Respiratory mech Flashcards by tcarlso 3

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

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What is the role of the rib cage?

Sustains a negative pressure around

the lungs.

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What is the most important muscle of inspiration?

Diaphragm

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What happens to inspiration in a subdiaphragmatic abscess?

Lowers the diaphragmatic action, and volume

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How are the internal and external intercostal muscles oriented relative to each other?

At 90 degrees from each other

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What happens in the intercostal muscles are paralyzed?

Not a whole lot, since the diaphragm is main effector of breathing

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What are the accessory muscles of inspiration?

Scalenes

SCM

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What is the attachment for the posterior scalene?

2nd rib

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What is the attachment for the anterior and middle scalene?

1st rib

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What are the most important muscles of expiration?

Abdominal muscles

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What happens to breathing if the abdominal muscles are congenitally absent?

Pneumonia and death in the first few months of life

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What happens if there is an incisional pain in the abdominal muscles after surgery?

Inhibits expiration

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What is the intrapleural pressure usually (negative or positive)? What does this cause?

Negative

Suction

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As the pressure difference between the alveoli and the pleural pressure increases, what happens to the elastic recoil of the lung?

Increases

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What must be present for air to flow into the lungs?

A pressure gradient between the atmosphere and the alveoli

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What is the transmural (transpulmonary) pressure?

The difference between the alveoli and the intrapleural pressure

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How does the pleural pressure relate to lung volume?

Inverse relationship

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Expiration is active when?

In pathological states

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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

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According to Hooke’s law, the relationship between the increase in volume and pressure is what type?

Linear

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How is compliance represented in a graph?

Elasticity of the graph (i.e. more inelastic, more compliant)

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The more distensible the lung is the (BLANK) the compliance

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What are the determinants of lung compliance?

Elastin and collagen deposition

Water tension

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The more elastic recoil the (easier/harder) it is to inspire

Harder

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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?

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