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.

• Compliance depends on two factors I. Elastic FibersII. Surface tension in alveoli

• Elastance is the property of lung to come back to its original volume when stretching force is removed.

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

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

Airway resistance

• Poiseuille’s Law

R is directly proportional to Lη/r

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.

Factors affecting Airway Resistance

Obstructive Airway Diseases

• Chronic Bronchitis• Asthma• Emphysema

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.

Pulmonary Ventilation

Pulmonary ventilation is defined as inflow &

outflow of air between the atmosphere & the lung alveoli

Inflow Inspiration

Outflow Expiration

The recording spirometer

Spirogram

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

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.

FRC determination