Resp 17 - Lung mechanics Flashcards
How does TLC change in obstructive and restrictive disease?
Obstructive - increases because RV increases a lot (because alveoli have less recoil). Other volumes decrease.
Restrictive - decreases (every volume, especially RV)
How does the change in volume per unit pressure change as you move further from FRC?
Change in volume per unit pressure DECREASES as you move further from FRC - basically gradient of curve decreases. This is because it is easier to breather around FRC and when you inspire/expire a lot it’s hard to change volume significantly. (sigmoid shaped curve)
What is transrespiratory pressure?
The pressure between the inside of the airways and the outside atmosphere
How does the pleural pressure change from FRC to a) end of tidal inspiration and b) end of tidal expiration?
End of tidal inspiration - more negative than FRC
End of tidal expiration - FRC (lungs passively recoil inwards to return the pleural pressure to FRC)
You can only get a more positive intrapleural pressure than FRC if you do FORCED expiration.
What is the significance of the shape of the curve with regards to ease of tidal breathing?
Close to FRC, you get a large change in volume per unit pressure (gradient) so we can relatively easily inspire and expire in tidal breathing. The further we deviate from FRC, the more difficult it becomes to increase the volume.
How does the volume-pressure curve change in obstructive and restrictive disease?
Obstructive - moves up and squished (FRC higher) - gradient is higher - larger volume for smaller pressure because tissue looses elasticity so takes up lots of volume (then unable to get it out)
Restrictive - moves down and spreads (FRC lower) - gradient lower, have to generate more pressure
Describe negative pressure breathing referring to the alveolar pressure and volume.
The respiratory muscles work to decrease intrathoracic pressure and so the alveoli are pulled open thus increasing their volume and decreasing their pressure (generating negative pressure). This creates a pressure gradient between the alveoli and the atmosphere so air is drawn into the alveoli to re-establish the initial pressure. Once pressure is re established, lungs recoil creating positive alveolar pressure, thus air flows out.
Define compliance.
The willingness of a material to distend under pressure.
Define elastance.
The tendency of something to recoil to its original volume.
In terms of change in volume per unit pressure, how is the ease of inflation of the lung different to deflation?
Inflation is more difficult that deflation (requires more pressure per unit change in volume) because the lungs have a natural tendency to recoil
How is the ease of inflating and deflating a fluid-filled lung different to an air-filled lung?
It is much easier to inflate a fluid-filled lung - it is more compliant. The air-filled lung has a surfactant-air interface which has surface tension and hence decreases compliance. The fluid-filled lung has a fluid-water interface, which doesn’t have surface tension so the lung is more compliant.
(surface tension = when you have surface of water not exposed to opposing force like air)
What type of cell produces surfactant?
Type II pneumocyte
What is the role of surfactant?
It breaks up the water molecules, reduces surface tension and hence prevents alveolar collapse.
What are the effects of surfactant on surface tension and compliance?
It reduces the surface tension and hence increases the compliance of the lungs
What is conductance?
How well the airways will conduct and allow air to pass through.
Why doesn’t the resistance of the airways increase as you go down the generations?
Because flow also decreases - you must consider flow not only the size of airways. Until 4th generation, airways get smaller so more resistance. However, when air can go through many many branches, resistance will decrease as flow is divided.
When does peak resistance occur?
Around the 4th generation
How do conductance and resistance change with increasing lung volume? Why does this happen?
Conductance increases and resistance decreases with increasing volume because when the lungs inflate, the airways dilate (i.e. the radius increases).
Describe the phenomenon of interdependence with regards to alveoli.
The function of any single alveolus is dependent on the function of the alveoli around it.
Describe what is considered a ‘stress point’ in obstructive and restrictive disease.
In a lung with obstructive and restrictive disease, there will be a border between normal lung tissue and lung tissue that is either resistance to stretch (restrictive) or wants to stretch too much (obstructive)
Explain why forced expiration can lead to the collapsing of airways.
Forced expiration leads to a dramatic increase in pleural pressure. There is a gradient of pressure between the alveoli and the atmosphere. The sudden increase in pleural pressure could mean that at a point along the collapsible tubes, the pleural pressure exceed the internal pressure of the airways and hence the airways collapse.
