Compliance

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Compliance

• Compliance is the extent to which the lungs
• expand for each unit increase in
• transpulmonary pressure.
• Total lung compliance of both lungs together
• in normal adults average about 200 ml of
  air /
• cm of H2O i.e. every time transpulmonary
• pressure increases by 1 cm of H2O, the lung
• volume expands 200 ml.
• The compliance of thoracic cage and lung
• tissue is 110 ml/ cm of H2O.

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• Compliance depends on two factors
• Elastic Fibers
• Surface tension in alveoli
• Elastance is the property of lung to come back to
  its original volume when stretching force is
  removed.

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Surface Tension in Alveoli

• The law of LaPlace states that the pressure
  within a fluid-lined alveolus depends on two
  factors the surface tension of the fluid and the
  radius of the alveolus. This relationship is
  expressed by the equation
• P 2 . T/ r

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Surfactant

• It is a mixture containing lipoprotein such as
  dipalmitoylphosphatidylcholine, apoproteins and
  calcium ions
• Secreted by type II alveolar cells.
• Secretion starts at 25th week of gestation, peak
  at 32nd week.
• Hyaline membrane disease

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Role of surfactant for preventing alveolar
collapse
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Airway resistance

• Poiseuilles Law
• R is directly proportional to L?/r

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Factors affecting Airway resistance

• Length --- constant ,not a factor
• Viscosity of air--- Usually constant.Humidity and
  altitude may alter slightly
• Diameter of upper airways is affected by physical
  obstruction e.g.mucus and other factors
• Diameter of bronchioles
• Bronchoconstriction---Parasympathetics,
• , histamine.
• Bronchodilation---CO2, epinephrine.

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Factors affecting Airway Resistance
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Obstructive Airway Diseases

• Chronic Bronchitis
• Asthma
• Emphysema

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Fibrotic lung diseases

• Often results from the chronic inhalation of fine
  particulate matter that escapes the mucus lining
  of the airways and reaches the exchange
  epithelium of the alveoli ,eventually resulting
  in formation of inelastic scar tissue.
• The proliferation of inelastic scar tissue in the
  lung is called fibrotic lung disease or fibrosis.
• Inorganic particles that can trigger fibrosis are
  asbestos,coal dust,silicon,and even dust and
  pollutants of urban areas.

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Pulmonary Ventilation

• Pulmonary ventilation is defined as inflow
  outflow of air between the atmosphere the lung
  alveoli
• Inflow ? Inspiration
• Outflow ? Expiration

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The recording spirometer
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Spirogram
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Lung volumes

1. Tidal volume is the volume of air that moves in a
   single normal inspiration or expiration.
2. Inspiratory reserve volume is the additional
   volume inspired above the tidal volume
3. Expiratory reserved volume is the amount of air
   exhaled after the end of a normal expiration
4. Residual volume is the volume of air in the
   respiratory system after maximum exhalation

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Lung capacities

1. Inspiratory capacity is the amount of air a
   person can breathe in, beginning at the normal
   expiratory level and distending the lungs to the
   maximum amount.
2. Functional residual capacity is the amount of
   air that remains in the lung at end of normal
   passive expiration
3. Vital capacity is the maximum amount of air that
   can be voluntarily moved in to or out of the
   respiratory system with one breath.
4. Total lung capacity is the volume to which lungs
   can be expanded with the greatest possible
   effort.

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FRC determination