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53 Cards in this Set
- Front
- Back
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Normally, is the pressure in the intrapleural space is above, or below, atmospheric pressure?
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Below atmospheric pressure. Said to be 'subatmospheric'.
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At the end of a normal expiration, which recoils match?
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The outward elastic recoil of the chest wall balances the inward elastic recoil of the lungs
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At the end of a normal expiration, what is the normal intrapleural pressure?
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-5cm H2O, alveolar pressure is 0 and transmural pressure gradient across the alveolus is +5 cm H2O
As alveolar pressure is equal to atmospheric pressure, no airflow occurs |
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During inspiration, what does intrapleural pressure decrease to?
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~-7.5 cm H2O
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Define 'transmural pressure'
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The difference in pressure between two sides of a wall or equivalent separator.
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The difference in pressure between two sides of a wall or equivalent separator.
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Transmural pressure
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During inspiration, does the transmural pressure gradient increase or decrease?
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Increases
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During inspiration, what happens to the alveolar pressure?
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It falls below atmospheric pressure (whereas at the end of expiration it is zero)
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Does the presence of surface tension reduces/increases the compliance of the lung?
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It reduces the compliance of the lung
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What is 'hysteresis'?
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The phenomenon in which the value of a physical property lags behind changes in the effect causing it.
Lung volume at any given pressure during inhalation is less than the lung volume at any given pressure during exhalation |
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The phenomenon in which the value of a physical property lags behind changes in the effect causing it.
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Hysteresis
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Lung volume at any given pressure during inhalation is less than the lung volume at any given pressure during exhalation
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.
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What kind of cells secrete surfactant?
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Type II alveolar cells
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A substance that tends to reduce the surface tension of a liquid in which it is dissolved
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Surfactant
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Define 'surfactant'.
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A substance that tends to reduce the surface tension of a liquid in which it is dissolved.
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What effect does surfactant have on alveoli? How?
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It stabilises alveoli by optimising their surface tension, which is responsible for 50% lung elastic recoil.
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It stabilises alveoli by optimising their surface tension, which is responsible for 50% lung elastic recoil.
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The effect of surfactant on alveoli
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It allows alveoli to expand more readily with air during inspiration
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Effect of surfactant on alveoli
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Without surfactant, what would happen to alveoli upon inspiration?
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They would not fill with air because the respiratory effort would be insufficient to overcome surface tension forces (Laplace's Law)
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Surfactant reduces surface tension more in large alveoli than small ones T/F
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False! Surfactant reduces surface tension more in small alveoli than large! (Explains why smaller alveoli do not empty their contents into larger ones)
2006051210 |
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Define 'airway resistance'
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The mechanical factors that limit the access of air to the pulmonary alveoli, and thus determine airflow
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The mechanical factors that limit the access of air to the pulmonary alveoli, and thus determine airflow
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Airway resistance
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Where is airway resistance greatest?
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At the bronchi of intermediate size, between the fourth and eighth bifurcation (division of something into two branches or parts)
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Define 'bifurcation'
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The division of something into two branches or parts
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The division of something into two branches or parts defines...
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Bifurcation
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How can airway resistance be calculated?
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R = (8nl)/[(pi)r⁴]
R = resistance n = viscosity l = length r = radius |
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The main site of resistance is at about the fourth airway generation.
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After this the resistance drops steeply because of the significant branching, producing a large number of parallel paths further down the tree.
(Concept also applies to cardiovascular system) |
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What is the shorthand for Barometric (atmospheric) pressure?
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P(B) (subscript B)
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What is the shorthand for alveolar pressure?
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P(A) (subscript A)
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P(A) < P(B) during inspiration/expiration
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Inspiration
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P(A) > P(B) during inspiration/expiration
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Expiration
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Transpulmonary pressure =
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P(A) - P(pl)
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P(A) - P(pl) =
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Transpulmonary pressure
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Transthroacic pressure =
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P(B) - P(A)
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P(B) - P(A) =
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Transthroacic pressure
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Define 'Compliance' wrt the lungs
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The change in the volume of the chest that results from a given change in intrapleural pressure
It is a measure of the ease with which the chest volume can be changed. |
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The change in the volume of the chest that results from a given change in intrapleural pressure
It is a measure of the ease with which the chest volume can be changed. |
'Compliance' wrt the lungs
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What is the shorthand for airway resistance?
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R(AW) (AW is subscripted)
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A term used to describe the difference between
the alveolar pressure and the intrapleural pressure in the lungs. |
Transpulmonary pressure
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Define 'Transpulmonary pressure'
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A term used to describe the difference between
the alveolar pressure and the intrapleural pressure in the lungs. |
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How do you calculate transpulmonary pressure?
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P(A)-Ppl
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P(A)-Ppl =
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Transpulmonary pressure
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Transpulmonary pressure is always positive T/F
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T
Because pleural pressure is always negative (-5 cmH2O) due to ribcage. |
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The reciprocal (mathematically) of elasticity is
compliance |
E = 1/C
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How do you calculate elasticity?
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Elasticity = 1/Compliance
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How can compliance be calculated?
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By measuring the change in
volume for a given change in pressure. (C = compliance, V = lung volume, and PL = the pulmonary pressure) C= ΔV/ΔPL |
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Lung elasticity can be affected by kyphoscoliosis T/F
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T
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Flared nostrils, rapid breathing, and
audible grunting are sure signs that a premature infant is suffering from Respiratory Distress Syndrome |
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Compliance is high/low in newborn babies. Why?
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Low, less surfacant (especially in premature babies)
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2T (surface tension)/r =
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= P (gas pressure)
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The amount of work done (by definition) for P-V changes is
defined as: |
W = P x ΔV
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What are the two segments of the diaphragm?
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Crural and costal
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What are the three types of resistance in the airways?
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Laminar, turbulent, tracheo-bronchial
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