presentation of mechanics of breathing

1. MECHANICS OF
BREATHING
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2. SPECIFIC LEARNING OBJECTIVES
• Describe the mechanics of normal respiration
• Describe pressure changes during ventilation
• Describe pressure-volume characteristics of
lung and chest wall
• Describe alveolar surface tension,cmpliance
2

3. Mechanism of Inspiration
• Active process
• Brought about by enlargement of thorax- Rib
movements and descent of diaphragm
• Accessory muscles of inspiration – become
active during deep inspiration
3

4. Mechanism of Expiration
• Passive process
• Forced expiration → contraction of expiratory
muscles. (abdominal & int. intercostal
muscles)
4

5. Change in antero - posterior diameter
Sternum
Vertebrae
Rib-cage Side view
Vertebrae
Pump Handle Movement
Handbook of Physiology,
The Respiratory System, 1986
-The Anatomical Basis of Clinical
Practice, 40th ed, Gray’s
5

6. Change in lateral diameter
Vertebrae
Sternum
Bucket Handle Movement
-Handbook of Physiology, The Respiratory System, 1986
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7. Pressure Changes During Ventilation
• Intra-pulmonary (or Intra-alveolar) pressure:
1.Pressure within the lung parenchyma.
2. Normal: 760 mmHg
3.With inspiration ↓s by 1 mmHg; with
expiration ↑s by 1 mmHg
4.Factors affecting
a) Valsalva manoeuvre → ↑ ≥100 mmHg
b) Muller’s manoeuvre → ↓ ≤80 mmHg
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8. Intra-pleural (or Intra-thoracic)
pressure
• Pressure between two layers of pleura
• Normal: –2 mmHg
• Factors affecting: Physiological
(i) deep inspiration → ↓s by 30 mmHg
(ii) Valsalva manoeuvre → ↑s by 60-70 mmHg
(iii) effect of gravity: in standing position: more
negative (–7 mmHg) at the apices of lungs
compared to the base (–2 mmHg) i.e., 5 mmHg
greater at the bases. 8

9. Physiology;Ganong 8th edition 7

10. 10
Pressure Volume Changes During
Normal Breathing

11. LUNG VOLUMES
 Tidal Volume (TV):
volume of air inhaled or exhaled with
each breath during quiet breathing
 Inspiratory Reserve Volume(IRV):
maximum volume of air inhaled from the
end-inspiratory tidal position
 Expiratory Reserve Volume (ERV):
maximum volume of air that can be
exhaled from resting end-expiratory tidal
position
 Residual Volume (RV):
Air left in the lungs after maximal
expiratory effort

12. LUNG CAPACITIES:
 Total Lung Capacity (TLC):
Sum of all volume compartments or volume of
air in lungs after maximum inspiration
 Vital Capacity (VC):
TLC minus RV or maximum volume of air
exhaled from maximal inspiratory level
 Inspiratory Capacity (IC):
Sum of IRV and TV or the maximum volume of
air that can be inhaled from the end-expiratory
tidal position
 Expiratory Capacity (EC):
TV+ ERV
 Functional Residual Capacity (FRC):
Sum of RV and ERV or the volume of air in the
lungs at end-expiratory tidal Position

13. Lung Volume and Capacities
Static Lung Volumes and Capacities
1. Tidal volume: 500 mL
2. Inspiratory reserve volume: Normal: 2000-
3200 mL
3. Expiratory reserve volume: Normal: 750-1000
mL
4. Residual volume: Normal: 1200 mL
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14. CONT….
5. Closing volume
6. Inspiratory capacity: Normal: 2500-3700
mL
7. Expiratory capacity: Normal: 1200-1500 mL
8. Vital capacity (VC): Normal: 4.8 L in males;
3.2 L in females
9. Functional residual capacity(FRC):Normal
2.5 L
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15. Dynamic Lung Volumes and Capacities
• Timed vital capacity (TVC) or Forced vital
capacity (FVC)-
(i) FEV1 Normal: 80% of FVC
(ii) FEV2 Normal: 95% of FVC
(iii) FEV3 Normal: 98-100% of FVC
• Forced expiratory flow during 25-75% of
expiration (FEF25-75%)- 300 L/min
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16. CONT…
• Minute or pulmonary ventilation (MV or PV) –
Normal: 6L/min
• Peak expiratory flow rate (PEFR) – Normal:
400-450 L/min
• Maximum breathing capacity (MBC) or
Maximum voluntary ventilation (MVV) –
Normal: 90-170 L/min
• Pulmonary reserve or breathing reserve i.e
MVV-PV
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17. Lung Compliance
• Compliance is magnitude of change in volume
produced by a given change in pressure
• Greater the lung compliance,easier it is to expand
the lung at any given change in transpulmonary
pressure
• This is the stretchability of the lungs, i.e. the effort
required to inflate the alveoli
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18. Determination of characteristics of
compliance curve
1. Elastic forces of lung
2. Elastic forces caused by surface tension of fluid
that lines inside walls of alveoli
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19. Elastic properties of lung
 Elasticity is the property of a substance that
tends to return to its original shape and size after
the force that deforms it is removed
 Hooke’s law: law stating that the strain in a
solid is proportional to the applied stress within
the elastic limit of that solid.
Major components of the lung connective tissue
network
elastin and collagen
AE
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20. Elastic Recoil
• Elastic recoil is the tendency of an elastic
structure to oppose stretching
• Lungs naturally have a tendency to collapse
because of elastic recoil
• They are held open by negative pleural pressure
• Chest wall naturally expands, but is also held by
negative pleural pressure
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21. Surface Tension
• H2O molecules at interface with air are
attracted to each other. This causes the H2O
at the surface to contract (collapsing the
alveoli)
• The pressure caused by surface tension can be
calculated from
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22. P1
P2
T
T
r1
r2
Laplace’s law
r
T
P


2
2
r
P
2
r
P
T 2
2
1
1 



Small alveoli Collapses
If r1> r2 then, P2 > P1
Surface tension in alveoli
Factors causing stability to alveoli
 Pulmonary surfactant
 Interdependence
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23. Surfactants
• Surfactants in water decrease surface tension and
are secreted by type II alveolar epithelial cells
• Surfactant is a complex mixture of phospholipids,
proteins, and ions
• Surfactants can decrease surface tension by up to 10-
fold.
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24. Composition of surfactant
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25. Role of surfactant
1. Increased Compliance
2. Maintenance of uniformity in alveolar size
3. Prevent pulmonary Oedema
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26. Brain initiates inspiratory effort
Phrenic nerves carry the inspiratory command to the inspiratory muscles
Contraction of diaphragm (mainly) and external intercostal muscles
Ribs 2-10 rotate upward & outward upper ribs rotate the sternum
upward &outward
↑The transverse diameter ↑ the anterior-posterior
diameter
(bucket-handle movement) (water pump–handle
movement)
Thoracic volume increases as the chest wall expands
Intrapleural pressure becomes more negative (-2.5 to -6 mmhg)
↑ Alveolar transmural pressure gradient
Expansion of alveoli
Alveolar pressure (falls below atmospheric)
Air flows into the alveoli
INSPIRATION
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27. EXPIRATION
Brain stops inspiratory command
Inspiratory muscles relax
Thoracic volume decreases
Intrapleural pressure becomes less negative (-6
to -2.5 mmhg)
↓ Alveolar transmural pressure gradient
↑ Elastic recoiling of the alveoli (↓ alvelolar
volume)
↑ Alveolar pressure above atmospheric pressure
Air flows out of the alveoli
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28. Thank you
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