Lung Mechanics Flashcards
Normal vs Obstructive vs Restrictive
TLC is going to increase for ………………. and decrease for ……………..
Vital capacity is going to decrease in …………….. …………….. ……… ……………..
Residual volume is GREATER in …………….. and lower in ……………..
In COPD you get the narrowing of airways and break down of parenchyma so the alveoli have less recoil
The bronchi will close and the air will be trapped distal to the upper airway
Normal vs Obstructive vs Restrictive
TLC is going to increase for obstructive and decrease for restrictive
Vital capacity is going to decrease in BOTH obstructive and restrictive
Residual volume is GREATER in OBSTRUCTIVE and lower in restrictive
In COPD you get the narrowing of airways and break down of parenchyma so the alveoli have less recoil
The bronchi will close and the air will be trapped distal to the upper airway
End of INSIPRATION = DECREASE in pleural pressure (MORE NEGATIVE)
End of EXPIRATION = FRC
The most important thing to take in is the shape of the graph:
Mechanics of Ventilation continued…
The default point for restrictive lung disease is ………..
The default point for obstructive lung disease is ………….
The ……. is different in both restrictive and obstructive
(The sigmoid graph)
Mechanics of Ventilation continued…
The default point for restrictive lung disease is lower
The default point for obstructive lung disease is higher
The FRC is different in both restrictive and obstructive
llustration of Tidal Breathing showing the alveoli
Alveolar pressure follows 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: change in alveolar pressure CAUSES the change in flow rate, not the other way around
We begin with pressure at 0 mm Hg and a comfortable volume
The respiratory muscles then work to expand the chest wall and increase the capacity of the thoracic cavity so we create a NEGATIVE pressure inside which makes air flow in
When the alveoli fill up with gas they 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 the start of expiration, you release the tension in the inspiratory muscles that were being used to hold your breath - it compresses the gas molecules (fourth image) and creates a positive pressure which forces the air out and then you’re back where you started
If you superimpose the volume graph (top) over the pleural pressure graph (and invert it) and look at the difference between the two - it is equal to the difference between the volume and flow rate graphs
Both curves (going down and going up) have a steep part and a flatter part - there is a fast phase then a slow phase in terms of the changes in pleural pressure
Define Compliance and elastance?
Structural Properties of Lung Tissue
Compliance is the willingness of a structure to change shape when pressure is applied
Elastance is the OPPOSITE - it is the tendency of something to recoil to its original volume
Condom has high compliance, balloon has high elastance and a tyre has very low compliance
Ventilation & Perfusion
Is plueral pressure more negative at the top or bottom of the lung?
Is the transmural pressure greater at the top or bottom of the lung?
Are the alveoli larger and less complient at the top or bottom of the lung?
Is there less ventilation at the top or bottom of the lung?
Is the lower intravascular pressure at the top or bottom of the lung?
Is the less recruitment at the top or bottom of the lung?
is there greater resistance at the top or bottom of the lung?
Is there lower flow rate at the top ot bottom of the lung?
When lungs are fluid filled are they more or less compliant then when airfilled?
Explain why
Ventilating Fluid-Filled Lungs
The changes in pressure in relation to volume for inflation and deflation do NOT overlap
It is harder to INFLATE (more pressure needed) than to deflate
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
Type II Pneumocytes produce ………………. which breaks up the ……………….. ………………..
What does the molecule produced by type II pneumocytes do to water molecules and what does it reduce between the water molecules?
……………… prevents ………………. of small airways and INCREASES …………………… (it changes the change in volume you achieve per unit change in pressure)
Pulmonary Surfactant
Type II Pneumocytes produce SURFACTANT which breaks up the surface tension
The surfactant splits the water molecules on the surface and reduces the surface tension between them
Surfactant prevents collapse of small airways and INCREASES COMPLIANCE (it changes the change in volume you achieve per unit change in pressure)
This means that you have to work less hard to breathe
Conductance steadily increases with increasing lung volume
why?
