Respiratory mech Flashcards
What are the three goals of the respiratory mechanics?
Provide a thin interface between air and blood
Deliver air and blood evenly over the interface as efficiently
Keep clean and dry
What is the role of the rib cage?
Sustains a negative pressure around
the lungs.
What is the most important muscle of inspiration?
Diaphragm
What happens to inspiration in a subdiaphragmatic abscess?
Lowers the diaphragmatic action, and volume
How are the internal and external intercostal muscles oriented relative to each other?
At 90 degrees from each other
What happens in the intercostal muscles are paralyzed?
Not a whole lot, since the diaphragm is main effector of breathing
What are the accessory muscles of inspiration?
Scalenes
SCM
What is the attachment for the posterior scalene?
2nd rib
What is the attachment for the anterior and middle scalene?
1st rib
What are the most important muscles of expiration?
Abdominal muscles
What happens to breathing if the abdominal muscles are congenitally absent?
Pneumonia and death in the first few months of life
What happens if there is an incisional pain in the abdominal muscles after surgery?
Inhibits expiration
What is the intrapleural pressure usually (negative or positive)? What does this cause?
Negative
Suction
As the pressure difference between the alveoli and the pleural pressure increases, what happens to the elastic recoil of the lung?
Increases
What must be present for air to flow into the lungs?
A pressure gradient between the atmosphere and the alveoli
What is the transmural (transpulmonary) pressure?
The difference between the alveoli and the intrapleural pressure
How does the pleural pressure relate to lung volume?
Inverse relationship
Expiration is active when?
In pathological states
What is Hooke’s law?
For an elastic structure, the increase in length (or volume) varies directly with the increase in force (or pressure) until the elastic limit is reached
According to Hooke’s law, the relationship between the increase in volume and pressure is what type?
Linear
How is compliance represented in a graph?
Elasticity of the graph (i.e. more inelastic, more compliant)
The more distensible the lung is the (BLANK) the compliance
More
What are the determinants of lung compliance?
Elastin and collagen deposition
Water tension
The more elastic recoil the (easier/harder) it is to inspire
Harder
What is hysteresis? What is this due to?
The difference in inspiration and expiration limbs of pressure volume loop
Due to surface tension
What is the law of Laplace?
P=2T/r,
Where:
T= alveolar surface tension
r = alveolar radius
P= pressure tending to collapse an alveolus
What is the role of surfactant in the lungs?
Disrupt intermolecular forces between water molecules to reduce surface tension
What cell secretes surfactant?
Type II alveolar cells
What is the main component of surfactant?
Lecithin
When in gestation does lecithin increase?
around week 32
When is surfactant produced in gestation?
~24 weeks
What is the cause of infantile respiratory distress syndrome?
Low surfactant production in children
What do we measure to determine the maturity of the lungs of a fetus? What does it need to be for the fetus to be ready for birth?
Lecithin / sphingomyelin ratio
Ratio needed to be high
What happens to the chest wall collapsing force with increasing airway pressure?
Increases, but to a lesser extent than the lung
What happens when there is a loss of elastic fibers in the lungs, as occur in COPD? How is this reflected in the lung compliance graph?
The lug compliance increases, leading to an increased tendency to collapse, and an upward shift in the curve
What happens to the FRC with increased lung compliance?
Increases
What is the etiology of decreased lung compliance?
Collapsed alveoli (atelectasis pnuemonia, TB etc)
What happens to the slope of the airway pressure/volume curve in fibrosis or decreased lung compliance?
Decreases the slope
What is the most common cause of decreased lung compliance?
Pneumonia
What happens to the FRC in restrictive lung disease?
lowers
What is the equation for the pulmonary resistance?
R = 8(viscosity)L / (pi)r^4
What happens to resistance as the bronchial size increases?
Decreases
What happens in parasympathetic stimulation of the lungs as far as resistance goes?
