(21) Respiratory Mechanics Flashcards
What were methods used to measure the compliance of the lungs?
Put lungs in negative pressure container and see how much the volume of the lung changes
Graph the pressure/volume relationship
Describe what is occuring at very low volumes of the lungs
At low lung volumes,
it takes a fairly big pressure change to make a small increase in volume
Describe what is occuring here
Once there is a little air in the lungs,
A little pressure change produces a large change in volume
*It becomes easy to stretch the lungs
Describe what occurs when the lung gets close to TLC
What does the slope of this line represent?
The Compliance of the lungs
Define:
Compliance of the lungs
Stetchability of the lungs
(change in V/change in P)
The compliance of the lungs is highest…
in the normal breathing range
We don’t have to work particularly hard to get a decent Vt
Compliance of first breath?
VERY LOW
Baby has to work VERY hard
B/c prior to first breath, lung volume is very low. Compliance is low and the effort to breathe is high
When successive breaths, the baby’s lungs…
Inflate and become compliant so work decreases
What is unique about inspiration vs expiration?
Lung does not deflate the same way it inflated!
(Red line = Inspiration)
(Blue line= expiration)
What happens if we inflate the lungs with saline?
The whole shape changes!!!
No air-water interface!!!! No surface tension!!!
What is the hysteresis on the inspiration and expiration graph?
The difference b/w inspiration and expiration
Its due to the molecules of surfactant moving one direction during inspiration, but coming back a different way
The rib cage on it’s own wants to…
Be at a larger volume.
Hits its resting point at a very high volume
Lungs themselves want to be…
SMALLER
They will get there when they get down to minimal volume
B. Pneumothorax
D;
Once the coupling between the lugns and thorax is disrupted by air, the recoil of the rib cage (thorax) causes the rib cage to spring away from the lungs to a larger volume
A;
minimal volume
Once free of the rib cage’s pull, the lungs collapse and go to minimal volume
What is useful for identifying changes in pulmonary mechanics?
The RATIO of Forced Expiratory Volume (FEV)1 to FVC
Measuring how they breathe out!
What is the blue line showing?
Obstructive Disease due to
low FEV1/FVC ratio
*example of emphysema or asthma
What is the pink line revealing?
Restrictive diease
(Interstitial lung diease)
FEV1/FVC ratio is higher than normal
Takeaways from this graph?
-Note the huge drop off in expiratory flow
Expiration is on top
Inspiration on bottom
What is interdependence refering to?
Each alveoli depends on the others
b/c they share the same wall
What disease state do we see a loss of alveolar walls?
COPD
What does a loss of interdependence mean?
Small airways collapse during an expiratory effort
What does this green area represent in the work of breathing?
The work done
to stretch the lungs/thorax
What is this?
Work done to
overcome airway resistance
At what point does expiration have to be active?
When the work to deflate the lungs exceeds the work put into stretching the lungs
