Unit 1 Lecture 3: Respiratory Compliance Flashcards
What does compliance mean and how is it related to elasticity?
Compliance means how easy is it to stretch or distend the lungs & this is the opposite of elasticity of the lungs
What is the formula for compliance?
ΔV/ΔP
Change in volume of air over the transpulmonary pressure
What does increased compliance mean?
The lungs don’t need to work hard to expand, but this means the elasticity is low and the lungs cannot properly deflate
Why does a increased compliance plot have a steeper slope?
Steeper slope represents how easy it is for the volume to fill up with little transpulmonary pressure change
What is decreased compliance?
When there is more transpulmonary pressure for as volume tries to increase
Lot of work to expand lung = lot of work to increase Ptp (hence bigger)
Pulmonary fibrosis is an example of decreased compliance; the lungs cannot fill but they can easily recoil
Why does a decreased compliance plot have a flatter slope?
Extra work is required to actually try to bring the air in; more pressure for little volume
What does the bottom of the normal compliance sigmoid curve mean? Top of the curve?
The bottom is representing end of expiration where the lung is empty and the top represents when the lung is filled with air
If you were to breathe in more after full inspiration, what would happen?
You would feel more pressure trying to get the air in, because the recoil pressure (elasticity of lung) wants to overcome the compliance
Remember the recoil pressure isn’t necessarily the Ptp rather its the elastic nature of the lung
What is Emphysema an example of?
Emphysema is an example of increased compliance. The destruction of the alveoli means that there is a lot of space for air to move in but it’s harder for the alveoli to collapse and make the lung collapse when the alveoli is destroyed
Increased compliance ==> Easier for Ptp to increase (less work hence why small change in pressure with significantly increased volume)
What are two factors lung compliance relies on?
- Elastic connective tissue in lungs
- Alveolar Surface Tension
70% of lung compliance is due to alveolar surface tension
What is alveolar surface tension?
Surface tension is the ability of the water molecules to attract and pull one another to each other. This is what allows for the alveoli to collapse & it minimizes surface area
What is surfactant?
Anti-surface tension; a liquid that lines each alveoli and reduces the tendency of the lung to recoil
What creates surfactant?
Type 2 Alveolar Cells
Regulates pressure across the alveoli
What are the benefits of pulmonary surfactant?
- Reduces work of the lungs/optimizes lung compliance
- Reduces recoil pressure of smaller alveoli more than larger alveoli
What is the Law of LaPlace?
P = 2T/R
T is tension and R is radius
This is an example of two alveoli (one big and one small) without surfactant. Using LaPlace’s Law explain how pressure is working on both alveoli?
Since there is no surfactant both alveoli are susceptible to surface tension but the smaller one is likelier to collapse. Due to the radius of both using LaPlace’s Law shows that the smaller one has a bigger pressure but because pressure follows a gradient, the air will flow from the smaller alveoli to the bigger alveoli. This means the smaller alveoli will completely collapse without surfactant
This is an example of two alveoli (one big and one small) with surfactant. Using LaPlace’s Law explain how pressure is working on both alveoli?
Since surfactant reduces surface tension, the alveoli both receive an equal amount of surfactant which prevents the collapse of the alveoli. Using LaPlace’s Law, we see that the pressure between both alveoli are equal so there is no one way flow of air; distributed equally
It is possible that the smaller alveoli contains more surfactant than the bigger one in order to keep up with the surface tension of the bigger one, but it’s also a small alveoli so the concentration might seem bigger
