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Mechanics of Ventilation Prof. K. Sivapalan. Introduction 20132Mechanics of Ventilation.

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Presentation on theme: "Mechanics of Ventilation Prof. K. Sivapalan. Introduction 20132Mechanics of Ventilation."— Presentation transcript:

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 Mechanics 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 Recording Chest Movements 2013Mechanics of Ventilation5

6 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 Mechanics of Ventilation

7 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 20137Mechanics of Ventilation

8 Surface Tension in Alveoli 20138Mechanics of Ventilation

9 Pleural pressure 20139Mechanics of Ventilation

10 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 Mechanics of Ventilation

11 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 L/m Mechanics of Ventilation

12 Compliance is the change in lung volume per unit change in airway pressure [V/ P]- a measure of stretchability. The stretchability varies with volume as shown in the curve. Pressure is zero [equal to atmospheric pressure] at the end of quite expiration. The compliance is higher when measured by deflation than by inflation. [measured with saline shows the contribution of surface tension. Compliance is reduced in pulmonary congestion and fibrosis and increased in emphysema. Compliance Mechanics of Ventilation

13 Work of Breathing Mechanics of Ventilation

14 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 Mechanics of Ventilation

15 Measuring Dead Space CO2 Method- TV x F e CO 2 = AVxF a CO 2 AV= TV x F e CO 2 / F a CO 2 DV= TV-AV Nitrogen Method- Pure oxygen inspired. Monitor nitrogen in expired air. V D = GrayxV E / Pink+Gray Mechanics of Ventilation

16 Ventilation Mechanics of Ventilation

17 Perfusion Mechanics of Ventilation

18 Features of Pulmonary Circulation Mechanics of Ventilation

19 Ventilation Perfusion Ratio Mechanics of Ventilation


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