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.]
Pulmonary Ventilation
- Minute ventilation
- Volume of air breathed in and out in one
minute
Alveolar Ventilation
[More important than pulmonary ventilation]
- Volume of air exchanged between the
atmosphere and the alveoli per minute
=> functional respiration
- Less than pulmonary ventilation due to
anatomic dead space
- Volume of air in conducting airways that is
useless for exchange
Averages about 150 ml in adults
Alveolar ventilation=
(tidal volume – dead space) x respiratory rate
Effect of dead space volume on the exchange of tidal volume between the atmosphere and the alveoli.
- Even though 500 ml of air move in and out
between the atmosphere and the respiratory
system and 500 ml move in and out of the
alveoli with each breath, - only 350 ml are actually exchanged between the atmosphere and the alveoli because of the anatomic dead space
(the volume of air in the respiratory airways).
effect of a local change in O2 on pulmonary and systematic arterioles
Decreased O2 Increased O2
Pulmonary Vasoconstriction Vasodilation
arterioles
Systematic Vasodilation Vasoconstriction
arterioles
Local control matches ventilation and perfusion
- Ventilation in alveoli is matched to perfusion through pulmonary capillaries
- [ Ventilation-perfusion mismatch]
If ventilation decreases in a group of alveoli, PCO2 increases, and PO2 decreases. Blood flowing past those alveoli doesn’t get oxygenated - [Local control mechanisms try to keep ventilation and perfusion matched]
Decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting blood to better ventilated alveoli
Local controls to match airflow and blood flow to an area of the lung.
- CO2 acts locally on bronchiolar smooth muscle
- O2 acts locally on arteriolar smooth muscle
to adjust ventilation and perfusion, respectively, to match airflow and blood flow to an area of the lung.
(and vice versa-for the picture)
Differences in ventilation, perfusion, and ventilation-perfusion ratios at the top and bottom of the lungs as a result of
- gravitational effects.
Note that the top of the lungs receives less air and blood than the bottom of the lungs, but the top of the lungs receives relatively more air than blood and the bottom of the lungs receives relatively less air than blood.
match perfusion with ventilation - make respiration functional
O2 via capillary radius control
and Co2 via bronchial radius control
