Ions (calcium) • Secreted by type II alveolar epithelial cells

40. Type II alveolar epithelial cells

42. Alveolar surfactant • Physiological effect of surfactant Reduces surface tension • Maintains the stability of the alveoli in different size • Keeps the dryness of the alveoli • Eases expansion of lung (increases compliance)

44. In the absence of surfactant, the attraction between water molecules (H-bonds) can cause alveolar collapse. By reducing the surface tension of water, surfactant helps prevent alveolar collapse.

45. Neonatal respiratory distress syndrome (NRDS): lack of surfactant cyanosis retraction of soft tissue on inspiration (“seesaw”)

46. Non-elastic resistance • Inertia resistance • Viscosity resistance • Airway resistance: 80~90% • R =ΔP/ V • R1/r4 (laminar flow) • R1/r5 (turbulent flow)

48. Regulation of the respiratory smooth muscle • Vagus nerve: Ach M receptor  Contraction • Sympathetic nerve: NE 2-receptor  Relaxation • Histamine, Bradykinin  Contraction • NE, E, Isoproterenol  Relaxation

49. Asthma Pathophysiology of asthma

50. Pulmonary volumes and capacities • Spirometer