21. 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 lung volume change is measured
As negative pressure around the lungs (intrapleural pressure) becomes more negative, what does air and volume in lungs do?
Air flows into lungs and lung volume increases
Change in volume is not equal to the change in pressure. It varies. At low(start of breath) and high lung volumes(TLC) in the lung, what pressure is needed to make a small change in volume?
you need a fairly large pressure change to make a small increase in volume at high and low volumes
What is the compliance of the lungs and how is it measured?
Compliance is the measure of stretchability of the lungs, and can be calculated by find the slope of the line (Change Volume/Change Pressure)
What is elastance of the lungs?
Opposite of compliance, instead of stretchability it is recoilability… 1/compliance
When is the compliance of the lungs highest during breathing?
During normal breathing range when there is the largest slope. We do not have to work heard to get a decent Vt
At either extreme-too small or too large volume, compliance will be?
low, meaning we have to work hard to inflate the lungs at low and high volume
What is compliance at birth and how much work needs to be done to get air into the lungs?
First breath, lung volume is v low, compliance is very low, meaning the effort to breath is very high (crying helps baby get past this step)
The lung does not deflate the same way it inflates. What occurs if we inflate 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! (2T/r=P)
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
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
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
When you put the lungs and rib cages alone, together, you get the entire system. These balance eachother at the ______, which means what?
The FRC, is where if you exhale normally, airway pressure goes down to zero, due to elastic recoil of both even eachother out. With forced expiration, goes below FRC to residiual volume
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 x n(vicosity) L(tube) / r^4 (radius tube)
So if there is a small change in radius=huge change in resistance
Airway resistance occurs by contraction of bronchial smooth muscle which changes?
the radius of the airway and the resistance
Froced expiratory volume (FEV) can be used to identify pulmonary mechanics, the amount of air exhaled in the first second is used as (FEV1)?
one measure of pulmonary function
However the ratio of FEV1/FVC is very important to test pulmonary functions
What percent of air is exhaled in the normal person in the first second?
70-80% of air / of the FVC
What occurs to the FVC and FEV1 during exhalation of air of someone with emphysema/asthma - OBSTRUCTIVE disease?
It takes longer for air to get out of th lungs, FVC is reduced because air is trapped in the lungs and FEV1 is reduced even more. FEV1/FVC will be below 70%
In a person with a RESTRICTIVE disease, FVC and FEV1 are reduced due to the inability of lungs to expand. What does this lead to?
FEV1/FVC ratio is higher than normal (90%) because the elastic recoil of the lungs forces air out more rapidly
The elastic recoil of the lung would normall creat collapse of the small airways and alveoli. However, why does this not happen?
The shared walls of the alveoli and airways prevent the collapse because their recoil opposes the recoil of other alveoli
What is interdependence?
Each alveoli depends on the others, because their shared walls are stablized due to oppose recoil on eachother
In COPD, when the walls of the alveoli are lost due to tissue destruction, how does this affect interdependence?
No walls= lowered interdependence, causing a reduced peak expiratory flow, scalloped appearance and decreased FVC
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
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)
While the work done to overcome airway resistance is added, what else must increase?
An increase in airway resistance can make the inspiratory loop bigger
What changes more on the pressure/volume respiration chart, expiration or inspirtation during work?
Expiration altered more by increase in airway resistance d/t airway collapse
Work is done to elastic recoil of lungs or resistance of airflow, elastic recoil having the greater effort. What does it mean if the work to exhale due to airway resistance exceeps the work done to inflate the lungs (elastic work)?
it means that expiration must be active!
Respiratory activity uses a lot of oxygen, so an increased work of breathing means more oxygen must be supplied to?
the respiratory muscles
