Respiratory Mechanics Flashcards
How are respiratory mechanics performed outside of the body, to determine pressure/volume relationships?
Negative pressure is created in a container with the lung.
The change of the volume of the lung is calculated.
In respiratory mechanics, as the intrapleural pressure (pressure around the lung) becomes more negative, what happens?
Air flows into the lungs= lung volume increases.
Is the change in volume for a given change in pressure constant?
No.
The line produces is not straight.
How are pressure and volume related in respiratory mechanics?
At a low lung volume, it takes a big amount of pressure to get a small increase in volume.
Once a little bit of air enters the lungs, a little change in pressure produces a large change in volume.
Thus, it becomes easier to stretch the lungs.
When the lungs get close to TLC, what happens?
It becomes hard to stretch (inflate) again.
Thus, a large pressure change will only change the volume a little.
What is compliance of the lung?
How easy it is to stretch our lungs.
to calculate=
Change in volume/ change in pressure
What is the opposite of compliance?
Elasticity- ability to recoil
When is compliance the highest?
When we are in normal breathing range (normal Tidal Volume).
Thus, we dont have to work hard.
At either extreme of the pressure/volume relationship curve (sigmoidal), (very small lung volume or very big lung volume), what is compliance?
Compliance is low.
What does a high compliance mean?
Very stretchable and easy to inflate.
At birth, bb must inflate its lungs for the 1st time. What is the compliance of the lungs for the first breath and how hard does the bb have to work?
Very very low compliance bc lung volume is v low.
BB has to work v hard.
Do the lungs inflate and deflate the same?
No.
Thus, exhalation and inhalation is different.
What would happen if we inflated the lungs with saline (instead of air)?
Saline allows for high compliance due to there being no air/water surface, so there is no surface tension, allowing rapid intake of saline, exhale also occurs at the same place
What is the main reason the inhale and exhale graphs do not align (also know as hysteresis)?
- Due to surfactant molecules moving one way during inspiration and different during expiration /
- LaPlaces Law! (P=2T/Radius)
Why does the gap between the expiration and inspiration line (hysteresis)?
Surfactant= differences in surface tension
Surfactant is not evenly distributed on the alveolar surface, instead it is small droplets randomly positioned. So if the alveolar volume is small…?
the droplets are close together and pull apart during inspiration and fuse together during expiration
What is the SLIGHT hysteresis in the saline-filled curve due to?
Resistance caused by tissue sliding over one another. (ST)
When there is low compliance, there is ____ stretchability and _____ to inflate… vice versa for high compliance
low stretchability and hard to inflate high stretchability and easy to inflate with high compliance or high slope of deltaV/deltaP
What is the pressure/volume relationship for the lungs?
Looks like what we saw for INSPIRATION.
Normal resting point (without the rib cage) is low (because they want to collapse).
What is the normal resting point for lungs alone, which is VERY small, referred to as?
Minimal volume.
However, we do not usually see in person because the rib cage is attached.
Pressure/volume relationship of the rib cage?
The rib cage wants to move outward (thus, have a larger volume).
The normal resting point of the rib cage when the pressure is 0 cmH20 relaxed.
The normal resting point of the lungs alone is quite small and known as the minimal volume(near 0) due to elastic recoil. The rib cage rests?
At a higher volume, where pressure is near 0cmH2O due to orientation of ribs, joints and muscles
The elastic recoil of the lungs and rib cage balance each other out at ______
FRC (functional residual capacity). – volume of hair present at the end of a passive expiration.
In this situation, airway pressure goes down to zero, due to elastic recoil of both even each other out.
With forced expiration, goes below FRC –> residiual volume
If the lungs could pick, where would they go to? FRC, RV, MV
Minimal volume. They want to be smaller so minimal volume is what they COULD shrink to.
So for instance, if there is a pneumothorax, what would happen to the lungs and rib cage, separate?
Rib cage would increase in volume while the lungs would collapse and decrease in volume
How is airway resistance calculated?
R= 8*n*L/r4
Resistance is<strong> directly proportional t</strong>o the [<em>viscosity</em>] and the <em>[length of the tube]</em>.
<strong>Inversely proportional</strong> the<em> [radius of the tube]. </em>
FEV
How much a person can breath out during a forced breath. It is very sensitive to changes in airway resistance.
Normally, it takes a person 3 seconds to get out all of the air.
In one second, a person will get out a substantial amount of air.
What measurements are helpful in identifying changes in pulmonary mechanics?
1. FEV
2. How fast the air can be moved out
How we use FEV to determine airway resistance?
FEV1 is the amount of air that is exhaled in the first sentence.
To determine resistance:
FEV1/FVC (forced vital capacity: total amount of air we get out in a FEV test)
A normal person ~70-80% of the ____ is exhaled in the 1st second of a forced expiration.
FVC
What will FEV1/FVC ratio look like for someone with an obstructive dz: emphysema or athasma?
It will take longer to get the air out of the lungs.
FVC is reduced because air is trapped in lungs.
FEV1 is even more reduced.
Thus, FEV1/FVC ratio is below ~70%
What will FEV1/FVC ratio look like for someone with an restrictive dz: interstitial lung dz.
Absolute values of FEV1 and FVC are both reduced because the lungs cannot expand.
But the ratio is higher than normal (<90%) because the elastic recoil of the lungs forces the air out more rapidly.
The FEV1/FVC ratio is used to determine what?
Obstructive or restrictive disease
Normally, the elastic recoil of the lungs would cause what?
Collapse of the small airway and alveoli.
Why do the aleoli and airways not collapse?
INTERDEPENDENCE
Shared walls of alveolar and airways prevent collapse because their recoil opposes the recoil of the other aveoli.
What would happen if we lost some of the walls?
We would alter or lose forces that COUNTER the collapse of alveoli.
Structure and stability of _____ airways and alveoli depend on all of the connecting airways and alveoli.
SMALL
What happens during COPD?
We lose the alveolar walls due to tissue destruction. As a result, remaining alveoli can collpase.
What happens as airway resistance increases?
We need more pressure to cause air to flow into the lungs.
Thus, we need more pressure to cause a change in volume
Decreased interdepedence means the alveoli are collapsing upon exhalation, leading to?
- less air being forced out of lung,
- peak and instantaneous ariflow are reduced due to increased airway resistance
- Decreased FVC
What represents the work done to stretch (elastic forces) the lungs/thorax?
0AECD0= work of breathing to overcome the elastic forces (compliance)
What 2 forces does breathing overcome?
1. Elastic
2. Resitance
What area is the work required to overcome resistive forces?
ABCEA
Increase in airway resistance means it takes a greater pressure to generate flow into lungs. What do we have to change to change the amount of work being done to stretch the lungs/rib cage?
Change the compliance. Decrease in compliance = work harder to stretch lungs = increase in area (pneumonia, pneumonia, overwight all decrease compliance)
On the P/V curve, what would happen if we increased resistance?
Inspiratory loop would become bigger.
What is altered the most when you increase resistance?
Expiration because of airway collapse.
-shift to the L on the chart
Work is done to overcome elastic recoil of the lungs or to overcome the resistance to airflow.
What does it mean if the work to exhale due to airway resistance exceeds the work done to inflate the lungs (elastic work)?
it means that expiration must be active!
If the world to exhale due to airway resistance exceeds the work done to inflate the lungs (elastic), then?
expiration must be active
The _______ is the greater effort (bigger area of the curve).
elastic recoil
