18 Lung Mechanics Flashcards
(37 cards)
Q: What’s the difference between obstructive and restrictive lung disease in terms of:
TLC? VC? Residual volume? ERV? IVR? TV?
A: increases for O
decreases for R
decreases in both
greater in O
lower in R
last 3 decrease in both
Q: What happens in COPD? (5)
A: -narrowing of airways
- break down of parenchyma
- so the alveoli have less recoil
- bronchi will close
- and the air will be trapped distal to the upper airways
Q: What would happen hypothetically if you removed the chest wall and lungs?
A: The chest wall, if you take it out of the body, is going to have a larger volume than at FRC
The lung, if you take it out of the body, is going to shrink and have a smaller volume than at FRC
Q: What is FRC?
A: functional residual capacity
sum of Expiratory Reserve Volume (ERV) and Residual Volume (RV)
Q: Draw a pressue (x) volume (y) graph (flow rate graph) for the chest wall, lungs and combined (transrespiratory system pressure).
- What happens if you apply pressure to either the lungs or chest wall at beginning?
- As you follow the curve up?
- When do you you get a greater change in volume per unit pressure?
Summary? (2)
A: REFER: Around the volumes in the middle of the graph, a small change in pressure will cause a large change in volume (the triangle is about as tall as it is wide)
- a small pressure change will result in a large change in volume to begin with
- it takes a more substantial pressure to bring about the same change in volume
- when you’re closer to the y axis (closer to FRC)
- End of INSIPRATION = DECREASE in pleural pressure (MORE NEGATIVE)
- End of EXPIRATION = FRC
Q: What is transrespiratory system pressure?
A: the lung and chest wall combined when they are stuck together and interacting
Q: How is lung tissue connected to the chest wall? movement?
A: lung tissue and the chest wall have a pleural membrane and in between the membranes there is a sealed volume of pleural fluid and the two layers work as if they are holding hands tightly - if one layer is pulled in a certain direction, it will pull the other layer as well
Q: What does the tension between the pleural membrane layers change according to?
A: tension between the two layers will increase or decrease depending on whether there is a pulling force (end of inspiration/start of expiration) or a pushing force (end of expiration/start of inspiration)
Q: Describe the relationship between the chest wall and lungs at FRC. Pressure? Air movement?
A: At FRC (zoom in on the top left lung schematic) the lungs are pulling in and the chest wall is pushing out the same amount so there is negative pressure in the middle because the pleural layers are being pulled in both directions and hence there is negative pressure (a little vacuum)
Because the Transrespiratory Pressure (between outside and inside) is ZERO, there is NO NET MOVEMENT OF AIR at FRC
Q: Describe the air movement at the end of tidal inspiration. Pleural pressure compared to FRC?
A: there is also no air movement because the transrespiratory system pressure is ZERO (like at FRC)
pleural pressure is MORE NEGATIVE than FRC because there is a greater recoil force on one side (the lung recoil inwards is greater than the chest recoil outwards)
Q: Why is expiration a passive process? What’s pleural pressure at the end?
A: due to the natural tendency of the lungs to recoil inwards to at the end of expiration, pleural pressure will return to the same pressure as it was at FRC (-5 mm Hg)
Q: How can you make the pressure more positive than FRC?
A: if you do FORCED expiration
Q: Draw and describe how a pressure (x)-volume (y) graph (flow rate graph) changes when obstructive and restrictive.
A: REFER: similar shapes (obstructive is above normal and restrictive below)
The default point for restrictive lung disease is lower = all lower and need much more pressure to achieve more volume
The default point for obstructive lung disease is higher = all higher up and not as wide
- apply small pressure and get larger volume
- has lost compliance and recoil
The FRC is different in both restrictive (lower) and obstructive (higher)
-lost elasticity
Q: Draw a graph for volume and pressure (y) by time (x) for alveoli. Add pleural pressure line.
A: REFER
- volume is normal distribution curve (volume change)
- pressure is a trig graph starting at mid going down (flow rate matches this graph)
REFER (inhale and gets more neg)
Q: What does alveolar pressure follow? why?
A: the flow rate because the flow rate is dictated by two pressures (atmospheric (which we can’t change) and alveolar pressure) - so to ventilate we either need to create positive outside pressure or negative inside pressure
Therefore, the flow changes depending on how WE change alveolar pressure
NOTE:
Q: Does change in alveolar pressure cause the change in flow rate or does change in flow rate change alveolar pressure?
A: change in alveolar pressure CAUSES the change in flow rate, not the other way around
Q: Describe how alveolar pressure and volume changes in a breath. (4)
A: -begin with pressure at 0 mm Hg and a comfortable volume
- respiratory muscles work to expand chest wall and increase capacity of thoracic cavity -> create NEGATIVE pressure inside which makes air flow in
- alveoli fill up with gas -> return to equilibrium (third image) so there is no pressure difference (this is what happens when you take a deep breath in and hold in)
- at start of expiration, you release tension in inspiratory muscles that were being used to hold your breath - it compresses gas molecules (fourth image) and creates a positive pressure which forces the air out and then you’re back where you started
Q: Name 2 structural properties of lung tissue. Define. Eqn?
A: Compliance = willingness of a structure to change shape when pressure is applied (tendency to distort under pressure (change in vol over change in pressure)
Elastance is the OPPOSITE = tendency of something to recoil to its original volume (change in pressure over change in vol)
elastance graph has steeper balloon (vol is x axis)
compliance graph has steeper condom (pressure is x)
Q: What is the difference between air filled and fluid filled lungs in terms of:
inflation?
compliance?
reason?
A: -harder to INFLATE (more pressure needed) than to deflate fluid filled lungs
-When lungs are fluid-filled they are much more compliant than when air-filled
EXPLANATION: There is a small amount of water lining the lungs (surfactant) and the air-water interface exhibits SURFACE TENSION whereas the fluid-water interface does NOT exhibit surface tension
Q: In terms of a pressure volume graph, how do air filled and fluid filled lungs differ? Draw. What did this lead to?
A: for fluid filled: changes in pressure in relation to volume for inflation and deflation do NOT overlap
REFER (anticlockwise)
fluid filled lungs require less pressure to change volume
Fluid filled lungs are more compliant than airfilled lungs
-possibly due to surface tension
Q: What creates surface tension? (3)
A: The water molecules all interact
At the top layer, there is air on one side so there is no matching force on one side
This makes some of the upper water molecules disappear down and causes a tension across the top - the molecules come under strain
Q: Describe surface tension in alveoli. (2) Small alveolus?
A: Because of the shape of the alveoli, the distribution of water is more dense around the outside
On the inside, the water molecules are all attracted across the alveolar space to water molecules on the opposite side
This means that if the alveolus is too small, these forces will pull the alveoli together and collapse them
Q: What produces surfactant? function? how? What’s it made of? (3)
A: Type II Pneumocytes produce SURFACTANT which breaks up the surface tension
surfactant splits the water molecules on the surface and reduces the surface tension between them
80% polar phospholipids; 10% non-polar lipids; 10% protein
Q: 3 advantages of surfactant. Eqn.
A: prevents collapse of small airways
INCREASES COMPLIANCE (it changes the change in volume you achieve per unit change in pressure)
reduces work of ‘breathing’
law of laplace: pressure= 2T/r
