Mechanics of Respiration

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Mechanics of Respiration & Surfactant

1. MECHANICS OF RESPIRATION
Dr. NabeelBeeran
19/11/2019

2. Specific Learning Objectives
At the end of the class students should be able to:
•Describe the mechanics of normal respiration.
•Describe the pressure changes during ventilation.
•Describe the composition, synthesis and functions of surfactant.
•Explain hyaline membrane disease.

3. Muscles of Respiration
•Respiratory muscles are of two types:
1. Inspiratory muscles
2. Expiratory muscles
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4. Muscles of Respiration
Inspiration
•Diaphragm –increases vertical diameter
•External intercostal muscles -increases
transverse and anteroposterior diameter.
Accessory muscles (Work
during forced inspiration,
exercise, airway obstruction)
•Scalene
•Sternocleidomastoid muscles
•Neck and back muscles
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6. Expiration
•Passive process
•Elastic recoil of chest wall and lungs
Forced expiration
•Abdominal muscles
•Internal intercostalmuscles.
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7. Movements of Thoracic Cage
•Inspiration causes enlargement of thoracic cage.
•Thoracic cage enlarges because of increase in all diameters (anteroposterior,
transverse and vertical).
•The change in the size of thoracic cavity occurs because of the movements of:
1. Thoracic lid
2. Upper costal series
3. Lower costal series
4. Diaphragm.
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8. Pump handle movement Bucket handle movement
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9. Movements of Lungs
•During inspiration, due to the enlargement of thoracic cage, the
negative pressure is increased in the thoracic cavity, which causes
expansion of the lungs.
•During expiration, the thoracic cavity decreases in size to the pre-
inspiratory position and also the pressure in the thoracic cage
decreases, thus compressing the lung tissues and the air expels out of
lungs.
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10. •Factors Causing Collapse of Lungs
1. Elastic property of lung tissues
2. Surface tension: It is the tension exerted by the fluid secreted from
alveolar epithelium on the surface of alveolar membrane.
•Factors Preventing Collapsing Tendency of Lungs
1. Surfactant
2. Intra-pleural pressure
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11. Pressures That Cause the Movement of
Air In and Out of the Lungs
(Pressure changes during ventilation)
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12. 12
Chest Wall
(muscle, ribs)
Diaphragm
(muscle)
Lungs
Gas Exchange
Pleural Cavity
Imaginary Space between
Lungs and chest wall
Pleural Cavity
Very small space
Maintained at negative pressure
Transmits pressure changes
Allows lung and ribs to slide

13. Respiratory Pressures
1.Intra-pleural pressure or intra-thoracic pressure
2.Intra-alveolar pressure or intra-pulmonary pressure
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14. Pressure Relationships in the Thoracic Cavity
•Respiratory pressure is always described relative to atmospheric
pressure.
•Atmospheric pressure (P
atm)-pressure exerted by the air surrounding
the body.

15. Intra pulmonary pressure/ alveolar pressure:
Pressure in the alveolus
Expiration: +1mm Hg
Inspiration: -1 mm Hg
Intra pleural pressure:
Pressure in the pleural space
Expiration: -2.5 mm Hg
Inspiration: -6 mm Hg
Transmural pressure:Pressure difference across the lung.
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16. •Inspiration: volume of air increases by 500 ml
•Expiration: volume of air decreases by 500 ml
Lung volume changes during respiratory cycle
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18. Injury to the Chest Wall
•Pneumothorax:
•allows air into pleural cavity
•Atelectasis:
•also called a collapsed lung
•result of pneumothorax

19. Pressure in the Pleural Cavity
Pneumothorax results in collapsed lung that can not function normally

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22. Alveolar surface tension: The force that pulls the surface molecules
together of a liquid at a air liquid interface is called surface tension.
AIR LIQUID
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23. •Surfactant is a surface acting material or agent
that is responsible for lowering the surface
tension of a fluid.
•Mixture of lipoprotein rich in phospholipid.
•Secreted by type II pneumocytes.
•Alveolar surface tension is inversely proportional
to concentration of surfactant.
Surfactant
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24. Composition of surfactant:
•Lipids : 90%
Dipalmitoylphosphatidylcholine(DPPC)
Phosphatidylglycerol
Phosphatidylserine.
•Proteins : 8%
Albumin, IgA
Apoproteins: SP-A, SP-B, SP-C, SP-D
•Carbohydrates : 2%
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25. Synthesis and secretion of surfactant:
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26. Functions of surfactant:
•Surfactant reduces the surface tension in the alveoli of lungs and
prevents collapsing tendency of lungs.
•Promotes alveolar stability.
•Helps prevent oedemain lungs.
•Decreases work of breathing.
•Promote phagocytosis of bacteria and viruses by alveolar macrophage.
•Provides immunity: SP-A and SP-D.
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27. Hyaline membrane disease/ Infant respiratory distress
syndrome:
•Premature babies
•Deficiency of surfactant
•Causes collapse of lungs
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28. Signs and symptoms:
•Respiratory work is increased
•Lung collapses
•Inadequate exchange of gases due to alveolar instability
•Pulmonary edema
•Deficiency of surfactant also increases the susceptibility for
bacterial and viral infections.
•All this will result in severe respiratory insufficiency -death.
Therapy of RDS:
•Administration of exogenous surfactant.
•Application of positive-end expiratory pressure (PEEP).
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29. Summary
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30. References
1.Ganong’sReviewofMedicalPhysiology-25thEdition.
2.GuytonandHallTextbookofMedicalPhysiology.
3.AK Jain, Textbook of Physiology.
4.InduKhuranaTextbook of Medical Physiology.
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31. •PPT reviewed by review committee on 25/11/2019.
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32. THANK YOU
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