Respiratory Mechanics Flashcards
Relationship between pressure and volume at low lung volumes?
At low lung volumes, it takes a fairly big pressure change to make a small increase in volume
What happens once there is some air in the lungs?
Once there is some air in the lungs, a little pressure change produces a large volume change-in other words, it becomes easy to stretch the lungs
When the lung gets close to the TLC?
It again becomes difficult to inflate-so a large pressure change produces a small change in volume
Compliance of the lungs
- What is it?
- How is it measured?
- Measure of the “stretchability” of the lungs
- (change in volume)/(change in pressure)
When is compliance highest?
- The compliance of the lungs is highest in the normal breathing range
- Don’t have to work particularly hard to get a decent Vt
What happens to compliance at either extreme (too small or too large)?
Compliance is low-have to work harder to inflate the lungs at low or high volumes
Thought question
- What is the compliance of the lungs for the first breath?
- How hard does the baby have to work?
- Prior to the first breath, lung volume is very low, compliance is low, and the effort to breath is high
- With successive breaths, the baby’s lungs inflate and become more compliant, so work decreases
Describe the pressure-volume curve of the normal lung and explain the differences observed in inspiration versus expiration
-Respiratory mechanics: pressure and volume relationships
- Something really interesting happens when we allow our lung model to “exhale”-The lung doesn’t deflate the same way it inflated
- Even better, if we inflate the lungs with saline (rather than air), the whole shape changes and the lung mostly deflates the same way it inflated
Why is surfactant important?
Alleviates surface tension-reduces tension in the smallest alveoli more than in larger alveoli
The difference in the inspiratory and expiratory lines on the graph is mostly due to?
the presence of surfactant
Hysteresis
difference between inspiration and expiration
It is believed that the hysteresis is due to?
the molecules of surfactant moving one direction during inspiration but coming back a different way
- surfactant is not evenly distributed on the alveolar surface
- small droplets randomly positioned
- if the alveolar volume is small, the droplets are close together and pull apart during inspiration/fuse during expiration
The slight hysteresis of the saline filled curve is due to?
the resistance of the tissue sliding over one another
Define compliance
-equation?
change in volume/change in pressure
What does low compliance mean?
Low stretchability; hard to inflate
(high compliance is the opposite)