1. Mechanics of Ventilation Prof. K. Sivapalan

2. Introduction 20132Mechanics of Ventilation

3. Pleural Cavity. The lungs are separated from the chest wall and the diaphragm by the pleural cavity containing a thin film of fluid. The surface tension allows sliding but keeps both surfaces attached to each other. Expansion- chest muscles out words and the diaphragm downwards. 20133Mechanics of Ventilation

4. Diaphragm – contraction pulls the lung downwards. Increase diameter of the chest cavity- – Elastic fibers in chest wall – External intercostals – Sternocleinomastoid – Anterior serrati – Scalini Decreasing the chest cavity- – Elastic recoil of lungs – Internal intercostals – Abdominal muscles Respiratory Muscles 20134Mechanics of Ventilation

5. Changes in Pressure and Volume in Quiet Inspiration Diaphragm and external intercostals contract. Elasticity of the wall facilitates but the elasticity of lungs and surface tension in alveoli opposes Pleural pressure decreases to -7.5 cm H 2 O Intrapulmonary pressure falls to -1 Air flows in. 20135Mechanics of Ventilation

6. Changes in Pressure and Volume in Quiet Expiration Diaphrgm and external intercostals relax. Pleural pressure increases to -5 cm H 2 O – not to zero. Elasticity of the wall is over powered by the elasticity of lungs and surface tension in alveoli. Intrapulmonary pressure rises to +1 Air flows out 20136Mechanics of Ventilation

7. Surface Tension in Alveoli 20137Mechanics of Ventilation

8. Pleural pressure 20138Mechanics of Ventilation

9. Lung volumes are measured by a spirometer. Tidal volume- inspired or expired with normal breath- 500 ml in adult male Inspiratory Reserve Volume- extra volume inspired by maximal inspiration. [3 L] Inspiratory Capacity = TV+IRV Expiratory Reserve volume- extra volume expired by maximal expiration.[1.1 L] Residual Volume- Volume remaining after maximal expiration.[1.2 L] Functional Residual Capacity= RV+ERV Vital Capacity=ERV+TV+IRV- maximal expiration after maximal inspiration. Lung Volumes 20139Mechanics of Ventilation

10. Forced Vital Capacity FVC is the Vital capacity obtained by forced expiration after maximal inspiration. FEV 1 is the fraction of the FVC expelled in the FIRST SECOND.[>80%]. Also peak flow. MVV- maximal voluntary ventilation- 125-170 L/m 201310Mechanics of Ventilation

11. Dead space is the non functional – not participating in gas exchange- space in the respiratory tract Anatomical- nose, pharynx, trachea,..up to terminal bronchiole. Equals in ml to approximately the weight in pounds [150 ml] Physiological- includes nonfunctional alveoli as well Dead Space 201311Mechanics of Ventilation

12. Ventilation 201312Mechanics of Ventilation

13. Perfusion 201313Mechanics of Ventilation

14. Features of Pulmonary Circulation 201314Mechanics of Ventilation

15. Ventilation Perfusion Ratio 201315Mechanics of Ventilation