compliance of lung 2003

8/3/2019 Compliance of Lung 2003

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Pulmonary compliance (or lung compliance) is the

ability of the lungs to stretch during a change in

volume relative to an applied change in pressure.

Compliance is calculated using the followingequation, where V is the change in volume, and

P is the change in pleural pressure

c= V/ P
http://en.wikipedia.org/wiki/Lungshttp://en.wikipedia.org/wiki/Lungs


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For example if a patient inhales 500 mL of air from a

spirometer and intrapleural pressure before inspiration

is 5 cm H2O and -10 cm H2O at the end of inspiration.Then:

C= .5/(-5-(-10)) L/cm H2O

=0.1 L/cm H20

The total compliance of both lungs together in

the normal adult human being averages about200 milliliters of air per centimeter of water

transpulmonarypressure.


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More compliance means more air will flow for

a given change in pressure.

Reduced compliance means less air will flow

for a given change in pressure.

Steeper the line more compliant the lung, Restful breathing works on the steepest most

compliant part of the lung

With deeper inspiration the lung move towardthe flatter part of the curve and thus will have

the reduced compliance


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In summary: compliance is the index of the

effort required to expand the lung( to

overcome recoil)

It does not relate to airway resistance.

Very compliant lung(easy to inflate ) have low

recoil

Stiff lung (difficult to inflate) have a large

recoil force.


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Components of lung recoil

1. The tissue itself, more specifically the

collagen and elastin fibres of the lung.

the greater is the stretch of the tissue the

greater is the recoil force. One third force

2. The surface tension forces in the fluid lining

the alveoli two third force.

recoil force always try to collapse the lung or

alveoli


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fibrosis is associated with a decrease in

pulmonary compliance.

emphysema/COPD may be associated withan increase in pulmonary compliance due to

the loss of alveolar and elastic tissue
http://en.wikipedia.org/wiki/Fibrosishttp://en.wikipedia.org/wiki/Emphysemahttp://en.wikipedia.org/wiki/Chronic_obstructive_pulmonary_diseasehttp://en.wikipedia.org/wiki/Chronic_obstructive_pulmonary_diseasehttp://en.wikipedia.org/wiki/Emphysemahttp://en.wikipedia.org/wiki/Fibrosis


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Surface tension

The surface tension acts at the air-water

interface

Surface tension forces tend to reduce the area

of the surface and generate the pressure.

In alveoli they act to collapse the alveoli.

These forces contribute to the lung recoil.

So surface tension force are the greatest

component of lung recoil.
http://en.wikipedia.org/wiki/Surface_tensionhttp://en.wikipedia.org/wiki/Surface_tension


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Law of laplace

Pressure = 2surface tensionradius of alveoli surface tension in the alveoli is inversely

affected by the radius of the alveolus,

which means that the smaller the alveolus,the greater the alveolar pressure caused bythe surface tension.

Thus, when the alveoli have half the normalradius (50 instead of 100 micrometers), thepressures are doubled.


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For the average-sized alveolus with a radius ofabout 100 micrometers and lined with normal

surfactant, this calculates to be about 4centimeters of water pressure (3 mm Hg).

If the alveoli were lined with pure waterwithout any surfactant, the pressure wouldcalculate to be about 18 centimeters of waterpressure, 4.5 times as great

Thus, one sees how important surfactant is in

reducing alveolar surface tension andtherefore also reducing the effort required bythe respiratory muscles to expand the lungs.


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Pulmonary surfactant

Pulmonary surfactant is a surface-active

lipoprotein complex (phospholipoprotein)

formed by type II alveolar cells

surface active agent in water, which means

that itgreatly reduces the surface tension of

water
http://en.wikipedia.org/wiki/Pulmonary_alveolushttp://en.wikipedia.org/wiki/Pulmonary_alveolus


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Composition

~40% dipalmitoylphosphatidylcholine (DPPC)

40% other phospholipids (PC);

~5% surfactant-associated proteins (SP-A, B, Cand D);

Cholesterol (neutral lipids);

Traces of other substances.
http://en.wikipedia.org/wiki/Dipalmitoylphosphatidylcholinehttp://en.wikipedia.org/wiki/Phospholipidhttp://en.wikipedia.org/wiki/Proteinshttp://en.wikipedia.org/wiki/Cholesterolhttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/Chemical_substancehttp://en.wikipedia.org/wiki/Chemical_substancehttp://en.wikipedia.org/wiki/Lipidshttp://en.wikipedia.org/wiki/Cholesterolhttp://en.wikipedia.org/wiki/Proteinshttp://en.wikipedia.org/wiki/Phospholipidhttp://en.wikipedia.org/wiki/Dipalmitoylphosphatidylcholine


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Function

To increase pulmonary compliance.

To prevent atelectasis (collapse of the lung) atthe end of expiration

It reduces capillary filtration forces and thusreduces the tendency to develop pulmonary

edema.
http://en.wikipedia.org/wiki/Pulmonary_compliancehttp://en.wikipedia.org/wiki/Atelectasishttp://en.wikipedia.org/wiki/Atelectasishttp://en.wikipedia.org/wiki/Pulmonary_compliance


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Diseases

Infant respiratory distress syndrome (IRDS) is

caused by lack of surfactant, commonly

suffered by premature babies born before 28

32 weeks of gestation.

Hyaline membrane disease is an older term

for IRDS. It is based on the pathological

findings at autopsy of premature infants. The

hyaline membranes were proteinaceousmaterial in the damaged alveoli.

Congenital surfactant deficiency
http://en.wikipedia.org/wiki/Infant_respiratory_distress_syndromehttp://en.wikipedia.org/wiki/Hyaline_membrane_diseasehttp://en.wikipedia.org/wiki/Congenital_surfactant_deficiencyhttp://en.wikipedia.org/wiki/Congenital_surfactant_deficiencyhttp://en.wikipedia.org/wiki/Hyaline_membrane_diseasehttp://en.wikipedia.org/wiki/Infant_respiratory_distress_syndrome

compliance of lung 2003

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