respiration 3 Flashcards
Compliance
- Refers to how much effort is required to
stretch or distend the lungs - How much Δ in lung volume results from a Δ in
transmural pressure
The less _______ the lungs are, the more work is required to produce a given degree of inflation
compliant
poor compliance =
stiff lung
compliance is decreased by factors such as
pulmonary fibrosis
Elastic Recoil
- Refers to how readily the lungs rebound after
having been stretched - Responsible for lungs returning to their pre-
inspiratory volume when inspiratory muscles
relax at end of inspiration
Elastic Recoil depends on 2 factors
- Highly elastic connective tissue in the lungs
- Alveolar surface tension
Alveolar surface tension
- Thin liquid film lines each alveolus
- Reduces tendency of alveoli to recoil
- Helps maintain lung stability
> Newborn respiratory distress syndrome
Surface tension
Unequal attraction of water molecules to each other at water air interface
The _______ the surface tension, the less compliant (stiffer)
greater
Emphysema:
loss of elastic
- fibers - decrease in elastic
- recoil - expiration dysfunctional
2 factors opposing alveoli collapse
- Surfactant (surface active agent)
- LaPlace
Surfactant
(surface active agent)
- lipids/proteins by pneumocytes II
> increases complicance, reduces recoil
LaPlace:
collapsing pressure ~ surface tension
collapsing pressure~ 1/radius
P=2T/r
Role of pulmonary surfactant in counteracting the tendency for small alveoli to collapse into larger alveoli.
- According to the law of LaPlace, if two alveoli
of unequal size - but the same surface tension
are connected by the same terminal airway,
the smaller alveolus—because it generates a
larger inward-directed collapsing pressure—
has a tendency (without pulmonary surfactant)
to collapse and empty its air into the larger
alveolus. - Pulmonary surfactant reduces the surface
tension of a smaller alveolus more than that
of a larger alveolus. This reduction in surface
tension offsets the effect of the smaller radius
in determining the inward-directed pressure.
Consequently, the collapsing pressures of
the small and large alveoli are comparable.
Therefore, in the presence of pulmonary
surfactant a small alveolus does not collapse and empty its air into the larger alveolus.
Alveolar interdependence
- When an alveolus in a group of interconnected alveoli starts to collapse, the surrounding alveoli are stretched by the collapsing alveolus.
- As the neighbouring alveoli recoil in resistance to being stretched, they pull outward on the collapsing alveolus.
- This expanding force pulls the collapsing alveolus open.
Forces keeping the alveoli open
- transmural pressure gradient
- pulmonary surfactant
(opposes alveolar surface tension) - alveolar interdependence
Forces promoting alveolar collapse
- Elasticity of stretched pulmonary connective
tissue fibres - Alveolar surface tension
Work of Breathing
- Normally requires 3% of total energy
expenditure for quiet breathing - Lungs normally operate at about “half full”
Work of breathing is increased in the following situations
- When pulmonary compliance is decreased
- When airway resistance is increased
- When elastic recoil is decreased
- When there is a need for increased ventilation
Decrease in radius, increase resistance to airflow (airway). Caused by: - allergy-induced spasm - excess mucus - edema of the walls - airway collapse
Bronchoconstriction
Increase in radius of airway, decreased resistance to airflow
Hormone control:
Epinephrine
Bronchodilation
a device that measures the volume of air breathed in and out; it consists of an air-filled drum floating in a water-filled chamber. As a person breathes air in and out of the drum through a connecting tube, the resultant rise and fall of the drum are recorded as a spirogram, which is calibrated to the magnitude of the volume change.
A spirometer.
Variations in lung volume in a healthy young adult male.
Values for females are somewhat lower.
(Note that residual volume cannot be measured with a spirometer but must be determined by another means.)
vital capacity
The difference between the maximum volume of the lungs at maximum inspiration and the minimum volume of the lungs at maximum expiration
[the maximum volume of air that can be moved out during a single breath following a maximum inspiration.]