Increases resistance
What are the parasymp receptors for the lungs?
M3
What are the symp receptors for the lungs?
beta 2
What happens to resistance with high lung volumes?
decreases
Symp stimulation changes resistance how?
decreases
Contraction of the external intercostals produces what motion?
Raises ribs
Contraction of the internal intercostal muscles does what?
Lowers the rib cage, facilitating expiration
True or false: under normal conditions, the intercostals contribute to inspiration.
False-there is little contribution
What is alveolar pressure?
The pressure of the air inside the lung alveoli
What is the recoil pressure?
A measure of the elastic forces in the lungs that tend to collapse the lungs at each instant of
respiration
This is equivalent to the transmural pressure
What is positive pressure ventilation?
Forcing air into the lungs, as in a ventilator
How are the more centrally located alveoli pulled via the diaphragm?
Via other alveoli interconnections
What happens to the intrapleural pressure with inspiration? What is the result of this?
Decreases
Causes the visceral pleural to follow the parietal pleura
What happens to the transmural pressure with inspiration?
Increases
What is lung compliance?
The extent to which the
lungs will expand for each unit increase in transpulmonary
pressure
What causes the graph of transpulmonary pressure/%volume graph to not be a straight line?
The distensibility of the lungs decreases at larger pressures
The inverse of elasticity is what?
Compliance
Lungs with a high compliance will have a steep or shallow slope on the transmural pressure vs lung volume curve?
Steep (highly inelastic)
What accounts for the difference between the inspiration and expiration limbs of the lung compliance curve?
the
recoil due to surface tension forces
Where are the intermolecular forces between water the highest: at the beginning or end of inspiration?
At the beginning (this is why the curve is flatter, and then spike later
Where does LaPlace’s law apply in the lungs?
Relating the pressure tending to collapse a an alveolus to the surface tension of the lung
Using LaPlace’s law, a large alveolus (one with a large radius) will have a (BLANK) collapsing pressure.
Low collapsing pressure and, therefore, will require only minimal pressure to keep it
open
Using LaPlace’s law, a small alveolus (one with a small radius) will have a (BLANK) collapsing pressure.
High collapsing pressure
This requires more pressure to keep it open
According to LaPlace’s law, small alveoli are not ideal because of
their tendency to collapse. Yet, from the standpoint of gas exchange, alveoli need to be as small
as possible to increase their total surface area. How is this resolved?
Surfactant
What happens to surface tension of water with surfactant present?
Goes down
What is the treatment for a fetus whose surfactant levels are low?
Glucocorticoids
What is the equation for the total compliance for the chest wall and the lung?
1/total = (1/ Lung compliance) + (1/chest wall compliance)
What is the functional residual capacity?
the equilibrium volume of the combined lung and chest-wall system
What happens when the functional residual capacity = lung volume?
at FRC, the equilibrium position, the collapsing force on the lungs is exactly equal to the expanding
force on the chest wall,
When lung volume is less than FRC, what happens?
there is less volume in the lungs and the collapsing (elastic) force of the lungs is smaller.
The expanding force on the chest wall is greater,
What happens when lung volume is greater than FRC?
There is
more volume in the lungs and the collapsing (elastic) force of the lungs is greater
What happens to the amount of elastic fibers in COPD? What is the result of this?
loss of elastic fibers in the lungs. As a result, the compliance of
the lungs increases
An increase in compliance is associated with (steeper/shallower) slope of the volume-pressure
curve for the lung.
Steeper
What is the equation for pulmonary resistance?
R= 8nl / (pi)r^4
What are the two conditions discussed in class that decrease chest wall compliance?
Pectus excavatum
Kyphosis
Recall that pulmonary resistance is given by the following equation:
R = 8(viscosity)L / (pi)r^4
With this information, which bronchioles have a larger increase in resistance in asthma, the smaller ones, or the larger ones?
Smaller ones (greater proportional increase in r
