2. OBJECTIVES.
Pulmonary Elastance
Elastance of thoracic cage
Elastance of Lungs
Alveolar surface tension
Pulmonary surfactant
Pulmonary Compliance
Def, NR
Measurement
Static Vs Specific
Work of breathing
3. PULMONARY ELASTANCE
Elastance –
Def – recoil of Retractive tendency of any structure.
Elastance of Thoracic cage
Elastance of lungs
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4. ELASTANCE OF THORACIC CAGE
Constant tendency of thoracic cage to expand
which is normally kept partially pulled inward.
It is because of the elastic nature of ribs, muscles
and tendons.
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5. ELASTANCE OF LUNGS
Constant tendency of lungs to collapse
Tissue forces
Presence of many elastic tissues such as smooth
muscle, elastic and collagen in the lung parenchyma
Surface forces – alveolar surface tension.
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6. ALVEOLAR SURFACE TENSION
Surface of alveolar
membrane lined by liquid
Unbalance attraction of
liquid molecules at surface
creates surface tension --
Vander wall forces.
Surface tension increases
the tendency of the lungs
to deflate/collapse.
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7. Law of laplace
P=2T/r
Therefore, small alveoli
tend to become still smaller
whereas large alveoli tend
to become still larger
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8. PULMONARY SURFACTANT
Source – type II alveolar epithelial
cells(granular pneumocytes).
Composition – DPPC (Dipalmitoyl-
phosphatidylcholine)
Mechanism of action
Hydrophilic portion
Hydrophobic portion
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9. Mechanism of action.
Hydrophilic portion
Hydrophobic portion
This causes spreading of surfactant molecules
over the surface of fluid lining the alveoli.
Apoproteins and calcium ions are responsible
for uniform and quick spreading of surfactant
molecules over the surface.
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10. Functions
The tendency of alveoli to collapse
Work of breathing
Prevents pulmonary oedema Pulls fluid from the
capillaries into the interstitial space surrounding the
alveoli and into the alveoli leading to pulmonary oedema.
Alveolar stabilization.
Pulling pressure 18 cm of H2O
4 cm of H2O
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11. MECHANISM OF ALVEOLAR
STABILIZATION
In the presence of
surfactant
ST = 1/ Surfactant.
Other factors
Interdependence of
alveolar septa
Fibrous tissue.
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12. Factors affecting pulmonary
surfactant
.
• Long term inhalation
of 100% O2
.
• Occlusion
• Main bronchus
• Pulmonary artery.
.
• Cigarate smoking.
• Cutting vagi.
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• Thyroid hormones
. • Glucocorticoids
.
14. Respiratory distress syndrome of
newborn.(Hyaline membrane disease)
In the newborn babies
(especially premature) -
Inadequate formation of
surfactant
The formation of hyaline
(translucent) membrane
by an albuminous fluid in
the wall of alveoli and
respiratory bronchioles
An elevated alveolar
surface tension -
extremely difficult to
expand the lungs
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15. Treatment
Therapy of RDS includes administration of
exogenous surfactant and application of
positive-end expiratory pressure (PEEP).
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16. Adult respiratory distress
syndrome
Due to the abnormal surfactant function
caused by a variety of severe pulmonary
injuries.
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17. Patchy atelectasis.
In patients who have undergone cardiac
surgery during which a pump oxygenator is
used and the pulmonary circulation is
interrupted.
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19. Definition & Normal value
C= δV/ δ P
Transpulmonary pressure = alveolar
pressure – pleural pressure.
Normal value
Both 0.13L/cm of H2O
Lung alone 0.22 L/cm of H2O
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22. FACTORS AFFECTING COMPLIANCE
Elastic forces of the
lung tissue – mainly
due to elastic &
collagen fibres (1/3rd)
Elastic forces caused
by surface tension
(2/3rd)
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23. Static vs Specific Lung
Compliance
Static compliance
Depend upon size
Amount of functional
lung tissue.
Specific lung
compliance
Compliance of the lung
at relaxation volume
i.e. at the end of tidal
expiration
FRC.
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24. LUNG COMPLIANCE CHANGES
• Emphysema
• Ageing process
• .
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• Lung diseases (TB,
Silicosis)
• Destruction of
functional lung tissue.
• RLD
25. Work of breathing
Contraction of respiratory
muscles.
Expansion of thoracic cage
& Lungs
Decreases intra alveolar
pressure & push air inside
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28. AIRWAY RESISTANCE
Friction of gas molecules and wall of airways.
Factors affecting
Rate of gas flow
Airway radius. Poiseuille-Hagen formula
Resistance α 1/r4
Length of airway
Type of airflow
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29. CONTROL OF AIRWAY DIAMETER
Sympathetic adrenergic – Bronchodilataion
Vagus – bronchoconstriction & Mucous
formation.
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30. COMPONENTS OF WORK OF
BREATHING
Work done to overcome
Elastic resistance (65%)
Viscous resistance (7%)
Airway resistance (28%)
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31. CALCULATION OF WORK OF
BREATHING
Work done during inspiration
Work done during Expiration
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32. WORK DONE DURING
INSPIRATION
Compliance work refers to
the work done by respiratory
muscles to inflate the lungs
against the elastic resistance
of chest wall and lungs.
It is represented by the
triangular area Thus most of
the work done (65%) is used
to overcome elastic
resistance.
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33. Non-elastic resistance work
Work is done to overcome the nonelastic
resistance.
It includes the work done to overcome:
Viscous resistance of lungs (7%) and
Airway resistance (28%).
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34. WORK DONE DURING
EXPIRATION
Since in quiet breathing,
expiration is a passive
process so no work is done
during expiration.
When the lungs are recoiling
back some energy is required
to overcome non-elastic
resistance, i.e. the airway
resistance plus viscous tissue
resistance.
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37. APPLIED
Work of breathing in
Restrictive lung diseases
Obstructive lung diseases.
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38. FACTORS AFFECTING TOTAL WORK
OF BREATHING.
Total work of breathing in quiet respiration
0.3-0.8 kg mt/min.
Increases
As resistance increases
Muscular exercise.
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39. Objectives seen……
Pulmonary Elastance
Elastance of thoracic cage
Elastance of Lungs
Alveolar surface tension
Pulmonary surfactant
Pulmonary Compliance
Def, NR
Measurement
Static Vs Specific
Work of breathing
Friday, May 14, 2021