Unit Seven: Respiration

1. Unit Seven: Respiration Chapter 37: Pulmonary Ventilation Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Respiration • Four Major Functions of Respiration • Pulmonary ventilation • Diffusion of oxygen and carbon dioxide between the alveoli and the blood • Transport of oxygen and carbon dioxide in the blood and body fluids • Regulation of ventilation

3. Mechanics of Pulmonary Ventilation • Muscles That Cause Lung Expansion and Contraction • Lungs can be expanded and contracted in two ways: • By downward and upward movement of the diaphragm • to lengthen and shorten the chest cavity • By elevation and depression of the ribs to increase and • decrease the anteroposterior diameter of the chest • cavity

4. Mechanics of Pulmonary Ventilation Fig. 37.1 Contraction and expansion of the thoracic cage during expiration and inspiration

5. Mechanics of Pulmonary Ventilation (cont.) • Normal quiet breathing is accomplished almost • entirely by movement of the diaphragm • During inspiration, contraction of the diaphragm • pulls the lungs downward • During expiration, the diaphragm simply relaxes, • and the elastic recoil compresses the lungs and • expels the air

6. Mechanics of Pulmonary Ventilation (cont.) • During heavy breathing the elastic forces are not • powerful enough, so extra force is generated by • the abdominal muscles • Muscles that raise the rib cage are the external • intercostals (most important), sternocleidomastoid, • anterior serratus, and scalenes • Muscles that pull the rib cage downward during • expiration are the abominal rectus, and the internal • intercostals

7. Mechanics of Pulmonary Ventilation (cont.) • Pressures That Cause the Movement of Air In and • Out of the Lungs • Pleural pressure- pressure of the fluid in the thin • space between the lung pleura and the chest pleura; • there is a slight suction so the pressure is negative • Alveolar pressure- pressure of the air inside the lung • alveoli • Transpulmonary pressure- difference between the • pleural and alveolar pressures (recoil pressure)

8. Fig. 37.2 Changes in lung volume, alveolar pressure, pleural pressure, and transpulmonary pressure during normal breathing

9. Mechanics (cont.) • Compliance of the Lungs- the extent to which the • lungs will expand for each unit increase in • transpulmonary pressure • Compliance Diagram of the Lungs • Inspiratory compliance curve • Expiratory compliance curve • Characteristics of the diagrams are dependent on • Elastic forces of the lung tissue • Elastic forces caused by surface tension of the • fluid that lines the inside walls of the alveoli

10. Mechanics (cont.) Fig. 37.3 Compliance diagram in a healthy person Fig. 37.4 Comparison of the compliance of saline and air-filled lungs when the alveolar pressure is maintained at atmospheric pressure and pleural pressure is changed

11. Mechanics (cont.) • Surfactant, Surface Tension, and Collapse of the Alveoli • Principle of Surface Tension-when water forms a surface • with air, the water molecules on the surface of the water • have an especially strong attraction for one another. As a • result, the water surface is always trying to contract. • Surfactant-surface active agent that reduces the surface • tension of water; secreted by Type II alveolar cells

12. Mechanics (cont.) • Effect of the Thoracic Cage on Lung Expansibility • Compliance of the thorax and the lungs • Work of breathing (3 fractions) • Compliance or elastic work • Tissue resistance work • Airway resistance work

13. Pulmonary Volumes and Capacities • Recording Changes in Pulmonary Volume-Spirometry Fig. 37.5 Spirometer

14. Pulmonary Volumes and Capacities • Pulmonary Volumes • Tidal Volume (TV)-amount of air inspired or expired • with each normal breath; usually about 500 ml • Inspiratory Reserve Volume (IRV)-extra volume that can be inspired over and above the TV; usually about 3000 ml • Expiratory Reserve Volume (ERV)-max extra volume that can be expired at the end of a normal TV; usually about 1100 ml

15. Pulmonary Volumes and Capacities • Pulmonary Volumes (cont.) • Residual Volume (RV)-amount of air remaining in the lungs after the most forceful expiration; usually about 1200 ml • Pulmonary Capacities • Inspiratory Capacity- (TV + IRV); about 3500 ml • Functional Residual Capacity- (ERV + RV); about • 2300 ml

16. Pulmonary Volumes and Capacities • Pulmonary Capacities (cont.) • Vital Capacity (VC)- (IRV + TV + ERV); usually about • 4600 ml • d. Total Lung Capacityi (VC + RV); usually about 5800 ml

17. Pulmonary Volumes and Capacities Fig. 37.6 Diagram showing pulmonary volumes and pulmonary capacities

18. Minute Respiratory Volume • Minute Respiratory Volume- total amount of new air moved into the respiratory passages each minute • Equal to the TV x Respiratory Rate • Usually 500ml x 12 bpm = 6 L/min

19. Alveolar Ventilation • Effect of “Dead Space” – air that does not reach the gas exchange areas but simply fill respiratory passages where gas exchange does not occur (dead air space) • Rate of Alveolar Ventilation- alveolar ventilation per minute is the total volume of new air entering the alveoli each minute

20. Functions of the Respiratory Passages Fig. 37.8 Respiratory passages