Resistance and Conductance
INTUITIVE STANDPOINT - the smaller the calibre of the airways, the smaller the tube, the greater the resistance
However, YOU MUST ALSO CONSIDER FLOW
If you have low flow through a small tube and really high flow through a large tube then the large tube may have greater resistance
You breathe in 500 mL of tidal breath and the airways then rapidly bifurcate and the air gets split across smaller and smaller bronchioles so flow rapidly decreases
Peak Resistance occurs around the FOURTH GENERATION
Resistance can be mathematically expressed using Poiseuille’s Law (n=viscosity, l=length, r=radius)
Conductance = how well will the airways conduct and allow air to pass through
Conductance steadily increases with increasing lung volume
As lung volume increases, resistance DECREASES
This is because as you breathe in, not only are your tissues expanding, your airways also expand
Therefore, the radius of the airways increases and hence resistance decreases when you breathe in
Explain the interdependance of alveolis?
Interdependence
The model of alveoli looking like a bunch of grapes is inaccurate because the alveoli actually share walls - they are NOT totally independent units - when one alveolus moves, the others also move
If the alveoli around a dysfunctional alveolus are functional, they could help the dysfunctional alveolus expand
The function of any single alveolus is dependent on the function of the alveoli around it
Homogenous and Non-Homogenous Expansion
Think of the lungs and airways as a whole and imagine that the whole of the airways are expanding homogenously - they are all expanding at the same rate and to a similar volume
Restrictive Lung Disease (e.g. fibrosis) - where one part of the lung (e.g. one lobe) is very resistant to expansion it’s going to create a stress point in between where on one side, the tissue is happy to expand and on the other it isn’t happy to expand
Obstructive Lung Disease (e.g. emphysema) - there will be parts of the lung that want to expand even more because they’ve had more of the tissue broken down and its structural integrity is a lot worse. There will be a connection point between these two tissues which is a real focal point for damage
At the connection point there is elastic tissue and structural tissue like collagen which could be subject to permanent damage
Flow in Collapsible Tubes
Some of the airways have a structural support (e.g. cartilage rings) but not all airways do
Patency = whether the airways are open and active and able to allow air through
Preinspiratory Lung - the transmural pressure is positive and the airway is patent
It is patent during mid-inspiration and end-inspiration as well
However, is you try forced expiration where you rapidly go from TLC to RV then there is going to be a massive increase in ……………… .pressure
REMEMBER: there is a GRADIENT of INTERNAL pressure between the lungs and the atmosphere (gradually decreasing as you get to the atmosphere)
If the pleural pressure …………… the internal pressure of any of the collapsible tubes then the airways might CLOSE making forced expiration very difficult (LOOK CAREFULLY AT THE FAR RIGHT DIAGRAM)
To put it simply…during forced expiration, the intrapleural pressure is very high and exerts a pressure inwards on the collapsible tubes. If this inwards pressure is greater than the outwards pressure exerted by the tubes themselves, then the tube will collapse.
Flow in Collapsible Tubes
Some of the airways have a structural support (e.g. cartilage rings) but not all airways do
Patency = whether the airways are open and active and able to allow air through
Preinspiratory Lung - the transmural pressure is positive and the airway is patent
It is patent during mid-inspiration and end-inspiration as well
However, is you try forced expiration where you rapidly go from TLC to RV then there is going to be a massive increase in INTRAPLEURAL pressure
REMEMBER: there is a GRADIENT of INTERNAL pressure between the lungs and the atmosphere (gradually decreasing as you get to the atmosphere)
If the pleural pressure EXCEEDS the internal pressure of any of the collapsible tubes then the airways might CLOSE making forced expiration very difficult (LOOK CAREFULLY AT THE FAR RIGHT DIAGRAM)
To put it simply…during forced expiration, the intrapleural pressure is very high and exerts a pressure inwards on the collapsible tubes. If this inwards pressure is greater than the outwards pressure exerted by the tubes themselves, then the tube will collapse.
look at laz notes- loop diagrams
look at laz notes- loop diagrams
